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acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 1 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface the main function of the SX8722 is to acquire signal from wheatstone bridges or single ended sensors. the input can be a pressure sensor, a gmr or amr magnetic sensor, a chemical sensor, a thermistor or a mix of several of these sensors. the SX8722 sensor interface is totally configurable through an i2c compatible interface. several parameters are configurable through this interface such as alarms or signal post processing. ? pressure sensing (industrial, altimeter, diving computer) ? chemical sensing (monitoring, security) ? magnetic sensing (compass) ordering information ? 16 + 10 bits differential acquisition ? preamplifier programmable gain up to 1000 ? sensor offset compensation up to 15 times full scale of input signal ? 4 differential or 7 single ended signal inputs ? 2 differential reference inputs ? i2c compatible connection to application ? internal rc and 32 khz oscillators ? low power modes - sleep - shutdown ? 4 full configuration pre selections including: - zoomingadc? configuration - 2 alarms with on & off thresholds - digital filtering ? i2c eeprom interface ? stand alone mode for alarm monitoring ? clock out pin ? calibration pin ? reset pin ? ready / busy pin general description application part number temperature range package SX8722i070lf -40c to 125c mlpq44-7x7 tools part number evaluation kit xe8000ev120 key product features signal mux ref mux ready ac0 ac1 ac2 ac3 ac4 ac5 pga adc zoomingadc tm vbatt reset scl sda ar2n ar2p ar1n ar1p SX8722 vmult control osc i 2 c mcu ac6 ac7 bias single ended differential sleep power shut post-process ee_pow ee_scl ee_sda xin xout ckout cal gnd alrm1 alrm2 vreg gpio gpio vbatt example of application typical pressure & temperature sensing application with sleep control gpio
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 2 section page table of contents advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 1. specifications............................................................................................................. .............................................. 6 1.1. absolute maximum ratings ....................... .......................................................................... ............................ 6 1.2. operating conditions ..................................................................................................... ................................... 6 1.3. zoomingadc specifications ...................... .......................................................................... ............................ 7 2. pin configuration and marking information .................................................................................. .......................... 10 2.1. pin configuration ........................................................................................................ .................................... 10 2.2. marking information ...................................................................................................... ................................. 10 3. pin description............................................................................................................ ........................................... 11 4. timing characteristics ..................................................................................................... ...................................... 13 4.1. i2c timing waveforms.. ................................................................................................... ............................... 13 4.2. time specification without the 32.768 khz xtal ........................................................................... .................. 14 4.3. start-up time with the 32.768 khz xtal presence.......................................................................... ................. 14 4.4. changing power mode by pin signal........................................................................................ ...................... 14 4.5. changing power mode by i2c command....................................................................................... ................ 15 5. circuit description ........................................................................................................ .......................................... 16 5.1. detailed bloc diagram .................................................................................................... ................................ 16 5.2. functional description ................................................................................................... ................................. 16 5.3. zoomingadc ............................................................................................................... .................................. 19 6. access the SX8722 .......................................................................................................... ..................................... 20 6.1. description .............................................................................................................. ....................................... 20 6.2. SX8722 configuration..................................................................................................... ................................ 20 7. i2c commands............................................................................................................... ....................................... 20 8. serial communication ....................................................................................................... ..................................... 21 8.1. write data direct........................................................................................................ ..................................... 21 8.2. write data masked ........................................................................................................ ................................. 22 8.3. read data ................................................................................................................ ...................................... 22 8.4. other commands ........................................................................................................... ................................ 23 8.5. unknown commands ......................................................................................................... ............................ 23 8.6. reading data after a meas urement. ........................................................................................ ...................... 23 9. predefined settings ........................................................................................................ ........................................ 24 9.1. introduction ............................................................................................................. ....................................... 24 9.2. features covered by pred efined settings.................................................................................. ..................... 24 9.3. input multiplexers....................................................................................................... .................................... 25 9.3.1. overview ............................................................................................................... .................................. 25 9.3.2. input channel selection ................................................................................................ ........................... 25 9.3.3. reference channel selection............................................................................................ ....................... 26 9.3.4. application example.................................................................................................... ............................ 26 9.4. programmable gain amplifie r settings..................................................................................... ....................... 28 9.4.1. overview ............................................................................................................... .................................. 28
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 3 section page table of contents advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 9.4.2. configuration flow ..................................................................................................... .............................. 29 9.4.3. enable/disable pgas .................................................................................................... .......................... 30 9.4.4. pga3 gain configuration ................................................................................................ ......................... 30 9.4.5. pga2 gain configuration ................................................................................................ ......................... 30 9.4.6. pga1 gain configuration ................................................................................................ ......................... 31 9.4.7. application example.................................................................................................... ............................ 31 9.5. offset cancellation ...................................................................................................... ................................... 32 9.5.1. overview ............................................................................................................... .................................. 32 9.5.2. application example.................................................................................................... ............................ 34 9.6. adc parameters ........................................................................................................... ................................. 35 9.6.1. overview ............................................................................................................... .................................. 35 9.6.2. adc settings ........................................................................................................... ................................ 36 9.7. measurement engine ....................................................................................................... .............................. 36 9.7.1. overview ............................................................................................................... .................................. 36 9.7.2. measurement engine settings............................................................................................ ..................... 37 10. default configuration..................................................................................................... ......................................... 38 10.1. zoomingadc default settings ............................................................................................. ........................... 38 11. advanced configur ation .................................................................................................... ..................................... 39 11.1. overview ................................................................................................................ ........................................ 39 11.2. measurement engine ...................................................................................................... ............................... 40 11.2.1. overview .............................................................................................................. ................................... 40 11.2.2. functional flowchart .................................................................................................. .............................. 40 11.3. control registers....................................................................................................... ...................................... 41 11.3.1. sxctrl1 - SX8722 control register 1 ................................................................................... .................... 41 11.3.2. sxctrl2 - SX8722 control register 2 ................................................................................... .................... 41 11.3.3. sxcfgen - configuration enabling register ............................................................................. ................ 42 11.3.4. sxupdated - updated configuration register ............................................................................ .............. 42 11.3.5. configuration register - measurement mode ............................................................................. ............. 42 11.4. filtering ............................................................................................................... ........................................... 43 11.4.1. filter types .......................................................................................................... .................................... 43 11.4.2. configuration register - filtering.................................................................................... ........................... 43 11.4.3. filter size register.................................................................................................. .................................. 44 11.5. alarms.................................................................................................................. .......................................... 44 11.5.1. configuration register - alarms....................................................................................... ......................... 44 11.5.2. alarm threshold registers ............................................................................................ ........................... 44 11.5.3. sxctrl2 - SX8722 control register 2 ................................................................................... .................... 45 11.6. i2c eeprom......... ................ ................ ................ ................. ............. ............ ........... ................................... 46 11.6.1. overview .............................................................................................................. ................................... 46 11.6.2. schematic ............................................................................................................. .................................. 46
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 4 section page table of contents advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11.7. using the SX8722 stand alone............................................................................................ .......................... 47 11.7.1. schematic ............................................................................................................. .................................. 47 11.8. frequency calibration process ........................................................................................... ............................ 48 11.8.1. overview .............................................................................................................. ................................... 48 11.8.2. using an 32.768 khz xtal.............................................................................................. ....................... 48 11.8.3. using a 32.768 khz external clock source .............................................................................. ............... 49 11.9. working below 3 v ....................................................................................................... .................................. 50 11.9.1. operating range ....................................................................................................... ............................... 50 11.9.2. internal voltage multiplier ........................................................................................... ............................. 50 11.9.3. schematic ............................................................................................................. .................................. 50 12. zoomingadc ................................................................................................................ ......................................... 51 12.1. zoomingadc features ..................................................................................................... ............................. 51 12.1.1. overview .............................................................................................................. ................................... 51 12.2. acquisition chain ....................................................................................................... .................................... 51 12.3. zoomingadc detailed block diagram........... ............................................................................ ..................... 53 12.4. zoomingadc register map ................................................................................................. ........................... 54 12.5. zoomingadc? registers table ..................... ........................................................................ ......................... 56 12.6. input multiplexers...................................................................................................... ..................................... 57 12.7. programmable gain amplif iers ............................................................................................ .......................... 58 12.7.1. pga & adc enabling .................................................................................................... ......................... 58 12.7.2. pga1 .................................................................................................................. .................................... 58 12.7.3. pga2 .................................................................................................................. .................................... 59 12.7.4. pga3 .................................................................................................................. .................................... 60 12.8. adc characteristics..................................................................................................... .................................. 62 12.8.1. conversion sequence................................................................................................... .......................... 62 12.8.2. sampling frequency .................................................................................................... ........................... 63 12.8.3. over-sampling ratio................................................................................................... ............................ 63 12.8.4. elementary conversion s................................................................................................ ......................... 64 12.8.5. resolution ............................................................................................................ ................................... 64 12.8.6. conversion time & throughput .......................................................................................... .................... 65 12.8.7. output code format .................................................................................................... ........................... 67 12.9. power saving modes ...................................................................................................... ............................... 69 12.10. input impedance........................................................................................................ .................................... 69 12.11. switched capacitor principle........................................................................................... .............................. 70 12.12. pga settling or input ch annel modifications ............................................................................ .................... 71 12.13. pga gain & offset, linearity and noise ................................................................................. ...................... 71 12.14. power reduction ........................................................................................................ ................................... 71 12.15. noise .................................................................................................................. ........................................... 72 12.16. gain error and offset error ................ ............................................................................ ............................... 73
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 5 section page table of contents advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 13. typical performances ...................................................................................................... ...................................... 75 13.1. current consumption.... ................................................................................................. ................................. 75 13.2. zoomingadc .............................................................................................................. ................................... 76 13.2.1. integral non-linearity ................................................................................................ ............................... 76 13.2.2. differential non-linearity ........................................................................................... .............................. 77 13.2.3. resolution vs acquisition time........................................................................................ ......................... 78 14. register memory map and description ......... .............................................................................. .......................... 79 14.1. memory map .............................................................................................................. .................................... 79 14.2. register description .................................................................................................... ................................... 82 14.2.1. SX8722 general configuration.......................................................................................... ....................... 82 14.2.2. configuration 1 registers............................................................................................. ............................ 84 14.2.3. configuration 2 registers............................................................................................. ............................ 88 14.2.4. configuration 3 registers............................................................................................. ............................ 92 14.2.5. configuration 4 registers............................................................................................. ............................ 96 15. power modes............................................................................................................... ........................................ 100 15.1. power modes transitions................................................................................................. ............................. 100 15.2. active mode ............................................................................................................. .................................... 101 15.2.1. description ........................................................................................................... ................................. 101 15.2.2. how to set SX8722 in active mode ...................................................................................... ................. 101 15.3. sleep mode.............................................................................................................. .................................... 101 15.3.1. description ........................................................................................................... ................................. 101 15.3.2. operating specifications of the sleep mode ............................................................................ .............. 101 15.3.3. SX8722 sleep current consumption below 3v vbat........................................................................ ...... 102 15.3.4. SX8722 sleep current consumption with the 32. 768 khz xtal ............................................................. . 102 15.3.5. SX8722 sleep current consumption without the 32 .768 khz xtal......................................................... 102 15.3.6. how to set SX8722 in sleep mode....................................................................................... ................. 102 15.3.7. wake up from sleep mode to active mode ................................................................................ ............ 102 15.4. shutdown mode ........................................................................................................... ................................ 103 15.4.1. description ........................................................................................................... ................................. 103 15.4.2. operating specifications in shutdown mode ............................................................................. ............ 103 15.4.3. how to set SX8722 in shutdown mode .................................................................................... ............. 103 15.4.4. wake-up from shutdown mo de to active mode............................................................................. ........ 104 15.4.5. change from shutdown mode to sleep mode ............................................................................... ........ 104 16. pcb layout considerations................................................................................................. ................................ 105 17. how to evaluate.................................... ....................................................................... ........................................ 105 18. package outline drawing: ml pq44-7x7mm ..................................................................................... .................. 105 19. land pattern drawing: mlpq 44-7x7mm........................................................................................ ..................... 106 20. tape and reel specification............................................................................................... ................................. 107
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 6 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 1. specifications 1.1. absolute maximum ratings stresses above the values listed below may cause permanent device failure. exposure to absolute maximum ratings for extended periods may af fect device reliability. note: this device is esd sens itive. use of standard esd han dling precautions is required. 1.2. operating conditions all values are valid whithin the operati ng conditions unless otherwise specified. parameter symbol condition min max units power supply v bat vss - 0.3 6 v storage temperature t store -55 150 c max sensor common mode v vr p v vr n vss - 300 v batt + 300 mv input voltage vss - 300 v batt + 300 mv peak soldering temperature t 260 c parameter symbol condition min typ max unit operating conditions power supply v bat 2.4 5.5 v operating temperature t op -40 125 c curent consumption active current i op 300 a sleep current (1) i sleep temperature < 85c 1 5.0 a sleep current (2) i sleep temperature < 85c 3 10.0 a shutdown current i shut temperature < 85c 0.5 3.5 a digital i/o input logic high v ih 0.7 x v bat v input logic low v il 0.3 x v bat v output logic high v oh i oh < 4 ma v bat - 0.4 v output logic low v ol i ol < 4 ma 0.4 v
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 7 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface (1) with external 32.768khz xtal connected (2) without external 32.768khz xtal connected 1.3. zoomingadc specifications unless otherwise spec ified: temperature t a = +25c, v batt = +5v, gnd = 0v, v ref = +5v, v in = 0v, rc frequency f rc = 2mhz, sampling frequency f s = 300 khz, overall pga gain gd tot = 1, offsets gd off2 = gd off3 = 0. power operation: normal (ib_amp_adc[1:0] = ib_amp_pga[1:0] = '11'). for resolution n = 12 bits: osr = 32 and n elconv = 4. for resolution n = 16 bits: osr = 512 and n elconv = 2. parameter comments/co nditions value units min typ max analog input characteristics differential input voltage range v in = v inp -v inn gain = 1, osr = 32 (note 1) -2.42 +2.42 v gain = 100, osr = 32 -24.2 +24.2 mv gain = 1000, osr = 32 -2.42 +2.42 mv reference voltage range v ref,adc = v refp -v refn v batt v programmable gain amplifier total pga gain gd tot 0.5 1000 v/v pga1 gain gd 1 see table 15 1 10 v/v pga2 gain gd 2 see table 16 1 10 v/v pga3 gain gd 3 step = 1/12 v/v, see table 47 127/12 v/v gain settings precision (each stage) -3 +/- 0.5 +3 % gain temperature dependance offset +/- 5 ppm / c pga2 offset gd off2 step = 0.2 v/v, see table 46 -1 +1 v/v pga3 offset gd off3 step = 1.12 v/v, see table 48 -63/12 +63/12 v/v offset settings precision (pga2 or pga3) (note 2) -3 +/- 0.5 +3 % offset temperature dependance +/-5 ppm / c input impedance pga1 pga1 gain = 1 (note 3) 1500 k pga1 gain = 10 (note 3) 150 k input impedance pga2 ,pga3 m aximal gain = 1 (note 3) 150 k output rms noise pga1 (note 4) 205 v pga2 (note 5) 340 v pga3 (note 6) 365 v
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 8 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 1. zoomingadc specifications adc static performances resolution n (note 7) 6 16 bits no missing codes (note 8) gain error (note 9) +/- 0.15 % of fs offset error n = 16 bits (note 10) +/- 1 lsb integral non-linearity inl resolution n = 16 bits (note 11) +/- 1.0 lsb differential non-linearity dnl resolution n = 16 bits (note 12) +/- 0.5 lsb power supply rejection ratio psrr v batt = 5v +/- 0.3v (note 13) 78 db v batt = 3v +/- 0.3v (note 13) 72 db adc dynamic performances throughput rate (continuous mode) t conv n = 12 bits (note 14) 3 133 cycles / f s n = 16 bits (note 14) 0 1027 cycles / f s throughput rate (continuous mode) 1/t conv n = 12 bits, f s 3.76 ks/s n = 16 bits, f s 0.49 ks/s nbr of initialization cycles n init 02 cycles nbr of end conversion cycles n end 0 5 cycles pga stabilization delay (note 15) osr cycles time base max adc oversampling frequency f smax @ 25c, with a 32k xtal 270 300 330 khz min adc oversampling frequency f smin @ 25c, with a 32kxtal 33 37.5 42 khz digital output adc output data coding see table 55 and table 56 binary two?s complement temperature specified range -40 +85 c operating range -40 +125 c parameter comments/co nditions value units min typ max
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 9 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface notes (1) gain defined as overall pga gain gdtot = gd1 x gd2 x gd3. maximum input voltage is given by: v in,max = (v ref /2) (osr/osr+1). (2) offset due to tolerance on gdo ff2 or gdoff3 setting. for small in trinsic offset, use only adc and pga1. (3) measured with block connected to inputs through amux block. normalized input sampling frequency for input impedance is f s = 512 khz. this figure must be multiplied by 2 for f s = 256 khz, 4 for f s = 128 khz. input impedance is proportional to 1/f s . (4) figure independent from pga1 gain and sampling frequency f s . see equation eq. 21 to calculate equivalent input noise. (5) figure independent on pga2 gain and sampling frequency f s . see equation eq. 21 to calculate equivalent input noise. (6) figure independent on pga3 gain and sampling frequency f s . see equation eq. 21 to calculate equivalent input noise. (7) resolution is given by n = 2 log 2 (osr) + log 2 (n elconv ). osr can be set between 8 and 1024, in powers of 2. n elconv can be set to 1, 2, 4 or 8. (8) if a ramp signal is applied to the input, all digital codes appear in the resulting adc output data. (9) gain error is defined as the amount of deviation between the ideal (theoretical) tr ansfer function and the measured transfe r function (with the offset error removed). (10) offset error is defined as the output code error for a ze ro volt input (ideally, output code = 0). for 1 lsb offset, n elconv must be 2. (11) inl defined as the deviation of the dc transfer curve of eac h individual code from the best-f it straight line. this specif ication holds over the full scale. (12) dnl is defined as the difference (in lsb) between the ideal (1 lsb) and measured code transitions for successive codes. (13) values for gains = 1 to 100. psrr is defined as the amount of change in the adc output value as the power supply voltage changes. (14) conversion time is given by: t conv = (n elconv (osr + 1) + 1) / f s . osr can be set between 8 and 1024, in powers of 2. n elconv can be set to 1, 2, 4 or 8. (15) pgas are reset after each writing operation to registers cxregadc1-5 . the adc must be started after a pga or inputs common- mode stabilisation delay. this is done by writing bit start several cycles after pga settings modification or channel switching . delay between pga start or input channel switching and adc start should be equivalent to osr (between 8 and 1024) number of cycles. this delay does not apply to conversions made without the pgas. (16) nominal (maximum) bias currents in pgas and adc, i.e. ib_amp_pga[1:0] = '11' and ib_amp_adc[1:0] = '11'. (17) bias currents in pgas and adc set to 3/4 of nominal values, i.e. ib_amp_pga[1:0] = '10', ib_amp_adc[1:0] = '10'. (18) bias currents in pgas and adc set to 1/2 of nominal values, i.e. ib_amp_pga[1:0] = '01', ib_amp_adc[1:0] = '01'. (19) bias currents in pgas and adc set to 1/4 of nominal values, i.e. ib_amp_pga[1:0] = '00', ib_amp_adc[1:0] = '00'.
