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1 LTC1857/ltc1858/ltc1859 185789f 8-channel, 12-/14-/16-bit, 100ksps softspan a/d converters with shutdown the ltc ? 1857/ltc1858/ltc1859 are 8-channel, low power, 12-/14-/16-bit, 100ksps, analog-to-digital con- verters (adcs). these softspan tm adcs can be software- programmed for 0v to 5v, 0v to 10v, 5v or 10v input spans and operate from a single 5v supply. the 8-chan- nel multiplexer can be programmed for single-ended inputs or pairs of differential inputs or combinations of both. in addition, all channels are fault protected to 25v. a fault condition on any channel will not affect the conversion result of the selected channel. an onboard high performance sample-and-hold and pre- cision reference minimize external components. the low 40mw power dissipation is made even more attractive with two user selectable power shutdown modes. dc speci- fications include 3lsb inl for the ltc1859, 1.5lsb inl for the ltc1858 and 1lsb for the LTC1857. the internal clock is trimmed for 5 s maximum conver- sion time and the sampling rate is guaranteed at 100ksps. a separate convert start input and data ready signal (busy) ease connections to fifos, dsps and microprocessors. sample rate: 100ksps 8-channel multiplexer with 25v protection single 5v supply software-programmable input ranges: 0v to 5v, 0v to 10v, 5v or 10v single ended or differential 3lsb inl for the ltc1859, 1.5lsb inl for the ltc1858, 1lsb inl for the LTC1857 power dissipation: 40mw (typ) spi/microwire tm compatible serial i/o power shutdown: nap and sleep signal-to-noise ratio: 87db (typ) for the ltc1859 operates with internal or external reference internal synchronized clock 28-pin ssop package , ltc and lt are registered trademarks of linear technology corporation. com ch0 ch1 ch2 ch3 ch4 ch5 ch6 ch7 muxout + muxout C adc + adc C agnd1 convst rd sck sdi dgnd sdo busy ov dd dv dd av dd agnd3 agnd2 refcomp v ref LTC1857/ ltc1858/ ltc1859 software-programmable single-ended or differential inputs (0v to 5v, 0v to 10v, 5v or 10v) 10 f 10 f 1 f 10 f 3v to 5v 5v 5v 2.5v 10 f p control lines 100khz, 12-bit/14-bit/16-bit sampling adc industrial process control multiplexed data acquisition systems high speed data acquisition for pcs digital signal processing softspan is a trademark of linear technology corporation. microwire is a trademark of national semiconductor corporation. code C32768 inl (lsb) 0 0.5 1.0 0 1859 ta02 C 0.5 C1.0 C2.0 C16384 16384 32767 C1.5 2.0 1.5 ltc1859 typical inl curve descriptio u features applicatio s u typical applicatio u
2 LTC1857/ltc1858/ltc1859 185789f a u g w a w u w a r b s o lu t exi t i s supply voltage (ov dd = dv dd = av dd = v dd ) ........... 6v ground voltage difference dgnd, agnd1, agnd2, agnd3 ...................... 0.3v analog input voltage adc + , adc C (note 3) ................... (agnd1 C 0.3v) to (av dd + 0.3v) ch0-ch7, com .................................................. 25v digital input voltage (note 4) ...... (dgnd C 0.3v) to 10v digital output voltage .... (dgnd C 0.3v) to (dv dd + 0.3v) power dissipation .............................................. 500mw operating temperature range LTC1857c/ltc1858c/ltc1859c ............ 0 c to 70 c LTC1857i/ltc1858i/ltc1859i .......... C 40 c to 85 c storage temperature range ................. C 65 c to 150 c lead temperature (soldering, 10 sec) ................. 300 c t jmax = 110 c, ja = 95 c/w (notes 1, 2) order part number LTC1857cg LTC1857ig ltc1858cg ltc1858ig ltc1859cg ltc1859ig consult ltc marketing for parts specified with wider operating temperature ranges. package/order i for atio uu w 1 2 3 4 5 6 7 8 9 10 11 12 13 14 top view g package 28-lead plastic ssop 28 27 26 25 24 23 22 21 20 19 18 17 16 15 com ch0 ch1 ch2 ch3 ch4 ch5 ch6 ch7 muxout + muxout C adc + adc C agnd1 convst rd sck sdi dgnd sdo busy ov dd dv dd av dd agnd3 agnd2 refcomp v ref the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. muxout connected to adc inputs. (notes 5, 6) co verter a d ultiplexer characteristics u w u LTC1857 ltc1858 ltc1859 parameter conditions min typ max min typ max min typ max units resolution 12 14 16 bits no missing codes 12 14 15 bits transition noise 0.06 0.26 1 lsb rms integral linearity error (notes 7, 15) 1 1.5 3lsb differential linearity error (note 15) C1 1 C1 1.5 C2 4 lsb bipolar zero error (note 8) 9 17 28 lsb bipolar zero error drift 0.1 0.1 0.1 ppm/ c bipolar zero error match 4 6 10 lsb unipolar zero error (note 8) 6 15 25 lsb unipolar zero error drift 1 1 1 ppm/ c unipolar zero error match 1.2 2 8lsb bipolar full-scale error external reference (note 11) 0.35 0.15 0.1 % internal reference (note 11) 0.45 0.40 0.4 % bipolar full-scale error drift external reference 2.5 2.5 2.5 ppm/ c internal reference 7 7 7 ppm/ c bipolar full-scale error match 5 10 15 lsb unipolar full-scale error external reference (note 11) 0.45 0.25 0.20 % internal reference (note 11) 0.75 0.85 0.75 % unipolar full-scale error drift external reference 2.5 2.5 2.5 ppm/ c internal reference 7 7 7 ppm/ c unipolar full-scale error match 5 12 15 lsb input common mode range unipolar mode 0 to 10 0 to 10 0 to 10 v bipolar mode 10 10 10 v input common mode rejection ratio 96 96 96 db
