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sx8650 www.semtech.com page 1 worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd advanced communications & sensing datasheet revision v2.19/october 2010 ?2010 semtech corp. 4 the sx8650 is an ultra low power 4-wire resistive touchscreen controller optimized for portable equip ment where power and board-space are at a premium. it incorporates a highly accurate 12-bit adc for da ta conversion and operates from a single 1.65 to 3.7v supply voltage. the sx8650 features a built-in preprocessing algori thm for data measurements, which greatly reduces the host processing overhead and bus activity. this complete touchscreen solution includes four user-selectable operation modes which offer programmability on diff erent configurations such as conversion rate and settling time, thus enable optimization in throughput and power consumption for a wide range of touch sensing appli cations. the touch screen inputs have been specially designe d to provide robust on-chip esd protection of up to 15k v in both hbm and contact discharge, and eliminates the need for external protection devices. the sx8650 supports the fast-mode i2c (400kbit/s) s erial bus data protocol and includes 2 user-selectable sl ave addresses. a custom i2c address is possible on requ est. the sx8650 is offered in two tiny packages: 3.0 mm x 3.0 mm dfn and a 1.5 mm x 2.0 mm wafer-level chip-s cale package (wlcsp). portable equipment mobile communication devices cell phone, pda, mp3, gps, dsc touch screen monitors extremely low power consumption: 23ua@1.8v 8ksps superior on-chip esd protection 15kv hbm (x+,x-,y+,y-) 2kv cdm 25kv air gap discharge 15kv contact discharge 300v mm single 1.65v to 3.7v supply/reference integrated preprocessing block to reduce host loadi ng and bus activity four user programmable operation modes provides flexibility to address different application needs manual, automatic, pen detect, pen trigger high precision 12-bit resolution low noise ratiometric conversion selectable polling or interrupt modes touch pressure measurement 400khz fast-mode i2c interface hardware reset & i2c software reset -40c to 85c operation 12-ld (3.0 mm x 3.0 mm) dfn package 12-ball (1.5 mm x 2.0 mm) wlcsp package pin-compatible with sx8651 pb-free, halogen free, rohs/weee compliant product windows ce 6.0, linux driver support available general description applications block diagram key product features ordering information part number package sx8650icstrt 1 1. 3000 units / reel 12 - ball wlcsp (1.5 mm x 2.0 mm) sx8650iwltrt 1 12 - lead dfn (3.0 mm x 3.0 mm) touch screen interface sx8650 vdd aux x+ y+ x- y- a0 nirq nrst scl sda gnd host control i2c digital filter ref+ ref- adc in out osc por vref
sx8650 www.semtech.com page 2 section page advanced communications & sensing datasheet table of contents revision v2.19/october 2010 ?2010 semtech corp. 1. general description ............................ ................................................... ................................................... ............... 4 1.1. dfn pinout diagram and marking information (t op view)........................................... ................................... 4 1.2. wlcsp pinout diagram and marking information (top view) ......................................... ............................... 4 1.3. pin description.............................. ................................................... ................................................... ............. 5 1.4. simplified block diagram ..................... ................................................... ................................................... ...... 5 2. electrical characteristics ..................... ................................................... ................................................... .............. 6 2.1. recommended operating conditions............. ................................................... .............................................. 6 2.2. thermal characteristics ...................... ................................................... ................................................... ....... 6 2.3. electrical specifications .................... ................................................... ................................................... ......... 7 2.4. host interface specifications ................ ................................................... ................................................... ..... 9 2.5. host interface timing waveforms.............. ................................................... ................................................. 1 0 2.6. typical operating characteristics ............ ................................................... ................................................... 11 3. functional description ......................... ................................................... ................................................... ............ 13 3.1. general introduction ........................ ................................................... ................................................... ....... 13 3.2. channel pins................................. ................................................... ................................................... ........... 13 3.2.1. x+, x-, y+. y- ............................. ................................................... ................................................... ....... 13 3.2.2. aux ........................................ ................................................... ................................................... ........... 13 3.3. host interface and control pins .............. ................................................... ................................................... . 14 3.3.1. nirq ....................................... ................................................... ................................................... .......... 14 3.3.2. scl ........................................ ................................................... ................................................... ........... 14 3.3.3. sda ........................................ ................................................... ................................................... ........... 14 3.3.4. a0 ......................................... ................................................... ................................................... ............. 15 3.3.5. nrst ....................................... ................................................... ................................................... ......... 15 3.4. power management pins........................ ................................................... ................................................... . 15 3.4.1. vdd........................................ ................................................... ................................................... ........... 15 3.4.2. gnd ........................................ ................................................... ................................................... .......... 15 4. detailed description........................... ................................................... ................................................... .............. 16 4.1. touch screen operation....................... ................................................... ................................................... ... 16 4.2. coordinates measurement...................... ................................................... ................................................... . 17 4.3. pressure measurement......................... ................................................... ................................................... ... 17 4.4. pen detection ................................ ................................................... ................................................... .......... 18 5. data processing ................................ ................................................... ................................................... .............. 19 5.1. host interface and control ................... ................................................... ................................................... .... 19 5.1.1. i2c address ................................ ................................................... ................................................... ...... 19 5.1.2. i2c write registers ........................ ................................................... ................................................... ... 20 5.1.3. i2c read registers ......................... ................................................... ................................................... .. 21 5.1.4. i2c host commands .......................... ................................................... .................................................. 21 5.1.5. i2c read channels ......................... ................................................... ................................................... . 22 5.1.6. data channel format ....................... ................................................... ................................................... 23