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 10 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 2. pin configuration and marking information 2.1. pin configuration 2.2. marking information nnnnnn = part number (example: SX8722) yyww = date code (example: 0752) xxxxxxxxx = semtech lot no. (example a01e90101) alrm1 alrm2 ckout ee_sda SX8722 (top view) nc nc cal dnc ac4 nc ac5 ac6 ac7 bias ee_pow ee_scl 8 9 10 11 12 13 14 15 23 24 25 26 41 42 43 44 ac1 ac2 ac3 27 28 29 scl sda nc 16 17 18 nc nc nc 5 6 7 dnc xout xin 38 39 40 ac0 30 vss ar1n ar1p 31 32 33 nc 19 ntest ar2p ar2n 20 21 22 ready 4 shut nc sleep 1 2 3 vmult 37 reset vreg vbat 34 35 36
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 11 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 3. pin description pin symbol type function status at por 1 nc not connected 2 sleep digital input setting this pin to 0 puts the SX8722 in sleep mode, power consumption ~1.5ua, otherwise the pin can be floating internal pull-up 3 shut digital input setting this pin to 0 puts the SX8722 in shutdown mode, power consumption ~0.5ua, ot herwise the pin can be floating internal pull-up 4 ready digital output is high when a measurement data is available low 5 nc not connected 6 nc not connected 7 nc not connected 8 bias digital output bias pin, is set to v bat voltage when a measurement is performed low 9 ee_pow digital output must be used to power the opti onal i2c eeprom low 10 ee_sda digital io must be connected to sda pin of the optional eeprom when used. otherwise must remain floating (see chapter eeprom connection) low 11 ee_scl digital io must be connected to scl pin of the optional eeprom when used. otherwise must remain floating (see chapter eeprom connection) low 12 alrm1 digital output alarm1 pin, is high when "on" threshold is reached and low when "off" threshold is reached, when not used can reamin floating low 13 alrm2 digital output alarm2 pin, is high when "on" threshold is reached and low when "off" threshold is reached, when not used can reamin floating low 14 ckout digital output system clock output low 15 nc not connected 16 scl digital io serial clock line of the i2c compatible interface input 17 sda digital io serial data line of the i2c compatible interface input 18 nc not connected 19 nc not connected 20 ntest digital input must be connected to v bat 21 ar2p analog input second analog in put reference (positive input) 22 ar2n analog input second analog in put reference (negative input) 23 ac7 analog input zoomingadc tm input 7
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 12 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 24 ac6 analog input zoomingadc tm input 6 25 ac5 analog input zoomingadc tm input 5 26 ac4 analog input zoomingadc tm input 4 27 ac3 analog input zoomingadc tm input 3 28 ac2 analog input zoomingadc tm input 2 29 ac1 analog input zoomingadc tm input 1 30 ac0 analog input zoomingadc tm input 0 31 ar1p analog input first analog re ference input (positive input) 32 ar1n analog input first analog reference input (negative input) 33 vss power negative power supply 34 vbat power positive power supply 35 vreg analog input connected to the internal voltage regulator. must be connected through 1uf capacitor to the ground. 36 reset digital input reset pin, active hi gh, must be tied to ground through a 3k3 resistor. 37 vmult analog input external capacitor for the internal voltage multiplier. vmult capacitor must be connected through 2nf to the ground when vbat < 3v 38 xin digital input xtal connection, left unconnected when not used 39 xout digital output xtal connection, left unconnected when not used 40 dnc do not connect 41 dnc do not connect 42 cal digital input calibration pin, set low to use xtal. internal pull-up 43 nc not connected 44 nc not connected pin symbol type function status at por
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 13 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 4. timing characteristics (1) all timings specifications are referred to vilmin and vihmax voltage levels defined for the scl and sda pins. with 32?768 hz xtal presence. 4.1. i2c timing waveforms figure 1. i2c start and stop timing figure 2. i2c data timings parameter symbol condition min typ max unit i2c timing specifications (1) scl clock frequency f scl 0 100 khz scl low period t low 4.7 s scl high period t high 4.0 s data setup time t su;dat 250 ns data hold time t hhd;dat 4.0 ns repeated start setup time t su;sta 4.7 s start condition hold time t hd;sta 4.0 s stop condition hold time t su;sto 4.0 s bus free time between stop and start t buf 4.7 s sda scl t su;sta t hd ;sta t su;sto t buf sda scl t low t high t su ;d at t hd;dat t sp
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 14 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 4.2. time specification without the 32.768 khz xtal the internal SX8722 rc oscillator accuracy depends on technology tole rance. it can re ach 50% difference from one chip to another in this case, and if no calibration is do ne, the rc clock is centred around 1.2 mhz. SX8722 timing values without xtal can thus differ of 50% to these with a xtal. 4.3. start-up time with th e 32.768 khz xtal presence the mean time of eeprom loading at the start-up is typically 140 ms if configuration data are saved in. in this case SX8722 will provide th e first sample after typically 180ms. figure 3. start-up timing diagram with eeprom loading 4.4. changing power mode by pin signal table 2. power mode changing timings by pin setting (1) instantaneous to from shut sleep active shut 640ms 650ms sleep 660ms active inst. (1) inst. (1) SX8722 power- on sample available time before eeprom loading: 7.5 [ms] time after eeprom loading: 140 [ms] eeprom loading t t t time to have the first sample: 180 [ms]
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 15 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 4.5. changing power mode by i2c command table 3. power mode changing timings by i2c command (1) instantaneous note: when time to change a power mode is instantaneous, it doesn't mean that the chip is totally ready to work. there are for e xample initialization times, eeprom loading or code execution. the transition time is considered as not low power. to from shut sleep active shut 770us 700us sleep 470us active inst. (1)
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 16 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 5. circuit description 5.1. detailed bloc diagram figure 4. SX8722 detailed bloc diagram 5.2. functional description ? the SX8722 is a zoomingadc? with i2c compat ible interface allowin g multiple setups. ? the major modules of the SX8722 are the zoomingadc?, the signal post processing, the control unit and the power management ? the SX8722 offers several configuration poss ibilities allowing the develope r to use it as a peripheral of its system or to use it as a stand alone system generating alarms. SX8722 mcu supply ac0 ac1 ready ac6 ac7 bias ar1p ar1n i2c eeprom reset rc oscillator i2c post process 10 + 16 bits zoomingadc? parameters ram xtal oscillator dfll sleep shut vreg xout xin ckout vss alrm1 alrm2 vmult ee_sda ee_scl vbat i2c power mgmt voltage multiplier regulator cal control ee_pow ground vbat gpio gpio gpio gpio / ckout gpio i2c ckin/gpio gpio gpio ground * * * * * optional components
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 17 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface ? the zoomingadc? is made of 1 input multiplexer, 3 program mable gain amplifiers and a 16 bits sigma-delta adc. the input multiplexer allows measuring 4 differential sensors or 7 single ended sensors or a combination of differential and single-ended. the total gain of the pga enables an amplificat ion of 1000 and the offset correction can reach up to 15 times the full scale input signal. ? the SX8722 is not only giving access to the very efficient zoomingadc? technology, it also gives access to a very low power acquisition system entirely configurab le to reach as low as 0.5ua in shut down mode. the low power modes can be reached through pins or specific serial commands. ? the whole chip is controlled by a set of registers; these regi sters have factory default settings and can be modified in 2 ways: the serial interface commands or an optional external eeprom. at startup the SX8722 checks for eeprom presence and updates its registers with eeprom contents. ? the whole chip is working at 1.2mhz using its internal rc oscillator, this frequency ca n be calibrated. ? the clock calibration can be done using several methods: ex ternal 32.768 khz xtal, external 32.768 khz reference signal, or eeprom para meter configuration. ? several corrections can be applied on the measur ed signal such as different digital filters. ? the SX8722 offers two alarm pins. "on" and "off" thresholds can be set independently. ? a clock out pin can be enabled to have the exact frequency of rc oscillator. ? external eeprom and sensors can be biased by the dedi cated SX8722 pins ee_pow an d bias allowing the most efficient power management. ? the pin ready is a single signal that can be used to interrupt th e host microcontroller. ? the reset pin enables the host system to reset the SX8722 to its startup settings at any time. ? the internal voltage multiplie rs is automatically enabled when working below 3 volts. ? the SX8722 implements 4 configuration register sets. each of these sets completely defines the behavior of the zoomingadc?. this allows the user to preset 4 different meas urement configurations that ca n be activated by setting a single bit.