3 LTC1857/ltc1858/ltc1859 185789f the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. (note 5) a alog i put u u parameter conditions min typ max units analog input range ch0 to ch7, com 0 to 5, 0 to 10 v 5, 10 v adc + , adc C (note 3) 0 to 2.048 v 0 to 4.096 v adc C 1.024 v adc C 2.048 v impedance ch0 to ch7, com unipolar 42 k ? bipolar 31 k ? muxout + , muxout C unipolar 10 k ? bipolar 5 k ? adc + , adc C hi-z k ? capacitance ch0 to ch7, com 5 pf sample mode adc + , adc C 0v to 2.048v, 1.024v 24 pf 0v to 4.096v, 2.048v 12 pf hold mode adc + , adc C 4pf input leakage current adc + , adc C , convst = low 1 a the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. muxout connected to adc inputs. (notes 5 and 12) LTC1857 ltc1858 ltc1859 symbol parameter conditions min typ max min typ max min typ max units s/(n + d) signal-to-(noise + distortion) ratio 1khz input signal 74 83 87 db thd total harmonic distortion 1khz input signal, C101 C101 C101 db first five harmonics peak harmonic or spurious noise 1khz input signal C103 C103 C103 db channel-to-channel isolation 1khz input signal C120 C120 C120 db C3db input bandwidth 1 1 1 mhz aperture delay C70 C70 C70 ns aperture jitter 60 60 60 ps transient response full-scale step 4 4 4 s (note 9) overvoltage recovery (note 13) 150 150 150 ns dy a ic accuracy u w
4 LTC1857/ltc1858/ltc1859 185789f the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. (note 5) parameter conditions min typ max units v ref output voltage i out = 0 2.475 2.50 2.525 v v ref output temperature coefficient i out = 0 10 ppm/ c v ref output impedance C0.1ma i out 0.1ma 8 k ? v refcomp output voltage i out = 0 4.096 v the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. (note 5) symbol parameter conditions min typ max units v ih high level input voltage v dd = 5.25v 2.4 v v il low level input voltage v dd = 4.75v 0.8 v i in digital input current v in = 0v to v dd 10 a c in digital input capacitance 5pf v oh high level output voltage v dd = 4.75v, i o = C10 a, ov dd = v dd 4.74 v v dd = 4.75v, i o = C200 a, ov dd = v dd 4v v ol low level output voltage v dd = 4.75v, i o = 160 a, ov dd = v dd 0.05 v v dd = 4.75v, i o = 1.6ma, ov dd = v dd 0.10 0.4 v i oz hi-z output leakage v out = 0v to v dd , rd = high 10 a c oz hi-z output capacitance rd = high 15 pf i source output source current v out = 0v C10 ma i sink output sink current v out = v dd 10 ma i ter al refere ce characteristics uu u digital i puts a d digital outputs u u parameter conditions min typ max units positive supply voltage (notes 9 and 10) 4.75 5.00 5.25 v positive supply current 8.0 13 ma nap mode 5.5 8 ma sleep mode convst = 0v or 5v 8.0 15 a power dissipation 40.0 mw nap mode 27.5 mw sleep mode convst = 0v or 5v 40.0 w the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. (note 5) power require e ts w u
5 LTC1857/ltc1858/ltc1859 185789f the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. (note 5) ti i g characteristics u w symbol parameter conditions min typ max units f sample(max) maximum sampling frequency through ch0 to ch7 inputs 100 khz through adc + , adc C only 166 khz t conv conversion time 45 s t acq acquisition time through ch0 to ch7 inputs 4 s through adc + , adc C only 1 s f sck sck frequency (note 14) 0 20 mhz t r sdo rise time see test circuits 6 ns t f sdo fall time see test circuits 6 ns t 1 convst high time 40 ns t 2 convst to busy delay c l = 25pf, see test circuits 15 30 ns t 3 sck period 50 ns t 4 sck high 10 ns t 5 sck low 10 ns t 6 delay time, sck to sdo valid c l = 25pf, see test circuits 25 45 ns t 7 time from previous sdo data remains c l = 25pf, see test circuits 520 ns valid after sck t 8 sdo valid after rd c l = 25pf, see test circuits 11 30 ns t 9 rd to sck setup time 20 ns t 10 sdi setup time before sck 0ns t 11 sdi hold time after sck 7ns t 12 sdo valid before busy rd = low, c l = 25pf, see test circuits 520 ns t 13 bus relinquish time see test circuits 10 30 ns note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: all voltage values are with respect to ground with dgnd, agnd1, agnd2 and agnd3 wired together unless otherwise noted. note 3: when these pin voltages are taken below ground or above av dd = dv dd = ov dd = v dd , they will be clamped by internal diodes. this product can handle currents of greater than 100ma below ground or above v dd without latchup. note 4: when these pin voltages are taken below ground they will be clamped by internal diodes. this product can handle currents of greater than 100ma below ground without latchup. these pins are not clamped to v dd . note 5: v dd = 5v, f sample = 100khz, t r = t f = 5ns unless otherwise specified. note 6: linearity, offset and full-scale specifications apply for a single- ended analog mux input with respect to ground or adc + with respect to adc C tied to ground. note 7: integral nonlinearity is defined as the deviation of a code from a straight line passing through the actual end points of the transfer curve. the deviation is measured from the center of the quantization band. note 8: bipolar zero error is the offset voltage measured from C 0.5lsb when the output code flickers between 0000 0000 0000 0000 and 1111 1111 1111 1111 for the ltc1859, between 00 0000 0000 0000 and 11 1111 1111 1111 for the ltc1858 and between 0000 0000 0000 and 1111 1111 1111 for the LTC1857. unipolar zero error is the offset voltage measured from 0.5lsb when the output codes flicker between 0000 0000 0000 0000 and 0000 0000 0000 0001 for the ltc1859, between 00 0000 0000 0000 and 00 0000 0000 0001 for the ltc1858 and between 0000 0000 0000 and 0000 0000 0001 for the LTC1857. note 9: guaranteed by design, not subject to test. note 10: recommended operating conditions. note 11: full-scale bipolar error is the worst case of Cfs or +fs untrimmed deviation from ideal first and last code transitions, divided by the full-scale range, and includes the effect of offset error. for unipolar full-scale error, the deviation of the last code transition from ideal, divided by the full-scale range, and includes the effect of offset error. note 12: all specifications in db are referred to a full-scale 10v input. note 13: recovers to specified performance after (2 ? fs) input overvoltage. note 14: t 6 of 45ns maximum allows f sck up to 10mhz for rising capture with 50% duty cycle and f sck up to 20mhz for falling capture (with 5ns setup time for the receiving logic). note 15: the specification is referred to the 10v input range.
