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16-bit, 250 ksps pulsar adc in msop AD7694 rev. 0 in fo rmation furn is h e d by an al o g dev i ces is believed to be a ccu rate and r e liable. how e ver, no r e spons i bili ty is assumed by analog devices fo r its use, nor f o r an y i n fri n geme nt s of p a t e nt s or ot her ri g h t s o f th ird parties th at may result fro m its use . specifications subject to chan g e witho u t n o tice. no licen s e is g r an te d by implicati o n or ot he rwi s e un der a n y p a t e nt or p a t e nt r i ghts of anal og de vices. trad emarks an d registered tra d ema r ks are the prop erty o f their respective ow ners. one technolog y way, p.o . box 9106, norwood, ma 02062-9106, u.s.a. t e l: 781. 329. 4 700 www.analog.com fax: 781. 326. 87 03 ? 2004 analog de vices, i n c. al l r i ght s r e ser v ed . fea t ures 16-bit resolut i on with no missing codes throughput: 250 ksps @ 5 v in l: 4 lsb max s/(n + d): 92 d b @ 20 khz thd: C1 06 db @ 20 kh z pseudo- d iffere ntial analog in put range: 0 v to v re f with v re f up to vd d n o pipeline delay single-supply operation: 2.7 v or 5 v serial interf ace spi?/qspi? /mi c rowire?/dsp-compatible supply c u rrent : 540 a @ 2.7 v/100 ks ps, 800 a @ 5 v/1 00 ksps standby curre nt: 1 na 8-lea d msop package improved 2 nd source to ltc18 64 and ltc186 4l applic a t io ns battery-powered eq uipment data acq u isitio n instrumentation medical instr u ments process control applic ation diagram AD7694 ref gnd vdd in+ in? sck sdo cnv 3-wire spi interface 1v to vdd 2.5v to 5v 0 to v ref 05003-001 fi g u r e 1 . table 1. msop , qfn (lfcsp)/sot-23, 16-bi t pulsar adc type 100 ksps 250 ksps 500 ksps true differential ad7684 ad7687 ad7688 pseudo differential/uni polar ad7683 ad7685 AD7694 ad7686 unipol ar ad7680 general description the AD7694 is a 16-b i t, c h a r g e r e dis t r i b u tio n , succes si v e a p p r o x im a t ion, pu lsar? a n a l og-t o-d i g i t a l co n v er t e r (ad c ) tha t o p er a t es f r o m a sin g l e p o w e r s u p p l y , vd d , betw een 2.7 v t o 5.25 v . i t co n t a i n s a lo w p o w e r , hig h s p ee d , 16 -b i t s a m p lin g ad c wi t h n o m i ssin g co des (b g r ade), a n in t e r n a l co n v ersio n clo c k, a nd a s e r i a l , s p i-com p a t ib le in t e r f ace p o r t . th e p a r t a l s o co n t a i n s a lo w no is e, wid e b a ndwi d t h , sh o r t a p e r t u r e del a y t r ack-and- h o ld cir c ui t. on t h e cnv r i sin g e d ge, i t s a m p les a n a n alog in p u t, in+, betw een 0 v t o ref wi th res p ec t t o a g r o u nd s e n s e , in?. the r e f e r e n c e v o l t a g e , ref , is a p p l ied ext e r n al l y a n d c a n b e s e t up to t h e s u pply vol t age. it s p o w e r s c a l e s l i n e a r l y w i t h t h r o u g h p u t . the AD7694 is h o us e d in a n 8-l e ad mso p p a c k a g e wi t h a n o p era t i n g t e m p era t ur e sp e c if ie d f r o m ?40c to +85c.
AD7694 rev. 0 | page 2 of 16 table of contents specifications ..................................................................................... 3 timing specifications ....................................................................... 5 absolute maximum ratings ............................................................ 6 esd caution .................................................................................. 6 pin configuration and function descriptions ............................. 7 te r m i no l o g y ...................................................................................... 8 typical performance characteristics ............................................. 9 application information ................................................................ 12 circuit information .................................................................... 12 converter operation .................................................................. 12 transfer functions ...................................................................... 12 typical connection diagram ................................................... 13 analog input ............................................................................... 13 driver amplifier choice ............................................................ 13 voltage reference input ............................................................ 14 power supply ............................................................................... 14 supplying the adc from the reference .................................. 14 digital interface .......................................................................... 14 layout .......................................................................................... 15 evaluating the AD7694s performance .................................... 15 outline dimensions ....................................................................... 16 ordering guide .......................................................................... 16 revision history 7/04revision 0: initial version
AD7694 rev. 0 | page 3 of 16 specifications vdd = 2.7 v to 5.25 v; v ref = vdd; t a = C40c to +85c, unless otherwise noted. table 2. a grade b grade parameter conditions min typ max min typ max unit resolution 16 16 bits analog input voltage range in+ ? in? 0 v ref 0 v ref v absolute input voltage in+ ?0.1 vdd + 0.1 ?0.1 vdd + 0.1 v in? ?0.1 0.1 ?0.1 0.1 v leakage current at 25c acquis ition phase 1 1 na input impedance see the analog input section. accuracy no missing codes 15 16 bits integral linearity error ?6 +6 ?4 +4 lsb transition noise ref = vdd = 5 v 0.5 0.5 lsb gain error 1 , t min to t max 2 30 2 15 lsb gain error temperature drift 0.3 0.3 ppm/c offset error 1 , t min to t max 0.7 3.5 0.7 3.5 mv offset temperature drift 0.3 0.3 ppm/c power supply sensitivity vdd = 5 v 5% 0.05 0.05 lsb throughput conversion rate vdd = 4.75 v to 5.25 v 0 250 0 250 ksps vdd = 2.7 v to 4.75 v 0 150 0 150 ksps ac accuracy signal-to-noise f in = 20 khz, v ref = 5 v 90 88 92 db 2 f in = 20 khz, v ref = 2.5 v 86 87 db spurious-free dynamic range f in = 20 khz ?100 ?106 db total harmonic distortion f in = 20 khz ?100 ?106 db signal-to-(noise + distortion) f in = 20 khz, v ref = 5 v 89 88 92 db f in = 20 khz, v ref = 2.5 v 86 87 db 1 see section. these specificatio ns do include full temperature range variation, but do not include the error contri bution from the external reference. terminology 2 all specifications in db refer to a full-scale input, fs. tested with an input signal at 0.5 db below full scale, unless otherw ise specified.