sx8650 www.semtech.com page 3 section page advanced communications & sensing datasheet table of contents revision v2.19/october 2010 ?2010 semtech corp. 5.1.7. invalid qualified data ..................... ................................................... ................................................... ... 23 5.2. i2c register map ............................ ................................................... ................................................... ........ 23 5.3. host control writing......................... ................................................... ................................................... ........ 24 5.4. host commands ................................ ................................................... ................................................... ...... 26 5.5. power-up ..................................... ................................................... ................................................... ............ 27 5.6. reset........................................ ................................................... ................................................... ................ 27 6. modes of operation ............................ ................................................... ................................................... ............ 27 6.1. manual mode .................................. ................................................... ................................................... ......... 28 6.2. automatic mode ............................... ................................................... ................................................... ........ 29 6.3. pendet mode .................................. ................................................... ................................................... ...... 30 6.4. pentrig mode ................................. ................................................... ................................................... ...... 30 7. application information ........................ ................................................... ................................................... ............ 31 7.1. acquisition setup ............................ ................................................... ................................................... ......... 31 7.2. channel selection............................ ................................................... ................................................... ........ 31 7.3. noise reduction.............................. ................................................... ................................................... ......... 31 7.3.1. powdly..................................... ................................................... ................................................... ...... 31 7.3.2. setdly ..................................... ................................................... ................................................... ....... 32 7.3.3. aux input .................................. ................................................... ................................................... ........ 32 7.4. interrupt generation......................... ................................................... ................................................... ........ 32 7.5. coordinate throughput rate ................... ................................................... ................................................... 32 7.5.1. i2c communication time..................... ................................................... ................................................ 33 7.5.2. conversion time ............................ ................................................... ................................................... ... 33 7.5.3. auto mode .................................. ................................................... ................................................... .. 33 7.6. esd event.................................... ................................................... ................................................... ............ 33 7.7. application schematic........................ ................................................... ................................................... ...... 34 7.8. application examples......................... ................................................... ................................................... ...... 34 7.8.1. soft keyboard .............................. ................................................... ................................................... ..... 34 7.8.2. slider controls............................ ................................................... ................................................... ....... 34 7.8.3. game ....................................... ................................................... ................................................... ......... 35 7.8.4. handwriting application.................... ................................................... ................................................... . 35 8. packaging information .......................... ................................................... ................................................... ........... 36 8.1. dfn package.................................. ................................................... ................................................... ......... 36 8.2. wlcsp package ................................ ................................................... ................................................... ..... 38
sx8650 www.semtech.com page 4 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 1. general description 1.1. dfn pinout diagram and marking information (t op view) figure 1. sx8650sx8650 dfn top view, pad on botto m side yyww : date code xxxxx: lot number 1.2. wlcsp pinout diagram and marking information (top view) figure 2. sx8650 wlcsp top view, solder bumps on bottom side yyww : date code xxxxx: lot number 1 2 3 4 5 6 12 11 10 9 8 7 vdd aux x+ y+ x- y- a0 nirq nrst scl sda gnd sx8650 top view 13 8650 yyww xxxx pin 1 identifier sx8650 top view solder bumps on bottom side vdd aux x+ y+ a a0 nirq nrst scl sda gnd b c d 32 1 x- y- 8650 eyww ball a1 identifier
sx8650 www.semtech.com page 5 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 1.3. pin description table 1 pin description 1.4. simplified block diagram the sx8650 simplified block diagram is shown in fig ure 3. figure 3. simplified block diagram of the sx8650 pin number # name type description dfn wlcsp 1 a2 vdd power input power supply connect to a 0.1uf capa citor to gnd 2 a3 x+ analog x+ channel input 3 b3 y+ analog y+ channel input 4 c3 x- analog x- channel input 5 d3 y- analog y- channel input 6 d2 gnd ground ground 7 b1 nirq digital output / open drain output interrupt o utput, active low. need external pull-up resistor 8 c1 sda digital input / open drain output i2c data inpu t/output 9 d1 scl digital input / open drain output i2c clock, in put/output 10 c2 nrst digital input / output reset input, active lo w. need external 50k pull-up resistor 11 b2 a0 digital input i2c slave address selection input 12 a1 aux digital input/analog input analog auxiliary input or conversion synchronization 13 gnd ground die attach paddle, connect to ground touch screen interface sx8650 vdd aux x+ y+ x- y- a0 nirq nrst scl sda gnd control i2c digital filter ref+ ref- adc in out osc por vref
