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8-channel, 1.5 msps, 12-bit and 10-bit parallel adcs with a sequencer prelim inary technical data ad7938/AD7939 fea t ures fast throughput rate: 1.5 ms ps specified for v dd of 2.7 v to 5. 25 v low power 8 mw max at 1. 5 msps with 3 v supplies 16 mw max at 1.5 msps with 5 v s u pplies 8 analog input channels with a sequencer software configurable analog inputs 8-channel singl e-ende d inputs 4-channel fu lly differentia l inp u ts 4-channel pseu do-differenti a l inputs 7-channel pseu do-differenti a l inputs accurate on-chip 2.5 v referen c e wide input bandwidth 70 db s n r at 5 0 kh z input fr e q uency n o pipeline delays high speed par a llel interface word/byte modes full sh utdown mode: 1 a m a x 32-lea d lfcsp and tqfp pack age func ti on a l bl ock di a g r a m 03715-0-001 v in 7 t/h parallel interface/control register sequencer 12-/10-bit sar adc and control i/p mux 2.5v vref db0 db11 v drive v dd ad7938/AD7939 v in 0 agnd v refin/ v refout clkin busy convst cs dgnd rd wr w/b fi g u r e 1 . gener a l description the ad7938/AD7939 a r e 12-b i t a nd 10-b i t, hig h s p e e d , lo w p o w e r , successi v e a p p r o x im a t ion (sar) ad cs. the p a r t s o p era t e f r o m a s i n g le 2.7 v t o 5. 25 v p o w e r s u p p l y a n d f e a t ur e thr o ug h p u t ra t e s u p t o 1.5 ms p s . th e p a r t s con t a i n a lo w n o is e , wid e b a n d wi d t h , dif f er en t i a l t r a c k-and- h o ld am plif ier t h a t can ha nd le in p u t f r e q uen c ies u p t o 20 mh z. the ad7938/AD7939 f e a t ur e eig h t a n alog in p u t c h a n n e ls wi th a c h a n ne l s e q u e n cer tha t al lo w a p r ep r o g r a mme d s e le c t io n o f cha n n e ls t o b e c o n v er t e d s e q u e n t i al l y . th e s e p a r t s ca n o p er a t e wi t h e i t h er si n g le-e n d e d , f u l l y dif f er en t i al , o r ps eudo- d i f f er en ti al a n alog i n p u t s . the con v ersio n p r o c es s an d da t a acq u isi t ion a r e co n t r o l l e d usin g st anda r d co n t r o l in pu ts t h a t a l lo w e a sy i n t e r f acin g w i t h micr o p r o cess o r s a nd dsp s . t h e in p u t sig n a l is s a m p le d on t h e fallin g edg e o f co n v s t a nd t h e con v ersio n is a l s o ini t i a te d a t t h is p o in t. the ad7938/AD7939 ha v e a n acc u ra t e on-c hi p 2.5 v r e f e r e n c e th a t ca n be use d a s th e r e f e r e n c e so ur ce f o r th e a n alog- t o- d i g i tal co n v ersio n . a l te r n a t i vely , t h is p i n can b e o v er dr i v en to p r o v id e an e x te r n a l re f e re nc e. th e s e p a r t s us e ad van c e d desig n t e chniq u es t o achie ve v e r y lo w p o w e r d i s s i p at i o n at h i g h t h r o u g hp u t r a t e s . t h e y a l s o f e at u r e f l e x ibl e p o we r m a n a ge me n t opt i ons . a n o n - c h i p c o n t ro l re g i ste r al lo ws t h e us er t o s e t u p dif f er en t o p era t i n g condi t i on s, in cl u d in g ana l og in p u t ra n g e and co nf igura t ion, o u t p u t co d i ng, p o w e r ma na ge m e n t , and cha n n e l s e q u e n ci n g . produc t highlight s 1. h i g h t h r o ug h p u t w i t h lo w p o wer co n s um p t io n . 2. eig h t ana l og in p u ts wi t h a channel s e q u en c e r . 3. a c c u ra t e on-c hi p 2.5 v r e f e r e n c e . 4. s o f t w a re c o n f i g u r abl e an a l o g i n put s . si ng l e - e nd e d , p s e u d o - dif f er en t i a l , o r f u l l y dif f er en t i al a n alog in p u t s t h a t a r e s o f t wa r e s e le c t ab le . 5. sing l e -s u p ply op er a t ion wi t h v dr iv e fu n c ti o n . th e v dr iv e f u nc t i on a l l o w s t h e p a r a l l el i n te r f a c e to c o nne c t di re c t ly to 3 v , o r 5 v p r o c es s o r sys t em s indep e n d en t o f v dd . 6. n o p i p e lin e de l a y . 7. a c c u ra t e con t r o l o f t h e s a m p ling in st an t v i a a co n v s t i n put a n d o n c e of f c o n v e r s i on c o n t ro l. pr n in fo rmation furn ished by an alog d e v i c e s is believed to be accurate and reliable. how e ver, n o resp on sibili ty is assume d b y a n alog de vices fo r its use, nor for an y i n fri n geme nt s of p a t e nt s or ot h e r ri ght s o f th ird parties th at may result fro m its use . s p ecificatio n s subj ec t to ch an g e witho u t n o tice. no licen s e is g r an te d by implicati o n or ot herwi s e u n der a n y p a t e nt or p a t e nt ri ghts of analog de v i ces. trademarks 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 . rev.