AD7694 rev. 0 | page 4 of 16 parameter conditions min typ max unit vdd = 2.7 v to 5.25 v; v ref = vdd; t a = C40c to +85c, unless otherwise noted. table 3. reference voltage range 1 vdd v load current 250 ksps, v in+ ? v in? = v ref /2 = 2.5 v 50 a sampling dynamics ?3 db input bandwidth 9 mhz digital inputs logic levels v il vdd = 4.75 v 0.8 v vdd = 2.7 v 0.45 v v ih vdd = 5.25 v 3.15 v vdd = 3.3 v 1.9 v i il ?1 +1 a i ih ?1 +1 a digital outputs data format serial, 16 bits straight binary pipeline delay conversion results available immediately after completed conversion v ol i sink = +500 a 0.4 v v oh i source = ?500 a vdd ? 0.3 v power supplies vdd specified performance 2.7 5.25 v operating current vdd vdd = 5 v, 100 ksps throughput 0.8 1.2 ma vdd = 2.7 v, 100 ksps throughput 540 960 a standby current 1 , 2 vdd = 5 v, 25 c 1 50 na temperature range specified performance t min to t max ?40 +85 c 1 with all digital inputs forced to vdd or gnd, as required. 2 during acquisition phase.
AD7694 rev. 0 | page 5 of 16 timing specifications vdd = 4.75 v to 5.25 v; t a = ?40c to +85c, unless otherwise stated. table 4. parameter symbol min typ max unit conversion time: cnv rising edge to data available t conv 3.2 s time between conversions t cyc 4 s sck period t sck 50 ns sck low time t sckl 20 ns sck high time t sckh 20 ns sck falling edge to data remains valid t hsdo 5 ns sck falling edge to data valid delay t dsdo 20 ns cnv low to sdo, d15 msb valid t en 60 ns cnv high to sdo high impedance t dis 60 ns vdd = 2.7 v to 4.75 v; t a = ?40c to +85c, unless otherwise stated. table 5. parameter symbol min typ max unit conversion time: cnv rising edge to data available t conv 4.66 s time between conversions t cyc 6.66 s sck period t sck 125 ns sck low time t sckl 50 ns sck high time t sckh 50 ns sck falling edge to data remains valid t hsdo 5 ns sck falling edge to data valid delay t dsdo 50 ns cnv low to sdo, d15 msb valid t en 120 ns cnv high to sdo high impedance t dis 120 ns
AD7694 rev. 0 | page 6 of 1 6 absolute maximum ra tings table 6. p a r a m e t e r r a t i n g analog inputs in+ 1 , in? 1 gnd ? 0.3 v to vdd + 0.3 v or 130 ma ref gnd ? 0.3 v to vdd + 0.3 v supply voltages vdd to gnd ?0.3 v to +7 v digital inputs to gnd ?0.3 v to vdd + 0.3 v digital outputs to gnd ?0.3 v to vdd + 0.3 v storage temperature range ?65c to +150c junction tempe r ature 150c ja thermal impedance 200c/w (msop -8) jc thermal impedance 44c/ w (msop- 8 ) lead temperature range vapor phase (60 sec) 215c infrared (15 sec) 220c 1 s e e the a n al o g input s e ctio n. s t r e s s es a b o v e t h os e lis t e d u n de r a b s o l u t e m a xi m u m r a t i n g s ma y c a us e p e r m a n en t dama ge t o t h e de vice . this is a s t r e s s ra t i n g onl y ; f u n c t i o n al o p era t ion o f t h e de vice a t t h es e o r an y o t h e r con d i t io ns a b o v e t h o s e i ndic a te d i n t h e op er a t io na l s e c t io n o f t h is sp e c if ic a t io n is no t im plie d . e x p o sur e t o a b s o l u te max i m u m ra t i ng co ndi t i on s fo r ex ten d e d p e r i o d s ma y a f fe c t de vice r e l i ab i l i t y . esd c a ution esd (electrostatic discharge) sensitive device. ele c tros tatic charg e s as high as 4000 v readily accumulate on the human body and test eq uipment and can discharge wi thout detection. although this product features proprietary esd protection circu i try, permanent dama ge may occur on devices subjected to high energy electrostatic discharges. theref ore, prop er esd precautions a r e recommended to avoid perform a nce degradation or l o ss of functiona l ity. 05003-002 500 ai ol 500 ai oh 1.4v to sdo c l 50pf f i gure 2 . l o a d cir c ui t fo r di g i ta l inter f a c e t i mi ng v il v ih v oh v ol v ol v oh t delay t delay 05003-003 f i gure 3. v o ltag e r e ferenc e l e vels fo r t i ming