sx8650 www.semtech.com page 6 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 2. electrical characteristics stresses above the values listed in absolute maximu m ratings may cause permanent damage to the device . this is a stress rating only and functional operati on of the device at these, or any other conditions beyond the recommended operating conditions, is not implied. exposure to absolute ma ximum rating conditions for extended periods may af fect device reliability . (i) tested to tlp (10a) (ii) tested to jedec standard jesd22-a114 (iii) tested to jedec standard jesd78 2.1. recommended operating conditions 2.2. thermal characteristics ( iii) q ja is calculated from a package in still air, mounted to 3" x 4.5", 4 layer fr4 pcb with thermal vias und er exposed pad (if applicable) per jesd51 standards. parameter symbol min. max. unit supply voltage v ddabs -0.5 3.9 v input voltage (non-supply pins) v in -0.5 3.9 v input current (non-supply pins) i in 10 ma operating junction temperature t jct 125 c reflow temperature t re 260 c storage temperature t stor -50 150 c esd hbm (human body model) high esd pins: x+, x-,y+,y- esd hbm1 15 (i) kv 8 (ii) kv all pins except high esd pins: aux,a0,nrst,nirq,sda,scl esd hbm2 2 kv esd (contact discharge) high esd pins: x+, x-,y+,y- esd cd 15 kv latchup i lu 100 (iii) ma table 2. absolute maximum ratings parameter symbol min. max unit supply voltage v dd 1.65v 3.7 v ambient temperature range t a -40 85 c parameter symbol min. max unit thermal resistance with dfn package - junction to am bient (i) q ja 39 c/w thermal resistance with wlcsp package - junction to am bient (i) q ja 65 c/w
sx8650 www.semtech.com page 7 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 2.3. electrical specifications parameter symbol conditions min. typ max unit current consumption manual i pwd manual (converter stopped, pen detection off, i2c listening, osc stopped) 0.4 0.75 ua pen detect i pndt pen detect mode (converter stopped, pen detection activated, device will generate interrupt upon detection, i2c listening, osc stopped). 0.4 0.75 ua pen trigger i pntr pen trigger mode (converter stopped, pen detection activated, device will start conversion upon pen detection. i2c listening, osc stopped 0.4 0.75 ua automatic i wt automatic (converter stopped, pen detection off, i2c listening, osc and timer on, device is waiting for timer expiry) 1.5 ua operation @8ksps, vdd=1.8v i opl x,y conv. rate=4ksps, n filt =1 powdly=0.5us, setdly=0.5us 23 50 ua operation @42ksps, vdd=3.3v i oph x,y conv. rate=3ksps, n filt =7 powdly=0.5us, setdly=0.5us 105 140 ua digital i/o high-level input voltage 1 v ih 0.7v dd v dd +0.5 v low-level input voltage v il v ss -0.3 0.3v dd v sda / scl hysteresis of schmitt trigger inputs vdd > 2 v vdd < 2 v v hys 0.05v dd 0.1v dd v low-level output voltage v ol i ol =3ma, v dd >2v i ol =3ma, v dd <2v 00 0.4 0.2v dd v input leakage current l i cmos input 1 ua aux input voltage range v iaux 0 v dd v input capacitance c x+ ,c x- ,c y+ , c y- 50 pf c aux 5 pf
sx8650 www.semtech.com page 8 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. all values are valid within the recommended operati ng conditions unless otherwise specified. input leakage current i iaux -1 1 ua startup power-up time (delay t por time between rising edge vdd and rising nirq 1 ms reset reset low time t nrst 50 ns adc resolution a res 12 bits offset a off 1 lsb gain error a ge at full scale 0.5 lsb differential nonlinearity a dnl 1 lsb integral nonlinearity a inl 1.5 lsb resistors x+, x-, y+, y- resistance r chn touch pad biasing resistance 5 ohm pen detect resistance r pndt_00 r pndt = 0 100 kohm r pndt_01 r pndt = 1 200 kohm r pndt_10 r pndt = 2 50 kohm r pndt_11 r pndt = 3 25 kohm external components recommendations capacitor between vdd, gnd c vdd type 0402, tolerance +/-50% 0.1 uf 1. scl, sda, nrst and nirq can be pulled up to a potent ial higher than the chip vdd but must not exceed th e maximun voltage of 3.7v. parameter symbol conditions min. typ max unit
sx8650 www.semtech.com page 9 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 2.4. host interface specifications table 3 host interface specifications notes: (i) all timing specifications refer to voltage level s (v il , v ih , v ol ) defined in table 3 unless otherwise mentioned. parameter symbol condition min typ max unit i2c timing specifications (i) scl clock frequency f scl 0 400 khz scl low period t low 1.3 us scl high period t high 0.6 us data setup time t su;dat 100 ns data hold time t hd;dat 0 ns repeated start setup time t su;sta 0.6 us start condition hold time t hd;sta 0.6 us stop condition setup time t su;sto 0.6 us bus free time between stop and start t buf 1.3 us data valid time t vd;dat 0.9 us data valid ack time t vd;ack 0.9 us pulse width of spikes that must be suppressed by the input filter t sp 50 ns i2c bus specifications capacitive load on each bus line scl, sda c b 400 pf
sx8650 www.semtech.com page 10 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 2.5. host interface timing waveforms figure 4. i2c start and stop timing figure 5. i2c data timing sda scl t su;sta t hd;sta t su;sto t buf 70% 30% 70% sda scl t low t high t hd;dat t su;dat t sp 30% 70% 30% 70%
sx8650 www.semtech.com page 11 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 2.6. typical operating characteristics at ta= -40c to +85c, vdd=1.7v to 3.7v, powdly=0.5 us, setdly=0.5us, filt=1, resistive touch screen se nsor current not taking in account, unless otherwise noted. current in pen trigger mode 0 100 200 300 400 500 1.5 2 2.5 3 3.5 v dd (v) supply current (na) touch sensor not activated supply current in manual mode vs temperature 0 100 200 300 400 500 600 700 -40 -20 0 20 40 60 80 100 temperature (c) manual mode supply current (na) v dd =3.3v v dd =1.85v supply current vs conversion rate vdd=1.8v - x,y conversion 0 10 20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 conversion rate (kcps) supply current (ua) filt=7 filt=5 filt=3 filt=1 supply current vs conversion rate vdd=1.8v - x,y, z1, z2 conversion 0 10 20 30 40 50 60 70 80 90 100 110 120 130 0 1 2 3 4 5 conversion rate (kcps) supply current (ua) filt=7 filt=5 filt=3 filt=1 supply current vs sample rate 0 100 200 300 400 500 0 1 2 3 4 5 sample rate (kcps) supply current (ua) touch sensor x+ to x- =1000 ohm y+ to y- =1000 ohm v dd =3.3v v dd =2.5v v dd =1.65v
sx8650 www.semtech.com page 12 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. typical operating characteristics (continued) at ta= -40c to +85c, vdd=1.7v to 3.7v, powdly=0.5 us, setdly=0.5us, filt=1, resistive touch screen se nsor current not taking in account, unless otherwise noted. change in adc gain vs. temperature -2 -1 0 1 2 -40 -20 0 20 40 60 80 100 temperature (c) delta from +25c (lsb) change in adc offset vs. temperature -2 -1 0 1 2 -40 -20 0 20 40 60 80 100 temperature (c) delta from +25c (lsb) adc inl @ vdd=3.3v -1 -0.75 -0.5 -0.25 0 0.25 0.5 0.75 1 0 0.5 1 1.5 2 2.5 3 v x+ (v) error (lsb)
sx8650 www.semtech.com page 13 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 3. functional description 3.1. general introduction this section provides an overview of the sx8650 arc hitecture, device pinout and a typical application. the sx8650 is designed for 4-wire resistive touch s creen applications (figure 6).the touch screen or t ouch panel is the resistive sensor and can be activated by either a f inger or stylus. the touch screen coordinates and t ouch pressure are converted into i2c format by the sx8650 for transfe r to the host. figure 6. sx8650 with screen 3.2. channel pins 3.2.1. x+, x-, y+. y- the sx8650's channel pins (x+, x-, y+, y-) directly connect to standard touch screen x and y resistive layers. the sx8650 separately biases each of these layers and converts the resistive values into (x,y) coordinates. the channel pins are protected to vdd and ground. figure 7 shows the simplified diagram of the x+, x- , y+, y- pins. figure 7. simplified diagram of x+, x-, y+, y- pi ns 3.2.2. aux the sx8650 interface includes an aux pin that serve s two functions: an adc input; and a start of convers ion trigger. when used as an adc, the single ended inpu t range is from gnd to vdd, referred to gnd. when the aux input is configured to start conversions, t he aux input can be further configured as a rising and / or falling edge trigger. the aux is protected to vdd and ground. figure 8 shows a simplified diagram of the aux pin. figure 8. simplified diagram of aux touch screen interface sx8650 vdd aux x+ y+ x- y- a0 nirq nrst scl sda gnd host control i2c digital filter ref+ ref- adc in out osc por vref vdd_host vdd x+ x- y+ y- touch screen interface r chn aux adc control vdd