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 18 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface the diagram below page explains the registers system more in details. figure 5. register sets system the measurement engine copies the configuration register sets in the zoomingadc? physical registers and writes back the conversion results. the communication engine controls read/write ac cess from the i2c or the external eeprom. 10 + 16 bits measurement engine alarms control & configuration registers sets zoomingadc ? registers communication engine SX8722 filtering i2c external eeprom alarm pins service pins
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 19 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 5.3. zoomingadc the SX8722 core is the zoomingadc?, the diagram below shows mo re in detail the architecture of this acquisition chain. figure 6. acquisition chain architecture the block schematic above is separated in function boxes: a. input multiplexers ? routing of the input signal. ? routing of the reference. b. programmable gain amplifiers ? can be enabled/disabled separately. ? each pga has programmable gain from 1 to 10. ? total pga gain available = pga1 x pga2 x pga3 = 1000. c. offset cancellation ? subtract or add a reference multiple to the input signal. ? can compensate up to 15 times the full scale signal. d. adc ? sigma-delta adc. ? offers several sampling frequencies. ? over sampling rates and elementary conversion combinations allow setting the ideal resolution for the ideal conversion time. e. measurement engine ? manages up to 4 zoomingadc? configurations. ? updates the measured values. + - + - + - pga2 + - + - adc + - pga1 pga3 + - + - 1 2 3 4 5 6 7 0 0 1 2 3 + - + - off3 off2 ac ar mux mux v in v ref f s f s measurement engine a b d e c v in, adc 1 - 10 1 - 2 - 5 - 10 5/5 ... -5/5 63/12 ... -63/12 0/12 to 127/12
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 20 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 6. access the SX8722 6.1. description the SX8722 is configured trough register sets and general control registers. all the accesses to the SX8722 registers are done th rough the i2c interface using read and write commands. the next paragraph describes two approaches to configure the SX8722 6.2. SX8722 configuration as it will be shown in the next ch apter there are two ways to writ e data in the SX8722 registers: ? direct write: this command writes 8 bits to a defined address. this implie s knowledge of the value to be written to this address. ? masked write: this command can write a single bit in a byte using a mask. 7. i2c commands this chapter describes the commands that are coded in the SX8722. the SX8722 commands are summarized below, detailed timing diagrams can be found ?serial communication? chapter. table 4. SX8722 commands type command description byte data access write_direct writes 8bit data to a given address 0x10 write_masked writes bits to given address using a given mask 0x20 read reads 8bit data from a given address 0x30 power modes sleep sets the SX8722 to sleep mode 0x40 shutdown sets the SX8722 to sleep mode 0x50 reset resets the SX8722 0x60 eeprom save_eeprom saves the sx87 22 registers in the exter nal eeprom (if present) 0x70 load_eeprom loads the SX8722 registers in the external eeprom (if present) 0x80
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 21 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 8. serial communication the serial interface is a read-write 2 wire slave device. the scl wire carries the clock information and sda carries the data. the output drivers on the bus are open drain current sinks. the scl wire is controlled by the master on the bus. since the SX8722 is fairly slow, it may stretch the low clock phase when required. the sda wire is controlled by the ma ster or the slave depending on the operation. sda only changes while the clock signal is low exce pt for the (repeated) start or stop conditions. the (repeated) start condition for the transmission is a high to low transition on sda while scl is high. the stop condition is a low to high transition while scl is high. to read data from the SX8722, the master has to send successi vely a start bit, the slave address, a write bit. if the slave address corresponds to the address of the SX8722 and th e preceding operation is completed, the SX8722 sends an acknowledge bit. the master then sends the read command which is acknowledged by the salve, the memory address that it would like to read which is also acknowledged by the slave. the master issues a repeated start, repeats the slave address and read bit. the slave acknowledges and returns the data to the master. the master terminates the communication by a "not acknowledge" and a stop bit. to write data to the SX8722, the format is very similar. only the data direction is different and the acknowledgement of the slave after the data reception. 8.1. write data direct the diagram below shows the write operation. figure 7. i2c frame: write register, command 0x10 the diagram below shows the write operation at successive addresses (burst mode) figure 8. i2c frame: write burst register, command 0x10 sda s t a r t device address m s b l s b a c k w r i t e s t o p register address register value a c k a c k command a c k sda s t a r t s t o p device address m s b l s b a c k w r i t e a c k register address register value (n) a c k a c k register value (n + x) a c k command
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 22 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 8.2. write data masked the diagram below show the write masked operation. figure 9. i2c frame: write mask register, command 0x20 8.3. read data read data diagram. figure 10. i2c frame: read register, command : 0x30 read data diagram successive addresses (burst mode) figure 11. i2c frame: read burst register, command 0x30 note: if a read sequence is initiated without sending previously an address, the data shifted out will be the latest conversion result and its corresponding configuration id (24 bits). see next page for more information. sda s t a r t s t o p device address m s b l s b a c k w r i t e a c k register address register value a c k a c k register mask a c k command sda s t a r t device address m s b l s b w r i t e s t o p n o a c k a c k register address a c k r e a d device address r e s t a r t register value a c k command a c k sda s t a r t device address m s b l s b w r i t e s t o p n o a c k a c k register address a c k r e a d device address r e s t a r t register value (n+x) command a c k register value (n) a c k a c k
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 23 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 8.4. other commands the diagram below shows the other commands syntax. figure 12. i2c frame: other commands, 0x40 - 0x80 8.5. unknown commands the SX8722 does not answer to unknown commands. 8.6. reading data after a measurement. the SX8722 performs measurements successively and stores t he latest results in the enabled configurations data out registers. every time a measurement is performed the pin ready makes a positive pulse allowing the host microcontroller to retrieve data from the SX8722. when the SX8722 is addressed and read the output is as show n below. config id indicates which channel is shifted out. figure 13. i2c frame: reading after a measurement sda s t a r t device address m s b l s b w r i t e a c k command s t o p a c k sda s t a r t device address m s b l s b r e a d s t o p n o a c k data msb a c k data lsb r e s t a r t config id a c k a c k
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 24 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 9. predefined settings 9.1. introduction this chapter intends to ease the handling of the SX8722 using a set of predefined settings. these settings are covering a large range of the sx87 22 possibilities. however to avoid too much co mplexity some features are not handled by these settings. a more detailed use of the SX8722 can be found unde r the "advanced configuration" of this document. this chapter contains predefined co mmand using the masked write mode. all the settings described in this chapter use the addresses of the 1 st configuration register set, use the registers definition table to translate them to other register sets. 9.2. features covered by predefined settings figure 14. features covered by predefined settings the block schematic above shows th e functions covered and controlled by the predefined settings set. it includes: a. the input multiplexers b. the programmable gain amplifiers c. the offset cancellation d. the adc e. the measurement engine note: grayed out blocks in the schematic mean s that they are used in the current function. 1 - 10 1 - 2 - 5 - 10 5/5 ... -5/5 63/12 ... -63/12 0/12 to 127/12 + - + - + - pga2 + - + - adc + - pga1 pga3 + - + - 1 2 3 4 5 6 7 0 0 1 2 3 + - + - off3 off2 ac ar mux mux v in v ref f s f s measurement engine a b d e c v in, adc
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 25 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 9.3. input multiplexers 9.3.1. overview figure 15. input multiplexer overview the diagram above shows the input multiplexer organization; these are enabling the selectio n of both the input and the reference sources. 9.3.2. input channel selection the following settings allo w configuring the input mult iplexers of the zoomingadc? table 5. differential mode function address data mask ac0 - ac1 0x0f 0x00 0x06 ac2 - ac3 0x02 ac4 - ac5 0x04 ac6 - ac7 0x06 1 - 10 1 - 2 - 5 - 10 5/5 ... -5/5 63/12 ... -63/12 0/12 to 127/12 + - + - + - pga2 + - + - adc + - pga1 pga3 + - + - 1 2 3 4 5 6 7 0 0 1 2 3 + - + - off3 off2 ac ar mux mux v in v ref f s f s measurement engine a b d e c v in, adc
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 26 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface . table 6. single-ended mode table 7. invert input polarity 9.3.3. reference channel selection table 8. reference channel selection 9.3.4. application example in this example we want to measure a signal between ac 0 and ac1 in single ended having a reference voltage between ar1p and ar1n. the following settings mu st be sent to SX8722: table 9. reference channel selection note: this command can be optimized, since the reference and i nput setting are sharing the same address the mask and the setting s can be added. function address data mask ac0 - ac1 0x0f 0x22 0x2e ac0 - ac2 0x24 ac0 - ac3 0x26 ac0 - ac4 0x28 ac0 - ac5 0x2a ac0 - ac6 0x2b ac0 - ac7 0x2c function address data mask sign inversion 0x0f 0x10 0x10 function address data mask ar1p - ar1n 0x0f 0x00 0x01 ar2p - ar2n 0x01 function address data mask set input to ac1 - ac2 0x0f 0x00 0x06 set reference to ar1p - ar1n 0x0f 0x00 0x01
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 27 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface the following command shows the optimized way table 10. optimized command function address data mask set input to ac1 - ac0, set reference to ar1p - ar1n 0x0f 0x00 0x07
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 28 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 9.4. programmable ga in amplifier settings 9.4.1. overview figure 16. programmable gain amplif iers (pga) in the acquisition chain the diagram above shows the programmable gain amplifier organization, these are 3 pga that are cascaded, the gain is made by multiplying them (disabled pgas have the equivalent gain of 1). 1 - 10 1 - 2 - 5 - 10 5/5 ... -5/5 63/12 ... -63/12 0/12 to 127/12 + - + - + - pga2 + - + - adc + - pga1 pga3 + - + - 1 2 3 4 5 6 7 0 0 1 2 3 + - + - off3 off2 ac ar mux mux v in v ref f s f s measurement engine ab d e c v in, adc
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 29 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 9.4.2. configuration flow the diagram below shows the flow to set the gain of your configuration: figure 17. gain configuration flowchart gain = pga3 enable pga3 gain < 10 ? set gain yes set pga 3 gain enable pga2&3 set pga 2 gain set pga 3 gain set pga 1 gain set pga 2 gain set pga 3 gain gain = pga2 x pga3 gain = pga1 x pga2 x pga3 gain < 100 ? yes no enable pga1,2&3 no end
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 30 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 9.4.3. enable/disable pgas table 11. pga enable/disable settings 9.4.4. pga3 gain configuration table 12. pga3 gain configuration 9.4.5. pga2 gain configuration table 13. pga2 gain configuration function address data mask enable pga3 0x0b 0x08 0x08 disable pga3 0x00 enable pga2&3 0x0a 0x0a disable pga2&3 0x00 enable pga1,2&3 0x0e 0x0e disable pga1,2&3 0x00 function address data mask gain = 1 0x0d 0x0c 0x7f gain = 2 0x18 gain = 3 0x24 gain = 4 0x30 gain = 5 0x3c gain = 6 0x48 gain = 7 0x54 gain = 8 0x60 gain = 9 0x6c gain = 10 0x78 function address data mask gain = 1 0x0c 0x00 0x30 gain = 2 0x10 gain = 5 0x20 gain = 10 0x30
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 31 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 9.4.6. pga1 gain configuration table 14. pga1 gain configuration 9.4.7. application example the total gain to set in this example is 300. the following settings mu st be sent to SX8722: table 15. application ex ample of pga gain settings note: this command can be optimized, since pga1 and pga3 gains are sharing the same address the mask and the settings can be added. the following list of sett ings shows the optimized table 16. optimized command of pga gain settings function address data mask gain = 1 0x0d 0x00 0x80 gain = 10 0x80 function address data mask enable pga1,2&3 0x0b 0x0e 0x0e pga3 gain = 3 0x0d 0x24 0x7f pga2 gain = 10 0x0c 0x30 0x30 pga1 gain = 10 0x0d 0x80 0x80 function address data mask enable pga1,2&3 0x0b 0x0e 0x0e pga3 gain = 3, pga1 gain = 10 0x0d 0xa4 0xff pga2 gain = 10 0x0d 0x80 0x30
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 32 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 9.5. offset cancellation 9.5.1. overview figure 18. offset cancellation in the acquisition chain the offset cancellation consists in adding or subtracting a fracti on or a multiple of the reference to the signal before the ad c input. in the predefined settings only the addition or the subtraction of vref/2 is implemented. more offsets configuration can be defined using the "a dvanced configuration" at the end of this document. the drawings below explain the offset concept. figure 19. differential signal 1 - 10 1 - 2 - 5 - 10 5/5 ... -5/5 63/12 ... -63/12 0/12 to 127/12 + - + - + - pga2 + - + - adc + - pga1 pga3 + - + - 1 2 3 4 5 6 7 0 0 1 2 3 + - + - off3 off2 ac ar mux mux v in v ref f s f s measurement engine a b d e c v in, adc vref / 2 0 vin adc t - vref / 2 gain x2 vref / 2 0 t - vref / 2 (ac1 ? ac0)
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 33 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface figure 20. single ended signal, ac0 = v ss the following settings add 0.5 x v ref or subtract 0.5 x v ref from the signal. table 17. example: adding or remove 0.5 x vref function address data mask offset 3 = 0.5 x v ref 0x0e 0x06 0x7f offset 3 = -0.5 x v ref 0x46 vref 0 (ac1 ? ac0) t vref / 2 0 vin adc t - vref / 2 offset 0.5 x vref
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 34 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 9.5.2. application example case 1 input signal = v ref / 2 input selection = ac0 - ac1. (see "input multiplexers" chapter) offset to remove is v ref / 2. the following command must be sent to SX8722: case 2 input signal = v ref input selection = ac0 - ac1. (see "input multiplexers" chapter) offset to remove is -v ref / 2. the following command must be sent to SX8722: function address data mask offset 3 = 0.5 x v ref 0x0e 0x06 0x7f function address data mask offset 3 = -0.5 x v ref 0x0e 0x46 0x7f
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 35 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 9.6. adc parameters 9.6.1. overview table 18 adc in the acquisition chain the adc parameters are mainly the resolution and acquisition speed. detailed adc parameters and configuration can be found in the "advanced configuration" chapter the table below gives the main configurations available usi ng the predefined settings a nd their main characteristics: table 19. adc predefined settings name resolution [bits] conversion time [ms] (typ) sampling frequency [khz] (typ) over- sampling ratio number of elementary conversion comments s16 16 27.3 300 1024 8 maximum resolution, thermal noise reduced to its minimum n16 16 6.8 1024 2 standard 16 bits resolution f16 16 3.4 1024 1 fastest 16 bits resolution n12 12 0.22 64 1 standard 12 bits resolution n8 8 0.06 16 1 standard 8 bits resolution 1 - 10 1 - 2 - 5 - 10 5/5 ... -5/5 63/12 ... -63/12 0/12 to 127/12 + - + - + - pga2 + - + - adc + - pga1 pga3 + - + - 1 2 3 4 5 6 7 0 0 1 2 3 + - + - off3 off2 ac ar mux mux v in v ref f s f s measurement engine a b d e c v in, adc