ad7938/AD7939 prelim inary technical data table of contents ad7938?s p ecif ica t io n s .................................................................. 3 AD7939?s p ecif ica t io n s .................................................................. 5 t i min g s p e c if ic a t io n s ....................................................................... 7 a b s o l u t e m a xim u m r a t i n g s ............................................................ 8 es d c a u t ion .................................................................................. 8 p i n f u n c t i on d e s c r i p t io n ................................................................ 9 t e r m in olog y .................................................................................... 11 t y p i cal p e r f o r ma n c e c h a r ac t e r i s t ics ........................................... 13 on-c hi p reg i sters .......................................................................... 16 cir c ui t i n fo r m a t io n ........................................................................ 18 c o n v er t e r o p er a t io n .................................................................. 18 ad c t r a n sfer f u n c t i on ............................................................. 18 t y p i cal c o nn e c t i o n d i a g ram ................................................... 19 analog i n p u t s t r u c t ur e .............................................................. 19 analog i n p u ts .............................................................................. 20 analog i n p u t s e le c t io n .............................................................. 22 refer e nce s e c t io n ....................................................................... 23 p a ral l e l i n t e r f ac e ......................................................................... 25 p o w e r m o des o f o p era t io n ....................................................... 28 p o w e r vs. thr o ug h p u t r a te ....................................................... 29 micr o p r o ces s o r i n t e r f acing ....................................................... 29 a p plica t ion h i n t s . .......................................................................... 31 g r o u n d in g an d l a yo u t .............................................................. 31 pcb d e sig n g u ide l in es fo r c h i p s c ale p a c k a g e .................... 31 e v al ua t i n g t h e ad7938/ad79 39 p e r f o r ma n c e . ..................... 31 o u t l in e dim e n s io n s ....................................................................... 32 or der i n g g u ide . ......................................................................... 32 revisi on h i s t or y 8/04r e v i si o n p r n: p r elimi n ar y v e rsi o n r e v. prn pa ge 2 o f 32
prelim inary technical data ad7938/AD7939 ad7938?specifications v dd = v dr i v e = 2.7 v t o 5.25 v , i n t e r n al/e xter nal v ref = 2.5 v , unles s o t h e r w is e n o t e d , f clkin = 24 mh z, f sam p l e = 1.5 ms ps; t a = t min to t max , u n l e ss ot he r w i s e note d. table 1. parameter b version 1 unit test condition s /comments dynamic p e rf ormance f in = 50 khz sine wave signal-to-nois e + distortion (sinad) 2 70 db min signal-to-noise ratio (snr ) 2 70 db min t o tal harmonic distortion (t hd) 2 75 db max 80 db typ peak harmonic or spurious noise (sfdr) 2 75 db max 82 db typ intermodulation distortion (imd) 2 fa = 40.1 khz, fb = 51.5 khz second-order terms 85 db typ third-order ter m s 85 db typ channe l to cha nnel iso l ation 85 db typ aperture delay 2 5 ns typ aperture i tter 2 50 ps typ full power ba nd wid t h 2, 3 20 mhz typ 3 db 2.5 mhz typ 0.1 db dc accuracy resolution 12 bits integral nonlinearity 2 1 lsb max differential non l inearity 2 0.95 lsb max guaranteed no missed cod e s to 12 bits total unadjusted error tbd lsb max single-ended and pseudo-differ e ntial inp ut straight binary output coding offset error 2 4.5 lsb max offset error match 2 0.5 lsb max gain error 2 2 lsb max gain error match 2 0.6 lsb max fully differential input t w os complement output codi ng positive gain error 2 2 lsb max positive gain error match 2 0.6 lsb max ero-code error 2 3 lsb max ero-code error match 2 1 lsb max negative gain error 2 2 lsb max negative gain error match 2 0.6 lsb max analog in put single-ended input range 0 to v ref or 0 to 2 v ref v depending on range bit settin g pseudo-differential input range: v in + 0 to v ref or 2 v ref v depending on range bit settin g v in 0.1 to +0.4 v fully differential input range: v in + and v in v cm v ref / 2 v v cm = common- mode voltage 4 = v ref /2 v in+ and v in v cm v ref v v cm = v ref , v in + or v in must rema in within gnd/v dd dc leakage current 5 1 a max input capacitance 45 pf typ when in track 10 pf typ when in hold referenc e in p u t/output v ref input volta g e 6 2.5 v 1% for specifie d performance dc leakage current 1 a max v ref input impe dance 10 k typ v ref o u t output voltage 2.5 v 0.1% 25c v ref o u t temperature coefficient 15 ppm/ c typ v ref noise 10 v typ 0.1 hz to 10 hz bandwidth 130 v typ 0.1 hz to 1 mhz bandwidth r e v. prn pa ge 3 o f 32
ad7938/AD7939 prelim inary technical data parameter b ersin 1 unit test cnditin s /cmments ref outut imedance 10 ty ref inut caacitance 15 f ty hen in trac 25 f ty hen in hld logic inputs inut hih lt ae, inh 2. min inut lw ltae, inl 0 . 8 m a inut current, i in 1 a ma t y ically 10 na, in 0 r drie inut caacitance, c in 5 1 0 f m a logic outputs outut hih l t ae, oh 2. min i sou r ce 200 a outut lw ltae, ol 0. ma i sin 200 a flatin-state leaae current 10 a ma flatin-state outut caacitance 5 10 f ma outut cdin coding it 0 straiht natural binary tws cmlem e nt coding it 1 conersion r a te cnersi n tim e t 2 13 t cl t 20 n s trac-and-hld acquisitin tim e 135 ns ma full-scale ste i n ut thruhut rat e 1.5 msps ma poer reuir emen ts dd 2.7/5.25 min/ma drie 2.7/5.25 min/ma i dd 7 diital i/ps 0 r drie nrmal mdestatic 0.5 ma ty dd 2.7 t 5. 25 , scl n r nrmal mde oeratinal 3.2 ma ma dd .75 t 5 . 25 2. ma ma dd 2.7 t 3. aut-standy mde 1.55 ma ty f sample 250 sps 90 a ma static aut-shutdwn mde 1 ma ty f sample 250 sps 1 a ma static full shutdwn mde 1 a ma scl n r pwer dissi ati n nrmal mde oeratinal 1 m ma dd 5 8 m ma dd 3 aut-standy mde static 50 ma dd 5 270 ma dd 3 aut-shutdwn mde s tatic 5 ma dd 5 3 ma dd 3 full shutdwn mde 5/3 ma dd 5 /3 1 tem era t ure ra n es a s llw s b er s i n s 0 c t 85 c. 2 se e t h e t e rmin l y s e ct in . 3 a n al inuts with sl e w rate s e cee d i n 27 /s ull - s c ale inut s i ne wae 3.5 mh within the acquis iti n time may caus e a n i n cr r ect re sult t e ret urn ed y t h e c ne r te r. fr u ll cmmn-mde rane see fi a n d . u r e 2 8 f i u r e 2 9 5 saml e tes t ed d uri n initial rel e ase t ens ure cml iance. th i s d e i ce i s er a t i n a l wi t h a n etern a l re er e n c e i n t h e ra n e 0.1 t 3. 5 i n di eren t i a l m de a n d 0.1 t dd i n seu d- d i e re n t i a l a n d si n le- e n d ed m des . s e e the re e re nce se cti n r mre inrmatin. 7 mea s ure d wi t h a m i dsca l e dc i n ut . r e . prn pa e 32