sx8650 www.semtech.com page 14 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 3.3. host interface and control pins the sx8650 host and control interface consists of: nirq, i2c pins scl and sda, a0, and nrst. 3.3.1. nirq the nirq pin is an active low, open drain output to facilitate interfacing to different supply volta ges and thus requires an external pull-up resistor (1- 10 kohm). the nirq pin does not have protection to vdd. the nirq function is designed to provide an interrupt to the host processor. interrupts may occur when a pen is detected, or when channel data is available. figure 9 shows a simplified diagram of the nirq pin. figure 9. simplified diagram of nirq 3.3.2. scl the scl pin is a high-impedance input and open- drain output pin. the scl pin does not have protection to vdd to conform to i2c slave specifications. an external pull-up resistor (1-10 kohm) is required. figure 10 shows the simplified diagram of the scl pin. figure 10. simplified diagram of scl 3.3.3. sda sda is an i/o pin. it can be used as an open-drain output (with external pull-up resistor) or as an input. an external pull-up resistor (1-10 kohm) is required. the sda i/o pin does not have protection to vdd to conform to i2c slave specifications. figure 11 shows a simplified diagram of the sda pin. figure 11. simplified diagram of sda nirq control host vdd irq scl host vdd in out scl i2c sda host vdd in out sda i2c
sx8650 www.semtech.com page 15 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 3.3.4. a0 the a0 pin is connected to the i2c address select c ontrol circuitry and is used to modify the device i2c addr ess. the a0 pin is protected to ground. figure 12 shows a simplified diagram of the a0 pin. figure 12. simplified diagram of a0 3.3.5. nrst the nrst pin is an active low input that provides a hardware reset of the sx8650's control circuitry. the nrst pin is protected ground to enable interfacing with devices at a different supply voltages. figure 13 shows a simplified diagram of the nrst pin. figure 13. simplified diagram of nrst 3.4. power management pins the sx8650's power management input consists of the following power and ground pins. 3.4.1. vdd the vdd is a power pin and is the power supply for the sx8650. the vdd has esd protection to ground. figure 14 shows a simplified diagram of the vdd pin . figure 14. simplified diagram of vdd 3.4.2. gnd the sx8650 has one power management ground pin, gnd . (the die attach paddle on dfn is also connected to gnd.) the gnd has esd protection to vdd. figure 15 shows a simplified diagram of the gnd pin . figure 15. simplified diagram of gnd a0 i2c nrst control host vdd vdd vdd gnd vdd
sx8650 www.semtech.com page 16 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 4. detailed description 4.1. touch screen operation a resistive touch screen consists of two (resistive ) conductive sheets separated by an insulator when not pressed. each sheet is connected through 2 electrodes at the bord er of the sheet (figure 16). when a pressure is app lied on the top sheet, a connection with the lower sheet is establi shed. figure 17 shows how the y coordinate can be m easured. the electrode plates are connected through terminals x+ , x- and y+, y- to an analog to digital converter ( adc) and a reference voltage. the resistance between the terminals x+ an d x- is defined by rxtot. rxtot will be split in 2 resistors, r1 and r2, in case the screen is touched. the resistance between the terminals y+ and y- is represented by r3 and r4 . the connection between the top and bottom sheet is represented by the touch resistance (r t ). figure 16. 4-wire touch screen figure 17. touch screen operation ordinate measur ement (y) x- y+ y- x+ top conductive sheet bottom conductive sheet electrodes electrodes x- x+ y- y+ r3 r4 r2 r1 + - adc ypos vref + - r t
sx8650 www.semtech.com page 17 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 4.2. coordinates measurement the top resistive sheet (y) is biased with a voltag e source. resistors r3 and r4 determine a voltage d ivider proportional to the y position of the contact point. since the conv erter has a high input impedance, no current flows through r1 so that the voltage x+ at the converter input is given by the v oltage divider created by r3 and r4. the x coordinate is measured in a similar fashion w ith the bottom resistive sheet (x) biased to create a voltage divider by r1 and r2, while the voltage on the top sheet is me asured through r3. figure 18 shows the coordinates measurement setup. the resistance r t is the resistance obtained when a pressure is appl ied on the screen. r t is created by the contact area of the x and y resistive sheet and varies with the applied pressure. figure 18. ordinate (y) and abscissa (x) coordina tes measurement setup the x and y position are found by: 4.3. pressure measurement the pressure measurement consists of two additional setups: z1 and z2 (see figure 19). figure 19. z1 and z2 pressure measurement setup the corresponding equations for the pressure: x- x+ r2 r1 vref + - r t y- y+ r4 r3 ypos x- x+ r2 r1 vref + - r t y- y+ r4 r3 xpos xpos 4095 r 2 r 1 r 2 + -------------------- = ypos 4095 r 4 r 3 r 4 + -------------------- = x- x+ r2 r1 r t y- y+ r4 r3 z1 x- x+ r2 r1 vref + - y- y+ r4 r3 z2 vref + - r t z 1 4095 r 4 r 1 r 4 r t + + --------------------------------- = z 2 4095 r 4 rt + r 1 r 4 r t + + --------------------------------- =
sx8650 www.semtech.com page 18 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. the x and y total sheet resistance (rxtot, rytot) a re known from the touch screen supplier. r4 is proportional to the y coordinate. the r4 value is given by the total y plate resistan ce multiplied by the fraction of the y position over the full coordinate range. by re-arranging z1 and z2 one obtains which results in: the touch resistance calculation above requires thr ee channel measurements (ypos, z2 and z1) and one s pecification data (rytot).an alternative calculation method is using xpos, ypos, one z channel and both rxtot and rytot shown in the next calculations r1 is inverse proportional to the x coordinate. substituting r1 and r4 into z1 and rearranging term s gives: 4.4. pen detection the pen detection circuitry is used both to detect a user action and generate an interrupt or start an acquisition in pendet and pen trg mode respectively. doing a pen detection prior to conversion avoids fe eding the host with dummy data and saves power. if the touchscreen is powered between x+ and y- thr ough a resistor r pndt , no current will flow so long as pressure is not applie d to the surface (see figure 20). when some pressure is applied, a curren t path is created and brings x+ to the level defined by the resistive divider de termined by r pndt and the sum of r1, r t and r4. the level is detected by a comparator. figure 20. pen detection r pndt should be set to the greatest value 200 kohm for o ptimal detection (see table 6). increasing powdly s ettings can also improve the detection on panel with high resis tance. the pen detection will set the penirq bit of the re gstat register. in pendet mode, the pen detection will set nirq low . the penirq bit will be cleared and the nirq will be de-asserted as soon as the host reads the status register. rxtot r 1 r 2 + = rytot r 3 r 4 + = r 4 rytot ypos 4095 ------------ = r t r 4 z 2 z 1 ----- 1 C = r t rytot ypos 4095 ------------ z 2 z 1 ----- 1 C = r 1 rxtot 1 xpos 4095 ------------- C = r t rytot y pos 4095 ------------------------------- 4095 z 1 ------------ 1 C rxtot 1 xpos 4095 ------------- C C = x- x+ r2 r1 vref + - r t y- y+ r4 r3 r pndt