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 36 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 9.6.2. adc settings table 20. adc register settings 9.7. measurement engine 9.7.1. overview figure 21. measurement engine the measurement engine manages the configuration re gister sets and controls registers contents. based on these parameters it configures the zoomingadc?, su pervises post processing of the measurements, stores the results and flags the ready signal. once enabled the configuration 1 will be a pplied to the zoomingadc? and measurem ent will be done until the configuration is disabled using the disable command. note: all the predefined settings refer to configuration 1, to ch ange other configurations simply adapt the address value. more detailed functionalities are described in ?advanced configuration? chapter. function address data mask s16 0x0c 0x7c 0x7c n16 0x3c f16 0x1c n12 0x0c n8 0x04 1 - 10 1 - 2 - 5 - 10 5/5 ... -5/5 63/12 ... -63/12 0/12 to 127/12 + - + - + - pga2 + - + - adc + - pga1 pga3 + - + - 1 2 3 4 5 6 7 0 0 1 2 3 + - + - off3 off2 ac ar mux mux v in v ref f s f s measurement engine a b d e c v in, adc
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 37 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 9.7.2. measurement engine settings table 21. measurement engine settings application address data mask configuration 1 enabled 0x02 0x01 0x01 configuration 1 disabled 0x00
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 38 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 10. default configuration the SX8722 default configuration is described in this chapter. the SX8722 default hardware configuration is as follow: ? 1uf vreg capacitor connected to vreg pin ? ee_sda connected to ground ? 3.0 - 5.0 power supply on vbat, 0v on gnd ? wheatstone bridge type sensor connected to ac0-ac1 biased through bias pin ? vref = vbias = vbat ? host micro controller i2c connected to sda and scl of the SX8722 ? host micro controller gpio connec ted to reset input of the SX8722 figure 22. schematic of the default configuration note: startup conditions reset = ?0? 10.1. zoomingadc default settings the SX8722 starts upon a power on reset and then goes into measurement mode. by default the measurement mode parameters are as follows: differential measurement on channel ac0 - ac1, gain 1, 16 bits resolution, reference on ar1p - ar1n, no filtering, continuous measurements. the ready pin will pulse from "0" to "1" at every sample av ailable. the host microcontr oller can then read the data. signal mux ref mux ready ac0 ac1 ac2 ac3 ac4 ac5 pga adc zoomingadc tm vbatt reset scl sda ar2n ar2p ar1n ar1p SX8722 vmult control osc i 2 c mcu ac6 ac7 bias differential sleep power shut post-process ee_pow ee_scl ee_sda xin xout ckout cal gnd alrm1 alrm2 vreg sda scl vbatt gpio
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 39 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11. advanced configuration 11.1. overview the advanced configuration section is entering more in depth in the SX8722 usage. in this section you will find: ? measurement engine ? configuration control ? filtering ? alarms ? i2c eeprom ? using the SX8722 stand alone ? calibration process ? working below 3 volts ? control registers
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 40 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11.2. measurement engine 11.2.1. overview the measurement engine is the interface between the configuration register sets and the zoomingadc?. 11.2.2. functional flowchart figure 23. measurement engine flowchart the flowchart above shows the measuremen t engine function. it performs successi vely the measurements for each enabled configuration. if in one or more configurations the bit cont is set to 1, t he measurements are performed again until the cont bit is set to 0 through the i2c interface. the engine goes out from the idle mode every time an event occurs on the i2c interface. idle mode read enabled configurations [sxctrlen] conf 1 ? measure conf 1 cont bit ? yes conf 2 ? measure conf 2 yes conf 3 ? measure conf 3 yes conf 4 ? measure conf 4 yes yes initialization, eeprom load reset / power on reset measure conf n start configure zoomingadc using configuration n parameters start conversion compute average mcounter + 1 mcounter = naverage ? store result in configuration n out registers measure conf n end wait for conversion to finish (idle mode) store intermediate values update [sxupdated n] clear single bit set ready bit
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 41 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11.3. control registers the parameters available on these registers affect the whol e SX8722 and are common to all configuration register sets. 11.3.1. sxctrl1 - SX8722 control register 1 table 22. control register; address 0x00 11.3.2. sxctrl2 - SX8722 control register 2 table 23. control register 2; address 0x01 note: more information about the alarms condition usage on alarm section register76543210 sxctrl1 ee_d xtal_d ckout reserved ee sleep shut cal bit sxctrl1 rw reset description 7 ee_d r x indicates if an eeprom was detected at startup 6 xtal_d r x indicates if an xtal was detected at startup 5 ckout rw 0 enabled the clock output on ckout pin 4 reserved rw 0 3 ee r 0 is set to 1 when SX8722 loaded its configuration from the eeprom at startup 2 sleep rw 0 when set to 1 his bit activates the sleep mode of the SX8722. setting pin sleep to 1 has the same effect. 1 shut rw 0 when set to 1 his bit activates the shutdown mode of the SX8722. setting pin shut to 1 has the same effect. 0 cal r 0 this flag shows if the SX8722 clock has been successfully calibrated. register76543210 sxctrl2 reserved reserved reserved re served al1onc al1offc al2onc al2offc bit sxctrl1 rw reset description 3 al1onc rw 0 sets the logical condition for alarm 1 on (0 = or, 1 = and) 2 al1offc rw 0 sets the logical condition for alarm 1 on (0 = or, 1 = and) 1 al2onc rw 0 sets the logical condition for alarm 1 on (0 = or, 1 = and) 0 al2offc rw 0 sets the logical condition for alarm 1 on (0 = or, 1 = and)
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 42 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11.3.3. sxcfgen - configuration enabling register writing this register allows enabling or disabling the different configuration register sets. note: when the configuration is set to single, the bit conf x is cleared automatically after the measurement is done. table 24. configuration enabling register; address 0x02 11.3.4. sxupdated - updated configuration register the configuration update registers contain which configuration has been updated by a measurement result. table 25. updated configurat ion register; address 0x03 these bits are set to 1 every time a measurement is done on one of the 4 configurations. when the registers are read, these bits are set back to 0 by the communication engine, the bits 4 to 7 indicates an overflow. 11.3.5. configuration register - measurement mode this register is present in each configuration; the bits 0 & 1 are contro lling the measur ement mode. table 26. measurement mode in configuration registers; addresses 0x10, 0x30, 0x50, 0x70 the bit single is set by the user, once the measurement is done; the measurement engine clears the conf bit of the configuration. the bit cont is set by the user, the measurement is do ne continuously until this bit is cleared by the user. register76543210 sxcfgen reserved reserv ed reserved reserved conf4 conf3 conf2 conf1 register76543210 sxupdated ovf4 ovf3 ovf2 ovf1 uconf4 uconf3 uconf2 uconf1 register76543210 cxsxcfg reserved filter type[2:0] alrm1 alrm2 single cont
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 43 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11.4. filtering 11.4.1. filter types there are 2 different filtering types: 1. average filtering. 2. moving average filtering. the average filtering is an addition of n values divided by n, this kind of filter is useful w hen having a very noisy signal; t he maximum average value is 256. advantage: reduces noise due to the high quantity of samples. disadvantage: takes the acquisition time of n samples to have a result. the sliding window averaging is a filter that takes the n last measurements and gives the mean value of them. ? advantage: result on each acquisition. ? disadvantage: limited at ten samples. additional delay. important note: the adc filtering is faster, these additional filters sh ould be used only if the number of conversion (n elconv ) and the over sampling rate (osr) are set to their maximum. 11.4.2. configuration register - filtering this register is present in each configuration; the bits 4 to 6 are cont rolling the filtering mode. table 27. filtering mode in configuration registers; addresses 0x10, 0x30, 0x50, 0x70 the table below shows the filter selection. table 28. filter selection register76543210 cxsxcfg reserved filter type[2:0] al rm1 alrm2 single cont filter type [6:4] code mode 000 none 001 average filtering 010 moving average filtering 011 reserved
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 44 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11.4.3. filter size register this register is present in each configuration; the bits 0 to 7 are controlling the filter size. table 29. filter size registers; addresses 0x11, 0x31, 0x51, 0x71 this register contains the number of samples used for the filtering. note that for a moving average filtering, this number is limited to 10. (putting a higher value will be interpre ted as 10.) 11.5. alarms the SX8722 offers two alarms pins that have configurable on & off thresholds; these thresholds are on 16 bits. each configuration register set has 2 alarms, which can be enabled, when more than one configuration is using the same alarm pin, logical function is interacting between the two alarms sources. this cond ition can be a logical or (default) or a logical and. 11.5.1. configuration register - alarms the bits 2 & 3 enable the alarm 1 & 2 when set to 1. table 30. alarm enabling in configuration r egisters; addresses 0x10, 0x30, 0x50, 0x70 11.5.2. alarm threshold registers table 31. alarm threshold registers; addresses 0x12 to 0x19, 0x32 to 0x39, 0x52 to 0x59 and 0x72 to 0x79 register76543210 cxfparam filter size [7:0] register76543210 cxsxcfg reserved filter type [2:0] alrm1 alrm2 single cont registers76543210 cxalrm1onmsb s1alrm1on cxalrm1onlsb s1alrm1on cxalrm1offmsb s1alrm1off cxalrm1offlsb s1alrm1off cxalrm2onmsb s1alrm2on cxalrm2onlsb s1alrm2on cxalrm2offmsb s1alrm2off cxalrm2offlsb s1alrm2off
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 45 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11.5.3. sxctrl2 - SX8722 control register 2 this register is common to all configurations; it se ts the relationship between the different alarm sources. table 32. alarm sources in control register 2; address 0x02 when set to 1 the condition is and and when set to 0 the condition is or. the diagram below shows the interaction between alarms sources. figure 24. alarms sources interaction the flowchart below shows the management of t he alarms flag (when at least one alarm is on). figure 25. alarms flag managment register76543210 sxctrl2 reserved reserved reserved re served al1onc al1offc al2onc al2offc alarm1 on flag set configuration 1 alarm1 on threshold reached ? configuration 2 alarm1 on threshold reached ? configuration 3 alarm1 on threshold reached ? configuration 4 alarm1 on threshold reached ? al1onc alarm1 off flag set al1offc configuration 1 alarm1 off threshold reached ? configuration 2 alarm1 off threshold reached ? configuration 3 alarm1 off threshold reached ? configuration 4 alarm1 off threshold reached ? alarm mgmt alarm1 on flag set ? alarm1 off flag set ? set alarm 1 pin to ? 1 ? set alarm 1 pin to ? 0 ? alarm mgmt end
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 46 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11.6. i2c eeprom 11.6.1. overview the SX8722 can interface a standard i2c eeprom. this allows: ? stand alone usage. ? parameters saving by save command. ? parameters restore by load command. the ee_pow pin allows the SX8722 to power the eeprom in order to guarantee the lowest power having the eeprom unpowered when unused. when no eeprom is us ed, the ee_sda pin mu st be tied to ground. 11.6.2. schematic the schematic below shows the conn ections using standard i2c eepprom. figure 26. eeprom connection signal mux ref mux ready ac0 ac1 ac2 ac3 ac4 ac5 pga adc zoomingadc tm vbatt reset scl sda ar2n ar2p ar1n ar1p SX8722 vmult control osc i 2 c mcu ac6 ac7 bias differential sleep power shut post-process ee_pow ee_scl ee_sda xin xout ckout cal gnd alrm1 alrm2 vreg sda scl vbatt gpio eeprom scl vbatt sda gnd
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 47 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11.7. using the SX8722 stand alone the SX8722 can be used stand alone to monitor signals and to generate alarms on configured thresholds. using a preprogrammed eeprom allows t he setup of these monitoring tasks. 11.7.1. schematic the schematic below shows an exampl e of a stand alone configuration. figure 27. example of stand alone configuration signal mux ref mux ready ac0 ac1 ac2 ac3 ac4 ac5 pga adc zoomingadc tm vbatt reset scl sda ar2n ar2p ar1n ar1p SX8722 vmult control osc i 2 c ac6 ac7 bias differential sleep power shut post-process ee_pow ee_scl ee_sda xin xout ckout cal gnd alrm1 alrm2 vreg eeprom scl vbatt sda gnd 5v 12v l1 l2 l3
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 48 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11.8. frequency calibration process 11.8.1. overview the SX8722 has an internal rc oscillator working at 1.2 mhz +/- 600k hz. the calibration is opti onal. the main reason to calibrate the rc frequency is to fix the input impedanc e of the acquisition chain, function of the rc frequency. this frequency can be calibrated using 2 methods. ? 32.768 khz xtal ? input of a 32.768 khz signal on the cal pin. 11.8.2. using an 32.768 khz xtal when the SX8722 is connected to a 32.768 xtal between xi n & xout, the cal pin must be grounded. this indicates to SX8722 that an xtal is present and allows frequency auto-calibration at power on. figure 28. calibration : using a 32?768 hz xtal signal mux ref mux ready ac0 ac1 ac2 ac3 ac4 ac5 pga adc zoomingadc tm vbatt reset scl sda ar2n ar2p ar1n ar1p SX8722 vmult control osc i 2 c ac6 ac7 bias differential sleep power shut post-process ee_pow ee_scl ee_sda xin xout ckout cal gnd alrm1 alrm2 vreg 5v mcu sda scl vbatt gpio 32?768 hz
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 49 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11.8.3. using a 32.768 khz external clock source the host microcontroller can at any time send a 32.768khz signal on cal pin, the de tection of a rising edge on the this pin initiates a calibration process. wh en the chip is calibrated, the pin ready rises to high level. figure 29. calibration : using a 32?768 hz signal note: if an external eeprom is present, the calibration value is saved in it. the tolerance signal must remain around 32.768 khz +/- 10% signal mux ref mux ready ac0 ac1 ac2 ac3 ac4 ac5 pga adc zoomingadc tm vbatt reset scl sda ar2n ar2p ar1n ar1p SX8722 vmult control osc i 2 c ac6 ac7 bias differential sleep power shut post-process ee_pow ee_scl ee_sda xin xout ckout cal gnd alrm1 alrm2 vreg mcu sda scl vbatt gpio gpio gpio 32?768 hz
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 50 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 11.9. working below 3 v 11.9.1. operating range the SX8722 operating range is 5.5 volts downto 2.4 volts. however, below 3 volts the SX8722 enables an internal voltage multiplier to power the zoomingadc?. 11.9.2. internal voltage multiplier this internal voltage multiplie r is automatically enabled when the power supp ly goes below 3 volts but the internal voltage multiplier requires an external capacitor between vmult pin an d ground, the value of this capacitor must be between 1 and 3 nf. 11.9.3. schematic the schematic below shows the capacitor connection: figure 30. SX8722 working below 3v schematic signal mux ref mux ready ac0 ac1 ac2 ac3 ac4 ac5 pga adc zoomingadc tm vbatt reset scl sda ar2n ar2p ar1n ar1p SX8722 vmult control osc i 2 c ac6 ac7 bias differential sleep power shut post-process ee_pow ee_scl ee_sda xin xout ckout cal gnd alrm1 alrm2 vreg mcu sda scl vbatt gpio gpio 2 nf vbatt < 3v
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 51 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 12. zoomingadc 12.1. zoomingadc features the zoomingadc is a complete and vers atile low-power analog front-end interface typically intended for sensing applications. the key features of the zoomingadc are: ? programmable 6 to 16-bit dynamic range oversampled adc ? flexible gain programming between 0.5 and 1000 ? flexible and large range offset compensation ? 4-channel differential or 8-channel single-ended input multiplexer ? 2-channel differential reference inputs ? power saving modes 12.1.1. overview figure 31. zoomingadc general functional block diagram the total acquisition chain consists of an input multiplexer, 3 programmable gain amplifier stages and an oversampled a/d converter. the reference voltage can be selected on two differ ent channels. two offset compensation amplifiers allow for a wide offset compensation range. the programmable gain and offset allow to zoom in on a small portion of the reference voltage defined input range. 12.2. acquisition chain the figure above shows the general block diagram of the acquisition chain (ac). analog inputs can be selected among eight input channels, wh ile reference input is selected between two differential channels. + - + - + - pga2 + - + - adc + - pga1 pga3 + - + - 1 2 3 4 5 6 7 0 0 1 2 3 + - + - off3 off2 ac ar mux mux v in, adc v in v ref f s f s 16 bits