6 LTC1857/ltc1858/ltc1859 185789f typical perfor a ce characteristics uw ltc1859 nonaveraged 4096-point fft plot ltc1859 sinad vs input frequency ltc1859 total harmonic distortion vs input frequency ltc1859 typical inl curve ltc1859 typical dnl curve ltc1859 channel-to-channel offset error matching vs temperature code C32768 dnl (lsb) 0 0.5 1.0 0 1859 g02 C 0.5 C1.0 C2.0 C16384 16384 32767 C1.5 2.0 1.5 frequency (khz) 01525 50 1869 g03 510 20 30 40 45 35 magnitude (db) C60 C40 C20 0 C80 C100 C70 C50 C30 C10 C90 C110 C130 C120 f sample = 100khz f in = 1khz sinad = 86.95db thd = C101.42db input frequency (khz) 1 74 sinad (db) 78 82 90 10 100 1859 g04 86 76 80 88 84 input frequency (khz) 1 C110 total harmonic distortion (db) C100 C90 C70 10 100 1859 g05 C80 temperature ( c) C50 C1.0 channel-to-channel offset error matching (lsbs) C0.5 0 0.5 1.0 C25 0 25 50 1959 g06 75 100 bipolar mode unipolar mode code C32768 inl (lsb) 0 0.5 1.0 0 1859 ta02 C 0.5 C1.0 C2.0 C16384 16384 32767 C1.5 2.0 1.5 change in refcomp voltage vs load current internal reference voltage vs temperature ltc1859 channel-to-channel gain error matching vs temperature temperature ( c) C50 C1.0 channel-to-channel gain error matching (lsbs) C0.5 0 0.5 1.0 C25 0 25 50 1959 g07 75 100 bipolar mode unipolar mode temperature ( c) C50 internal reference voltage (v) 25 75 1859 g08 C25 0 50 2.520 2.515 2.510 2.505 2.500 2.495 2.490 2.485 2.480 100 load current (ma) C50 C0.04 change in refcomp voltage (v) C0.02 0 0.02 0.04 C40 C30 C20 C10 1859 g09 010
7 LTC1857/ltc1858/ltc1859 185789f typical perfor a ce characteristics uw uu u pi fu ctio s com (pin 1): common input. this is the reference point for all single-ended inputs. it must be free of noise and is usually connected to the analog ground plane. ch0 (pin 2): analog mux input. ch1 (pin 3): analog mux input. ch2 (pin 4): analog mux input. ch3 (pin 5): analog mux input. ch4 (pin 6): analog mux input. ch5 (pin 7): analog mux input. ch6 (pin 8): analog mux input. ch7 (pin 9): analog mux input. muxout + (pin 10): positive mux output. output of the analog multiplexer. connect to adc + for normal operation. muxout (pin 11): negative mux output. output of the analog multiplexer. connect to adc C for normal operation. adc + (pin 12): positive analog input to the analog-to- digital converter. adc (pin 13): negative analog input to the analog-to- digital converter. agnd1 (pin 14): analog ground. v ref (pin 15): 2.5v reference output. bypass to analog ground with a 1 f tantalum capacitor. refcomp (pin 16): reference buffer output. bypass to analog ground with a 10 f tantalum and a 0.1 f ceramic capacitor. nominal output voltage is 4.096v. agnd2 (pin 17): analog ground. agnd3 (pin 18): analog ground. this is the substrate connection. av dd (pin 19): 5v analog supply. bypass to analog ground with a 0.1 f ceramic and a 10 f tantalum capacitor. dv dd (pin 20): 5v digital supply. bypass to digital ground with a 0.1 f ceramic and a 10 f tantalum capacitor. ov dd (pin 21): positive supply for the digital output buffers (3v to 5v). bypass to digital ground with a 0.1 f ceramic and a 10 f tantalum capacitor. busy (pin 22): output shows converter status. it is low when a conversion is in progress. sdo (pin 23): serial data output. ltc1859 power supply feedthrough vs ripple frequency supply current vs supply voltage supply current vs temperature ripple frequency (hz) C60 power supply feedthrough (db) C40 C20 C10 100 10k 100k 1m 1859 g10 C80 1k C30 C50 C70 f sample = 100khz v ripple = 60mv supply voltage (v) 4.5 supply current (ma) 8.0 8.5 5.5 1859 g11 7.5 7.0 4.75 5 5.25 9.0 f sample = 100khz temperature ( c) C50 7.0 positive supply current (ma) 7.5 8.0 8.5 9.0 C25 0 25 50 1859 g12 75 100 f sample = 100khz
8 LTC1857/ltc1858/ltc1859 185789f uu w fu ctio al block diagra 2.5v reference internal clock 1.6384x 4.096v 8k agnd1 control logic serial i/o input mux and range select agnd3 agnd2 refcomp v ref adc C muxout + muxout C adc + dgnd av dd dv dd mux address and range data out convst sdi busy sck rd ov dd sdo 1859 bd 12-/14-/16-bit sampling adc + C com ch7 ch1 ? ? ? ch0 dgnd (pin 24): digital ground. sdi (pin 25): serial data input. sck (pin 26): serial data clock. uu u pi fu ctio s rd (pin 27): read input. this active low signal enables the digital output pin sdo. convst (pin 28): conversion start. this active high signal starts a conversion on its rising edge. load circuits for access timing 1k (a) hi-z to v oh and v ol to v oh 25pf 1k 5v dn dn (b) hi-z to v ol and v oh to v ol 25pf 1859 tc01 load circuits for output float delay 1k (a) v oh to hi-z 25pf 1k 5v dn dn (b) v ol to hi-z 25pf 1859 tc02 test circuits
9 LTC1857/ltc1858/ltc1859 185789f t 1 (for short pulse mode) t 1 convst 50% 1859 td01 50% t 2 (convst to busy delay) t 2 convst busy 2.4v 0.4v 1859 td02 t 3 , t 4 , t 5 (sck timing) sck 1859 td03 t 4 t 5 t 3 t 6 (delay time, sck to sdo valid) t 7 (time from previous data remains valid after sck ) t 6 t 7 sck sdo 2.4v 0.4v 0.4v 1859 td04 t 8 (sdo valid after rd ) t 8 rd sdo 2.4v 0.4v 0.4v 1859 td05 hi-z t 9 (rd to sck setup time) t 9 0.4v 2.4v 1959 td06 rd sck t 10 (sdi setup time before sck ) t 10 sck sdi 2.4v 2.4v 0.4v 1859 td07 t 11 (sdi hold time after sck ) t 11 sck sdi 2.4v 2.4v 0.4v 1859 td08 ti i g diagra s w u w t 12 (sdo valid before busy , rd = 0) t 12 busy sdo 2.4v b15 2.4v 1859 td09 t 13 (bus relinquish time) t 13 rd sdo 2.4v 1859 td10 10% 90% hi-z