sx8650 www.semtech.com page 19 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 5. data processing the sx8650 offers 4 types of data processing which allows the user to make trade-offs between data throughput, power consumption and noise rejection. the parameter filt is used to select the filter order n filt . the noise rejection will be improved with a high order to the detriment of the power consumption. the k coefficient in table 4 is a filt er constant. its value is k=4079/4095. figure 21. filter structure . table 4. filter order 5.1. host interface and control the host interface consists of i2c (scl and sda) an d the nirq, a0, nrst signals. the i2c implemented on the sx8650 is compliant with : standard mode (100 kbit/s) & fast mode (400 kbit/s) slave mode 7 bit slave address 5.1.1. i2c address pin a0 defines the lsb of the i2c address. it is sh own on figure 22. filt n filt processing 0 1 no average. 1 3 3 adc samples are averaged 2 5 5 adc samples are averaged 3 7 7 adc samples are sorted and the 3 center samples a re averaged adc c n ,c n-1 ,c n-2 ,... i2c - = - = 1 0 1 n i i n n c n s sort: .>.>.>.>. preprocessing s n n filt s n c n = n 13 --- 4079 4095 ------------ c n c n 1 C c n 2 C + + ( ) = s n 1 5 --- 4079 4095 ------------ c n c n 1 C c n 2 C c n 3 C c n 4 C + + + + ( ) = c max 1 c max 2 c a c b c c c min 1 c min 2 3 3 3 3 3 3 n 1 3 --- 4079 4095 ------------ c a c b c c + + ( ) =
sx8650 www.semtech.com page 20 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. . figure 22. i2c slave address upon request of the customer, a custom i2c address can be burned in the nvm. the host uses the i2c to read and write data and co mmands to the configuration and status registers. d uring a conversion, the i2c clock can be stretched until the end of the processing. channel data read is done by i2c throughput optimiz ed formats. the supported i2c access formats are described in t he next sections: i2c write registers i2c read registers i2c host commands i2c read channels 5.1.2. i2c write registers the format for i2c write is given in figure 23. after the start condition [s], the sx8650 slave add ress (sa) is sent, followed by an eighth bit (w=0 ) indicating a write. the sx8650 then acknowledges [a] that it is being a ddressed, and the host sends 8-bit command and regi ster address consisting of the command bits 000 followed by th e sx8650 register address (ra). the sx8650 acknowledges [a] and the host sends the appropriate 8-bit data byte (wd0) to be written. again the sx8650 acknowledges [a]. in case the host needs to write more data, a succee ding 8-bit data byte will follow (wd1), acknowledge d by the slave [a]. this sequence will be repeated until the host termi nates the transfer with the stop condition [p]. figure 23. i2c write register 1 0 0 1 0 0 0 with pin a0 connected to ground sx8650 slave address(7:1) = 1 0 0 1 0 0 1 with pin a0 connected to vdd s sa w cr a a wd0 a wd1 a wdn a p optional optional s: start condition sa: sx8650 slave address(7:1) w: '0' a: acknowledge cr: '000' + register address(4:0) wdn: write data byte(7:0), 0...n p: stop condition from host to sx8650 from sx8650 to host clock stretching
sx8650 www.semtech.com page 21 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. the register address increments automatically when successive register data (wd1...wdn) is supplied by the host. this automatic increment can be used for the first 4 reg ister addresses (see table 6). the correct sampling of the screen by the sx8650 an d the host i2c bus traffic are events that might oc cur simultaneously. the sx8650 will synchronize these events by the use of clock stretching if that is required. the stret ching occurs directly after the last received command bit (see figure 23) . 5.1.3. i2c read registers the format for incremental i2c read for registers i s given in figure 24. the read has to start with a write of the read address. after the start condition [s], the sx8650 slave add ress (sa) is sent, followed by an eighth bit (w=0 ) indicating a write. the sx8650 then acknowledges [a] that it is being a ddressed, and the host responds with a 8-bit cr dat a consisting of 010 followed by the register address (ra). the sx 8650 responds with an acknowledge [a] and the host sends the repeated start condition [sr]. once again, the sx86 50 slave address (sa) is sent, followed by an eight h bit (r=1) indicating a read. the sx8650 responds with an acknowledge [a] and the read data byte (rd0). if the host needs to read mo re data it will acknowledge [a] and the sx8650 will send the next r ead byte (rd1). this sequence can be repeated until the host terminates with a nack [n] followed by a stop [p]. figure 24. i2c read registers the i2c read register format of figure 24 is mainta ined until the stop condition. after the stop condi tion the sx8650 is performing succeeding reads by the compact read for mat of the i2c read channels described in the next section. no clock stretching will occur for the i2c read reg isters. 5.1.4. i2c host commands the format for i2c commands is given in figure 25. after the start condition [s], the sx8650 slave add ress (sa) is sent, followed by an eighth bit (w=0 ) indicating a write. the sx8650 then acknowledges [a] that it is being a ddressed, and the host responds with an 8-bit data consisting of a 1 + command(6:0). the sx8650 acknowledges [a] and the host sends a stop [p]. the exact definition of command(6:0) can be found i n table 8. w cr a s sa a sr sa r a rd0 a rd1 a rdn n p from host to sx8650 from sx8650 to host optional s: start condition sr: repeated start condition sa: sx8650 slave address(7:1) w: '0' r: '1' a: acknowledge n: not acknowledge (terminating read stream) cr: '010' + register address(4:0) rdn: read data byte(7:0), 0...n p: stop condition
sx8650 www.semtech.com page 22 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. figure 25. i2c host command the sampling of the screen by the sx8650 and the ho st i2c bus traffic are events that might occur simu ltaneously. the sx8650 will synchronize these events by the use of clock stretching if that is required. the stretchin g occurs directly after the last received command bit (see figure 25). 5.1.5. i2c read channels the host is able to read the channels with a high t hroughput, by the format shown in figure 26. after the start condition [s], the sx8650 slave add ress (sa) is sent, followed by an eighth bit (r=1 ) indicating a read. the sx8650 responds with an acknowledge [a] and the rea d data byte (rd0). the host sends an acknowledge [a ] and the sx8650 responds with the read data byte (rd1). if t he host needs to read more data, it will acknowledg e [a] and the sx8650 will send the next read bytes. this sequence can be repeated until the host terminates with a n ack [n] followed immediately by a stop [p]. the nack [n] releases th e nirq line. the stop [p] must occur before the end of the conversion. the channel data that can be read is defined by the last conversion sequence. a maximum number of 10 data bytes is passed when al l channels (x, y, z1, z2 and aux) are activated in the i2cregchanmsk. the channel data is sent with the following order: x, y, z1, z2, aux. the first byte of the data conta ins the channel information as shown in figure 27. typical applications require only x and y coordinat es, thus only 4 bytes of data will be read. figure 26. i2c read channels s sa w cr a a p s: start condition sa: sx8650 slave address(7:1) w: '0' a: acknowledge cr: '1' + command(6:0) p: stop condition from host to sx8650 from sx8650 to host clock stretching s sa r a n s: start condition sa: sx8650 slave address(7:1) r: '1' a: acknowledge n: not acknowledge (terminating read stream) rdn: read data byte(7:0), 0...n p: stop condition from host to sx8650 from sx8650 to host rd0 a rd1 p channel (i+1) rdn-1 a rdn a channel (i) clock stretching
sx8650 www.semtech.com page 23 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. the sampling of the screen by the sx8650 and the ho st i2c bus traffic are events that might occur simu ltaneously. the sx8650 will synchronize these events by the use of clock stretching if that is required. the stretchin g occurs directly after the address and read bit have been sent for the i2c read channels command (see figure 26). 5.1.6. data channel format channel data is coded on 16 bits as shown in figure 27 figure 27. data channel format the 3 bits chan(2:0) are defined in table 9 and sho w which channel data is referenced. the channel dat a d(11:0) is of unsigned format and corresponds to a value between 0 and 4095. 5.1.7. invalid qualified data the sx8650 will return 0xffff data in case of inval id qualified data. this occurs: when the sx8650 converted channels and the host cha nnel readings do not correspond. e.g. the host conv erts x and y and the host tries to read x, y and z1 and z2. when a conversion is done without a pen being detec ted. 5.2. i2c register map the details of the registers are described in the n ext sections. i2c register address ra(4:0) register description 0 0000 i2cregctrl0 write, read 0 0001 i2cregctrl1 write, read 0 0010 i2cregctrl2 write, read 0 0100 i2cregchanmsk write, read 0 0101 i2cregstat read 1 1111 i2cregsoftreset write table 5. i2c register address c h a n (2:0) r d 0 d (11:8) d (7:0) r d 1 0