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 52 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface the core of the zooming section is made of three differen tial programmable amplifiers (pga). after selection of a combination of input and reference signals v in and v ref , the input voltage is modulated and amplified through stages 1 to 3. fine gain programming up to 1'000v/v is possible. in addit ion, the last two stages provide programmable offset. each amplifier can be bypassed if needed. the output of the pga stages is directly fed to the anal og-to-digital converter (adc), which converts the signal v in,adc into digital. like most adcs intended for instrumentation or sensing app lications, the zoomingadc is an over-sampled converter (see note1). the adc is a so-called increment al converter with bipolar operation (the adc accepts both positive and negative input voltages). in first approximation, the adc output result relative to full-scal e (fs) delivers the quantity: in two's complement (see section 12.8 .7 for details). the output code out adc is -fs/2 to +fs/2 for v in,adc , -v ref /2 to +v ref /2 respectively. as will be shown in section 0, v in,adc is related to input voltage v in by the relationship: where gd tot is the total pga gain, and gdoff tot is the total pga offset. note: over-sampled converters are operated with a sampling frequency f s much higher than the input signal's nyquist rate (typically f s is 20-1'000 times the input signal bandwidth). the sampling fre quency to throughput ratio is lar ge (typically 10-500). these converters include digital decimation filtering. they are ma inly used for high resolution, and/or low-to-medium speed applicati ons. (eq. 1) (eq. 2) 2 / 2 / , ref adc in adc v v fs out ? ref tot in tot adc in v gdoff v gd v ? ? ? = , v []
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 53 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 12.3. zoomingadc deta iled block diagram figure 32. zoomingadc detailed functional block diagram + - + - + - pga2 + - + - adc + - pga1 pga3 + - + - 1 2 3 4 5 6 7 0 0 1 2 3 + - + - off3 off2 cxadcreg6 cxadcreg5 cxadcreg4 cxadcreg3 cxadcreg2 cxadcreg1 cxdataoutmsb cxdataoutlsb ac ar inputs mux mux sampling frequency fs power saving modes pga enabling nb of elementary cycles oversampling ratio acquisition chain register bank v in, adc v in v ref f s f s
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 54 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 12.4. zoomingadc register map there are six registers in the acquisition chain (ac), namely cxzadcreg1 , cxzadcreg2 , cxzadcreg3 , cxzadcreg4 , cxzadcreg5 and cxzadcreg6 . tables below shows the mapping of control bi ts and functionality of these registers while table 33 gives an overview of these six. the register map only gives a short desc ription of the different configuration bi ts. more detailed info rmation is found in subsequent sections. table 33. adc settings registers table 34. cxzadcreg1; addresses 0x0a - 0x2a - 0x4a - 0x6a table 35. cxzadcreg2; addresses 0x0b - 0x2b - 0x4b - 0x6b registers addresses cxzadcreg1 0x0a - 0x2a - 0x4a - 0x6a cxzadcreg2 0x0b - 0x2b - 0x4b - 0x6b cxzadcreg3 0x0c - 0x2c - 0x4c - 0x6c cxzadcreg4 0x0d - 0x2d - 0x4d - 0x6d cxzadcreg5 0x0e - 0x2e - 0x4e - 0x6e cxzadcreg6 0x0f - 0x2f - 0x4f - 0x6f bit cxzadcreg1 rw reset description 7reservedrw0 6:5 set_nelconv [1:0] rw 01 sets the number of elementary conversions 4:2 set_osr [2:0] rw 010 sets the oversampling rate of an elementary conversion 1reservedrw0 0reservedrw0 bit cxzadcreg2 rw reset description 7:6 ib_amp_adc[1:0] rw 11 bias current selection of the a/d converter 5:4 ib_amp_pga[1:0] rw 11 bias curre nt selection of the pga stages 3:0 enable[3:0] rw 0000 enabled the different pga stages and the adc
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 55 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 36. cxzadcreg3; addresses 0x0c - 0x2c - 0x4c - 0x6c table 37. cxzadcreg4; addresses 0x0d - 0x2d - 0x4d - 0x6d table 38. cxzadcreg5; addresses 0x0e - 0x2e - 0x4e - 0x6e table 39. cxzadcreg6; addresses 0x0f - 0x2f - 0x4f - 0x6f bit cxzadcreg3 rw reset description 7:6 fin[1:0] rw 00 sampling frequency selection 5:4 pga2_pga[1:0] rw 00 pga2 stage gain selection 3:0 pga2_offset[3:0] rw 0000 pga2 stage offset selection bit cxzadcreg4 rw reset description 7 pga1_gain rw 0 pga1 stage gain selection 6:0 pga3_pga[6:0] rw 0000000 pga3 stage gain selection bit cxzadcreg5 rw reset description 7 reserved r 0 6:0 pga3_offset[6:0] rw 0000000 pga3 stage offset selection bit cxzadcreg6 rw reset description 7 pga1_gain r 0 activity flag 6 pga3_pga[6:0] r 0 select default configuration 5:1 amux[4:0] rw 00000 input channel configuration selector 0 vmux rw 0 reference channel selector
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 56 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 12.5. zoomingadc? registers table in table below the configuration of the peripheral registers is detailed. the system has a bank of eight 8-bit registers: six registers are used to configure the acquisition chain (cxzadcr eg1 to 6), and two registers are used to store the output code of the analog-to-digital conversion (cxdataoutmsb & lsb). table 40. zoomingadc registers note bits labelled r are reserved with: out: (r) digital output code of the analog -to-digital converte r. (msb = out[15]) set_nelc: (rw) sets the number of elementary conversions to 2 set_nelc[1:0] . to compensate for offset s, the input signal is chopped between elementary conversions (1,2,4,8). set_osr: (rw) sets the over-sampling rate (osr) of an elementary conversion to 2 (3+set_osr[2:0]) . osr = 8, 16, 32, ..., 512, 1024. cont: (rw) setting this bit starts a conversion. a new conversi on will automatically begin as long as the bit remains at 1. ib_amp_adc: (rw) sets the bias current in the adc to 0.25 x (1+ ib_amp_adc[1:0]) of the normal o peration current (25, 50, 75 or 100% of nominal current). to be used for low-power, low-speed operation. ib_amp_pga: (rw) sets the bias current in the pgas to 0.25 x (1 + ib_amp_pga[1:0]) of the normal operation current (25, 50, 75 o r 100% of nominal current). to be used for low-power, low-speed operation. enable: (rw) enables the adc modulator (bit 0) and the different stages of the pgas (pgai by bit i = 1,2,3). pga stages that are disabled are bypassed. fin: (rw) these bits set the sampling frequency of the acquisiti on chain. expressed as a fracti on of the oscillator frequency, the sampling frequency is given as: 00 ' 1/4 f rc , 01 ' 1/8 f rc , 10 ' 1/32 f rc , 11' ~8khz. pga1_gain: (rw) sets the gain of the first stage: 0 ' 1, 1 ' 10. pga2_gain: (rw) sets the gain of the second stage: 00 ' 1, 01 ' 2, 10 ' 5, 11 ' 10. register name bit position 76543210 cxdataoutlsb out[7:0] cxdataoutmsb out[15:8] cxzadcreg1 default values r 0 set_nc[1:0] 01 set_osr[2:0] 010 r 0 r 0 cxzadcreg2 default value ib_amp_adc[1:0] 11 ib_amp_pga[1:0] 11 enable[3:0] 0001 cxzadcreg3 default value fin[1:0] 00 pga2_gain[1:0] 00 pga2_offset 0000 cxzadcreg4 default value pga1_gain 0 pga3_gain[6:0] 0000000 cxzadcreg5 default value 0 pga3_offset[6:0] 0000000 cxzadcreg6 default value r 0 r 0 amux[4:0] 00000 vmux 0
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 57 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface pga3_gain: (rw) sets the gain of the third stage to pga3_gain[6:0] 1/12. pga2_offset: (rw) sets the offset of the se cond stage between -1 and +1, with increments of 0.2. the msb gives the sign (0 positive, 1 negative); amplitude is coded with the bits pga2_offset[5:0]. pga3_offset: (rw) sets the offset of the third stage between -5.2 5 and +5.25, with increments of 1/12. the msb gives the sign ( 0 positive, 1 negative); amplitude is coded with the bits pga3_offset[5:0]. amux(4:0): (rw) amux[4] sets the mode (0 ' 4 differential inputs, 1 ' 7 inputs with a(0) = common reference) amux(3) sets the s ign (0 ' straight, 1' cross) amux[2:0] sets the channel. vmux: (rw) sets the differential reference chan nel (0 ' r(1) and r(0), 1 ' r(3) and r(2)). (r = read; w = write; rw = read & write) 12.6. input multiplexers the zoomingadc has eight analog inputs ac_a(0) to ac_a(7) an d four reference inputs ac_r(0) to ac_r(3). let us first define the differential input voltage vin and reference voltage vref respectively as: and: as shown in table 41 the inputs can be configured in tw o ways: either as 4 differential channels (vin1 = ac_a(1) - ac_a(0),..., vin4 = ac_a(7) - ac_a(6)), or ac_a(0) can be used as a common re ference, providing 7 signal paths all referred to ac_a(0). the control word for the analog input sele ction is amux[4:0]. notice that the bit amux[3] controls the sign of the input voltage. table 41. analog input selection (eq. 3) (eq. 4) amux [4:0] (regaccfg5[5:1]) v inp v inn amux [4:0] (regaccfg5[5:1]) v inp v inn 00x00 00x01 00x10 00x11 ac_a(1) ac_a(3) ac_a(5) ac_a(7) ac_a(0) ac_a(2) ac_a(4) ac_a(6) 01x00 01x01 01x10 01x11 ac_a(0) ac_a(2) ac_a(4) ac_a(6) ac_a(1) ac_a(3) ac_a(5) ac_a(7) 10000 10001 10010 10011 10100 10101 10110 10111 ac_a(0) ac_a(1) ac_a(2) ac_a(3) ac_a(4) ac_a(5) ac_a(6) ac_a(7) ac_a(0) 11000 11001 11010 11011 11100 11101 11110 11111 ac_a(0) ac_a(0) ac_a(1) ac_a(2) ac_a(3) ac_a(4) ac_a(5) ac_a(6) ac_a(7) inn inp in v v v ? = v [] refn refp ref v v v v []
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 58 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface similarly, the reference voltage is chosen among two differential channels (vref1 = ac_r(1)-ac_r(0) or vref2 = ac_r(3)-ac_r(2)) as shown in table 42 the selection bit is vmux. the reference inputs vrefp and vrefn (common- mode) can be up to the power supply range. table 42. analog input reference selection 12.7. programmable gain amplifiers the zooming function is implemented with three programmable gain amplifiers (pga). these are: ? pga1: coarse gain tuning ? pga2: medium gain and offset tuning ? pga3: fine gain and offset tuning all gain and offset settings are realized with ratios of capacito rs. the user has control over each pga activation and gain, as well as the offset of stages 2 and 3. these functions are examined hereafter. 12.7.1. pga & adc enabling depending on the application objectives, the user may enable or bypass each pga stage. this is done according to the word enable and the coding given in table 43. to reduce powe r dissipation, the adc can also be inactivate d while idle. table 43. pga and adc enabling 12.7.2. pga1 the first stage can have a buffer function (unity gain) or provide a gain of 10 (see table 44). the voltage v d1 at the output of pga1 is: vmux (regaccfg5[0]) v refp v refn 0ac_r(1)ac_r(0) 1ac_r(3)ac_r(2) enable [3:0] block xxx0 xxx1 adc disabled adc enabled xx0x xx1x pga1 disabled pga1 enabled x0xx x1xx pga2 disabled pga2 enabled 0xxx 1xxx pga3 disabled pga3 enabled (eq. 5) in d v gd v ? = 1 1 v []
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 59 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface where gd1 is the gain of pga1 (in v/v) controlled with the bit pga1_gain. table 44. pga1 gain settings 12.7.3. pga2 the second pga has a finer gain and offset tuning capability, as shown in table 45 and table 46. the voltage vd2 at the output of pga2 is given by: where gd2 and gdoff2 are respectively the gain and offset of pga2 (in v/v). these are controlled with the words pga2_gain[1:0] and pga2_offset[3:0]. table 45. pga2 gain settings pga1_gain pga1 gain [v/v] 01 110 (eq. 6) pga2_gain pga2 gain [v/v] 00 1 01 2 10 5 11 10 pga2_offset pga2 offset [v/v] 0000 0 0001 +0.2 0010 +0.4 0011 +0.6 0100 +0.8 0101 +1 1000 -0.2 1001 -0.4 1010 -0.6 1011 -0.8 ref d d v gdoff v gd v ? ? ? = 2 1 2 2 v []
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 60 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 46. pga2 offset settings 12.7.4. pga3 the finest gain and offset tuning is perf ormed with the third and last pga stage, according to the following coding tables. table 47. pga3 gain settings 1100 -1 pga3_gain[6:0] pga3 gain [v/v] 0000000 0 0000001 1/12 (=0.083) ... ... 0000110 6/12 ... ... 0001100 12/12 0010000 16/12 ... ... 0100000 32/12 ... ... 1000000 64/12 ... ... 1111111 127/12 (=10.58) pga3_gain[6:0] pga3 gain [v/v] 0000000 0 0000001 +1/12(=0.083) 0000010 +2/12 ... ... 0010000 +16/12 ... ... 0100000 +32/12 0111111 +63/12 (=+5.25) pga2_offset pga2 offset [v/v]
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 61 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 48. pga3 offset settings the output of pga3 is also the input of the adc. thus, similarly to pga2, we find that the voltage entering the adc is given by: where gd3 and gdoff3 are respectively the gain and offset of pga3 (in v/v). the contro l words are pga3_gain[6:0] and pga3_offset[6:0] . to remain wi thin the signal compliance of the pga stages, the condition: must be verified. finally, combining equations eq. 5 to eq. 7 for the three pga stages, the input voltage v in,adc of the adc is related to v in by: 1000000 0 1000001 -1/12(=-0.083) 1000010 -2/12 ... ... 1010000 -16/12 ... ... 1100000 -32/12 ... ... 1111111 -63/12(=5.25) (eq. 7) (eq. 8) (eq. 9) pga3_gain[6:0] pga3 gain [v/v] ref d adc in v gdoff v gd v ? ? ? = 3 2 3 , v [] dd d d v v v 2 1 , v [] ref tot in tot adc in v gdoff v gd v ? ? , v []
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 62 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface where the total pga gain is defined as: and the total pga offset is: 12.8. adc characteristics the main performance characteristics of the adc (resolution, conversion time, etc.) are determined by three programmable parameters: ? oversampling frequency f s , ? over-sampling ratio osr, and ? number of elementary conversions n elconv. the setting of these parameters and the resu lting performances are described hereafter. 12.8.1. conversion sequence a conversion is started each time the bit start or the bit def is set. as depicted in figure 3, a complete analog-to-digital conversion sequence is made of a set of n elconv elementary incremental conversions and a final quantization step. each elementary conversion is made of (osr+1) sampling periods ts=1/f s , i.e.: the result is the mean of the elementary conversion results. an important feature is that the elementary conversions are alternatively performed with the offset of th e internal amplifiers contributing in one direction and the other to the output co de. thus, converter internal offset is eliminated if at least two elementary sequences are performed (i.e. if n elconv = 2). a few additional clock cycles are also required to initiate and end the conversion properly. (eq. 10) (eq. 11) (eq. 12) 1 2 3 gd gd gd gd tot ? ? = v [] 2 3 3 gdoff gd gdoff gdoff tot ? vv ? [] s elconv f osr t / ) 1 ( s []
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 63 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface figure 33. analog-to-digital conversion sequence 12.8.2. sampling frequency the word f in [1:0] is used to select the sampling frequency f s (table 49). three sub-multiples of the internal rc-based frequency f rcext can be chosen. for f in = "11", sampling frequency is about 8 khz. additional informat ion on oscillators and their control can be found in the clock block documentation. table 49. sampling frequency settings (f rc = rc-based frequency) 12.8.3. over-sampling ratio the over-sampling ratio (osr) defines the number of integratio n cycles per elementary conversion. its value is set with the word set_osr[2:0] in power of 2 steps (see table 49) given by: fin[1:0] sampling frequency fs [hz] 00 1/4 f rc 01 1/8 f rc 10 1/32 f rc 11 1/64 f rc (eq. 13) set_osr[2:0] (regaccfg[4:2]) over-sampling ratio osr [-] 000 8 001 16 conversion index offset t elconv = (osr+1)/f s elementary conversion 1 + elementary conversion 2 - elementary conversion n elconv - 1 + elementary conversion n elconv - init end t conv conversion result 0] : set_osr[2 3 2 + = osr
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 64 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 50. over-sampling ratio settings 12.8.4. elementary conversions as mentioned previously, t he whole conversion sequence is made of a set of n elconv elementary incremental conversions. this number is set with the word set_nelc[1:0] in power of 2 steps (see table 50) given by: table 51. number of elementary conversion as already mentioned, n elconv must be equal or greater than 2 to reduce internal amplifier offsets. 12.8.5. resolution the theoretical resolution of the adc, with out considering thermal noise, is given by: 010 32 011 64 100 128 101 256 110 512 111 1024 (eq. 14) set_osr[2:0] (regaccfg[4:2]) # of elementary conversion n elconv [-] 00 1 01 2 10 4 11 8 (eq. 15) set_osr[2:0] (regaccfg[4:2]) over-sampling ratio osr [-] 0] : set_nelc[1 2 = elconv n ) ( log ) ( log 2 2 2 elconv n osr n + ? = bits []
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 65 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface figure 34. resolution vs. set_osr[2:0] and set_nelc[2:0] (shaded area: resolution truncated to 16 bits due to output register size cxdataoutmsb + cxdataoutlsb [15:0] ) table 52. resolution vs. set_osr[2:0] and set_nelc[1:0] settings using look-up table 52, resolution can be set between 6 and 16 bits. notice that, because of 16 -bit register use for the adc output, practical resolution is limited to 16 bits , i.e. n = 16. even if the resolution is truncated to 16 bit by the output register size, it may make sense to set osr and n elconv to higher values in order to reduce the influence of the thermal noise in the pga . 12.8.6. conversion time & throughput as explained using figure 3, conversion time is given by: set_osr [2:0] set_nelc 00 01 10 11 000 6789 001 8 9 10 11 010 10 11 12 13 011 12131415 100 141516 16 101 16 16 16 16 110 16 16 16 16 111 16 16 16 16 (eq. 16) 5 7 9 11 13 15 17 000 001 010 011 100 101 110 111 set _ osr resolution - n [bits] 11 10 01 00 set _ nelc= s elconv conv f osr n t / ) 1 ) 1 ( ( + + ? = s []