10 LTC1857/ltc1858/ltc1859 185789f applicatio s i for atio wu uu overview the LTC1857/ltc1858/ltc1859 are innovative, multi- channel adcs that provide software-selectable input ranges for each of their eight input channels. using on-chip resistors and switches, it provides an attenuation and offset that can be programmed for each channel on the fly. the precisely trimmed attenuators ensure accurate input ranges. because they precede the multiplexer, errors due to multiplexer on-resistance are eliminated. the input word that selects the input channel also selects the desired input range for that channel. the available ranges are 0v to 5v, 0v to 10v (unipolar), 5v and 10v (bipolar). they are achieved with the adc running on a single 5v supply. in addition to the range selection, single ended or differential inputs may be selected for each channel or pair of channels. finally, overrange protection is provided for unselected channels. an overrange condi- tion on an unused channel will not affect the conversion result on the selected channel. conversion details the LTC1857/ltc1858/ltc1859 use a successive approxi- mation algorithm and an internal sample-and-hold circuit to convert an analog signal to a 12-/14-/16-bit serial out- put respectively. the adcs are complete with a precision reference and an internal clock. the control logic provides easy interface to microprocessors and dsps. (please refer to the digital interface section for the data format.) the analog signals applied at the mux input channels are rescaled by the resistor divider network formed by r1, r2 and r3 as shown below. the rescaled signals appear on the muxout (pins 10, 11) which are also connected to the adc inputs (pins 12, 13) under normal operation. before starting a conversion, an 8-bit data word is clocked into the sdi input on the first eight rising sck edges to select the mux address, input range and power down mode. the adc enters acquisition mode on the falling edge of the sixth clock in the 8-bit data word and ends on the rising edge of the convst signal which also starts a conversion (see figure 7). a minimum time of 4 s will provide enough time for the sample-and-hold capacitors to acquire the analog signal. once a conversion cycle has begun, it cannot be restarted. during the conversion, the internal differential 12-/14-/ 16-bit capacitive dac output is sequenced by the sar from the most significant bit (msb) to the least significant bit (lsb). the input is successively compared with the binary weighted charges supplied by the differential capacitive dac. bit decisions are made by a high speed comparator. at the end of a conversion, the dac output balances the analog input (adc + C adc C ). the sar contents (a 16-bit data word) which represents the difference of adc + and adc C are loaded into the 12-/14-/16-bit shift register. driving the analog inputs the nominal input ranges for the LTC1857/ltc1858/ ltc1859 are 0v to 5v, 0v to 10v, 5v and 10v and the mux inputs are overvoltage protected to 25v. the input impedance is typically 42k ? in unipolar mode and 31k ? in bipolar mode, therefore, it should be driven with a low impedance source. wideband noise coupling into the input can be minimized by placing a 3000pf capacitor at the input as shown in figure 2. an npo-type capacitor gives the lowest distortion. place the capacitor as close to the device input pin as possible. if an amplifier is to be used to drive the input, care should be taken to select an amplifier with adequate accuracy, linearity and noise for the application. the following list is a summary of the op amps that are suitable for driving the LTC1857/ltc1858/ ltc1859. more detailed information is available in the linear technology data books and online at www.linear.com. lt ? 1007: low noise precision amplifier. 2.7ma supply current 5v to 15v supplies. gain bandwidth product 8mhz. dc applications. mux input r1 25k refcomp ch sel r3 10k 1859 ai03 r2 17k muxout bipolar
11 LTC1857/ltc1858/ltc1859 185789f lt1227: 140mhz video current feedback amplifier. 10ma supply current. 5v to 15v supplies. low noise and low distortion. lt1468/lt1469: single and dual 90mhz, 16-bit accurate op amp. good ac/dc specs. lt1677: single, low noise op amp. rail-to-rail input and output. up to 15v supplies. applicatio s i for atio wu uu 3000pf 1859 f02 a in + a in C ch0 ch1 muxout + muxout C adc + adc C ? ? ? ? figure 2. analog input filtering figure 1. LTC1857/ltc1858/ltc1859 simplified equivalent circuit lt1792: single, low noise jfet input op amp, 5v supplies. lt1793: single, low noise jfet input op amp, 10pa bias current, 5v supplies. lt1881/lt1882: dual and quad, 200pa bias current, rail- to-rail output op amps. up to 15v supplies. lt1844/lt1885: dual and quad, 400pa bias current, rail- to-rail output op amps. up to 15v supplies. faster response and settling time. internal voltage reference the LTC1857/ltc1858/ltc1859 have an on-chip, tem- perature compensated, curvature corrected, bandgap ref- erence, which is factory trimmed to 2.50v. the full-scale range of the LTC1857/ltc1858/ltc1859 is equal to 5v, 0v to 5v, 10v or 0v to 10v. the output of the reference is connected to the input of a gain of 1.6384x buffer through an 8k resistor (see figure 3). the input to the 2.5v reference internal clock 1.6384x 4.096v 8k agnd1 control logic serial i/o input mux and range select agnd3 agnd2 refcomp v ref adc C muxout + muxout C adc + dgnd av dd dv dd mux address and range data out convst sdi busy sck rd ov dd sdo 1859 bd 12-/14-/16-bit sampling adc + C com ch7 ch1 ? ? ? ch0