sx8650 www.semtech.com page 24 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 5.3. host control writing the host control writing allows the host to change sx8650 settings. the control data goes from the hos t towards the sx8650 and may be read back for verification. register bits default description i2cregctrl0 7:4 0000 rate set rate in coordinates per sec (cps) ( 20%) if rate equals zero then manual mode. if rate is larger than zero then automatic mode 0000: timer disabled -manual mode 0001: 10 cps 0010: 20 cps 0011: 40 cps 0100: 60 cps 0101: 80 cps 0110: 100 cps 0111: 200 cps 1000: 300 cps 1001: 400 cps 1010: 500 cps 1011: 1k cps 1100: 2k cps 1101: 3k cps 1110: 4k cps 1111: 5k cps 3:0 0000 powdly settling time ( 10%): the channel will be biased fo r a time of powdly before each channel conversion 0000: immediate (0.5 us) 0001: 1.1 us 0010: 2.2 us 0011: 4.4 us 0100: 8.9 us 0101: 17.8 us 0110: 35.5 us 0111: 71.0 us 1000: 0.14 ms 1001: 0.28 ms 1010: 0.57 ms 1011: 1.14 ms 1100: 2.27 ms 1101: 4.55 ms 1110: 9.09 ms 1111: 18.19 ms i2cregctrl1 7:6 00 auxaqc 00: aux is used as an analog input 01: on rising aux edge, wait powdly and start acquisition 10: on falling aux edge, wait powdly and start acquisition 11: on rising and falling aux edges, wait powdly and start acquisition the aux trigger requires the manual mode. 5 1 condirq enable conditional interrupts 0: interrupt always generated at end of conversion cycle. if no pen is detected the data is set to invalid qualified. 1: interrupt generated when pen detect is successfu l 4 0 reserved 3:2 00 rpdnt select the pen detect resistor 00: 100 kohm 01: 200 kohm 10: 50 kohm 11: 25 kohm 1:0 00 filt digital filter control 00: disable 01: 3 sample averaging 10: 5 sample averaging 11: 7 sample acquisition, sort, average 3 middle sa mples table 6. i2c registers
sx8650 www.semtech.com page 25 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. i2cregctrl2 7:4 0 reserved 3:0 0000 setdly settling time while filtering ( 10%) when filtering is enabled, the channel will initial ly bias for a time of powdly for the first conversion, and for a time of set dly for each subsequent conversion in a filter set. 0000: immediate (0.5 us) 0001: 1.1 us 0010: 2.2 us 0011: 4.4 us 0100: 8.9 us 0101: 17.8 us 0110: 35.5 us 0111: 71.0 us 1000: 0.14 ms 1001: 0.28 ms 1010: 0.57 ms 1011: 1.14 ms 1100: 2.27 ms 1101: 4.55 ms 1110: 9.09 ms 1111: 18.19 ms i2cregchanmsk 7 1 xconv 0: no sample 1: sample, report x channel 6 1 yconv 0: no sample 1: sample, report y channel 5 0 z1conv 0: no sample 1: sample, report z1 channel 4 0 z2conv 0: no sample 1:sample, report z2 channel 3 0 auxconv 0: no sample 1: sample, report aux channel 0 0 reserved 0 0 reserved 0 0 reserved i2cregstat the host status reading allows the host to read the status of the sx8650. the data goes from the sx8650 towards the host. host writing to this register is ignored. 7 0 convirq 0: no irq pending 1: end of conversion sequence irq pending irq is cleared by the i2c channel reading 6 0 penirq operational in pen detect mode 0: no irq pending 1: pen detected irq pending irq is cleared by the i2c status reading 5:0 000000 reserved i2cregsoftreset 7:0 0x00 if the host writes the value 0xde to this reg ister, then the sx8650 will be reset. any other data will not affect the sx8650 register bits default description table 6. i2c registers
sx8650 www.semtech.com page 26 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 5.4. host commands the host can write to and read from registers of th e sx8650 by the write and read commands as defined in table 7. .the host can issue commands to change the operatio n mode or perform manual actions as defined in tabl e 8. the channels are defined as in table 9. w/r command name cr(7:0) function 7 6 5 4 3 2 1 0 write(ra) 0 0 0 ra(4:0) write register (see table 5 for ra) read(ra) 0 1 0 ra(4:0) read register (see table 5 for ra) table 7. i2c w/r commands command name cr(7:0) function 7 6 5 4 3 2 1 0 select(chan) 1 0 0 0 x chan(2:0) bias channel (see table 9 for c han) convert(chan) 1 0 0 1 x chan(2:0) bias channel (see table 9 for chan) wait powdly settling time run conversion manauto 1 0 1 1 x x x x enter manual or automatic mode. pendet 1 1 0 0 x x x x enter pen detect mode. pentrg 1 1 1 0 x x x x enter pen trigger mode. table 8. i2c commands channel chan(2:0) function 2 1 0 x 0 0 0 x channel y 0 0 1 y channel z1 0 1 0 first channel for pressure measurement z2 0 1 1 second channel for pressure measurement aux 1 0 0 auxiliary channel reserved 1 0 1 reserved 1 1 0 seq 1 1 1 channel sequentially selected from i2cregchanmsk register, (see table 8) table 9. channel definition
sx8650 www.semtech.com page 27 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 5.5. power-up the nirq pin is kept low during sx8650 power-up. during power-up, the sx8650 is not accessible and i 2c communications are ignored. as soon as nirq rises, the sx8650 is ready for i2c communication. after startup, the host must wait t por before any communication with the sx8650. the por of the sx8650 will reset all registers and states of the sx8650 at power-up. figure 28. power-up, nirq 5.6. reset additionally the host can reset the sx8650 by asser ting the nrst pin (active low) and also via the i2c bus. if nrst is driven low, then nirq will be driven low by the sx8650. when nrst is released (or set to high) then nirq will be released by the sx8650. the circuit has also a soft reset capability. when writing the code 0xde to the register regsoftreset, the circuit will be reset. figure 29. reset 6. modes of operation the sx8650 has four operation modes that are config ured using the i2c commands as defined in table 8 a nd table 6. these 4 modes are: manual (command manauto and rate=0), automatic (command manauto and rate>0), pen detect (command pendet), pen trigger mode (command pentrg). at startup the sx8650 is set in manual mode. in the manual mode the sx8650 is entirely stopped e xcept for the i2c peripheral which accepts host com mands. this mode requires rate equal to be zero (rate = 0, see table 6). voltage time voltage time vdd nirq t por vdd/2 voltage time voltage time nrst nirq t por t nrst
sx8650 www.semtech.com page 28 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. in the automatic mode the sx8650 will sequence auto matic channel conversions. this mode requires rate to be larger than zero (rate > 0, see table 6). in the pendet mode the pen detection is activated. the sx8650 will generate an interrupt (nirq) upon p en detection and set the penirq bit in the i2c status register. to q uit the pendet mode the host needs to configure the manual mode. in the pentrg mode the pen detection is activated a nd a channel conversion will start after the detect ion of a pen. the sx8650 will generate an interrupt (nirq) upon pen d etection and set the convirq bit in the i2c status register. to quit the pentrig mode the host needs to configure the ma nual mode. the pentrg mode offers the best compromi se between power consumption and coordinate throughput . 6.1. manual mode in manual mode (rate=0) single actions are triggere d by the i2c commands described in table 10. when a command is received, the sx8650 executes the associated task and waits for the next command. it is up to the host to sequence all actions. table 10 convert and select command the channel can be biased for an arbitrary amount o f time by first sending a select command and then a convert command once the settling time requirement is met. the select command can be omitted if the large rang e of powdly settings cover the requirements. in the latter case, the convert command alone is enough to perform an a cquisition. with chan=seq, multiple channels are sampled. this requires programming the powdly field in register r egctrl0. the selected channel will be powered during powdly before a conversion is started. the channel bias is automatically removed after the conversion has completed. command action convert(chan) select and bias a channel wait for the programmed settling time (powdly) start conversion select(chan) select and bias a channel