AD7694 rev. 0 | page 7 of 1 6 pin conf igura t ion and fu nction descriptions ref 1 in+ 2 in? 3 gnd 4 vdd 8 sck 7 sdo 6 cnv 5 AD7694 top view (not to scale) 05003-004 f i g u re 4. 8-l e ad m s op pin conf ig u r at ion ta ble 7. pi n f u nct i on d e s c ri pt i o ns pin no. mnemonic type 1 function 1 r e f a i reference input voltage. the ref range is from 1 v to vdd. it is referred to the gnd pin. t h is pin should be decoupled closely to the pin with a ceramic capacitor of a few f. 2 i n + a i analog input. it is referred to in in?. the voltage range, i.e., the difference betwee n in+ and in?, is 0 v to v ref . 3 in? ai analog input ground sense. to be connected t o the anal og ground plane or t o a remote sen s e ground. 4 gnd p power supply g r ound. 5 cnv di convert input. on its lead ing e d ge, it initiates the conver sion s. it enables the s d o pin whe n lo w. 6 sdo do serial data output. the conversion result is output on this pin. it is synchro n ized to sck. 7 sck di serial data clock input. wh en cnv is low, the co nversio n result i s shifted out by this cloc k. 8 v d d p p o w e r s u p p l y . 1 ai = a n a l og i n put ; d i = di g i t a l i n put ; d o = di g i t a l out p ut ; a n d p = p o w e r .
AD7694 rev. 0 | page 8 of 16 terminology integral nonlinearity error (inl) linearity error refers to the deviation of each individual code from a line drawn from negative full scale to positive full scale. the point used as negative full scale occurs ? lsb before the first code transition. positive full scale is defined as a level 1 ? lsb beyond the last code transition. the deviation is measured from the middle of each code to the true straight line (see figure 19). differential nonlinearity error (dnl) in an ideal adc, code transitions are 1 lsb apart. dnl is the maximum deviation from this ideal value. it is often specified in terms of resolution for which no missing codes are guaranteed. offset error the first transition should occur at a level 1/2 lsb above analog ground (38.1 v for the 0 v to 5 v range). the offset error is the deviation of the actual transition from that point. gain error the last transition (from 111...10 to 111...11) should occur for an analog voltage 1 ? lsb below the nominal full scale (4.999886 v for the 0 v to 5 v range). the gain error is the deviation of the actual level of the last transition from the ideal level after the offset has been adjusted out. spurious-free dynamic range (sfdr) the difference, in decibels (db), between the rms amplitude of the input signal and the peak spurious signal. effective number of bits (enob) enob is a measurement of the resolution with a sine wave input. it is related to s/(n + d) by the following formula enob = (s/[n + d] db ? 1.76)/6.02 and is expressed in bits. total harmonic distortion (thd) thd is the ratio of the rms sum of the first five harmonic components to the rms value of a full-scale input signal and is expressed in db. signal-to-noise ratio (snr) snr is the ratio of the rms value of the actual input signal to the rms sum of all other spectral components below the nyquist frequency, excluding harmonics and dc. the value for snr is expressed in db. signal-to-(noise + distortion) ratio (s/[n + d]) s/(n+d) is the ratio of the rms value of the actual input signal to the rms sum of all other spectral components below the nyquist frequency, including harmonics but excluding dc. the value for s/(n+d) is expressed in db. aperture delay aperture delay is a measure of the acquisition performance and is the time between the rising edge of the cnv input and the time the input signal is held for conversion. transient response the time required for the adc to accurately acquire its input after a full-scale step function is applied.