prelim inary technical data ad7938/AD7939 AD7939?specifications v dd = v dr i v e = 2.7 v t o 5.25 v , i n t e r n al/e xter nal v ref = 2.5v , unles s o t h e r w is e n o ted , f clkin = 2 4 mh z, f sam p l e = 1.5 ms ps; t a = t min to t max , u n l e ss ot he r w i s e note d. table 2. p a r a m e t e r b version 1 unit test condition s /comments dynamic p e rf ormance f in = 50 khz sine wave signal-to-nois e + distortion (sinad) 2 60 db min signal-to-noise ratio (snr ) 2 60 db min t o tal harmonic distortion (t hd) 2 73 db max peak harmonic or spurious noise (sfdr) 2 73 db max intermodulation distortion (imd) 2 fa = 40.1 khz, fb = 51.5 khz second-order terms 75 db typ third-order ter m s 75 db typ channe l to cha nnel iso l ation 75 db typ aperture delay 2 5 ns typ aperture i tter 2 50 ps typ full power ba nd wid t h 2, 3 20 mhz typ 3 db 2.5 mhz typ 0.1 db dc accuracy resolution 10 bits integral nonlinearity 2 0.5 lsb max differential non l inearity 2 0.5 lsb max guaranteed no missed cod e s to 10 bits total unadjusted error tbd lsb max single-ended and pseudo-differ e ntial in put straight binary output coding offset error 2 4.5 lsb max offset error match 2 0.5 lsb max gain error 2 2 lsb max gain error match 2 0.6 lsb max fully differential input t w os complement output codi ng positive gain error 2 2 lsb max positive gain error match 2 0.6 lsb max ero-code error 2 3 lsb max ero-code error match 2 1 lsb max negative gain error 2 2 lsb max negative gain error match 2 0.6 lsb max analog in put single-ended input range 0 to v ref or 0 to 2 v ref v depending on range bit settin g pseudo-differential input range: v in + 0 to v ref or 2 v ref v depending on range bit settin g v in 0.1 to +0.4 v fully differential input range: v in + and v in v cm v ref / 2 v v cm = common- mode voltage 4 = v ref /2 v in+ and v in v cm v ref v v cm = v ref , v in + or v in must rema in within gnd/v dd dc leakage current 5 1 a max input capacitance 45 pf typ when in track 10 pf typ when in hold referenc e in p u t/output v ref input volta g e 6 2.5 v 1% for specifie d performance dc leakage current 5 1 a max v ref input impe dance 10 k v ref o u t output voltage 2.5 v 0.1% 25c v ref o u t temperature coefficient 15 ppm/ c typ v ref noise 10 v typ 0.1 hz to 10 hz bandwidth 130 v typ 0.1 hz to 1 mhz bandwidth r e v. prn pa ge 5 o f 32
ad7938/AD7939 prelim inary technical data p a r a m e t e r b ersin 1 unit test cnditin s /cmments ref outut imedance 10 ty ref inut caacitance 15 f ty hen in trac 25 f ty hen in hld logic inputs inut hih lt ae, inh 2. min inut lw ltae, inl 0 . 8 m a inut current, i in 1 a ma t y ically 10 na, in 0 r drie inut caacitance, c in 5 10 f ma logic outputs outut hih l t ae, oh 2. min i sou r ce 200 a outut lw ltae, ol 0. ma i sin 200 a flatin-state leaae current 10 a ma flatin-state outut caacitance 5 10 f ma outut cdin coding it 0 straiht natural binary tws cmlem e nt coding it 1 conersion r a te cnersi n tim e t 2 13 t cl t 20 n s trac-and-hld acquisitin tim e 135 ns ma full-scale ste i n ut thruhut rat e 1.5 msps ma poer reuir emen ts dd 2.7/5.25 min/ma drie 2.7/5.25 min/ma i dd 7 diital i/ps 0 r drie nrmal mdestatic 0.5 ma ty dd 2.7 t 5. 25 , scl n r nrmal mde oeratinal 3.2 ma ma dd .75 t 5 . 25 2. ma ma dd 2.7 t 3. aut-standy mde 1.55 ma ty f sample 250 sps 90 a ma static aut-shutdwn mde 1 ma ty f sample 250 sps 1 a ma static full shutdwn mde 1 a ma scl n r pwer dissi ati n nrmal mde oeratinal 1 m ma dd 5 8 m ma dd 3 aut-standy mde static 50 ma dd 5 270 ma dd 3 aut-shutdwn mde s tatic 5 ma dd 5 3 ma dd 3 full shutdwn mde 5 ma dd 5 3 ma dd 3 1 tem era t ure ra n es a s llw s b er s i n s 0 c t 85 c. 2 se e t h e t e rmin l y s e ct in . 3 an a l i n ut s wi t h s l ew ra t e s ece edi n 27 /s ul l- sca l e i n ut si n e wa e 3 .5 mh wi t h i n t h e a c q u i s i t i n t i m e m a y ca use a n i n crre ct cn ersi n r e su lt t e re turne d y the cne r te r. fr u ll cmmn-mde rane see fi a n d . u r e 2 8 f i u r e 2 9 5 saml e tes t ed d uri n initial rel e ase t ens ure cml iance. th i s d e i ce i s er a t i n a l wi t h a n etern a l re er e n c e i n t h e ra n e 0.1 t 3. 5 i n di eren t i a l m de a n d 0.1 t dd i n seu d- d i e re n t i a l a n d si n le- e n d ed m des . s e e the re e re nce se cti n r m re de tail s . 7 mea s ure d wi t h a m i dsca l e dc i n ut . r e . prn pa e 32
prelim inary technical data ad7938/AD7939 timing specifications 1 v dd = v dr i v e =2 .7 v t o 5.25v , i n t e r n al/e xt er nal v ref = 2.5 v , unles s o t h e r w is e no t e d , f clkin = 24 mh z, f sam p l e = 1.5 ms ps; t a = t min to t max , u n l e ss ot he r w i s e note d. table 3. limit at t min , t ma x parameter ad7938 AD7939 unit description f clk i n 2 1 0 1 0 khz min 24 2 4 mhz max t qu iet 10 10 ns min minimum time between end of read and start of next conversion (i.e., time from when the data bus goes into three-state unti l the next falli ng ed ge of convst ) t 1 10 10 ns min convst pulse width. t 2 20 20 ns min convst falling edge to clkin falling edge setup time. t 3 tbd tbd ns min clkin falling edge to busy rising edge. t 4 0 0 ns min cs to wr setup time. t 5 0 0 n s m i n cs to wr hold time. t 6 2 5 2 5 n s m i n wr pulse width. t 7 10 10 ns min data setup tim e before wr . t 8 5 5 ns min data hold after wr . t 9 0 . 5 t clk i n 0.5 t clk i n ns min new data valid be fore falling e d ge of busy. t 10 0 0 ns min cs to rd setup time. t 11 0 0 ns min cs to rd hold time. t 12 55 55 ns min rd pulse width. t 13 3 50 50 ns max data access time after rd . t 14 4 5 5 ns min bus relinquis h t ime after rd . 40 40 ns max bus relinquis h t ime after rd . t 15 15 15 ns min hben to rd setup time. t 16 5 5 ns min hben to rd hold time. t 17 10 10 ns min minimum time between reads/writes. t 18 0 0 ns min hben to wr setup time. t 19 5 5 ns min hben to wr hold time. t 20 tbd tbd ns max clkin falling edge to busy falling edge. 1 sa m p le t e st ed duri n g i n i t i a l relea s e t o en sure com p li a n ce. a l l i n put si gn a ls a r e sp eci f i e d wi t h t r = t f = 5 n s (10% t o 90% of v dd ) a n d t i m e d from a vo lt a g e l e vel o f 1.6 v. all timing specifica t ions given above a r e with a 25 pf loa d c a p a c i t a n c e ( s e e , , a n d . f i g u r e 3 8 figure 3 9 f i g u r e 4 0 f i g u r e 4 1 2 mark/ s pace ratio for clkin is 40/60 to 60/40. 3 the time re quired fo r the o u tput to cro s s tbd. 4 t 14 i s deri ve d from t h e m e a s ur ed t i m e t a ken by t h e da t a o u t p ut s t o ch a n ge 0. 5 v. th e m e a s ur ed n u m b er i s t h e n ext r a p ola t ed ba ck t o r e m o ve t h e e f f e ct s of ch a rgi n g or d i s c harging the 25 pf capacito r. this me ans that the tim e , t 14 , quoted in the timing char acteris t i c s is the true bus rel i nquis h time of the part and is ind e pend ent of the bus loa d i n g. r e v. prn pa ge 7 o f 32