sx8650 www.semtech.com page 29 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 6.2. automatic mode in automatic mode (rate > 0), sx8650 will automatic ally decide when to start acquisition, sequence all the acquisitions and aler ts the host if data is available for download with a nirq. the host will read the ch annels and the sx8650 will start again with the next conversion cycle. the fastest coordinate rate is obtained if the host reads the channels immediately after the nirq. to not loose data, the sx8650 will not begin conver sion before the host read the channels. if after the nirq a delay superior to the sampling period is made by the host to read the channels a slower coordinate r ate is obtained. when the control condirq bit (see register i2cregst at table 6) is set to 1 then the interrupts will only be generated if the p en detect occurred. this result in a regular interrupt stream, as long as the host per forms the read channel commands, and the screen is touched. when the scree n is not touched, interrupts does not occur. if the control condirq bit is cleared to 0, the i nterrupts will always be generated. in case there is no pen detected on the screen then the coordinate data will be qualified as invalid, see section [5.1 .7]. this result in a regular interrupt stream, as long as the host performs the read channel commands, independent of the screen being touched or not. this working is illustrated in figure 30. figure 30. auto mode flowchart figure 31 shows the i2c working in automatic mode. after the first sentence send throught the i2c to m ake the initialization, traffic is reduced as only reads ar e required. the processing time is the necessary time for the sx8650 to makes the pendetection, the settling time (powdly) and the conversion. this time increases with the number of channel selected and the filter used.all succeeding conversions notifies the host by an interrupt signal and the host only needs to issue the i2c read command. the reads occur at the rate interval. figure 31. i2c working in auto mode condirq=1 ? touch detected ? set timer=rate start timer start channel conversion set interrupt nirq=0 release interrupt nirq=1 yes timer expire all channel data read all conversion finished yes no auto mode touch nirq i2c read channels conversion time time is 1/ rate nak
sx8650 www.semtech.com page 30 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 6.3. pendet mode the pendet mode can be used if the host only needs to know if the screen has been touched or not and take from that information furth er actions. when pen detect circuitry is triggered the interrupt signal nirq will be generat ed and the status register bit penirq will be set. the bit is cleared by reading the status re gister regstat. figure 32. pendet mode flowchart 6.4. pentrig mode the pentrig mode offers the best compromise between power consumption and coordinate throughput. in this mode the sx8650 will wait until a pen is de tected on the screen and then starts the coordinate conversions. the host will be signalled only when the screen is touc hed and coordinates are available. the coordinate rate in pen trigger mode is determin ed by the speed of the host reading the channels an d the conversion times of the channels. the host performs the minimu m number of i2c commands in this mode. the host has to wait for the nirq interrupt to make the acquisition of the datas. the flowchart and the i2c working is illustrated in figure 33. touch detected ? set interrupt nirq=0 release interrupt nirq=1 regstat read yes no pendet mode
sx8650 www.semtech.com page 31 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. figure 33. pentrig mode flowchart and i2c working in pentrig mode 7. application information this section describes in more detail application o riented data. 7.1. acquisition setup prior to an acquisition, the sx8650 can be setup by writing the control registers. registers are writt en by issuing the register write command. they can be read by issuing the read command. please refer to the section [5.3 ]. if no registers are written, the circuit will start in manual mode. 7.2. channel selection the sx8650 can be setup to start a single channel c onversion or to convert several channels in sequenc e. for a single conversion, the channel to be converted is determin ed from the chan(2:0) field in the command word (de fined in table 9). several channels can be acquired sequentially by se tting the chan(2:0) field to seq. the channels will be sampled in the order defined by register regchanmsk from msb to ls b. if a one is written in a channel mask, the corres ponding channel will be sampled, in the opposite ca se, it is ignored and the next selected channel is chosen. 7.3. noise reduction a noisy environment can decrease the performance of the controller. for example, an lcd display locate d just under the touch screen can adds a lot of noise on the high im pedance a/d converter inputs. 7.3.1. powdly in order to perform correct coordinates acquisition properly, some time must be given for the touch sc reen to reach a proper level. it is a function of the pcb trace res istance connecting the sx8650 to the touchscreen an d also the capacitance of the touchscreen. if tau is this rc t ime constant then powdly duration must be programme d to 10 tau to reach 12 bit accuracy. adding a capacitor from the touch screen drivers to ground is a solution to minimize external noise. a low-pass filter created by the capacitor may increase settling time . therefore, use powdly to stretch the acquisition period. powdly can be estimated by the following formula : touch detected ? start channel conversion set interrupt nirq=0 release interrupt nirq=1 all channel data read all conversion finished yes no pentrig mode i2c bus touch nirq i2c read channels conversion time nak powdly 10 rtouch ctouch =
sx8650 www.semtech.com page 32 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. rtouch is the sum of the panel resistances plus any significant series input resistance, rxtot + rytot + ri. ctouch is the sum of the touch panel capacitance pl us any noise filtering and routing capacitances. 7.3.2. setdly a second method of noise filtering uses an averaging filter as described in section [5] (data processing). in this case, the chip will sequence up to 7 conversions on each channel. the parameter setdly sets the settling time between the consecutive conversions. in most applications, setdly can be set to 0. in some particular applications, where accuracy of 1lsb is required and ctouch is less than 100nf a specific value should be determined. figure 34. powdly and setdly timing with filt=2 7.3.3. aux input an alternate conversion trigger method can be used if the host system provides additional digital sign als that indicate noisy or noise-free periods. the sx8650 can be set up to start conversions triggered by the aux pin. a risin g edge, a falling edge or both can trigger the conversion. to enter t his mode, auxacq must be set to a different value t han '00' as defined in table 6. the aux edge will first trigger the bia s delay (powdly). following the programmed delay, t he channel acquisition takes place. 7.4. interrupt generation an interrupt (nirq=0) will be generated: during the power-up phase or after a reset after completion of a conversion in manual, pentrig or auto mode. convirq (bit [7] of regstat) will be set at the same time. after a touch on the panel is detected in pendet mo de. penirq (bit [6] of regstat) will be set at the same time. the nirq will be released and pulled high(nirq=1) b y the external pull-up resistor: when the power-up phase is finished when the host read all channels data that were prev iously converted by the sx8650 in manual, pentrig o r auto mode. convirq will be cleared at the same time. when the host read the status register in pendet mo de. penirq, will be cleared at the same time. an active nirq (low) needs to be cleared before any new conversions will occur. 7.5. coordinate throughput rate the coordinate throughput rate depends on the follo wing factors: the i2c communication time : t com the conversion time : t conv the coordinate rate is the frequency to get the x, y, z1 and z2 coordinate: powdly setdly start of the conversion time x+ 5 successive conversions coordrate 1 t com t conv + ------------------------------- =