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 66 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface and throughput is then simply 1/t conv . for example, consider an over-sampling ratio of 256, 2 elementary conversions, and a sampling frequency of 300 khz (set_osr = "101", set_nelc = "01", f rc = 1.2mhz, and fin = "00"). in this case, using table 53, the conversion time is 515 sampling periods, or 1.71m s. this corresponds to a thro ughput of 582hz in continuous- time mode. the plot of figure below illustrates the clas sic trade-off between resolution and conversion time. table 53. normalized conversion time (t conv x f s ) vs. set_osr[2:0] and set_nelc[1:0] (normalized to sa mpling period 1/f s ) table 54. resolution vs. normalized conver sion time for different set_nelc[1:0] set_osr [2:0] set_nelc 00 01 10 11 000 10193773 001 18 35 69 137 010 34 67 133 265 011 66 131 261 521 100 130 259 517 1033 101 258 515 1029 2057 110 514 1027 2053 4105 111 1026 2051 4101 8201 4.0 6.0 8.0 10.0 12.0 14.0 16.0 10.0 100.0 1000.0 10000.0 normalized conversion time - t conv *f s [-] resolution - n [bits] 00 set_nelc 01 10 11
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 67 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 12.8.7. output code format the adc output code is a 16-bit word in two's complement forma t (see table 55). for input voltages outside the range, the output code is saturated to the closest full-scale value (i.e. 0x7fff or 0x8000). for resolutions smaller than 16 bits, the non - significant bits are forced to the values shown in table 56. the output code, expressed in lsbs, corresponds to: recalling equation eq. 9, this can be rewritten as: where, from eq. 10 and eq. 11, the total pga gain and offset are respectively: and: (eq. 17) (eq. 18) adc input voltage v in,adc % of full scale (fs) output in lsbs output code in hex +2.49505 v +0.5 x fs +2 15 -1 = 32?767 7fff +2.49497 v ... +2 15 -2 = 32?767 7ffe ... ... ... ... +76.145 v... +1 0001 00 0 0000 -76.145 v... -1 8fff ... ... ... ... osr osr v v out ref adc in adc 1 2 , 16 + ? ? = lsb [] ? ? ? ? ? ? ? ? ? ? ? ? = in ref tot tot ref in adc v v gdoff gd v v out 16 2 osr osr 1 + ? lsb [] 1 2 3 gd gd gd gd tot ? ? = vv ? [] 2 3 3 gdoff gd gdoff gdoff tot ? vv ? []
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 68 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 55. basic adc relationships (example for: v ref = 5v, osr = 512, n = 16 bits) table 56. last forced lsbs in conversion output registers for resolution settings smaller than 16 bits (n < 16) (cxdataoutmsb[7:0] & cxdataoutlsb[7:0]) the equivalent lsb size at the input of the pga chain is: notice that the input voltage v in,adc of the adc must satisfy the condition: +2.49505 v ... -2 15 -1 = -32?767 8001 +2.49513 v -0.5 x fs -2 15 = -32?768 8000 set_osr[2:0] set_nelc = 00 set_nelc = 01 set_nelc = 10 set_nelc = 11 000 1000000000 100000000 10000000 1000000 001 10000000 1000000 100000 10000 010 100000 10000 1000 100 011 1000 100 10 1 100 10 1 - - 101 ---- 110 ---- 111 ---- (eq. 19) (eq. 20) adc input voltage v in,adc % of full scale (fs) output in lsbs output code in hex 1 2 1 + ? ? = osr osr gd v lsb tot ref n v [] 1 ) ( 2 1 , + ? ? ? osr osr v v v refn refp adc in vv ? []
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 69 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface to remain within the adc input range. table 57. adc & pga power saving modes and maximum sampling frequency 12.9. power saving modes during low-speed operation, the bias cu rrent in the pgas and adc can be programmed to save power using the control words ib_amp_pga[1:0] and ib_amp_adc[1:0] (see table 57). if the system is idle, the pgas and adc can even be disabled, thus, reducing power consumption to its mini mum. this can considerably improve battery lifetime. 12.10. input impedance the pgas of the zoomingadc are a switched capacitor base d blocks (see switched capaci tor principle chapter). this means that it does not use resistors to fix gains, but capacito rs and switches. this has import ant implications on the nature of the input impedance of the block. using switched capacitors is the reason wh y, while a conversion is done, the input impedance on the selected channel of the pgas is inversely proportional to the sampling freq uency fs and to stage gain as given in equation 21. the input impedance observed is the input impedance of the fi rst pga stage that is enabled or the input impedance of the adc if all three stages are disabled. pga1 (with a gain of 10), pga2 (with a gain of 10) and pga3 (with a gain of 10) each have a minimum input impedance of 256 kohm at fs = 300 khz. larger input impedance can be obtained by reducing the gain and/or by reducing the sampling frequency. therefore, with a gain of 1 and a sampling frequency of 75 khz, zin > 10.2 mohm. the input impedance on channels that are not selected is very high (>100mohm). ib_amp_adc [1:0] ib_amp_pga [1:0] adc bias current pga bias current max. f s [khz] 00 01 10 11 1/4 x i adc 1/2 x i adc 3/4 x i adc i adc 37.5 75 150 300 00 01 10 11 1/4 x i adc 1/2 x i adc 3/4 x i adc i adc 37.5 75 150 300 (eq. 21) gain f hz z s in ? ? 9 10 768 ohm []
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 70 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 12.11. switched capacitor principle basically, a switched capacitor is a way to emulate a resistor by using a capacitor. the capacitors are much easier to realize on cmos technologies and they show a very good matching precision. figure 35. the switched capacitor principle a resistor is characterized by the current that flows through it (positive current leaves node v 1 ): one can verify that the mean current leaving node v 1 with a capacitor switched at frequency f is: therefore as a mean value, the switched capacitor 1/ (f x c) is equivalent to a resistor. it is important to consider that this is only a mean value. if the current is not integrated (low impedance source), the impedance is infinite during t he whole time but the transition. what does it mean for the zoomingadc? if the fs clock is reduced, the mean impedance is increased. by dividing the fs clock by a factor 10, the impedance is increased by a factor 10. one can reduce the capacitor that is switched by using an amplifie r set to its minimal gain. in pa rticular if pga1 is used with gain 1, its mean impedance is 10x bigger than when it is used with gain 10. figure 36. the switched capacitor principle one can increase the effective impedance by increasing the elec trical bandwidth of the sensor node so that the switching current is absorbed through the sensor before the switching period is over. measur ing the sensor node will show short voltage spikes at the frequency fs, but these will not influen ce the measurement. whereas if the bandwidth of the node is (eq. 22) (eq. 23) v 1 v 2 r v 1 f fv 2 r v v i 2 1 ? = a [] () c f v v i ? ? ? = 2 1 a [] sensor c zoomingadc (model) v 1 f fv 2 sensor impedence node capacitance current integration
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 71 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface lower, no spikes will arise, but a small offset can be ge nerated by the integration of t he charges generated by the switched capacitors, this corresponds to the mean impedance effect. note: one can increase the mean input im pedance of the zoomingadc by lowering the acquisition clock fs. one can increase the mean input impedanc e of the zoomingadc by decreasing the gain of the first enabled amplifier. one can increase the effective input impedance of the zoomingadc by having a source with a high electrical bandwidth (sensor el ectrical bandwidth much higher than fs). 12.12. pga settling or i nput channel modifications pgas are reset after each writing operation to registers cx zadcreg1-5. similarly, input channels are switched after modifications of amux[4:0] or vmux. to ensure precise conversion, the adc must be started after a pga or inputs common-mode stabilization delay. this is done by writing bit start several cycl es after pga settings modification or channel switching. delay between pga start or input chan nel switching and adc start should be equivalent to osr (between 8 and 1024) num ber of cycles. this delay does not apply to conversions made without the pgas. if the adc is not settled within the specified period, there is most probably an input impedance problem (see previous section). 12.13. pga gain & off set, linearity and noise hereafter are a few design guidelines that should be taken into account when using the zoomingadc : 1. keep in mind that increasing the overall pga gain, or "z ooming" coefficient, improves linearity but degrades noise performance. 2. use the minimum number of pga stages necessary to produce the desired gain ("z ooming") and offset. bypass unnecessary pgas. 3. put most gain on pga3 and use pga2 and pga1 only if necessary. 4. pga3 should be always on for best linearity. 5. for low-noise applications where power consumption is not a primary concern, maintain the largest bias currents in the pgas and in the adc; i.e. set ib_a mp_pga[1:0] = ib_amp_adc[1:0] = '11'. 6. for lowest output offset error at the output of the adc, bypass pga2 and pga3. i ndeed, pga2 and pga3 typically introduce an offset of about 5 to 10 lsb (16 bit) at their outp ut. note, however, that the adc output offset is easily calibrat ed out by software. 12.14. power reduction the zoomingadc is particularly well suit ed for low-power applications. when very low power consumpt ion is of primary concern, such as in battery operated s ystems, several parameters can be used to reduce power consumption as follows: 1. operate the acquisition chain with a reduced supply voltage v batt . 2. disable the pgas which are not used during analog-to-digital conversion with enable[3:0]. 3. disable all pgas and the adc when the system is idle and no conversion is performed. 4. use lower bias currents in the pgas and the adc using the control words ib_amp_pga[1 :0] and ib_amp_adc[1:0]. 5. reduce sampling frequency. ] [ 2 v
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 72 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface finally, remember that power reduction is typically traded off with reduced linearity, larger noise and slower maximum sampling speed. 12.15. noise ideally, a constant input voltage v in should result in a constant output code. however, because of circuit noise, the output code may vary for a fixed input voltage. thus, a statistical analysis on the output code of 1200 conversions for a constant input voltage was performed to derive the equivalent noise levels of pga1, pga2, and pga3. the extracted rms output noise of pga1, 2, and 3 are given in table 58: standard output deviation and output rms nois e voltage. figure 37 shows the distribution for the adc alone (pga1, 2, and 3 bypassed). quan tization noise is dominant in this case, and, thus, the adc thermal noise is below 16 bits. the simple noise model of figure 38 is used to estimate the equivalent input referred rms noise v n,in of the acquisition chain in the model of figure 39. this is given by the relationship: where v n1 , v n2 , and v n3 are the output rms noise figures of table 58, gd1, gd2, and gd3 are the pga gains of stages 1 to 3 respectively. as shown in this equation, noise can be reduced by increasing osr and n elconv (increases the adc averaging effect, but reduces noise). table 58. pga noise measurements (n = 16 bits, osr = 512, n elconv = 2, v ref = 5 v) figure 37. adc noise (pga1, 2 & 3 bypassed, osr = 512, n elconv = 2) (eq. 24) parameter pga1 pga2 pga3 standard deviation at adc output (lsb) 0.85 1.4 1.5 output rms noise(uv) 205 x (v n1 ) 340 x (v n2 ) 365 x (v n3 ) () elconv n n n in n n osr gd gd gd v gd gd v gd v v ? ? ? ? ? ? ? ? ? ? ? + ? ? ? ? ? ? ? ? ? + ? ? ? ? ? ? ? ? = 2 3 2 1 3 2 2 1 2 2 1 1 2 , ] [ 2 rms v 0 20 40 60 80 -5 -4 -3 -2 -1 0 1 2 3 4 5 output code deviation from mean value [lsb] occurences [% of total samples]
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 73 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface figure 38. simple noise model for pgas and adc figure 39. total input referred noise as an example, consider the system where: gd2 = 10 (gd1 = 1; pga3 bypassed), osr = 512, n elconv = 2, v ref = 5 v. in this case, the noise contribution v n1 of pga1 is dominant over that of pga2. using equation 24, we get: v n,in = 6.4 v (rms) at the input of the acquisition chain, or , equivalently, 0.85 lsb at the output of the adc. considering 0.2 v (rms) maximum signal amplitude, the signal-to-noise ratio is 90db. noise can also be reduced by the additional average filter s implemented in the measurement engine. these filters are described in section 11.4 filtering. by making an average on a number of subsequent measur ements, the apparent noise is reduced the square root of the number of measurement used to make the average. 12.16. gain error and offset error gain error is defined as the amount of deviation between th e ideal transfer function (theoretical equation 18) and the measured transfer function ( with the offset error removed). the actual gain of the different stages can vary depending on the fabrication tolerances of the different elements. although these tolerances ar e specified to a maximum of +/-3%, they will be most of the time around 0.5% . moreover, the tolerances between the different stages are not correl ated and the probability to get the maximal error in the sa me direction in all stage s is very low. finally, these gain errors can be calibrated by the software at the same time with the gain errors of the sensor f or instance. figure 40 shows gain error drift vs. temperature for different pga gains. the curves are expressed in % of full-scale range (fsr) normalized to 25c. gd1 gd2 gd3 adc f s v n1 v n2 v n3 pga1 pga2 pga3 gd1 gd2 gd3 adc f s v n1 v n2 v n3 pga1 pga2 pga3 v n,in
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 74 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface offset error is defined as the output code error for a zero volt input (ideally, output code = 0). the offset of the adc and th e pga1 stage are completely suppressed if n elconv > 1. the measured offset drift vs. temperature curves for different pga gains are depict ed in figure 41. the output offset error, expressed in lsb for 16-bit setting, is normalized to 25c. noti ce that if the adc is used alone, the output offset error is below +/-1 lsb and has no drift. figure 40. gain error vs. temperature fo r different pga gains figure 41. offset error vs. temper ature for different pga gain s -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 -50 -25 0 25 50 75 100 temperature [c] gain error [% of fsr] 1 5 20 100 -40 -20 0 20 40 60 80 100 -50 -25 0 25 50 75 100 temperature [c] output offset error [lsb] 1 5 20 100
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 75 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 13. typical performances 13.1. current consumption SX8722 mean current consumption in active mode is around 2 00 [a], without enabled pga. the value of the gain of de pga can have a negligible influence on consumption in active mode. additional consumption depends on the acti ve pga and on the bias current parameter. table 59. pga current consumption example 1 : bias current 25% pga1: enabled pga2: enabled pga3: enabled SX8722 measured current consumption: ~330 a example 2 : bias current 100% pga1: enabled pga2: enabled pga3: enabled SX8722 measured current consumption: ~710 a current for each amplifier in [ua] i pga1 i pga2 i pga3 bias 25 %504050 bias 50 %957598 bias 75 % 140 110 145 bias 100 % 185 145 190
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 76 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 13.2. zoomingadc 13.2.1. integral non-linearity adc without pga -40c 25c 85c gain 1 -40c 25c 85c gain 10 -40c 25c 85c pga1 off; pga2 off; pga3 off; set_osr = 7, set_nelconv = 3, vbat=5v, vref=5v, vcommon=0v -10 -8 -6 -4 -2 0 2 4 6 8 10 0 500 1000 1500 2000 2500 vin [mv] inl[lsb] pga1 off; pga2 off; pga3 off; set_osr = 7; set_nelconv = 3; vbat = 5v; vref = 5v; vcommon = 0v -10 -8 -6 -4 -2 0 2 4 6 8 10 0 500 1000 1500 2000 2500 vin [mv] inl[lsb] pga1 off; pga2 off; pga3 off; set_osr = 7, set_nelconv = 3, vbat=5v, vref=5v, vcommon=0v -10 -8 -6 -4 -2 0 2 4 6 8 10 0 500 1000 1500 2000 2500 vin [mv] inl[lsb] pga1 off; pga2 off; pga3 = 1; set_osr = 7; set_nelconv = 3, vbat = 5v; vref = 5v; vcommon = 0v -10 -8 -6 -4 -2 0 2 4 6 8 10 0 500 1000 1500 2000 2500 vin [mv] inl[lsb] pga1 off; pga2 off; pga3 = 1; set_osr = 7; set_nelconv = 3, vbat = 5v; vref = 5v; vcommon = 0v -10 -8 -6 -4 -2 0 2 4 6 8 10 0 500 1000 1500 2000 2500 vin [mv] inl[lsb] pga1 off; pga2 off; pga3 = 1; set_osr = 7; set_nelconv = 3, vbat = 5v; vref = 5v; vcommon = 0v -10 -8 -6 -4 -2 0 2 4 6 8 10 0 500 1000 1500 2000 2500 vin [mv] inl[lsb] pga1 off; pga2 off; pga3 = 10; set_osr = 7; set_nelconv = 3; vbat = 5v; vref = 5v; vcommon = 0v -10 -8 -6 -4 -2 0 2 4 6 8 10 0 50 100 150 200 250 vin [mv] inl[lsb] pga1 off; pga2 off; pga3 = 10; set_osr = 7; set_nelconv = 3; vbat = 5v; vref = 5v; vcommon = 0v -10 -8 -6 -4 -2 0 2 4 6 8 10 0 50 100 150 200 250 vin [mv] inl[lsb] pga1 off; pga2 off; pga3 = 10; set_osr = 7; set_nelconv = 3; vbat = 5v; vref = 5v; vcommon = 0v -10 -8 -6 -4 -2 0 2 4 6 8 10 0 50 100 150 200 250 vin [mv] inl[lsb]