ad7938/AD7939 prelim inary technical data absolute maximum ratings t a = 2 5 c , u n l e ss ot he r w i s e not e d. table 4. p a r a m e t e r r a t i n g v dd to agnd/d gnd 0.3 v to +7 v v drive to agnd/dgnd 0.3 v to v dd +0.3 v analog input voltage to agnd 0.3 v to v dd + 0.3 v digital input voltage to dgnd 0.3 v to 7 v v drive to v dd 0.3 v to v dd + 0.3 v digital output v o ltage to dgnd 0 . 3 v t o v dr i v e + 0.3 v v ref i n to agnd 0.3 v to v dd + 0.3 v agnd to dg nd 0.3 v to + 0.3 v input current to any pin except supplies 1 10 ma operating tem p erature range commercia l (b version) 40c to +85c storage temperature range 65c to +150c unction tempe r ature 150c a thermal impedance 108.2c/w (lfc sp) 121c/w ( t q f p ) c thermal impedance 32.71c/w (lfc sp) 45c/w ( t q f p ) lead temperature, soldering reflow temperature (10 sec to 3 0 sec) 255c e s d 2 k v 1 transient currents of up to 100 ma wi ll not cau s e scr latch-up. 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 os e list e d i n t h e o p era t io nal s e c t io n s o f t h is sp e c if ic a t io n is n o t i m pli e d . e x p o sur e t o a b s o l u t e 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 caution esd (electrostatic discharge) sensitive device. ele c tr ostatic charg e s as high as 4000 v readily accumulate on the human body and test eq uipment and can discharg e wit h out detection. althou gh 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. r e v. prn pa ge 8 o f 32
prelim inary technical data ad7938/AD7939 pin function description 03715-0-006 d0 1 v driv e 9 dgnd 10 d8 /hbe n 11 d9 12 d1 0 13 d1 1 14 bus y 15 clkin 16 w/ b 32 v dd 31 v in 7 30 v in 6 29 v in 5 28 v in 4 27 v in 3 26 v in 2 25 d1 2 d2 3 d3 4 d4 5 d5 6 d6 7 d7 8 v in 1 24 v in 0 23 v refin /v refout 22 agnd 21 20 19 wr 18 convst 17 ad7938/AD7939 top view (not to scale) rd cs pin 1 identifier f i gure 2. pin config ur ation ta ble 5. pi n f u nct i on d e s c ri pt i o n pin no mnemonic function 1 to 8 db0 to db7 data bits 0 to 7. t h ree-state para llel d i gital i/ o pi ns that provid e the conversi on r e sult and also a l low the co ntrol and shadow regi sters to be program m ed . these pins are controlled b y cs , rd , and wr . the logic high/low vo ltage levels for these pins ar e determined by the v drive input. when reading from the AD7939, the two lsbs (db0 and db1) are always 0 a n d the lsb of the conversion re sult is avail a ble on db 2. 9 v drive logic power supply input. t h e voltage supp lie d at this pin determines at wh at voltage the par a lle l interface of the ad7938/ad793 9 operates. this pin shou ld be decoupled to dnd. the voltage at this pin may be different to that at v dd but should never exce ed v dd by more than 0.3 v. 10 dnd digital round. this is the ground reference point for a ll digital circuitry on the ad7938/ad793 9. this pin should connect to the dnd plane of a system. the dnd and an d voltages s h ould id eally be at the same potentia l and must not be more than 0.3 v apart, even on a transient b a sis. 11 db8/hben data bit 8/ high byte enable. when w/b is high, this pin acts as data bit 8, a three-state i/o pin tha t is controlled b y cs , rd , and wr . when w/b is low, this pin acts as the high byte enable pin. when hben is low, the low byte of data being written to or read from the ad7938/ ad79 39 is on db0 to db7. when hben is high, the top four bits of the data being written to or read from the ad7938/ad79 39 are on db0 to db3. when re ading from the device, db4 to db6 of the high byte will contai n the id of the channe l for which the c o nversio n result c o rresp ond s ( s ee the channel ad d r ess bits in table 9). when writing to the d evice, db4 to db7 of the high byte must be all 0s. note that when reading from the AD7939, the two lsbs of the low byte are 0s , and the remaini n g 6 bits, conve r sion data. 12 to 14 db9 to db11 data bits 9 to 11. t h ree-state par a lle l d i gital i/o p i ns that provid e the conversi on r e sult and also a l low the co ntrol and shad ow regi sters to be program m ed in word mod e . t h ese pins are contro lled b y cs , rd , and wr . the logic high/low voltage leve ls fo r these pins ar e determined by the v drive input. 15 bus busy output. lo gic output indic a ting th e status of the conversi o n . the bus output goes high following the falling edge of convst and sta y s high for the duration of the conversi on. on ce the conversi on is comp lete and the result is available in the output register, the bus output goes low. the trac k-and-hold returns to trac k mode ust prior to the falling edge of bus on the 13 th rising edge of scl, see figure 38. 16 clin master clock in put. t h e clock s o urce for the co nversio n pr oc ess is applied to this pin. con versi on time for the ad7938/ad793 9 takes 13.5 clock cycles. the fre q uency of the master clock inpu t therefore dete rmines the conver sion time and achievab l e thro ughput rate. the clin signal may be a cont inuous or burst clock. 17 convst conversion start input. a fall ing e d ge on convst is us ed t o ini t ia te a conv e r sion. the track-a n d-hol d goes fro m t r ack to hold mode on th e fallin g ed ge of con v s t and the conve r sion process is initiate d a t this poin t . followin g powe r-down , when opera tin g i n au to-sh u tdow n or a u to-s tan d b y mo des , a risin g edg e on con v s t is use d to powe r - u p the devic e . 18 wr write input. acti ve low logic in put used in con unction with cs to write data to th e internal regist ers. 19 rd read input. acti ve low logic in put used in con unction with cs to access the c o nve r sion re sult. t h e conver sion re sul t is pla c ed on the data bus fo llow i ng the falling ed ge of rd read while cs is low. 20 cs chip select. acti ve low l o gic in put used in con unction with rd and wr to read conversion data or to write data to r e v. prn pa ge 9 o f 32