AD7694 rev. 0 | page 9 of 1 6 typical perf orm ance cha r acte ristics 4 ?4 ?3 ?2 ?1 0 1 2 3 0 32768 16384 49152 65536 05003-005 code inl ( l sb) positive inl = +0.68 lsb negative inl = ? 1.14 lsb f i gure 5 . integr a l no nli n ea ri t y vs . c o d e 12000 10000 8000 6000 4000 2000 0 24e0 24e1 24e2 24e3 24e4 24e5 24e6 24e7 24e8 05003-006 code in hex counts 00 1 0 0 12500 10003 0 108568 vdd = ref = 5v f i g u re 6. his t og r a m of a dc input at t h e cod e ce nte r 0 ?180 ?160 ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 2 0 4 0 6 0 8 0 100 120 05003-007 frequency (khz) amp l itude (db of full s cale ) 16384 point fft vdd = ref = 5v f s = 250ksps f in = 20.43khz snr = 92.5db thd = ? 109.9db sfdr = ? 111.0db f i g u re 7. fft plot 2.0 ?2.0 ?1.5 ?1.0 ?0.5 0 0.5 1.0 1.5 0 32768 16384 49152 65536 05003-008 code dnl (ls b ) positive dnl = +0.59 lsb negative dnl = ? 0.56 lsb f i gur e 8 . d i ffe r e ntia l no nl inea ri t y vs . c o de 8000 7000 6000 5000 4000 3000 2000 1000 0 251b 251c 251d 251e 251f 2520 2521 2522 2523 2524 2525 2526 05003-009 code in hex counts vdd = ref = 2.5v 00 2 7 2808 50 10 0 28148 65487 2133 32418 f i g u re 9. his t og r a m of a dc input at t h e cod e ce nte r 0 ?180 ?160 ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 1 0 2 03 04 0 5 06 07 0 05003-010 frequency (khz) amp l itude (db of full s cale ) 16384 point fft vdd = ref = 2.5v f s = 150ksps f in = 20.43khz snr = 88.5db thd = ? 102.7db sfdr = ? 105.1db f i g u re 10. fft p l ot
AD7694 rev. 0 | page 10 of 16 100 95 90 85 80 17 16 15 14 13 2.5 3.0 3.5 4.0 4.5 5.0 05003-011 reference voltage (v) s nr, s / [n+d] (db) enob ( b it s) snr s/[n+d] enob f i gure 11. snr , s / ( n + d), a n d e n ob v s . r e fer e nce v o ltag e 100 95 90 85 80 75 70 0 5 0 100 150 200 05003-012 frequency (khz) s / [n+d] (db) v ref = 2.5v, ? 1db v ref = 5v, ? 10db v ref = 5v, ?1db fi g u r e 1 2 . s / [ n + d ] v s . fr e q u e n c y ?80 ?115 ?110 ?105 ?100 ?95 ?90 ?85 0 4 0 8 0 120 160 200 05003-013 frequency (khz) thd (db) v ref = 5v, ? 1db v ref = 2.5v, ?1db f i g u re 13. th d v s . f r equ e nc y 1200 1000 800 600 400 200 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 05003-014 supply (v) op e rating curre nt ( a) f s = 100ksps f i gure 14. o p er atin g current v s . sup p l y 800 900 400 500 600 700 300 200 100 0 ?55 125 105 85 65 45 25 5 ?15 ?35 05003-015 temperature ( c) op e rating curre nt ( a) vdd = 5v, f s = 100ksps vdd = 2.7v, f s = 100ksps f i gure 15. o p er atin g current v s . t e mper atu r e 1000 0 250 500 750 ? 5 5 ? 35 ?15 5 25 45 65 85 105 125 05003-016 temperature ( c) p o we r-down curre nt (na) f i gure 16. p o wer - d o wn cur r ent vs. t e mp e r atu r e
AD7694 rev. 0 | page 11 of 16 6 ?6 ?4 ?2 0 2 4 ?55 125 105 85 65 45 25 5 ?15 ?35 05003-017 temperature ( c) offs e t e rror, gain e rror (ls b ) offset error gain error f i gure 17. o ffs et a n d g a in e r r o r v s . t e mpe r atu r e
AD7694 rev. 0 | page 12 of 16 appli c a t ion inf o rma t ion sw+ msb 16,384c in+ lsb comp control logic switches control busy output code cnv ref gnd in? 4c 2c c c 32,768c sw? msb 16,384c lsb 4c 2c c c 32,768c 05003-018 f i gur e 1 8 . adc simpl i f ie d s c hema ti c circuit informa t ion the AD7694 is a lo w p o w e r , sin g le-s u p p l y , 16-b i t ad c usin g a successi v e a p p r o x ima t ion a r chi t e c t u r e . i t is c a p a b l e o f co n- v e r t in g 250,000 s a m p les p e r s e c o nd (250 ks ps) a nd p o w e rs do wn betw een c o n v ersio n s. w h en o p er a t in g a t 100 s p s, f o r exa m ple , i t con s um es typ i cal l y 4 w , ide a l fo r b a t t er y-p o w e r e