12 LTC1857/ltc1858/ltc1859 185789f buffer or the output of the reference is available at v ref (pin 15). the internal reference can be overdriven with an external reference if more accuracy is needed. the buffer output drives the internal dac and is available at refcomp (pin 16). the refcomp pin can be used to drive a steady dc load of less than 2ma. driving an ac load is not recommended because it can cause the performance of the converter to degrade. successive integer lsb values (i.e., 0.5lsb, 1.5lsb, 2.5lsb, fs C 1.5lsb). the output code is natural binary with 1lsb = fs/65536. figure 4b shows the input/output transfer characteristics for the bipolar mode in twos complement format. full scale and offset in applications where absolute accuracy is important, offset and full-scale errors can be adjusted to zero during a calibration sequence. offset error must be adjusted before full-scale error. zero offset is achieved by adjusting the offset applied to the C input. for single-ended inputs, this offset should be applied to the com pin. for differen- tial inputs, the C input is dictated by the mux address. for unipolar zero offset error, apply 0.5lsb (actual voltage will vary with input span selected) to the + input and adjust the offset at the C input until the output code flickers between 0000 0000 0000 0000 and 0000 0000 0000 0001 for the ltc1859, between 00 0000 0000 0000 and 00 0000 0000 0001 for the ltc1858 and between 0000 0000 0000 and 0000 0000 0001 for the LTC1857. for bipolar zero error, apply C 0.5lsb (actual voltage will vary with input span selected) to the + input and adjust the offset at the C input until the output code flickers between 0000 0000 0000 0000 and 1111 1111 1111 1111 for the ltc1859, between 00 0000 0000 0000 and applicatio s i for atio wu uu figure 3. internal or external reference source 2.5v reference 1859 f03 12-/14-/16-bit capacitive dac 1.6384x buffer 8k v ref 1 f 15 2.5v 16 refcomp 0.1 f 4.096v 10 f input voltage (v) 0v output code fs C 1lsb 1859 f4a 111...111 111...110 111...101 111...100 000...000 000...001 000...010 000...011 1 lsb unipolar zero 1lsb = fs 65536 input voltage (v) 0v output code C1 lsb 1859 f4b 011...111 011...110 000...001 000...000 100...000 100...001 111...110 1 lsb bipolar zero 111...111 fs/2 C 1lsb Cfs/2 1lsb = fs 65536 figure 4a. unipolar transfer characteristics (uni = 1) figure 4b. bipolar transfer characteristics (uni = 0) for minimum code transition noise the v ref pin and the refcomp pin should each be decoupled with a capacitor to filter wideband noise from the reference and the buffer. unipolar / bipolar operation figure 4a shows the ideal input/output characteristics for the ltc1859. the code transitions occur midway between
13 LTC1857/ltc1858/ltc1859 185789f applicatio s i for atio wu uu figure 5. ltc1859 histogram for 4096 conversions 11 1111 1111 1111 for the ltc1858 and between 0000 0000 0000 and 1111 1111 1111 for the LTC1857. as mentioned earlier, the internal reference is factory trimmed to 2.50v. to make sure that the reference buffer gain is not compensating for trim errors in the reference, refcomp is trimmed with an accurate external 2.5v ref- erence applied to v ref . for unipolar inputs, an input volt- age of fs C 1.5lsbs should be applied to the + input and the appropriate reference adjusted until the output code flickers between 1111 1111 1111 1110 and 1111 1111 1111 1111 for the ltc1859, between 11 1111 1111 1110 and 11 1111 1111 1111 for the ltc1858 and between 1111 1111 1110 and 1111 1111 1111 for the LTC1857. for bipolar inputs, an input voltage of fs C 1.5lsbs should be applied to the + input and the appropriate reference adjusted until the output code flickers between 0111 1111 1111 1110 and 0111 1111 1111 1111 for the ltc1859, between 01 1111 1111 1110 and 01 1111 1111 1111 for the ltc1858 and between 0111 1111 1110 and 0111 1111 1111 for the LTC1857. these adjustments as well as the factory trims affect all channels. the channel-to-channel offset and gain error matching are guaranteed by design to meet the specifica- tions in the converter characteristics table. dc performance one way of measuring the transition noise associated with a high resolution adc is to use a technique where a dc signal is applied to the input of the mux and the resulting output codes are collected over a large number of conversions. for example in figure 5 the distribution of output code is shown for a dc input that has been digitized 4096 times. the distribution is gaussian and the rms code transition is about 1lsb for the ltc1859. digital interface internal clock the adc has an internal clock that is trimmed to achieve a typical conversion time of 4 s. no external adjustments are required and, with the maximum acquisition time of 4 s, throughput performance of 100ksps is assured. 3v input/output compatible the LTC1857/ltc1858/ltc1859 operate on a 5v supply, which makes the devices easy to interface to 5v digital systems. these devices can also interface to 3v digital systems: the digital input pins (sck, sdi, convst and rd) of the LTC1857/ltc1858/ltc1859 recognize 3v or 5v inputs. the LTC1857/ltc1858/ltc1859 have a dedi- cated output supply pin (ovp) that controls the output swings of the digital output pins (sdo, busy) and allows the part to interface to either 3v or 5v digital systems. the output is twos complement binary for bipolar mode and offset binary for unipolar mode. timing and control conversion start and data read are controlled by two digital inputs: convst and rd. to start a conversion and put the sample-and-hold into the hold mode bring convst high for no less than 40ns. once initiated it cannot be restarted until the conversion is complete. converter status is indicated by the busy output and this is low while the conversion is in progress. figures 6a and 6b show two different modes of operation for the ltc1859. for the 12-bit LTC1857 and 14-bit ltc1858, the last four and two bits of the sdo will output zeros respectively. in mode 1 (figure 6a), rd is tied low. the rising edge of convst starts the conversion. the data outputs are always enabled. the msb of the data output is available after the conversion. in mode 2 (figure 6b), convst and rd are tied together. the rising edge of the convst signal starts the conversion. data outputs are in code C4 C3 0 count 200 600 800 1000 23 1800 1859 f05 400 C2 C1 0 14 1200 1400 1600