ad7938/AD7939 prelim inary technical data pin n mnemnic functin the internal reisters. 21 agnd anal grund. this is the rund reerence int r a ll anal circuitry n the ad7938/ad793 9. all anal inut sinal s and any eternal reere n c e sinal shuld e ree rred t t h is agnd ltae. the agnd a n d dgnd ltaes shuld ideally e at the same tent ial and must nt e mre than 0.3 aart, een n a tran si ent asis. 2 2 ref i n / ref o ut reerence inut/ outut. this in is cnn ected t the internal reerence and is the reerence surce r the ad c. the nmina l interna l reerence lta e is 2.5 and this aears at t h is in. t h is i n can e e r drien y an etern al reerence. the i n ut ltae ra ne r the eternal reeren c e is 0.1 t 3.5 r the die rential mde and is 0.1 t dd r the sinle-ended and seud-d ierential mdes, deen d in n dd . 23 t 30 in 0 t in 7 anal inut 0 t anal in ut 7. eiht anal inut channe ls that are multile ed int the n- c hi trac- and-hld. t h e anal in uts can e rr a mmed t e eiht sinle-e nded inuts, ur ully die rential air s, ur seud- dierential airs, r seen s eud-dierential in uts y se ttin the mode its in the cntrl rei ster ar riate l y see tale 9. the anal inut channe l t e c nerted can either e sele cted y writin t the address its add2 t add0 in the cntrl rei ster rir t the cn ersin r the n -chi sequenc e r can e used. the se and shd its in cn unctin with the address i ts in the c ntrl reister a ll w the shad w reister t e rrammed . t h e inut rane r all inut channels can either e 0 t ref r 0 t 2 ref , and the cdin can e inary r tw s cmlement, deendin n th e states the range and co di ng its in the cntrl reister. any unused inut channels shuld e cnnected t agnd t aid nise icu. 31 dd pwer suly inut. the dd ran e r the ad79 38/AD7939 is 2.7 t 5. 25 . th e suly shu ld e deculed t agnd with a 0.1 f caacitr and a 10 f tantal um caacitr. 32 /b rd/byte inut. hen th is inut is lic hih, data is transerr e d t and rm the ad7938/AD7939 in 12-it/10-it wrds n pins d b 0/db2 t db11. hen this in i s lic l w, yte transer md e is ena led. data and the channe l id are transerred n pins db0 t db7, and pi n db8/hben assumes its hben uncti nality. r e . prn pa e 10 32
ad7938/AD7939 prelim inary technical data terminology in t e g r a l no n l i n e a r i t y this is t h e maxi m u m d e v i a t io n f r o m a st ra ig h t l i ne p a ssin g th r o ugh th e en d p o i n t s o f th e ad c tra n sf e r fun c ti o n . th e end p o i n t s o f t h e t r a n sfer f u n c t i o n a r e zer o s c al e , a p o i n t 1 ls b b e lo w t h e f i rst c o de t r a n si t i o n , and f u l l s c a l e, a p o in t 1 l s b a b o v e t h e las t c o de t r a n si t i o n . ne g a t i v e g a i n e r r o r m a t c h this is t h e dif f er en ce in n e g a t i ve ga in er r o r b e t w e e n an y tw o chan nel s . c h an nel-t o -c h a n n el i s ol a t i o n c h a n n e l - t o -channe l is ol a t ion is a m e asur e o f t h e le v e l o f cr osst a l k b e twe e n cha n nels. i t is m e asur e d b y a p ply i n g a f u l l - s c a l e s i ne w a ve s i g n a l to a l l s e v e n nons el e c te d i n put ch an nel s a nd a p ply i n g a 50 khz sig n a l to t h e s e le c t e d cha n n e l. t h e cha n n e l- to -channel is ol a t ion is def i n e d as t h e r a t i o o f t h e p o w e r o f t h e 50 kh z sig n al o n t h e s e le c t e d chann e l t o t h e p o w e r o f t h e n o is e sig n a l t h a t a p p e a r s in t h e fft o f t h is cha nne l. d i f f erenti a l n o n l i n e a r i ty this is t h e dif f er en ce b e tw e e n t h e m e as ur e d a nd t h e ide a l 1 l s b c h a n g e be tw een a n y tw o a d j a cen t cod e s i n t h e a d c . off s et e r r o r this is t h e de via t io n o f t h e f i rs t co de tra n si tio n (00 . . .000) t o ( 0 0 . . . 0 0 1 ) f r o m t h e i d e a l , i . e . , a g n d + 1 l s b . p o w e r su pp l y re j e c t i o n r a t i o ( p sr r ) ps r r i s d e f i n e d a s th e ra ti o o f th e po w e r i n t h e a d c o u t p u t a t full - s c a l e f r eq u e n c y , f , t o t e o e r o f a 1 v - sine a e a l i e t o t e a d c v dd s l of f r e e n f s . t e f r e e n o f t e in t a r i es f r o 1 h to 1 mh . ff s et e r r o r ma t tis is t e if f er en e i n o f fs et e r r o r e t e e n an t o a n n e ls. a in er r o r tis is t e e ia t io n o f t e l a s t o e tra n s i tio n 111 . . .11 t o 111 . . . 111 f r o te ieal i .e ., v ref 1 s a f t e r t e o f fs et er r o r as e en a s t e o t. ps rr = 1 log pf/p f s pf is t e o e r a t f r e e n f in t e a d c o t t pf s is t e o e r a t f r e e n f s in t e a d c o t t. a in er r o r m a t tis is t e if f er en e i n ga i n er r o r e t e e n an t o a n n e ls. t r a -an-h o l a i s iti o n t i e te t r a - an - o l a lif ier r e t r n s in t o t r a o e a t t e en o f o n ersi o n . t e t r a - an- o l a isi t io n t i e is t e ti e r e i r e f o r t e o t t o f t e tra - a n - o l a l i f i e r t o r e a i t s f i na l a l e, i t i n 1/ 2 s , a f ter t e en o f o n ersio n . e r o -c o e e rro r tis a lies en sin g t e t os o le e n t o t t o i n g ot i on , i n a r t i l ar to t e 2 v ref in t ran g e i t v ref to +v ref i a s e a ot t e v refin o in t. i t is t e e i a t ion o f t e i s ale tra n si ti o n all s t o all 1s f r o t e i eal v in ol t ag e, i. e. , v ref . s i g n a l -t o-n o i s e + dis t o r t i o n r a t i o s in ad t i s i s t e e a s r e r a t i o of s i g n a l - t o - n oi s e + i stor t i on a t t e o t t o f t e a/ d on er t e r . t e sig n al is t e r s a li t e o f t e f na e n t a l . n o i s e is t e s o f al l n o nf na e n t al sig n als t o alf t e s a l i n g f r e en f s /2, el in g . te ra t i o is e e n e n t on t e n er o f an t i a t i o n l e e l s in t e i gi t i a ti o n r oe s s t e o r e le e l s, t e salle r t e a n ti a ti o n n o i s e . t e t eo r e tial si gn al-t o- n o i se + i s t o r tio n ra tio f o r a n i eal n- i t o n er t e r i t a sin e a e in t is g i e n e r o -c o e e rro r m a t tis is t e if f er en e i n er o -o e er r o r e t e e n an t o an nel s . po s i t i e a i n e r r o r tis a lies en sin g t e t os o le e n t o t t o i n g ot i on , i n a r t i l ar to t e 2 v ref in t ran g e i t v ref to +v ref i a s e a ot t e v refin o in t. i t is t e e i a t ion o f t e la st o e tra n s i tio n 11. . .11 t o 11 .. . 111 f r o te ieal i .e ., +v ref 1 s a f t e r t e er o - o e er r o r as e en a st e o t. sig n al - t o - n o i s e + d i s t or t i on = 6.2 n + 1.6 po s i t i e a i n e r r o r m a t tis is t e if f er en e i n o si t i e ga in er r o r e t e e n an t o an nel s . t s, f o r a 12- i t on er t e r , tis is 4 , an f o r a 1- i t o n er t e r , t is is 62 . ne g a t i e a i n e r r o r tis a lies en sin g t e t os o le e n t o t t o i n g ot i on , i n a r t i l ar to t e 2 v ref in t ran g e i t ? ?