d ap p l i c at i o n s . the AD7694 p r o v ides the us er wi t h o n -c hi p trac k-and-h o ld and d o e s no t e x h i b i t an y pip e l i ne d e l a y or l a te nc y , m a k i ng it i d e a l f o r m u l t i p le , m u l t i p lexe d c h a n ne l a p p l ica t io n s . the AD7694 is s p ecif ie d f r o m 2.7 v t o 5.25 v . i t is h o us e d in a 8-lead mso p . th e AD7694 is an im p r o v ed s e c o nd s o ur ce t o l t c1864 an d l t c1864l. f o r ev en bet t e r p e r f o r ma n c e , t h e ad7685 sh o u ld be co n s ider ed . c o nverter oper a t ion the AD7694 is a s u cces si v e a p p r o x ima t ion ad c bas e d o n a ch ar ge re d i st r i but i on d a c . f i g u re 1 8 show s t h e s i m p l i f i e d s c h e ma tic o f t h e ad c. th e c a p a ci ti v e d a c con s is ts o f tw o iden t i ca l a r ra y s o f 16 b i na r y w e ig h t e d c a p a ci t o rs, w h ich a r e co nne c t e d t o t h e tw o co m p a r a t o r in p u ts. duri n g th e a c q u i s i t i o n p h ase , t e rm i n als o f th e a r ra y ti ed t o th e c o m p ar a t or s i n put are c o n n e c t e d to g n d v i a s w + a n d s w ? . all i n de pen d en t s w i t ch e s a r e co n n ec t e d t o th e a n al og i n p u ts . t h us, the ca p a ci t o r a r ra ys a r e used as sam p lin g ca p a ci t o r s an d acq u ir e t h e a n al og sig n al o n th e in+ an d i n ? in p u ts. w h en t h e acq u isi t ion pha s e is co m p lete and t h e cn v i n pu t go es hig h , a co n v ersio n phas e b e g i n s . w h e n t h e con v ersio n phas e b e g i n s , s w + a n d s w ? are op e n e d f i rs t . t h e t w o c a p a c i tor ar r a y s are t h e n dis c onne c t e d f r o m t h e i n pu ts an d con n e c te d to t h e g n d in p u t. th us, t h e dif f er en t i al v o l t a g e b e t w e e n t h e in p u t s , in+ and in?, ca p t ur e d a t th e end o f the acq u isi t ion p h as e a p p l ies t o th e co m p a r a t o r in p u ts, ca usin g t h e co m p a r a t o r t o b e co me u n bal- a n ced . b y sw i t ch i n g ea ch e l em en t o f th e ca pa ci t o r a r ra y be t w een gnd and ref , t h e com p a r a t o r in p u t va r i es b y b i na r y w e ig h t e d v o l t a g e st eps (v ref /2, v ref /4...v re f /65536). th e c o n t r o l log i c t o g g l es t h es e s w i t ch es, s t a r t i n g wi t h t h e msb , in o r der t o b r in g th e com p a r a t o r bac k in t o a b a lan c e d con d i t ion. af t e r th e co m p le ti o n o f t h i s p r oce s s, th e pa r t r e t u rn s t o th e a c q u i s i t i o n phas e and t h e c o n t r o l log i c g e n e ra t e s t h e ad c o u t p ut co de. b e ca us e the AD7694 has a n on-bo a r d con v ersion c l o c k, t h e s e r i al c l o c k, sc k, is n o t r e q u ir e d f o r th e con v ersio n p r o c es s. tr ansfer func tio n s the ideal tran sf er f u n c tio n f o r t h e AD7694 is sh o w n in f i gur e 19 a nd t a b l e 8. 000...000 000...001 000...010 111...101 111...110 111...111 adc code (s traight binary ) analog input +fs ? 1.5 lsb + fs ? 1 lsb ? fs + 1 lsb ?fs ?fs + 0.5 lsb 05003-019 f i g u re 19. a d c ide a l t r ans f er f u nc t i o n ta ble 8. out p ut codes a n d i d ea l input volt a g es de scri pti o n a n a l og input v ref = 5 v digital output c o de hexadecim a l fsr C 1 lsb 4.999924 v ffff 2 midscale + 1 lsb 2. 500 076 v 800 1 midscale 2. 5 v 800 0 midscale C 1 lsb 2.499924 v 7fff Cfsr + 1 lsb 76. 3 v 000 1 Cfsr 0 v 000 0 3 2 this is al so the c o de for an overranged anal og input ( v in + C v in C above v re f C v gnd ). 3 this is al so the c o de for an un d e rranged anal og input ( v in + C v in C be low v gnd ).