sx8650 www.semtech.com page 33 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 7.5.1. i2c communication time the minimun time to read the channel data in pentri g mode is : the highest throughput will be obtained with a i2c frequency of 5mhz when the host read the channel da ta as quickly as possible after the nirq falling edge. 7.5.2. conversion time the maximum possible throughput can be estimated wi th the following equation with: n filt = {1,3,5,7} based on the order defined for the fil ter filt (see figure 4). n chan = {1,2,3,4,5} based on the number of channels defi ned in regchanmsk powdly = 0.5us to 18.19ms, settling time as defined in regctrl0 setdly = 0.5us to 18.19ms, settling time when filte ring as defined in regctrl2 tosc is the oscillator period (555ns +/- 15%) table 11 gives some examples of coordinate rate and sample rate for various setting in pentrig mode. table 11coordinate throughput examples 7.5.3. auto mode in auto mode, the coordinate throughput rate is the rate set in regctrl0 if the host retrieve channel data at this rate. the rate set should be superior or equal to the coo rdrate. 7.6. esd event in case of esd event, the chip can reset to protect its internal circuitry. polling a register may be used to check the chip reset event. esd event may trig the pen detection circuitry. in this case wrong data will be send to the host. to d etect this false coordinates on 4-wire touchscreen, a pressure measu rement can be done. when reading the values z1<10 a nd z2>4070, the data may not be valid and indicate an esdevent or a nch [1..5 ] nfilt [1 3 5 7] powdly [us] setdly [us] tconv [us] tcomm [us] total [us] cr [kcps] ecr [kcps] sr [ksps] esr [ksps] 2.0 1.0 0.5 0.5 51.7 91.2 142.9 7.0 14.0 7.0 14.0 2.0 3.0 35.5 0.5 170.6 91.2 261.8 3.8 7.6 11.5 22.9 2.0 5.0 2.2 0.5 152.8 91.2 244.0 4.1 8.2 20.5 41.0 4.0 3.0 35.5 0.5 315.0 181.2 496.2 2.0 8.1 6.0 24.2 t com 8 16 n chan + ( ) t spi = tconv us ( ) 47 tosc n + chan powdly n filt 1 C ( ) setdly 21 n filt 1 + ( ) tosc + + ( ) =
sx8650 www.semtech.com page 34 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 7.7. application schematic a typical application schematic is shown in figure 35 figure 35. typical application vdd_host can be higher than vdd but must not exceed the maximun voltage of 3.7v. the host gpio d0 output is connected to the sx8650 nrst input to allows sx8650 hardware reset. the host d0 may be a totem pole output. in this con figuration and if the host and the sx8650 are suppl y with the same vdd, the r1 pull-up resistor is not required. nirq pin is connected to a host interrupt pin. once nirq event happens, the host read the data by a i2 c read register. 7.8. application examples 7.8.1. soft keyboard a keyboard application can be designed with the hel p of the sx8650. the data are entered by tapping keys on the keyboard with a stylus. the sx8650 send the key coordinates to the microcontroller which interpret them as a symbol. when the keyboard is not activated, the chip stays in low power mode to save power. figure 36. keyboard 7.8.2. slider controls touch screen interface sx8651 vdd aux x+ y+ x- y- a0 nirq nrst scl sda gnd control i2c digital filter ref+ ref- adc in out osc por vref host int vdd_host 0.1 uf 2.2k 2.2k 2.2k sda scl i2c interface do touch scren 2.2k r1 r2 r3 r4 vdd vdd_host
sx8650 www.semtech.com page 35 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. every kind of controls such as rotative knob, slider, button could be emulated with a sx8650 associated to a touchscreen. figure 37. slider controls 7.8.3. game many kinds of game can be designed with touchscreen . with its high data throughput and its ability to sense pressure, sx8650 is the perfect controller for this kind of application. figure 38. game 7.8.4. handwriting application an handwriting application needs a powerful microco ntroller to run recognition algorithms. the sx8650 includes a prepr ocessing block to reduce host activity. figure 39. handwriting application
sx8650 www.semtech.com page 36 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 8. packaging information 8.1. dfn package figure 40. dfn package outline drawing (laser mark) indicator pin 1 1 n 2 min aaa bbb be l n e1 d1 e a1 a2 a dim millimeters nom dimensions max nom inches min max .114 .118 .122 2.90 3.00 3.10 a1 a2 lxn e1 d1 e/2 bxn d .114 .118 .122 2.90 3.00 3.10 d e e/2 d/2 a notes: controlling dimensions are in millimeters (angles i n degrees). coplanarity applies to the exposed pad as well as t erminals. 2. 1. .003 .006 .042 12 .008 .048 .000 .028 (.008) 0.08 0.20 12 .010 .052 0.15 1.06 .031 .002 0.00 0.70 1.31 0.25 1.21 0.05 0.80 (0.20) .004 0.10 0.45 bsc .018 bsc 0.30 .012 .020 .016 0.40 0.50 aaa c seating plane a bbb c a b b e c .074 .079 .083 1.87 2.02 2.12 0.02 0.75 .001 .030
sx8650 www.semtech.com page 37 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. figure 41. dfn package land pattern .087 .055 2.20 1.40 .150 .018 .010 .037 3.80 0.25 0.95 0.45 (.112) .075 1.90 (2.85) this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 2. 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 3. inches dimensions g k h xy p z c dim millimeters h k g y z p (c) x controlling dimensions are in millimeters (angles in degrees). 1.
sx8650 www.semtech.com page 38 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd revision v2.19/october 2010 ?2010 semtech corp. 8.2. wlcsp package figure 42. wlcsp package outline drawing figure 43. wlcsp land pattern 0.10 c 0.08 c 0.05 c a b controlling dimensions are in millimeters notes: 1. a b c a b c index area a1 corner 0.250.02 seating 1 2 3 d 1.50.10 2.00.10 0.50 1.00 0.25 0.50 1.50 12x ?0.3150.03 plane 0.625 max. this land pattern is for reference purposes only. consult your manufacturing group to ensure your notes: 2. company's manufacturing guidelines are met. 1. controlling dimensions are in millimeters 0.50 0.25 1.50 0.50 1.00 12x ?0.25
revision v2.19/october 2010 ?2010 semtech corp. sx8650 www.semtech.com page 39 iso9001 certified advanced communications & sensing datasheet ? s e m te c h 2 0 1 0 a ll rig h ts re s e rv e d . r e p ro d u c tio n in w h o le o r in p a rt is p ro h ib ite d w ith o u t th e p rio r w ritte n c o n s e n t o f th e c o p y rig h t o w n e r. t h e in fo rm a tio n p re s e n te d in th is d o c u m e n t d o e s n o t fo r m p a rt o f a n y q u o ta tio n o r c o n tra c t, is b e lie v e d to b e a c c u ra te a n d re lia b le a n d m a y b e c h a n g e d w ith o u t n o tic e . n o lia b ility w il l b e a c c e p te d b y th e p u b lis h e r fo r a n y c o n s e q u e n c e o f its u s e . p u b lic a tio n th e re o f d o e s n o t c o n v e y n o r im p ly a n y lic e n s e u n d e r p a te n t o r o th e r in d u s tria l o r in te lle c tu a l p ro p e rt y rig h ts . s e m te c h a s s u m e s n o re s p o n s ib ility o r lia b ility w h a ts o e v e r fo r a n y f a ilu re o r u n e x p e c te d o p e ra tio n re s u ltin g fro m m is u s e , n e g le c t im p ro p e r in s ta lla tio n , re p a ir o r im p ro p e r h a n d lin g o r u n u s u a l p h y s ic a l o r e le c tric a l s tre s s in c lu d in g , b u t n o t lim ite d to , e x p o s u re to p a ra m e te rs b e y o n d th e s p e c ifie d m a x im u m ra tin g s o r o p e ra tio n o u ts id e th e s p e c ifie d ra n g e . s e m t e c h p r o d u c t s a r e n o t d e s ig n e d , in t e n d e d , a u t h o r iz e d o r w a r r a n t e d t o b e s u it a b l e f o r u s e in l if e -s u p p o r t a p p l ic a t io n s , d e v ic e s o r s y s t e m s o r o t h e r c r it ic a l a p p l ic a t io n s . in c l u s io n o f s e m t e c h p r o d u c t s in s u c h a p p l ic a t io n s is u n d e r s t o o d t o b e u n d e r t a k e n s o l e l y a t t h e c u s t o m e r s o w n r is k . s h o u ld a c u s to m e r p u rc h a s e o r u s e s e m te c h p ro d u c ts fo r a n y s u c h u n a u th o riz e d a p p lic a tio n , th e c u s to m e r s h a ll in d e m n ify a n d h o ld s e m te c h a n d its o ffic e rs , e m p lo y e e s , s u b s id ia rie s , a ffilia te s , a n d d is trib u to rs h a r m le s s a g a in s t a ll c la im s , c o s ts d a m a g e s a n d a tto rn e y fe e s w h ic h c o u ld a ris e . a ll re fe re n c e d b ra n d s , p ro d u c t n a m e s , s e rv ic e n a m e s a n d tra d e m a rk s a re th e p ro p e rty o f t h e ir re s p e c tiv e o w n e rs . semtech corporation advanced communications & sensi ng products contact information e-mail: sales@semtech.comacsupport@semtech.comintern et: 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, abbe y park industrial estate, romsey, hampshire, so51 9dn. tel: +44 (0)1794 527 600 fax: +44 (0)1794 527 601

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