ad7938/AD7939 prelim inary technical data t o t a l ha r m on i c d i s t or t i on ( t h d ) t h d i s th e ra tio o f th e rm s s u m o f h a rm o n i c s t o th e f u ndam e n t al . f o r th e ad7938/ AD7939, i t is def i n e d as () 1 6 5 4 3 2 v v v v v v thd 2 2 2 2 2 2log + + + + ? = v 1 i s t e r s a l i t e o f t e fn a en tal a n v 2 , v 3 , v 4 , v 5 , an v 6 a r e t e r s a li t es o f t e s e o n t r o g t e si t a r o n i s . p e a h a ro n i o r s ri o s n o is e p e a a r o n i o r s r io s n o is e is ef i ne as t e r a t i o o f t e r s al e o f t e n e t la rg es t o on e n t i n t e ad c o t t s etr t o f s /2 a n el i n g t o t e r s al e o f t e f na e n t a l . n o r a l l , t e a le o f t is s e if ia t ion is et e r i n e t e la rg es t a r o n i in t e s e t r , t fo r ad cs er e t e a r o n i s a r e r i e i n t e no is e f l o o r , i t i l l e a n o ise ea . inte r o l at i o n d i s t or t i on i t in ts o nsis tin g o f sine a e s a t t o f r e en ies, fa an f , a n a t i e e i e i t n o nlin ea ri ti e s ill r ea t e i s t o r ti o n r o ts a t s a n if f er ene f r e en ies o f fa nf er e , n = , 1, 2, 3, et . i n ter o l a t i o n is t o r t i on t e r s a r e t os e f o r i n e i t e r n o r n a r e e al t o . f o r e a l e , t e seo n -o r er t e r s in l e fa + f a n fa f, ile t e tir - o r er t e r s in l e 2fa + f, 2fa f, fa + 2f a n fa 2f. te ad3/ad3 a r e t e s t e sin g te cci f s t a n a r er e t o in t f r e e n ies n e a r t e t o en o f t e i n t a n i t a r e s e . i n t i s as e , t e s e on-o r er t e r s ar e s al l ist an e i n f r e en f r o t e o r ig ina l sine a es i l e t e t ir -o r er t e r s a r e s al l a t a f r e en l os e t o t e i n t f r e en ies. a s a r e s l t , t e s e o n- an t ir - o r er ter s a r e s e if ie s e a ra t e l . t e a l l a t io n o f t e in t e r o l a t ion ist o r t i o n is a s e r t e th d s e if ia t ion er e i t is t e ra t i o o f t e r s s o f t e in i i al i s t o r ti o n r o t s t o t e r s a li t e o f t e s o f t e f na e n t als er es s e i n s. r e . prn pa ge 12 of 32
ad7938/AD7939 prelim inary technical data typical perf orm ance cha r acte ristics t a 25c, unles s t h e r w is e n te d . f i u r e 3 . p s r r s . s u l y ri le f r e q ue n c y w i t h u t s u ly de c u l i n f i u re . a d 79 38 c h ann e l-t - c hann el is l at i n f i u re 5. a d 79 38 si na d s . a n al in u t f r equ e nc y r a ri us su l y lt a es f i u re . a d 79 38 f f t dd 5 f i u re 7. a d 79 38 t y ic a l d n l dd 5 f i u re 8. a d 79 38 t y ic a l inl dd 5 r e . prn pa e 13 32
ad7938/AD7939 prelim inary technical data f i g u re 9. a d 79 38 c h ang e in inl v s . v re f fo r v dd = 5 v f i g u re 10 . a d7 93 8 chang e in dnl v s . v ref fo r v dd = 5 v f i gur e 1 1 . ad79 38 cha n ge i n enob vs . v ref for v dd = 5 v f i gur e 1 2 . ad79 38 o ffse t vs . v ref f i gur e 1 3 . ad79 38 h i sto g r a m o f co des @ v dd = 5 v wi th t h e interna l refer e nc e f i gur e 1 4 . ad79 38 h i sto g r a m o f co des @ v dd = 5 v wi th an ex t e r n al re fer e nc e r e v. prn | pa ge 14 of 32
prelim inary technical data ad7938/AD7939 f i ur e 1 5 . ad79 39 fft dd 5 f i ur e 1 . ad79 39 t y i c a l dnl dd 5 f i ur e 1 7 . ad79 39 t y i c a l inl dd 5 r e . prn pa e 15 32
ad7938/AD7939 prelim inary technical data on-chip registers the ad7938/AD7939 ha v e tw o o n -c hi p r e g i s t ers tha t a r e n e cess a r y f o r th e o p era t io n o f t h e de vice . th es e a r e t h e con t r o l r e g i st er , w h ich is us e d t o s et u p dif f er en t o p era t i n g co ndi t i o n s, and t h e s h ado w reg i s t er , w h ich is us e d t o p r og ra m t h e a n alog in p u t cha n ne ls t o b e co n v er t e d . co n t r o l r e g i s t e r the co n t r o l r e g i s t er o n t h e ad7 938/AD7939 is a 12-b i t, wr i te-onl y r e g i s t er . da t a is wr i t t e n t o t h is r e g i s t er using th e cs a nd wr pi ns . t h e co n t r o l r e g i s t er is s h own b e lo w a nd t h e f u n c t i on s o f t h e b i ts a r e des c r i b e d in . a t p o w e r u p , t h e def a u l t b i t s e t t in gs i n t h e co n t r o l r e g i s t er a r e al l 0 s . t a b l e 7 ta ble 7. co nt rol regi s t er bi t f u nct i on des c r i pt i o n table 6. co ntrol register bits m s b s b d 1 1 d 1 0 d 9 d 8 d 7 d 6 d 5 d 4 d 3 d 2 d 1 d 0 p m 1 p m 0 c o d i n g r e f a d d 2 a d d 1 a d d 0 m o d e 1 m o d e 0 s h d s e r a n g e bit no. mnemonic description 11 10 pm1 pm0 power manage ment bits. these two bits are used to select the power mo de of o p eration. the user can cho o se between either normal m o de or various po wer- down modes of operatio n as sh own in t a b l e 8. 9 coding this bit selects t h e output coding of the conversion result. if this bit is set to 0 th e output coding is straight (natural) binary. if this bit is set t o 1 the output coding is twos complement. 8 ref this bit selects whether the internal or e x ternal reference is used to perform the conversion. if this bit is ogic 0 an external refere n c e should be applied to the v ref pin and if this bit is ogic 1 th e internal referen c e is selected (see the reference section). 7 to 5 add2 to add0 these three address bits ar e use d to either selec t which ana l og i n put channel i s converted in the next conver sio n if the seq u encer is not used or to se lect the fina l channe l in a co nsecutive seque n ce when the se quencer is used as d e scribed in t a ble 10. t h e selec t ed input channel is decoded as s h o w n i n . 4 3 mode1 mode0 the two mode pins select the ty pe of analog input on the eight v in pins. the ad 7938/AD7939 can have either eight single-end ed inputs four fully differential inp uts four pseudo-differentia l inputs or seven pseudo- differential inputs (see table 9). 2 shd the shd bit in the control regi ster is used in conj unction with the se bit to c o ntrol the seq u encer function and access the shd register (see table 10). 1 se the se bit in the control regi ster is used in con j unctio n with the shd bit to c o ntrol the seq u encer function and access the shd register (see table 10). 