AD7694 rev. 0 | page 13 of 16 05003-020 AD7694 ref gnd vdd in? in+ sck sdo cnv 3-wire interface 100nf 2.7v to 5.25v 2.2 to 10 f (note 2) ref 0 to v ref 33 ? 2.7nf (note 3) (note 4) (note 1) note 1: see reference section for reference selection. note 2: c ref is usually a 10 f ceramic capacitor (x5r). note 3: see driver amplifier choice section. note 4. optional filter. see analog input section. f i gure 20. t y pic a l a p plic at ion d i agr a m t y p i c a l c o nnec t i o n di a g r a m f i gur e 20 s h o w s a n exa m ple o f t h e r e comm e n de d a p pli c a t io n dia g ra m f o r the AD7694. anal og input f i gur e 21 s h o w s a n eq u i valen t cir c ui t o f th e AD7694 in p u t s t r u c t ur e . th e t w o dio d es, d1 and d2, p r o v ide es d p r o t e c t i on f o r th e a n alog in p u ts, i n + an d in?. c a r e m u s t be ta k e n t o e n s u r e th a t th e a n alog i n p u t si g n al n e v e r e x cee d s th e s u p p l y ra i l s b y m o r e t h a n 0.3 v , b e c a us e t h is w i l l ca us e t h es e dio d es t o b e come fo r w a r d- b i as e d and st a r t co nd uc t i n g c u r r en t. h o w e ver , th es e dio d es can han d le a f o r w a r d-b i as e d c u r r en t o f 130 ma, maxim u m. f o r in s t an c e , t h es e c o n d i t io ns co u l d e v en t u al l y o c c u r w h e n t h e in p u t b u f f er s (u1) s u p p lies a r e dif f er en t f r o m vd d . i n such a cas e , an i n p u t b u f f er wi t h a sh or t-cir c ui t c u r r e n t limi t a tion can b e us ed t o p r o t ec t th e p a r t . 05003-021 c in r in d1 d2 c pin in+ or in ? gnd vdd f i g u re 21. equiv a le nt a n al og input c i rcuit this a n alog in pu t s t r u c t ur e al lo ws t h e s a m p l i n g o f t h e dif f er en tial sig n al betw een in+ a nd in?. b y usin g this d i f f er en ti al i n p u t , sm all si gn als co m m o n t o bo th i n p u ts a r e r e j e c t e d . f o r i n s t a n c e , b y u s i n g i n ? t o s e n s e a r e m o t e s i g n a l g r o u n d , g r o u nd p o ten t ia l dif f er en ces b e tw e e n t h e s e n s o r and t h e lo c a l a d c g r o u n d a r e e l imi n a t e d . d u r i n g t h e ac q u isi t ion phas e, t h e i m p e dan c e o f t h e a n a l o g in p u t i n + ca n b e mo dele d as a p a ra l l el com b in a t ion o f t h e ca p a c i t o r c pi n a nd t h e n e tw o r k f o r m ed b y the s e r i es co nn ec tion o f r in and c in . c pi n is p r ima r i l y th e p i n ca pa ci ta n c e . r in is typ i c a l l y 600 ? a n d is a l u m p ed c o m p o n e n t m a d e up of s o m e s e r i a l re s i stor s an d t h e on - r e sis t a n c e o f th e swi t ch es. c in is typ i cal l y 30 pf a nd is ma inl y t h e a d c s a m p l i ng c a p a c i tor . d u r i ng t h e c o n v e r s i on ph a s e, w h er e t h e s w i t ch es a r e o p e n e d , t h e i n p u t im p e da n c e is limi t e d to c pi n . r in a nd c in ma k e a 1-p o le , lo w-p a s s f i l t e r tha t r e d u ces un desira b l e aliasin g ef fe c t s a nd limi ts t h e n o is e . w h en t h e s o ur c e im p e dan c e o f t h e dr ivin g cir c ui t is lo w , t h e AD7694 can be dr i v en dir e c t l y . l a rg e s o ur ce im p e dan c es si gn i f i c a n tl y a f f e ct th e a c pe rf o r m a n c e , e s peci ally t o tal h a r m on i c d i stor t i on ( t h d ) . t h e d c p e r f or m a n c e s are l e ss s e n s i t i v e t o t h e i n p u t i m p e dan c e . driver am plifier ch o i ce al th o u g h the AD7694 is easy to dr i v e , th e dr i v er a m p l if ier n e e d s t o m e et t h e fol l o w in g r e quir em e n ts: ? the n o is e g e n e r a t e d b y t h e dr i v er a m plif ier ne e d s t o b e k e pt as lo w as p o s s i b le i n o r der t o p r es er v e t h e s n r and tra n si tion n o is e p e r f o r ma n c e o f th e AD7694. n o t e tha t the AD7694 has a no is e m u c h lo w e r tha n m o st o f th e o t h e r 16-b i t ad cs and , th er ef o r e , can be dr i v en b y a n o isier o p a m p w h i l e p r es er vin g t h e s a me o r b e t t e r sys t e m p e r f o r - ma nce . th e n o i s e co mi n g f r o m t h e dr i v er is f i l t er e d b y t h e AD7694 a n alog in p u t cir c ui t 1-p o le , lo w-p a s s f i l t er made b y r1 a nd c2 or b y t h e ext e r n al f i l t er , if o n e is us e d . ? fo r a c ap p l i c at i o n s , t h e d r i v e r n e e d s t o h a v e a t h d p e r f o r ma n c e s u i t a b le t o tha t o f th e AD7694. f i g u r e 13 gi v e s th e t h d v e r s us f r eq ue n c y th a t th e d r i v e r shou l d e x c e e d . ? f o r m u l t icha n n e l m u l t i p lexe d a p plica t io n s , t h e dr i v er a m p l if ier an d t h e AD7694 analog in p u t cir c ui t m u s t be a b le t o set t le f o r a f u ll-scale st ep o f th e ca p a ci t o r a r ra y a t a 16-b i t leve l (0.0 015%). i n t h e am p l if ier s da t a sh eet, s e t t l i n g a t 0.1 % t o 0.01 % is m o r e co mm o n l y sp ecif ie d. this co u l d d i f f e r si gn i f i c a n tl y f r o m th e se t t li n g tim e a t a 16- b i t lev e l a nd sh o u ld b e ver i f i e d p r io r to dr i v er s e le c t io n.