14 LTC1857/ltc1858/ltc1859 185789f figure 6a. mode 1 for the ltc1859*. convst starts a conversion, data output is always enabled (rd = 0) figure 6b. mode 2 for the ltc1859*. convst and rd tied together. convst starts a conversion, data is read by rd applicatio s i for atio wu uu sgl/ diff 1 t 4 rd = 0 sck sdi sdo convst busy 2 3 4 5 6 7 8 15 16 odd/ sign select 1 select 0 uni gain nap sleep dont care dont care b14 b13 b12 b15 (msb) b11 b10 b9 b8 b1 b0 (lsb) t acq t 7 t 6 t 2 t conv t 1 t 10 t 11 shift configuration word in sgl/ diff 12345678 1516 odd/ sign select 1 select 0 uni gain nap sleep dont care b14 b13 b12 b15 (msb) b11 b10 b9 b8 b1 1859 f06a b0 (lsb) shift a/d result out and new configuration word in t 5 t 3 t 12 t 12 sgl/ diff 1 t 4 convst = rd sck sdi hi-z sdo busy 2 3 4 5 6 7 8 15 16 odd/ sign select 1 select 0 uni gain nap sleep dont care dont care b14 b13 b12 b15 (msb) b11 b10 b9 b8 b1 b0 (lsb) t acq t 13 t 2 t conv hi-z t 10 t 11 shift configuration word in sgl/ diff 12345678 1516 odd/ sign select 1 select 0 uni gain nap sleep dont care b14 b13 b12 b15 (msb) b11 b10 b9 b8 b1 1859 f06b b0 (lsb) hi-z shift a/d result out and new configuration word in t 5 t 3 t 9 t 8 t 7 t 6 figure 7. operating sequence for the ltc1859* sgl/ diff 1 t 4 rd sck sdi hi-z sdo busy convst 2 3 4 5 6 7 8 15 16 odd/ sign select 1 select 0 uni gain nap sleep dont care dont care b14 b13 b12 b15 (msb) b11 b10 b9 b8 b1 b0 (lsb) t acq t 13 t 2 t 1 t conv hi-z t 10 t 11 shift configuration word in sgl/ diff 12345678 1516 odd/ sign select 1 select 0 uni gain nap sleep dont care b14 b13 b12 b15 (msb) b11 b10 b9 b8 b1 1859 f07 b0 (lsb) hi-z shift a/d result out and new configuration word in t 5 t 3 t 9 t 8 t 7 t 6 *for the 12-bit LTC1857 and 14-bit ltc1858, the last four and two bits of the sdo will output zeros respectively.
15 LTC1857/ltc1858/ltc1859 185789f applicatio s i for atio wu uu three-state at this time. when the conversion is complete (busy goes high), convst and rd go low to enable the data output for the previous conversion. serial data input (sdi) interface the LTC1857/ltc1858/ltc1859 communicate with mi- croprocessors and other external circuitry via a synchro- nous, full duplex, 3-wire serial interface (see figure 7). the shift clock (sck) synchronizes the data transfer with each bit being transmitted on the falling sck edge and captured on the rising sck edge in both transmitting and receiving systems. the data is transmitted and received simultaneously (full duplex). an 8-bit input word is shifted into the sdi input which configures the LTC1857/ltc1858/ltc1859 for the next conversion. simultaneously, the result of the previous conversion is output on the sdo line. at the end of the data exchange the requested conversion begins by applying a rising edge on convst. after t conv , the conversion is complete and the results will be available on the next data transfer cycle. as shown below, the result of a conversion is delayed by one conversion from the input word re- questing it. sgl/ diff select 1 select 0 uni gain nap mux address input range power down selection 1859 ai02 odd sign sleep sdi sdo sdo word 0 sdi word 1 data transfer sdo word 2 sdi word 3 sdo word 1 sdi word 2 data transfer t conv a/d conversion t conv a/d conversion 1859 ? ai01 figure 8. examples of multiplexer options on the LTC1857/ltc1858/ltc1859 0 1 2 3 4 5 6 7 channel com ( C ) 8 single-ended + + + + + + + 0,1 channel 4 differential 2,3 4,5 6,7 + ( C ) + + ( C ) + ( C ) + ( C ) C ( + ) C ( + ) C ( + ) C ( + ) 4 5 6 7 channel com ( C ) combinations of differential and single-ended + + + + + + 0,1 2,3 C C com (unused) changing the mux assignment ?n the fly com ( C ) 4,5 6,7 4,5 1st conversion 2nd conversion + C + C + C + + 7 6 { { { { { { { { { 1859 f08 mux address differential channel selection table 1. multiplexer channel selection mux address sgl/ diff select 1 0 odd sign 10 00 + C 10 01 + C 10 10 + C 10 11 + C 11 00 + C 11 01 + C 11 10 + C 11 11 + C sgl/ diff odd sign select 1 0 00 00+C 00 01 +C 00 10 +C 00 11 + C 01 00C+ 01 01 C+ 01 10 C+ 01 11 C + 0 1 23 4 56 7 0 1 2 3 4 5 6 7 com single-ended channel selection input data word the LTC1857/ltc1858/ltc1859 8-bit data word is clocked into the sdi input on the first eight rising sck edges. further inputs on the sdi pin are then ignored until the next conversion. the eight bits of the input word are defined as follows:
16 LTC1857/ltc1858/ltc1859 185789f applicatio s i for atio wu uu mux address the first four bits of the input word assign the mux configuration for the requested conversion. for a given channel selection, the converter will measure the voltage between the two channels indicated by the + and C signs in the selected row of table 1. note that in differential mode (sgl/diff = 0) measurements are limited to four adjacent input pairs with either polarity. in single-ended mode, all input channels are measured with respect to com. both the + and C inputs are sampled simulta- neously so common mode noise is rejected. input range (uni, gain) the fifth and sixth input bits (uni, gain) determine the input range for the conversion. when uni is a logical one, a unipolar conversion will be performed. when uni is a logical zero, a bipolar conversion will result. the gain input bit determines the input span for the conversion. when gain is a logical one, either 0v to 10v or 10v input spans will be selected depending on uni. when gain is a logical zero, either 0v to 5v or 5v input spans will be chosen. the input ranges for different uni and gain inputs are shown in table 2. table 2. input range selection uni gain input range 00 5v 1 0 0v to 5v 01 10v 1 1 0v to 10v p ower down selection (nap, sleep) the last two bits of the input word (nap and sleep) deter- mine the power shutdown mode of the LTC1857/ltc1858/ ltc1859. see table 3. nap mode is selected when nap = 1 and sleep = 0. the previous conversion result will be clocked out and a conversion will occur before entering the nap mode. the nap mode starts at the end of the con- version which is indicated by the rising edge of the busy signal. nap mode lasts until the falling edge of the 2nd sck (see figure 9). automatic nap will be achieved if nap = 1 is selected each time an input word is written to the adc. table 3. power down selection nap sleep power down mode 0 0 power on 1 0 nap x 1 sleep sleep mode will occur when sleep = 1 is selected, regardless of the selection of the nap input. the previous conversion result can be clocked out and the sleep mode will start on the falling edge of the last (16th) sck. notice that the convst should stay either high or low in sleep mode (see figure 10). to wake up from the sleep mode, apply a rising edge on the convst signal and then apply sleep = 0 on the next sdi word and the part will wake up on the falling edge of the last (16th) sck (see figure 11). in sleep mode, all bias currents are shut down and only the power on reset circuit and leakage currents (about 10 a) remain. sleep mode wake-up time is dependent on the value of the capacitor connected to the refcomp (pin 16). the wake-up time is typically 40ms with the recom- mended 10 f capacitor connected on the refcomp pin. dynamic performance fft (fast fourier transform) test techniques are used to test the adcs frequency response, distortion and noise at the rated throughput. by applying a low distortion sine wave and analyzing the digital output using an fft algorithm, the adcs spectral content can be examined for frequencies outside the fundamental. figure 12 shows a typical ltc1859 fft plot which yields a sinad of 87db and thd of C 101db.
17 LTC1857/ltc1858/ltc1859 185789f applicatio s i for atio wu uu figure 9. nap mode operation for the ltc1859* sgl/ diff 1 rd sck sdi hi-z sdo busy convst 2 3 4 5 6 7 8 15 16 odd/ sign select 1 select 0 uni gain nap = 1 sleep = 0 dont care dont care b14 b13 b12 b15 (msb) b11 b10 b9 b8 b1 b0 (lsb) t conv hi-z nap t acq t acq shift configuration word in sgl/ diff 12345678 1516 odd/ sign select 1 select 0 uni gain nap sleep dont care b14 b13 b12 b15 msb b11 b10 b9 b8 b1 1859 f09 b0 (lsb) hi-z shift a/d result out from previous conversion and new configuration word in figure 11. wake up from sleep mode for the ltc1859* figure 10. sleep mode operation for the ltc1859* sgl/ diff 1 rd sck sdi sdo busy convst 2 3 4 5 6 7 8 15 16 odd/ sign select 1 select 0 uni gain nap sleep = 0 dont care dont care b14 b13 b12 b15 (msb) b11 b10 b9 b8 b1 b0 (lsb) wake-up time ready t conv sleep shift wake-up configuration word in sgl/ diff 12345678 1516 odd/ sign select 1 select 0 uni gain nap sleep dont care b14 b13 b12 b15 (msb) b11 b10 b9 b8 b1 1859 f11 b0 (lsb) a/d result not valid shift a/d result out and new configuration word in t conv *for the 12-bit LTC1857 and 14-bit ltc1858, the last four and two bits of the sdo will output zeros respectively. sgl/ diff 1 rd sck sdi sdo busy convst 2 3 4 5 6 7 8 15 16 odd/ sign select 1 select 0 uni gain nap sleep = 0 dont care dont care b14 b13 b12 b15 (msb) b11 b10 b9 b8 b1 b0 (lsb) shift wake-up configuration word in 1859 f10 a/d result not valid convst should stay either high or low in sleep mode t conv sleep
18 LTC1857/ltc1858/ltc1859 185789f signal-to-noise ratio the signal-to-noise and distortion ratio (sinad) is the ratio between the rms amplitude of the fundamental input frequency to the rms amplitude of all other frequency components at the a/d output. the output is band limited to frequencies from above dc and below half the sampling frequency. figure 12 shows a typical sinad of 87db with a 100khz sampling rate and a 1khz input. total harmonic distortion total harmonic distortion (thd) is the ratio of the rms sum of all harmonics of the input signal to the fundamental itself. the out-of-band harmonics alias into the frequency band between dc and half the sampling frequency. thd is expressed as: thd = 20log v 2 2 3 2 4 22 1 ++ + vv v v n ... where v 1 is the rms amplitude of the fundamental fre- quency and v 2 through v n are the amplitudes of the second through nth harmonics. board layout, power supplies and decoupling wire wrap boards are not recommended for high resolu- tion or high speed a/d converters. to obtain the best performance from the LTC1857/ltc1858/ltc1859 , a printed circuit board is required. layout for the printed circuit board should ensure the digital and analog signal lines are separated as much as possible. in particular, care should be