0 range this bit selects t h e analog input range of the ad7938/AD7939. if it is set to 0 the n th e analog input range extends from 0 v to v ref . if it is set to 1 then the analog input range ex tends from 0 v to 2 v ref . hen this range is selected av dd must be 4.75 v to 5.25 v if a 2.5 v reference is us ed otherwise c a re must be taken to ensure that the analog input remains within th e supply rails. s e e section for more information. t a b l e 9 a n a l o g i n p uts table 8. power mode selection using the pow e r man a gement bits in the con t rol register p m 1 p m 0 m o d e d e s c r i p t i o n 0 0 normal mode hen operating in normal m o de all circui try is fully powered up at all times. 0 1 auto shutdown hen operating in auto-shutdown mode the ad7938/ AD7939 will enter full shutdown mode at the end of each con versi on . in this mode all circuitry is powered down. 1 0 auto standby hen the ad7938/AD7939 enter this mode all c i rcuitry is partially powered down. this mode is similar to auto-shutdown mode but it allows th e part to power-up in 1 sec. 1 1 full shutdown hen the ad7938/AD7939 enter this mode all circuitry is power ed down. the information in the control register is retain ed. r e v. prn pa ge 16 of 32
prelim inary technical data ad7938/AD7939 table 9. analo g input ty pe s e lection channel ad dre s s mode 0 = 0 , m o de1 = 0 mode 0 = 0 , m o de1 = 1 mode 0 = 1 , m o de1 = 0 mode 0 = 1 , m o de1 = 1 eight single -en d ed i/p channels four fully differ e ntial i/p channels fo u r ps eu d o -d iff e r e nt ia l i / p chan nels (ps e udo mode 1) s e ven pseudo- d ifferential i / p chan nels (ps e udo mode 2) a d d 2 a d d 1 add0 v in + v in - v in + v in - v in + v in - v in + v in - 0 0 0 vin0 agnd vin0 vi n1 vin0 vin1 vin0 vin7 0 0 1 vin1 agnd vin1 vi n0 vin1 vin0 vin1 vin7 0 1 0 vin2 agnd vin2 vi n3 vin2 vin3 vin2 vin7 0 1 1 vin3 agnd vin3 vi n2 vin3 vin2 vin3 vin7 1 0 0 vin4 agnd vin4 vi n5 vin4 vin5 vin4 vin7 1 0 1 vin5 agnd vin5 vi n4 vin5 vin4 vin5 vin7 1 1 0 vin6 agnd vin6 vi n7 vin6 vin7 vin6 vin7 1 1 1 vin7 agnd vin7 vin6 vin7 vin6 not all o w e d sequencer oper a t io n the co nf igura t i o n o f t h e s e q and s h d w b i ts i n t h e co n t r o l r e g i s t er al lo ws t h e us er t o s e le c t a p a r t ic u l a r m o de o f o p era t io n o f th e s e q u e n cer f u n c t i o n . t o u t l in es t h e fo ur m o de s o f o p era t io n o f t h e s e q u en cer . a b l e 1 0 table 10. sequ ence selection t a b l e 1 0 s e q s h d w sequence t y pe 0 0 this configuration is se lected when the sequen ce function is n o t used. the analog input chann e l sele cted on each individual conv ersion i s determined by the contents of th e channel address bits, add2 to ad d0, in each prior write operatio n . t h is mode of operati on refl ects the traditional operat ion of a mu ltich a nnel adc, with out the sequencer function being used, where each write to the ad 7938/AD7939 selects the ne xt channe l for conversion. 0 1 this configuration sele cts the shadow register f o r programmi n g . t h e following write operation load s the d a ta on db0 to db7 to the shad ow register. t h is will pr ogram th e sequence of c h anne ls to be c o nverted co ntinuously after each convst falling ed ge ( s e e the shad ow re gister d e scriptio n and t a ble 11) . 1 0 if the seq and s hadow bits are set in th is way, the seq u ence function is not in t e rrupted upon completio n of the writ e operatio n . t h is allo ws other bits in the control r e gister to be alt e red between c o nversi ons while in a sequenc e without terminating the cycle. 1 1 this configuration is used in conjun ction with t h e chann e l ad d r ess bits ( a dd2 to add0) to prog ram continuous conver sion s on a conse c utive se quence of cha n nels from ch an nel 0 through to a selected final channe l as d e te rmined by the channe l ad d r ess bits in the c o ntrol register. shado w register the s h ado w r e g i s t er o n t h e ad7938/AD7939 is a n 8-b i t, wr i t e-o n l y r e g i s t er . da ta is lo aded f r o m d b 0 t o d b 7 o n the r i sin g edg e o f wr . the eig h t ls b s lo ad in t o t h e s h ado w r e g i s t er . the info r m a t io n is wr i t t e n in t o t h e s h ado w r e g i s t e r p r o v ide d t h a t t h e s e q and sh d w bi ts in t h e con t r o l r e g i s t er w e r e s et to 0 a n d 1, r e s p e c t i v e ly in t h e p r e v io us wr i te t o t h e con t r o l r e g i st er . e a ch b i t r e pr es en ts an an a l o g i n put f r o m cha n n e l 0 thr o u g h cha n ne l 7. a s e q u ence o f c h a nne ls ma y be s e lec t ed t h r o u g h which t h e ad7938/ad79 39 c y c l es wi th e a c h co n s e c u t i v e con v ersio n a f t e r t h e wr i te t o t h e s h ado w r e g i s t er . t o s e le c t a s e q u e n ce o f cha n ne ls t o b e con v er t e d , if o p era t in g i n sin g le- en de d m o de o r p s eudo m o de 2, t h e as s o c i a t e d cha n n e l b i t in t h e s h ado w r e g i s ter m u s t b e s et fo r e a ch r e q u ir e d a n alog in pu t. w h en o p era t i n g i n dif f er en t i al m o de o r p s eudo m o de 1, t h e as s o c i a t e d p a ir o f cha n n e ls b i ts m u st b e s et fo r e a ch p a ir o f a n alog in p u ts r e q u ir e d in t h e s e q u ence . w i t h e a ch co n s e c u t i v e co n v s t p u ls e a f t e r th e s e q u en cer has been s e t u p , th e ad7938/AD7939 p r og r e s s thr o u g h the s e le c t e d cha n nels in as ce ndin g o r d er , b e g i nn ing wi t h t h e lo w e st cha n n e l. this co n t i n ues un t i l a wr i t e o p er a t ion o c c u rs w i t h t h e s e q a nd s h d w b i ts co nf igur e d in an y wa y excep t 1, 0 (s e e ) . w h en a s e q u e n ce is s et u p i n di f f er en t i al o r p s e u do m o de 1, t h e ad c do es n o t con v er t on t h e i n vers e p a irs (i .e ., vin1, vi n0). th e b i t f u n c t i o n s o f t h e s h ado w r e g i s t er a r e o u t l in e d i n . s e e t h e an s e c t ion fo r f u r t h e r info r m a t io n on usin g t h e s e q u e n ce r . t a b l e 1 1 table 11. sha d ow register bit functions a l og i n p u t s e le c t i o n v in 0 v in 1 v in 2 v in 3 v in 4 v in 5 v in 6 v in 7 r e v. prn pa ge 17 of 32