AD7694 rev. 0 | page 14 of 16 table 9. r e com m ende d dri v er amplifiers amplifier typical applica t ion ad8021 very low noise a n d high frequency ad8022 low noise and high frequency op184 low pow er, lo w noise, a n d low fr equency ad8605 , ad8615 5 v single-supp l y and low pow e r ad8519 small, l o w p o we r, and low frequ e ncy ad8031 high frequency and low power v o l t a g e reference input the AD7694 v o l t a g e r e f e r e nce in p u t, ref , has a d y na mic in p u t im p e d a n c e and sh o u ld t h er efo r e b e dr i v en b y a lo w im p e dan c e s o ur ce wi th ef f i cien t deco u p ling betw een t h e ref a n d gnd p i n s , as explai n e d in t h e l a yo u t s e c t io n. w h en ref is dr i v en b y a v e r y lo w im p e dance s o ur ce (e .g., a n un b u f f er e d r e fer e n c e v o l t a g e li k e t h e lo w t e m p era t ur e dr if t ad r43x re f e re nc e or a re f e re n c e bu f f e r u s i n g t h e ad8031 or th e ad8605 ), a 10 f (x5r , 0805 size) ceramic c h i p c a p a ci t o r is a ppropr i a t e f o r opt i m u m p e r f or m a n c e. i f d e s i re d, s m a l l e r re f e re nc e d e c o up l i ng c a p a c i t o r v a lu e s d o w n t o 2.2 f ca n be us ed wi th a minimal im p a c t on p e r f o r ma n c e , es p e c i al l y d n l. power sup p l y the AD7694 p o w e rs do wn a u t o ma tic a l l y a t t h e end o f eac h co n v ersio n phas e a n d , t h er efo r e , t h e p o w e r s c ales lin e a r l y wi t h th e s a m p lin g ra te , as sh o w n in f i gur e 22. this mak e s t h e p a r t ide a l f o r a lo w s a m p ling ra t e ( e v e n a f e w h z ) and lo w ba t t er y- p o w e r e d ap p l i c at i o n s . 10,000 1,000 100 10 1 0.1 0.01 10 100 1k 10k 100k 1m 05003-022 sampling rate (sps) op e rating curre nt ( a) vdd = 5v vdd = 2.7v f i gure 22. o p er atin g current v s . s a mp l i ng r a te suppl y i ng the adc from the reference f o r sim p lif i ed a p p l ica t io n s , the AD7694, wi th i t s lo w o p era t in g c u r r e n t , c a n b e supp l i e d d i re c t l y u s i n g t h e re f e re nc e c i rc u i t , a s sh own i n f i gur e 23. th e r e fer e nce line can b e d r i v en b y ei t h er ? the s y ste m p o we r su p p ly dire c t ly ? a r e fer e n c e v o l t a g e wi t h e n o u g h c u r r en t o u t p ut ca p a b i li ty , su ch as t h e adr43x ? a r e fer e n c e b u f f er , s u ch as t h e ad8031 , t h a t c a n a l s o f i l t e r t h e s y ste m p o we r su p p ly , as s h ow n in fig u re 2 3 05003-023 ad8031 AD7694 ref vdd 2.2 to 10 f 1 f 10 ? 10k ? 5v or 3v 5v or 3v 5v or 3v 1 f (note 1) note 1: optional reference buffer and filter f i g u re 23. e x a m pl e of an a p pl ic at i o n c i rcuit digit a l in t e rf a c e the AD7694 is co m p a t i b le wi th s p i, qs p i , dig i t a l h o s t s, and ds p s , e . g., b l ack f in? ads p -b f5 3x o r ads p -219 x. th e co nnec- t i o n d i a g r a m is sh own i n f i gur e 24 a nd t h e co r r esp o n d i n g t i min g d i a g ram is sh own i n f i g u r e 25. a r i sin g e d ge on cn v in i t ia t e s a co n v ersio n and fo r c es s d o t o hig h im p e dan c e. w h en the con v ersio n is co m p l e t e , the AD7694 en t e rs t h e ac q u isi t io n phas e and p o w e rs do wn. w h en c n v g o e s lo w , t h e ms b is o u t p ut o n t o sd o . th e r e maini n g da t a b i ts a r e t h e n clo c k e d b y subs e q uen t s c k fa l l in g e d ges. the da t a is va li d on b o t h s c k e d ge s . 05003-024 cnv sck sdo data in clk convert digital host AD7694 f i g u re 24. con n ec t i on d i ag r a m