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 77 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface figure 42. inl over temperature for different gains 13.2.2. differential non-linearity figure 43. adc differential non-linearity gain 100 -40c 25c 85c dnl: significantly lower than one lsb pga1 off; pga2 = 10; pga3 = 10; set_osr = 7; set_nelconv = 3; vbat = 5v; vref = 5v; vcommon = 0v -10 -8 -6 -4 -2 0 2 4 6 8 10 0 5 10 15 20 25 vin [mv] inl[lsb] pga1 off; pga2 = 10; pga3 = 10; set_osr = 7; set_nelconv = 3; vbat = 5v; vref = 5v; vcommon = 0v -10 -8 -6 -4 -2 0 2 4 6 8 10 0 5 10 15 20 25 vin [mv] inl[lsb] pga1 = 10; pga2 off; pga3 = 10; set_osr = 7; set_nelconv = 3; vbat=5v; vref = 5v; vcommon = 0v -10 -8 -6 -4 -2 0 2 4 6 8 10 0 5 10 15 20 25 vin [mv] inl[lsb]
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 78 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 13.2.3. resolution vs acquisition time figure 44. adc resolution vs acquisition time resolution vs acquisition time 0 2 4 6 8 10 12 14 16 18 10 100 1000 10000 100000 time [us] resolution [bits]
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 79 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 14. register memory map and description 14.1. memory map the table below describes the register/memory map that can be accessed through the i2c interface. it indicates the register name, register address and the register contents. adress register bit description SX8722 general configuration 0x00 sxctrl1 8 configuration register of the SX8722 0x01 sxctrl2 8 configuration register of the SX8722 0x02 sxcfgen 8 configuration enable register,enables configurations from 1 to 4 0x03 sxupdated 8 updated value on configuration registers 0x04 sxrcfrequ1 8 fine rc adjustment register 0x05 sxrcfrequ2 8 coarse rc adjustment register 0x06 sxtest 8 test purpose register puts SX8722 in remote mode 0x07 sxai1 8 reserved 0x08 sxai2 8 reserved 0x09 sxreserved1 8 reserved configuration 1 0x0a c1zadcreg1 8 zoomingadc register 01 0x0b c1zadcreg2 8 zoomingadc register 02 0x0c c1zadcreg3 8 zoomingadc register 03 0x0d c1zadcreg4 8 zoomingadc register 04 0x0e c1zadcreg5 8 zoomingadc register 05 0x0f c1zadcreg6 8 zoomingadc register 06 0x10 c1sxcfg 8 sx configurations related to this set 0x11 c1fparam 8 filter size 0x12 c1alrm1onmsb 16 alarm 1 "on" threshold 0x13 c1alrm1onlsb 0x14 c1alrm1offmsb 16 alarm 1 "off" threshold 0x15 c1alrm1offlsb 0x16 c1alrm2onmsb 16 alarm 2 "on" threshold 0x17 c1alrm2onlsb
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 80 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 0x18 c1alrm2offmsb 16 alarm 2 "off" threshold 0x19 c1alrm2offlsb 0x1a c1dataoutlsb 16 configuration 1 data out 0x1b c1dataoutmsb configuration 2 0x2a c2zadcreg1 8 zoomingadc register 01 0x2b c2zadcreg2 8 zoomingadc register 02 0x2c c2zadcreg3 8 zoomingadc register 03 0x2d c2zadcreg4 8 zoomingadc register 04 0x2e c2zadcreg5 8 zoomingadc register 05 0x2f c2zadcreg6 8 zoomingadc register 06 0x30 c2sxcfg 8 sx configurations related to this set 0x31 c2fparam 8 filter size 0x32 c2alrm1onmsb 16 alarm 1 "on" threshold 0x33 c2alrm1onlsb 0x34 c2alrm1offmsb 16 alarm 1 "off" threshold 0x35 c2alrm1offlsb 0x36 c2alrm2onmsb 16 alarm 2 "on" threshold 0x37 c2alrm2onlsb 0x38 c2alrm2offmsb 16 alarm 2 "off" threshold 0x39 c2alrm2offlsb 0x3a c2dataoutmsb 16 configuration 2 data out 0x3b c2dataoutlsb configuration 3 0x4a c3zadcreg1 8 zoomingadc register 01 0x4b c3zadcreg2 8 zoomingadc register 02 0x4c c3zadcreg3 8 zoomingadc register 03 0x4d c3zadcreg4 8 zoomingadc register 04 0x4e c3zadcreg5 8 zoomingadc register 05 0x4f c3zadcreg6 8 zoomingadc register 06 0x50 c3sxcfg 8 sx configurations related to this set 0x51 c3fparam 8 filter size adress register bit description
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 81 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 0x52 c3alrm1onmsb 16 alarm 1 "on" threshold 0x53 c3alrm1onlsb 0x54 c3alrm1offmsb 16 alarm 1 "off" threshold 0x55 c3alrm1offlsb 0x56 c3alrm2onmsb 16 alarm 2 "on" threshold 0x57 c3alrm2onlsb 0x58 c3alrm2offmsb 16 alarm 2 "off" threshold 0x59 c3alrm2offlsb 0x5a c3dataoutmsb 16 configuration 3 data out 0x5b c3dataoutlsb configuration 4 0x6a c4zadcreg1 8 zoomingadc register 01 0x6b c4zadcreg2 8 zoomingadc register 02 0x6c c4zadcreg3 8 zoomingadc register 03 0x6d c4zadcreg4 8 zoomingadc register 04 0x6e c4zadcreg5 8 zoomingadc register 05 0x6f c4zadcreg6 8 zoomingadc register 06 0x70 c4sxcfg 8 sx configurations related to this set 0x71 c4fparam 8 filter size 0x72 c4alrm1onmsb 16 alarm 1 "on" threshold 0x73 c4alrm1onlsb 0x74 c4alrm1offmsb 16 alarm 1 "off" threshold 0x75 c4alrm1offlsb 0x76 c4alrm2onmsb 16 alarm 2 "on" threshold 0x77 c4alrm2onlsb 0x78 c4alrm2offmsb 16 alarm 2 "off" threshold 0x79 c4alrm2offlsb 0x7a c4dataoutmsb 16 configuration 4 data out 0x7b c4dataoutlsb adress register bit description
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 82 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 14.2. register description the register descriptions are presented here in ascending order of register address. some re gisters carry several individual data fields of various sizes; from single -bit values (e.g. flags), upwards. some data fields are spread across multiple registers. unused bits are 'don't care' and writing either 0 or 1 will not affect any function of the device. after power on re set the registers will have th e values indicated in th e tables "reset" column. 14.2.1. SX8722 general configuration table 60. sxctrl1 (0x00) table 61. sxctrl2 (0x01) bit bit name mode reset description 7 ee_d r x indicates if an eeprom was detected at startup 6 xtal_d r x indicates if an xtal was detected at startup 5 ckout rw 0 enabled the clock output on ckout pin 4 reserved rw 0 3 ee r 0 is set to 1 when SX8722 loaded its configuration from the eeprom at startup. 2 sleep rw 0 when set to 1 his bit activates the sleep mode of the SX8722. setting pin sleep to 1 has the same effect. 1 shut rw 0 when set to 1 his bit activates the shutdown mode of the SX8722. setting pin shut to 1 has the same effect. 0 cal r 0 this flag shows if the SX8722 clock has been successfully calibrated. bit bit name mode reset description 7:4 reserved r x 3 al1onc rw 0 sets the logical condition for alarm 1 on (0 = or, 1 = and) 2 al1offc rw 0 sets the logical condition for alarm 1 off (0 = or, 1 = and) 1 al2onc rw 0 sets the logical condition for alarm 2 on (0 = or, 1 = and) 0 al2offc rw 0 sets the logical condition for alarm 2 off (0 = or, 1 = and) bit name mode reset description 7:4 reserved r x 3 conf4 rw 0 configuration 4 enabling 2 conf3 rw 0 configuration 3 enabling 1 conf2 rw 0 configuration 2 enabling
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 83 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 62. sxcfgen (0x02) table 63. sxupdated (0x03) table 64. sxrcfrequ1 (0x04) table 65. sxrcfrequ2 (0x05) 0 conf1 rw 0 configuration 1 enabling bit name mode reset description 7 ovf4 r 0 overflow on configuration 4 6 ovf3 r 0 overflow on configuration 3 5 ovf2 r 0 overflow on configuration 2 4 ovf1 r 0 overflow on configuration 1 3 uconf4 r 0 indicates that configuration 4 has been updated by a measurement result. 2 uconf3 r 0 indicates that configuration 3 has been updated by a measurement result. 1 uconf2 r 0 indicates that configuration 2 has been updated by a measurement result. 0 uconf1 r 0 indicates that configuration 1 has been updated by a measurement result. bit name mode reset description 7:0 fine rc rw x fine rc adjustment. set by the calibration procedure. bit name mode reset description 7:0 coarse rc rw x coarse rc adjustment. set by the calibration procedure. bit name mode reset description
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 84 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 14.2.2. configuration 1 registers table 66. c1zadcreg1 (0x0a) table 67. c1zadcreg2 (0x0b) table 68. c1zadcreg3 (0x0c) table 69. c1zadcreg4 (0x0d) bit name mode reset description 7 reserved r x 6:5 set_nelc rw 01 sets the number of elementary conversion to 2 set_nelc[1:0] . to compensate for offset the signal is chopped between elementary conversion. 4:2 set_osr rw 010 sets the adc over-sampling rate of an elementary conversion to 2 3+set_osr[2:0] . 1 reserved r x 0 reserved r x bit name mode reset description 7:6 ib_amp_adc[1:0] rw 11 bias current selection of the a/d converter. 5:4 ib_amp_pga[1:0] rw 11 bias current selection of the pga stages. 3:0 enable[3:0] rw 0000 enables the different pga stages and adc. ? xxx1 - adc enable ? xx1x - pga3 enable ? x1xx - pga2 enable ? 1xxx - pga1 enable bit name mode reset description 7:6 fin[1:0] rw 00 sampling frequency selection 5:4 pga2_gain[1:0] rw 00 pga2 stage gain selection 3:0 pga2_offset[3:0] rw 0000 pga2 stage offset selection bit name mode reset description 7 pga1_gain rw 0 pga1 stage gain selection 6:0 pga3_gain[6:0] rw 0000000 pga3 stage gain selection
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 85 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 70. c1zadcreg5 (0x0e) table 71. c1zadcreg6 (0x0f) table 72. c1sxcfg (0x10) table 73. c1fparam (0x11) bit name mode reset description 7 reserved r 0 unused 6:0 pga3_offset[6:0] rw 0000000 pga3 stage offset selection bit name mode reset description 7 reserved r 6 reserved r 5:1 amux[4:0] rw 00000 input channel configuration selector 0 vmux rw 0 reference channel selector bit name mode reset description 7 reserved r 6:4 filter type [2:0] r filter selection selection ? 000 - none ? 001 - average filtering ? 010 - moving average filtering ? 011 - reserved 3 alrm1 rw alarm 1 enable 2 alrm2 rw alarm 2 enable 1 single rw configuration 1 in single acquisition mode 0 cont rw configuration 1 in continuous acquisition mode bit name mode reset description 7:0 size rw 00000000 filter size. limited to 10 for a moving average filter.
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 86 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 74. c1alrm1onmsb (0x12) table 75. c1alrm1onlsb (0x13) table 76. c1alrm1offmsb (0x14) table 77. c1alrm1offlsb (0x15) table 78. c1alrm1onmsb (0x16) table 79. c1alrm1onlsb (0x17) bit name mode reset description 7:0 rw 00000000 alarm 1 threshold msb for configuration 1 bit name mode reset description 7:0 rw 00000000 alarm 1 threshold lsb for configuration 1 bit name mode reset description 7:0 rw 00000000 alarm 1 threshold msb for configuration 1 bit name mode reset description 7:0 rw 00000000 alarm 1 threshold lsb for configuration 1 bit name mode reset description 7:0 rw 00000000 alarm 2 threshold msb for configuration 1 bit name mode reset description 7:0 rw 00000000 alarm 2 threshold lsb for configuration 1 bit name mode reset description 7:0 rw 00000000 alarm 2 threshold msb for configuration 1
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 87 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 80 c1alrm1offmsb (0x18) table 81. c1alrm1offlsb (0x19) table 82. c1dataoutmsb (0x1a) table 83. c1dataoutlsb (0x1b) bit name mode reset description 7:0 rw 00000000 alarm 2 threshold lsb for configuration 1 bit name mode reset description 7:0 r 00000000 configuration 1 data out msb bit name mode reset description 7:0 r 00000000 configuration 1 data out lsb
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 88 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 14.2.3. configuration 2 registers table 84. c2zadcreg1 (0x2a) table 85. c2zadcreg2 (0x2b) table 86. c2zadcreg3 (0x2c) table 87. c2zadcreg4 (0x2d) bit name mode reset description 7 reserved r x 6:5 set_nelc rw 01 sets the number of elementary conversion to 2 set_nelc[1:0] . to compensate for offset the signal is chopped between elementary conversion. 4:2 set_osr rw 010 sets the adc over-sampling rate of an elementary conversion to 2 3+set_osr[2:0] . 1 reserved r x 0 reserved r x bit name mode reset description 7:6 ib_amp_adc[1:0] rw 11 bias current selection of the a/d converter. 5:4 ib_amp_pga[1:0] rw 11 bias current selection of the pga stages. 3:0 enable[3:0] rw 0000 enables the different pga stages and adc. ? xxx1 - adc enable ? xx1x - pga3 enable ? x1xx - pga2 enable ? 1xxx - pga1 enable bit name mode reset description 7:6 fin[1:0] rw 00 sampling frequency selection 5:4 pga2_gain[1:0] rw 00 pga2 stage gain selection 3:0 pga2_offset[3:0] rw 0000 pga2 stage offset selection bit name mode reset description 7 pga1_gain rw 0 pga1 stage gain selection 6:0 pga3_gain[6:0] rw 0000000 pga3 stage gain selection
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 89 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 88. c2zadcreg5 (0x2e) table 89. c2zadcreg6 (0x2f) table 90. c2sxcfg (0x30) table 91. c2fparam (0x31) bit name mode reset description 7 reserved r 0 unused 6:0 pga3_offset[6:0] rw 0000000 pga3 stage offset selection bit name mode reset description 7 reserved r 6 reserved r 5:1 amux[4:0] rw 00000 input channel configuration selector 0 vmux rw 0 reference channel selector bit name mode reset description 7 reserved r 6:4 filter type [2:0] r filter selection selection ? 000 - none ? 001 - average filtering ? 010 - moving average filtering ? 011 - reserved 3 alrm1 rw alarm 1 enable 2 alrm2 rw alarm 2 enable 1 single rw configuration 1 in single acquisition mode 0 cont rw configuration 1 in continuous acquisition mode bit name mode reset description 7:0 size rw 00000000 filter size. limited to 10 for a moving average filter.
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 90 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 92. c2alrm1onmsb (0x32) table 93. c2alrm1onlsb (0x33) table 94 c2alrm1offmsb (0x34) table 95. c2alrm1offlsb (0x35) table 96. c2alrm1onmsb (0x36) table 97. c2alrm1onlsb (0x37) bit name mode reset description 7:0 rw 00000000 alarm 1 threshold msb for configuration 2 bit name mode reset description 7:0 rw 00000000 alarm 1 threshold lsb for configuration 2 bit name mode reset description 7:0 rw 00000000 alarm 1 threshold msb for configuration 2 bit name mode reset description 7:0 rw 00000000 alarm 1 threshold lsb for configuration 2 bit name mode reset description 7:0 rw 00000000 alarm 2 threshold msb for configuration 2 bit name mode reset description 7:0 rw 00000000 alarm 2 threshold lsb for configuration 2
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 91 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 98 c2alrm1offmsb (0x38) table 99. c2alrm1offlsb (0x39) table 100. c2dataoutmsb (0x3a) table 101. c2dataoutlsb (0x3b) bit name mode reset description 7:0 rw 00000000 alarm 2 threshold msb for configuration 2 bit name mode reset description 7:0 rw 00000000 alarm 2 threshold lsb for configuration 2 bit name mode reset description 7:0 r 00000000 configuration 2 data out msb bit name mode reset description 7:0 r 00000000 configuration 2 data out lsb
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 92 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 14.2.4. configuration 3 registers table 102. c3zadcreg1 (0x4a) table 103. c3zadcreg2 (0x4b) table 104. c3zadcreg3 (0x4c) table 105. c3zadcreg4 (0x4d) bit name mode reset description 7 reserved r x 6:5 set_nelc rw 01 sets the number of elementary conversion to 2 set_nelc[1:0] . to compensate for offset the signal is chopped between elementary conversion. 4:2 set_osr rw 010 sets the adc over-sampling rate of an elementary conversion to 2 3+set_osr[2:0] . 1 reserved r x 0 reserved r x bit name mode reset description 7:6 ib_amp_adc[1:0] rw 11 bias current selection of the a/d converter. 5:4 ib_amp_pga[1:0] rw 11 bias current selection of the pga stages. 3:0 enable[3:0] rw 0000 enables the different pga stages and adc. ? xxx1 - adc enable ? xx1x - pga3 enable ? x1xx - pga2 enable ? 1xxx - pga1 enable bit name mode reset description 7:6 fin[1:0] rw 00 sampling frequency selection 5:4 pga2_gain[1:0] rw 00 pga2 stage gain selection 3:0 pga2_offset[3:0] rw 0000 pga2 stage offset selection bit name mode reset description 7 pga1_gain rw 0 pga1 stage gain selection 6:0 pga3_gain[6:0] rw 0000000 pga3 stage gain selection
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 93 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 106. c3zadcreg5 (0x4e) table 107. c3zadcreg6 (0x4f) table 108. c3sxcfg (0x50) table 109. c3fparam (0x51) bit name mode reset description 7 reserved r 0 unused 6:0 pga3_offset[6:0] rw 0000000 pga3 stage offset selection bit name mode reset description 7 reserved r 6 reserved r 5:1 amux[4:0] rw 00000 input channel configuration selector 0 vmux rw 0 reference channel selector bit name mode reset description 7 reserved r 6:4 filter type [2:0] r filter selection selection ? 000 - none ? 001 - average filtering ? 010 - moving average filtering ? 011 - reserved 3 alrm1 rw alarm 1 enable 2 alrm2 rw alarm 2 enable 1 single rw configuration 3 in single acquisition mode 0 cont rw configuration 3 in continuous acquisition mode bit name mode reset description 7:0 size rw 00000000 filter size. limited to 10 for a moving average filter.