taken not to run any digital track alongside an analog signal track or underneath the adc. the analog input should be screened by agnd. in applications where the mux is connected to the adc, it is possible to get noise coupling into the adc from the trace connecting the muxout to the adc. therefore, reducing the length of the traces connecting the muxout pins (pins 10, 11) to the adc pins (pins 12, 13) can minimize the problem. the unused mux inputs should be grounded to prevent noise coupling into the inputs. figure 13 shows the power supply grounding that will help obtain the best performance from the 12-bit/14-bit/16-bit adcs. pay particular attention to the design of the analog and digital ground planes. the dgnd pin of the LTC1857/ applicatio s i for atio wu uu figure 12. ltc1859 nonaveraged 4096 point fft plot frequency (khz) 0 magnitude (db) C60 C40 C20 0 40 1859 f12 C80 C100 C70 C50 C30 C10 C90 C110 C130 C120 10 20 30 545 15 25 35 50 f sample = 100khz f in = 1khz sinad = 86.95db thd = C101.42db
19 LTC1857/ltc1858/ltc1859 185789f applicatio s i for atio wu uu 1859 f13 adc + LTC1857/ltc1858/ltc1859 digital system ov dd dgnd 24 21 adc C 10 f dv dd 20 10 f av dd 19 agnd 14, 17, 18 10 f refcomp 16 10 f v ref 15 12 muxout + LTC1857/ ltc1858/ ltc1859 muxout C 10 ch0 ch1 ch2 ch3 ch4 ch5 ch6 ch7 com 11 13 1 f analog ground plane + C figure 13. power supply grounding practice u package descriptio g package 28-lead plastic ssop (5.3mm) (reference ltc dwg # 05-08-1640) ltc1858/ltc1859 can be tied to the analog ground plane. placing the bypass capacitor as close as possible to the power supply pins, the reference and reference buffer output is very important. low impedance common returns for these bypass capacitors are essential to low noise opera- tion of the adc, and the foil width for these tracks should be as wide as possible. also, since any potential difference in grounds between the signal source and adc appears as an error voltage in series with the input signal, attention should be paid to reducing the ground circuit impedance as much as possible. the digital output latches and the onboard sampling clock have been placed on the digital ground plane. the two ground planes are tied together at the power supply ground connection. information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 0.09 C 0.25 (.0035 C .010) 0 C 8 0.55 C 0.95 (.022 C .037) 5.00 C 5.60** (.197 C .221) g28 ssop 0204 7.40 C 8.20 (.291 C .323) 1234 5 6 7 8 9 10 11 12 14 13 9.90 C 10.50* (.390 C .413) 25 26 22 21 20 19 18 17 16 15 23 24 27 28 2.0 (.079) max 0.05 (.002) min 0.65 (.0256) bsc 0.22 C 0.38 (.009 C .015) typ millimeters (inches) dimensions do not include mold flash. mold flash shall not exceed .152mm (.006") per side dimensions do not include interlead flash. interlead flash shall not exceed .254mm (.010") per side * ** note: 1. controlling dimension: millimeters 2. dimensions are in 3. drawing not to scale 0.42 0.03 0.65 bsc 5.3 C 5.7 7.8 C 8.2 recommended solder pad layout 1.25 0.12
20 LTC1857/ltc1858/ltc1859 185789f ? linear technology corporation 2004 lt/tp 0904 1k ? printed in the usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com u typical applicatio related parts 2.5v reference internal clock 1.6384x 4.096v 8k agnd1 control logic serial i/o input mux and range select agnd3 agnd2 refcomp v ref adc C muxout + muxout C adc + dgnd av dd dv dd mux address and range data out convst 28 25 22 26 27 21 23 3v to 5v sdi busy sck rd ov dd sdo 1859 ta03 12-/14-/16-bit sampling adc + C com 19 20 5v 5v 1 2 3 9 ch7 14 11 10 12 13 15 16 17 18 24 1 f 0.1 f ch1 single-ended or differential channel selection (see table 1) input ranges: 0v to 5v 0v to 10v 5v and 10v ? ? ? ch0 10 f 0.1 f 10 f 8-bit serial data input 16 shift clock cycles 16-bit serial data out 10 f 0.1 f 10 f 0.1 f part number description comments sampling adcs ltc1417 14-bit, 400ksps serial adc 5v or 5v, 20mw, 81db sinad and C95db thd ltc1418 14-bit, 200ksps, single 5v or 5v adc 15mw, serial/parallel i/o ltc1604 16-bit, 333ksps, 5v adc 90db sinad, 220mw power dissipation, pin compatible with ltc1608 ltc1605 16-bit, 100ksps, single 5v adc 10v inputs, 55mw, byte or parallel i/o, pin compatible with ltc1606 ltc1606 16-bit, 250ksps, single 5v adc 10v inputs, 75mw, byte or parallel i/o, pin compatible with ltc1605 ltc1608 16-bit, 500ksps, 5v adc 90db sinad, 270mw power dissipation, pin compatible with ltc1604 ltc1609 16-bit, 200ksps serial adc configurable unipolar/bipolar input, single 5v supply ltc1850/ltc1851 10-bit/12-bit, 8-channel, 1.25msps adc programmable mux and sequencer, parallel i/o ltc1852/ltc1853 10-bit/12-bit, 8-channel, 400ksps adc single 3v-5v, programmable mux and sequencer, parallel i/o ltc1864/ltc1865 16-bit, 1-/2-channel, 250ksps adc in msop single 5v supply, 850 a with autoshutdown ltc1864l/ltc1865l 3v, 16-bit, 1-/2-channel, 150ksps adc in msop single 3v supply, 450 a with autoshutdown dacs ltc1588/ltc1589 12-/14-/16-bit, serial, softspan i out dacs software-selectable spans, 1lsb inl/dnl ltc1592 ltc1595 16-bit serial multiplying i out dac in so-8 1lsb max inl/dnl, low glitch, dac8043 16-bit upgrade ltc1596 16-bit serial multiplying i out dac 1lsb max inl/dnl, low glitch, ad7543/dac8143 16-bit upgrade ltc1597 16-bit parallel, multiplying dac 1lsb max inl/dnl, low glitch, 4 quadrant resistors ltc1650 16-bit serial v out dac low power, low gritch, 4-quadrant multiplication op amps lt1468/lt1469 single/dual 90mhz, 22v/ s, 16-bit accurate op amp low input offset : 75 v/125 v

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