AD7694 rev. 0 | page 15 of 16 05003-025 sdo *sdo remains low if further sck clocks are applied while cnv is low d15 d14 d13 d1 d0 t dis sck 1 2 3 1 4 1 5 16* t sck t sckl t sckh t hsdo t dsdo cnv conversion acquisition t conv t cyc acquisition t acq t en f i gure 25. s e ri al inter f ace ti ming la y o u t the p r in te d cir c ui t b o a r d t h a t ho us es t h e ad76 94 s h o u ld b e desig n e d s o t h a t t h e a n a l o g a nd dig i t a l s e c t io n s a r e s e p a r a te d a nd co nf i n e d to cer t a i n a r e a s o f t h e b o a r d . t h e p i n o u t o f t h e AD7694 wi t h al l i t s a n alog sig n als o n th e lef t side an d al l i t s dig i t a l sig n als o n the r i g h t side e a s e s this tas k . a v o i d r u nnin g dig i t a l li n e s u n der t h e de vice b e ca us e t h es e co u p le n o is e o n to t h e die, un less a g r o u nd plane un d e r t h e AD7694 is us ed as a s h ie ld . f a s t swi t c h in g sig n a l s, s u c h as cnv o r c l o c ks, s h o u l d n e v e r r u n n e ar a n alog sig n al p a th s. cr os s o v e r o f dig i t a l and ana l o g sig n a l s sho u ld b e a v o i d e d. a t leas t on e g r oun d plan e s h o u l d b e us ed . i t cou l d be comm o n o r spli t b e twe e n t h e dig i t a l an d a n a l og s e c t io n. i n such a ca s e , i t s h o u ld b e jo in e d under n e a th t h e AD7694s. the AD7694 v o l t a g e r e f e r e nce in p u t ref has a d y na mic in p u t im p e d a n c e and sh o u ld b e de cou p le d wi t h min i ma l p a r a si t i c ind u c t an ces. th a t is don e b y pl a c in g t h e r e fer e nce de co u p li n g c e r a m i c c a p a c i t o r cl o s e to , and i d e a l l y r i g h t up ag ai ns t , t h e r e f a nd g n d p i n s a nd b y co n n e c t i n g t h es e p i ns w i t h wi de, lo w im p e dan c e t r ac es. f i nal l y , th e p o wer s u p p l y , vd d , o f th e AD7694 sh o u ld be deco u p led wi th a cera mic c a p a c i t o r , typ i cal l y 10 0 nf . this ca pa ci t o r s h o u l d b e p l a c ed c l os e t o th e a d 7694 a n d co nn ec t e d usin g s h o r t and la rg e t r aces t o pr o v ide lo w im p e dan c e p a t h s a nd r e d u c e t h e ef fe c t o f g l i t ch e s o n t h e p o w e r su p p l y lin e s. ev al u a ting the ad76 94 s performance o t h e r r e co mm en de d l a yo u t s f o r th e AD7694 a r e o u tlined in t h e eval ua tion bo a r d f o r th e ad769 4 ( ev a l - a d 7 6 9 4 ). t h e e v a l ua t i on b o a r d p a ck a g e i n cl u d es a f u l l y ass e m b le d and teste d e v a l ua t i on b o a r d , do c u m e n t a t i o n, a nd s o f t wa re fo r co n t r o l l in g t h e b o a r d f r o m a pc vi a t h e ev a l - c on trol br d 2 .
AD7694 rev. 0 | page 16 of 16 outline dimensions 0.80 0.60 0.40 8 0 4 85 4.90 bsc pin 1 0.65 bsc 3.00 bsc seating plane 0.15 0.00 0.38 0.22 1.10 max 3.00 bsc coplanarity 0.10 0.23 0.08 compliant to jedec standards mo-187aa f i g u re 26. 8-l e ad m i cro s m al l o u t l in e p a ckag e [m s o p ] (rm-8) di me nsio ns sho w n i n m i ll im e t e r s ordering guide models integral nonlin earity temperature r a nge pack age (option) transport media, quantity branding AD7694arm 6 lsb max C40c to +85c msop (rm-8) tube, 50 c2h AD7694armrl7 6 lsb max C40c to +85c msop (rm-8) reel, 1,000 c2h AD7694brm 4 lsb max C40c to +85c msop (rm-8) tube, 50 c2j AD7694brmrl 7 4 lsb max C40c to +85c msop (rm-8) reel, 1,000 c2j eval-AD7694c b 1 evaluation bo ar d eval-control brd2 2 controll er boar d eval-control brd3 2 controll er boar d 1 th i s boa r d ca n be use d a s a st a n da lon e eva l ua t i on boa r d or i n con j u n c t i on wi t h t h e eval- c on t r ol br d x fo r eva l u a t i on /dem on st ra t ion purpose s . 2 th ese boa r d s a l l o w a p c t o con t r ol a n d com m u n i ca t e wi t h a ll an a l og d e vi c e s eva l ua t i on boa r ds en di n g i n c b de s i gn a t ors. ? 2004 a n al og devic e s , inc . a ll rig h t s r e ser v e d . t r a d em arks an d r e gist er e d tr adem ar ks ar e t h e proper t y of t h eir respec tiv e o w ners . d05003C0C 7/04(0)

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