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 94 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 110. c3alrm1onmsb (0x52) table 111. c3alrm1onlsb (0x53) table 112 c3alrm1offmsb (0x54) table 113. c3alrm1offlsb (0x55) table 114. c3alrm1onmsb (0x56) table 115. c3alrm1onlsb (0x57) bit name mode reset description 7:0 rw 00000000 alarm 1 threshold msb for configuration 3 bit name mode reset description 7:0 rw 00000000 alarm 1 threshold lsb for configuration 3 bit name mode reset description 7:0 rw 00000000 alarm 1 threshold msb for configuration 3 bit name mode reset description 7:0 rw 00000000 alarm 1 threshold lsb for configuration 3 bit name mode reset description 7:0 rw 00000000 alarm 2 threshold msb for configuration 3 bit name mode reset description 7:0 rw 00000000 alarm 2 threshold lsb for configuration 3
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 95 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 116 c3alrm1offmsb (0x58) table 117. c3alrm1offlsb (0x59) table 118. c3dataoutmsb (0x5a) table 119. c3dataoutlsb (0x5b) bit name mode reset description 7:0 rw 00000000 alarm 2 threshold msb for configuration 3 bit name mode reset description 7:0 rw 00000000 alarm 2 threshold lsb for configuration 3 bit name mode reset description 7:0 r 00000000 configuration 3 data out msb bit name mode reset description 7:0 r 00000000 configuration 3 data out lsb
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 96 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 14.2.5. configuration 4 registers table 120. c4zadcreg1 (0x6a) table 121. c4zadcreg2 (0x6b) table 122. c4zadcreg3 (0x6c) table 123. c4zadcreg4 (0x6d) bit name mode reset description 7 reserved r x 6:5 set_nelc rw 01 sets the number of elementary conversion to 2 set_nelc[1:0] . to compensate for offset the signal is chopped between elementary conversion. 4:2 set_osr rw 010 sets the adc over-sampling rate of an elementary conversion to 2 3+set_osr[2:0] . 1 reserved r x 0 reserved r x bit name mode reset description 7:6 ib_amp_adc[1:0] rw 11 bias current selection of the a/d converter. 5:4 ib_amp_pga[1:0] rw 11 bias current selection of the pga stages. 3:0 enable[3:0] rw 0000 enables the different pga stages and adc. ? xxx1 - adc enable ? xx1x - pga3 enable ? x1xx - pga2 enable ? 1xxx - pga1 enable bit name mode reset description 7:6 fin[1:0] rw 00 sampling frequency selection 5:4 pga2_gain[1:0] rw 00 pga2 stage gain selection 3:0 pga2_offset[3:0] rw 0000 pga2 stage offset selection bit name mode reset description 7 pga1_gain rw 0 pga1 stage gain selection 6:0 pga3_gain[6:0] rw 0000000 pga3 stage gain selection
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 97 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 124. c4zadcreg5 (0x6e) table 125. c4zadcreg6 (0x6f) table 126. c4sxcfg (0x70) table 127. c4fparam (0x71) bit name mode reset description 7 reserved r 0 unused 6:0 pga3_offset[6:0] rw 0000000 pga3 stage offset selection bit name mode reset description 7 reserved r 6 reserved r 5:1 amux[4:0] rw 00000 input channel configuration selector 0 vmux rw 0 reference channel selector bit name mode reset description 7 reserved r 6:4 filter type [2:0] r filter selection selection ? 000 - none ? 001 - average filtering ? 010 - moving average filtering ? 011 - reserved 3 alrm1 rw alarm 1 enable 2 alrm2 rw alarm 2 enable 1 single rw configuration 4 in single acquisition mode 0 cont rw configuration 4 in continuous acquisition mode bit name mode reset description 7:0 size rw 00000000 filter size. limited to 10 for a moving average filter.
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 98 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 128. c4alrm1onmsb (0x72) table 129. c4alrm1onlsb (0x73) table 130 c4alrm1offmsb (0x74) table 131. c4alrm1offlsb (0x75) table 132. c4alrm1onmsb (0x76) table 133. c4alrm1onlsb (0x77) bit name mode reset description 7:0 rw 00000000 alarm 1 threshold msb for configuration 4 bit name mode reset description 7:0 rw 00000000 alarm 1 threshold lsb for configuration 4 bit name mode reset description 7:0 rw 00000000 alarm 1 threshold msb for configuration 4 bit name mode reset description 7:0 rw 00000000 alarm 1 threshold lsb for configuration 4 bit name mode reset description 7:0 rw 00000000 alarm 2 threshold msb for configuration 4 bit name mode reset description 7:0 rw 00000000 alarm 2 threshold lsb for configuration 4
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 99 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface table 134 c4alrm1offmsb (0x78) table 135. c4alrm1offlsb (0x79) table 136. c4dataoutmsb (0x7a) table 137. c4dataoutlsb (0x7b) bit name mode reset description 7:0 rw 00000000 alarm 2 threshold msb for configuration 4 bit name mode reset description 7:0 rw 00000000 alarm 2 threshold lsb for configuration 4 bit name mode reset description 7:0 r 00000000 configuration 4 data out msb bit name mode reset description 7:0 r 00000000 configuration 4 data out lsb
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 100 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 15. power modes SX8722 has 3 operating modes: ? active mode ? sleep mode ? shutdown mode 15.1. power modes transitions start-up from shutdown: ? initializes the SX8722 ? load eeprom if present ? restores eeprom configurat ion and set the SX8722 start-up from sleep: ? restores the rc active value ? enables vld ? restores SX8722 configuration saved in ram sleep sequence: ? waits for i2c stop sequence ? stops the adc ? disable vld ? bias current off ? set the clock to rc minimum value or to xtal if present shutdown sequence: ? waits for i2c stop sequence ? stops the adc ? disable vld ? bias current off ? stops the SX8722 the timing of the transition states depends mainly on the xtal presence, the eeprom presence and if the transition is caused by an i2c command or by a pin signal (sleep, shut, reset).
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 101 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 15.2. active mode in this chapte r you will find: the description of the active mode how to set SX8722 in active mode 15.2.1. description in active mode, SX8722 and all its peripherals can work an d execute the measurement engine . the acquisition chain, the alarms and the signal post processi ng can be activated and parameterized. 15.2.2. how to set SX8722 in active mode start-up ? at start-up SX8722 is automa tically set in active mode. ? if there is no eeprom configuration load ed at start-up, pg a are not active. from sleep mode ? positive pulse on reset pin ? negative pulse on the sleep pin ? sleep bit toggle in the sxctrl1 register (i2c write mask command) ? other interruption from shutdown mode ? positive pulse on reset pin ? power-on-reset (negative pulse on vbat pin) 15.3. sleep mode 15.3.1. description the sleep mode is a low power mode. it can be called by an i2c sequence or by sending a negative pulse to SX8722 sleep pin. 15.3.2. operating specifications of the sleep mode summary ? SX8722 configuration saved in ram ? adc stopped ? vld stopped (voltage level detector) ? if xtal present, clock set to xtal 32k ? if xtal not present, clock set to rc minimum value (~80khz) ? bias current off
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 102 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface ? program halt, SX8722 needs an inte rrupt to wake up (i2c communication, sleep pin signal, reset, etc). 15.3.3. SX8722 sleep current consumption below 3v vbat below 3 volts SX8722 enables the internal voltage multiplier to power the zoomingadc?. this internal voltage multiplier is automatically enabled when the power supply goes below 3v vbat. this voltage multiplier increase s SX8722 consumption. this is why the chip consumption in sleep mode with 2.5v supply is higher than with 5.5v supply. there is a possibility to consume less current when the vbat voltage is lower than 3v: the sleep signal has to be sent to the sleep pin when vbat is higher than 3v, and then decrease th e vbat value. in this case, the voltage multiplier is not activated. 15.3.4. SX8722 sleep current consumption with the 32.768 khz xtal the sleep mode current consumpt ion with the presence of the 32.768 khz xtal is around 1a if the supply voltage is above 3v. below 3v, the current consumption is around 4 a because the vmult is enabled. in addition to set the precise rc frequency, the presence of an external 32.768 khz xtal allows SX8722 sleep current consumption 3x lower than without the xtal. in this case SX8722 main cl ock is generated by the xtal. 15.3.5. SX8722 sleep current consumption without the 32.768 khz xtal the current consumption in sleep mode without the 32.768 khz xtal is around 3 a if the supply voltage is above 3v. below 3v, the current consumption is around 9 a because the voltage multiplier is enabled. the rc min frequency is set and its value is around 80 khz. 15.3.6. how to set SX8722 in sleep mode i2c sleep through the i2c interface, s end a write mask command at add ress 00 and toggle the sleep bit of the sxctrl1 register. when SX8722 is in sleep mode , send a write mask command at address 00 and toggle th e sleep bit to restore SX8722 active mode. warning: the i2c sleep command doe s not allow reaching as low current consumpti on as the sleep pin co mmand or writing the sxctrl1 register sleep bit. the sleep mode called by i2c sleep command (0x40) has a current consumption around 80a. sleep pin put the sleep input signal to vss, the sleep input is active on negative edge. is the SX8722 in sleep mode? there are pulses on the ready pin in active mode every 36ms. in sleep mode there is no pulse on the ready pin. 15.3.7. wake up from sleep mode to active mode
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 103 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface in sleep mode the internal program is in "halt" assembler equivalent mode. the sleep bit toggling in sxctrl1 or a signal on the sleep pin can wake up the SX8722. see active mode sectio n for more information. 15.4. shutdown mode 15.4.1. description this is a very low-power mode because all circuit clocks and all peripherals are stopped. only some service blocks remain active. 15.4.2. operating specifications in shutdown mode summary ? adc stopped ? vld stopped ? if xtal present, clock set to xtal 32k ? if xtal not present, clock set to rc minimum value (~80khz) ? bias current off ? program halt, interrupt off ? no possible i2c communication internal voltage multiplier like in sleep mode, internal voltage multiplier is automatically enabled when the power supply goes below 3 volts but the internal voltage multiplier requires an external capacitor be tween vmult pin and vss, the value of this capacitor must be between 1 and 3nf. shutdown mode current consumption the current consumption in shutdown mode is around 0.5 a if the supply voltage is above 3v. below 3v, the current consumption is around 3.5 a because the voltage multiplier is enabled. how to set shutdown mode consumption around 0.5a by default, with a supply voltage below 3v the shutdown mode current is around 3.5a. to ob tain 0.5a consumption, the shut command (i2c, pin) has to be received by the SX8722 wh en the internal voltage multip lier is not enabled. it means when the supply voltage is above 3v. then, if the supply voltage is lowered under 3v, the SX8722 will conserve the 0.5a consumption. 15.4.3. how to set SX8722 in shutdown mode i2c shutdown command send the 0x50 command th rough the i2c interface. i2c shut bit toggle through the i2c interface, send a write mask command at add ress 00 and toggle the shut bit of the sxctrl1 register.
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 104 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface shut pin put the shut input signal to vss, the shut input is active on negative edge. 15.4.4. wake-up from shutdown mode to active mode there are two possible ways to wake-up from the shutdown mode: ? the por (power-on-reset caused by a power-down followed by power-on). ? the reset pin. in both case the ram in formation is lost. SX8722 conf iguration must be restored from the eeprom saved configuration. 15.4.5. change from shutdown mode to sleep mode this is not possible.
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 105 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 16. pcb layout considerations pcb layout considerations to be taken wh en using the SX8722 are relatively simple to get the highest performances out. the most important to achieve good performances is to have a good voltage reference. separating the digital from the analog lin es will be also a good choice to reduce the nois e induced by the digital lines. it is also advised to have separated ground planes for digital and anal og signals with the shortest return path, as well as making the power supply lines as wider as possibl e and to have good decoupling capacitors. 17. how to evaluate for evaluation purposes the xe8000ev120 evaluation kit can be ordered. this kit connects to any pc using a usb port. the "SX8722 evaluation tools" soft ware gives the user the ability to control the SX8722 and displaying configurations on the "graphical user interface". for more information please look at semtech web site (http://www.semtech.com). 18. package outline drawing: mlpq44-7x7mm a pin 1 indicator (laser mark) a1 a2 e d a lxn e/2 d/2 bxn millimeters 0.50 bsc .002 - 0.00 .000 a1 .271 .271 .197 .197 .017 .007 e1 aaa bbb n e l a2 d1 d e b .020 bsc .203 .021 .003 .004 44 .275 (.008) .203 .275 .010 - 5.00 .207 .025 0.45 .279 .279 .207 - .012 6.90 6.90 5.00 - 0.18 .031 min dim a max dimensions inches - nom .040 0.80 min - 0.05 7.10 7.10 5.25 5.25 0.65 0.30 5.15 0.55 0.10 0.08 44 7.00 (0.20) 5.15 7.00 0.25 - 1.00 max - nom b aaa c c seating plane 1 2 n bbb c a b coplanarity applies to the exposed pad as well as the terminals. controlling dimensions are in millimeters (angles in degrees). notes: 2. 1. d1 e1 e
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 106 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 19. land pattern dr awing: mlpq44-7x7mm thermal vias in the land pattern of the exposed pad shall be connected to a system ground plane. functional performance of the device. failure to do so may compromise the thermal and/or 2. y g this land pattern is for reference purposes only. consult your manufacturing group to ensure your notes: 1. dim x y h k p c g millimeters inches (6.80) .011 .039 .228 .021 .207 .207 (.268) 0.30 1.00 5.25 0.50 5.25 5.80 dimensions company's manufacturing guidelines are met. 7.80 .307 z h k (c) z x p
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 107 advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface 20. tape and reel specification mlp/qfn (0.70mm - 1.00mm package thickness) ? single sprocket holes ? tolerances for ao & bo are +/- 0.20mm ? tolerances for ko is +/- 0.10mm ? tolerance for pocket pitch is +/- 0.10mm ? tolerance for tape width is +/-0.30mm ? trailer and leader length are minimum required length ? package orientation and feed direction direction of feed direction of feed mlp (square) mlp (rectangular) carrier tape (mm) reel pkg size tape width (w) pocket pitch (p) ao bo ko reel size (in) reel width (mm) trailer length (mm) leader length (mm) qty per reel 2x2 8 4 2.25 2.25 1.00 7 8.4 160 400 3000 3x3 12 8 3.30 3.30 1.10 13 12.4 400 400 3000 4x4 12 8 4.35 4.35 1.10 13 12.4 400 400 3000 4x3 12 8 3.30 4.30 1.10 13 12.4 400 400 3000 5x5 12 8 5.25 5.25 1.10 7/13 12.4 200/400 400 500/3000 6x6 16 12 6.30 6.30 1.10 13 16.4 400 400 3000 6x5 12 8 5.30 6.30 1.10 13 12.4 400 400 3000 7x7 16 12 7.30 7.30 1.10 13 16.4 400 400 3000 9x9 16 12 9.30 9.30 1.10 13 16.4 400 400 3000 10x10 24 16 10.30 10.30 1.10 13 24.4 400 400 3000 11x11 24 16 11.40 11.40 1.20 13 24.4 400 400 3000
acs - revision 4.2 october 2008 ?2008 semtech corp. www.semtech.com page 108 iso9001 certified ? semtech 2008 a ll rights reserved. reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. th e information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. no liability will be accepted by the publisher for any consequence of its use. publication thereof does not convey nor imply any license under patent or other industrial or intellectual property rights. semtech assumes no responsibility or liability whatsoever for any failure or unexpected operation resulting from misuse, neglect improper installation, repair or improper handling or unusual physical or electrical stress including, but not limited to, exposure to parameters beyond the specified maximum ratings or operation outside the specified range. semtech products are not designed, intended, auth orized or warranted to be suitable for use in life-support applications, devices or systems or other critical applications. inclusion of semtech products in such applications is understood to be undertaken solely at the customer?s own risk. should a customer purchase or use semtech product s for any such unauthorized application, the customer shall indemnify and hold semtech and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs damages and attorney fees which could arise. advanced communications & sensing datasheet SX8722 high gain acquisition for sensor interface semtech corporation advanced co mmunications & sensing products contact information e-mail: sales@semtech.comacsupport@semtech.cominternet: http://www.semtech.com usa 200 flynn road, camarillo, ca 93012-8790. tel: +1 805 498 2111 fax: +1 805 498 3804 far east 12f, no. 89 sec. 5, nanking e. road, taipei, 105, twn, r.o.c. tel: +886 2 2748 3380 fax: +886 2 2748 3390 europe semtech ltd., units 2 & 3, park court, premier way, abbey park industrial estate, romsey, hampshire, so51 9dn. tel: +44 (0)1794 527 600 fax: +44 (0)1794 527 601

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