ad7938/AD7939 prelim inary technical data circuit i n formation the ad7938/AD7939 a r e fast, 8-c h a n n e l , 12-b i t a nd 10-b i t, s i ng l e -sup ply , su c c e ss ive a p p rox ima t ion ana l o g -to - d i g i t a l co n v er t e rs. th e p a r t s ca n o p er a te f r o m a 2.7 v to 5.25 v p o w e r s u pp l y an d f e atu r e t h rou g h put r a te s up to 1 . 5 m s p s . w h en t h e ad c s t a r ts a con v ersio n (f igur e 19), sw3 o p e n s an d sw1 and sw2 m o v e s t o p o si tio n b , c a usin g the co m p a r a t o r t o beco m e un bala n c e d . b o th in p u t s a r e d i sco n n e c t ed o n ce t h e co n v ersio n b e g i n s . th e co n t r o l log i c a n d t h e c h a r g e r e dist r i b u t i o n d a cs a r e us e d to add and sub t r a c t f i xe d am o u n t s o f c h a r g e f r o m th e s a m p lin g c a p a ci t o r a r ra ys t o b r in g t h e co m p a r a t o r back in t o a ba lan c e d con d i t io n. w h en the c o m p ar ator i s re b a l a nc e d , t h e c o n v e r s i on i s c o m p l e te. t h e co n t r o l log i c g e n e ra t e s t h e ad c? s ou t p u t co de . the o u t p u t im p e dan c es o f t h e s o ur ces dr i v i n g t h e v in + and th e v in ? pi n s m u s t b e ma t c h e d; o t h e r w is e , t h e tw o i n p u ts wi l l ha v e dif f er en t s e t t ling t i m e s, w h ic h r e s u l t s in e r r o r s. the ad7938/AD7939 p r o v ide th e us er wi t h a n o n -c hi p trac k- and- hol d , an ac c u r a te i n te r n a l re fe re nc e, an ana l o g - t o - di g i t a l c o n v e r te r , and a p a r a l l el i n te r f ac e hou s e d i n a 3 2 - l e a d l f c s p or tqf p p a ck age. the ad7938/AD7939 ha v e eig h t a n alog in p u t c h a n n e ls tha t can b e co nf igur e d to b e eig h t sin g le -ende d in p u ts, fo ur f u l l y dif f er en t i a l p a irs, fo ur ps eudo-dif fer e n t ia l p a irs, o r s e v e n ps eudo-dif fer e n t ial i n p u ts w i t h r e s p e c t t o on e c o mm on i n p u t. ther e is a n on-chi p us er -p r o g r a mma b l e chann e l s e q u e n cer t h a t al lo ws th e us er t o s e lec t a s e q u en ce o f c h a n ne ls thr o u g h which t h e ad c can p r og r e s s a n d c y cle wi t h e a ch co n s e c u t i v e fal l i n g ed g e o f co n v s t . 03715-0-024 v in+ v in? a b sw1 sw3 comparator control logic capacitive dac capacitive dac c s c s v ref sw2 b a the a n alog in p u t ra n g e f o r th e ad7938/ad79 39 is 0 t o v ref or 0 t o 2 v ref dep e ndin g o n t h e s t a t us o f th e r a n g e b i t in t h e co n t r o l r e g i s t er . the o u t p u t co di n g o f t h e ad c ca n b e e i t h er b i na r y o r tw o s co m p le m e n t , dep e ndin g on t h e st a t us o f t h e co d i n g b i t i n th e co n t r o l r e gi s t e r . f i g u re 19. a d c co nvers i on p h as e adc tra n s f er func ti on the ad7938/AD7939 p r o v ide f l exi b le p o w e r ma na g e m e n t o p t i o n s t o al lo w t h e us er t o achi e v e t h e b e s t p o w e r p e r f o r ma n c e fo r a g i v e n t h r o u g h p u t r a t e . thes e o p t i o n s a r e s e le c t e d b y p r ogra m m i n g t h e po w e r m a n a g e m e n t b i ts, pm1 a n d pm0, in t h e c o n t ro l re g i ste r . the o u t p u t co din g f o r th e ad79 38/AD7939 is ei th er s t ra ig h t b i na r y o r tw o s co m p le m e n t , dep e ndin g on t h e st a t us o f t h e c o d i n g b i t in t h e con t r o l r e g i s t er . the desig n e d co de t r a n si t i o n s o c c u r a t s u cces s i v e l s b val u es (i .e ., 1 ls b , 2 ls bs, a nd s o o n ) and t h e l s b si ze is v ref /4096 f o r th e ad7938 and v ref /1024 f o r th e AD7939. the ideal tra n sf er c h a r ac t e r i s t ics o f th e ad7938 /AD7939 f o r bo th s t ra ig h t b i na r y a nd tw os co m p le m e n t o u t p u t c o di n g a r e sh own i n f a n d , r e s p ecti v e l y . converter operation the ad7938/AD7939 is a s u cc es si v e a p p r o x ima t io n ad c bas e d arou nd t w o c a p a c i t i ve d a c s . f i g u re 1 8 and fi g u re 1 9 show sim p lif i e d s c h e ma t i cs o f t h e a d c in acq u isi t i o n an d con v ersio n ph a s e, re sp e c t i v e ly . t h e a d c c o m p r i s e s of c o n t ro l l o g i c , a s a r , a nd t w o ca p a c i t i v e d a cs. b o t h f i gur e s s h o w t h e o p era t ion o f t h e ad c in dif f er en t i a l /ps e udo - dif f er en t i al m o de . sin g le- e nde d m o de o p er a t i o n i s si m i la r b u t v in is in t e r n a l ly t i e d t o a g nd . i n acq u is i t io n phas e , sw3 is c l o s ed , s w 1 an d s w 2 a r e in p o si tio n a, th e co m p a r a t o r is he ld in a ba lan c e d co n d i t io n, and t h e s a m p li n g c a p a ci t o r a r ra ys acq u ir e t h e dif f er en t i al sig n al o n t h e i n p u t. i gur e 2 0 f i gur e 2 0 . ad79 38 /ad7 93 9 idea l t r a n s f e r cha r a c t e r i stic with str a ight bin a r y o u tput c o ding f i gur e 2 1 03715-0-025 000...000 111...111 1 lsb = v ref /4096 (ad7938) 1 lsb = v ref /1024 (AD7939) 1 lsb +v ref 1 lsb analog input adc code 0v note: v ref is either v ref or 2 v ref 000...001 000...010 111...110 111...000 011...111 03715-0-023 v in+ v in a b sw1 sw3 comparator control logic capacitive dac capacitive dac c s c s v ref sw2 b a f i g u re 18. a d c ac quis it i o n p h as e r e v. prn pa ge 18 of 32
prelim inary technical data ad7938/AD7939 analog input struc t ure 03715-0-026 100...000 011...111 1 lsb = v ref /4096 (ad7938) 1 lsb = v ref /1024 (AD7939) 1 lsb = 2 & v ref /4096 (ad7938) 1 lsb = 2 & v ref /1024 (AD7939) ?v ref + 1 lsb v ref +v ref ? 1 lsb adc code 100...001 100...010 011...110 000...001 000...000 111...111 f i gur e 23 s h o w s t h e e q ui vale n t cir c ui t o f t h e a n alog in p u t s t r u c t ur e o f th e ad7938/ad79 39 in dif f er en t i a l /ps e udo dif f er en t i a l mo de. i n sing le-e nde d m o de, v in? is in t e r n a l ly t i e d to a g n d . t h e f o u r d i o d e s prov i d e e s d prot e c t i on f o r t h e a n alog i n p u ts . c a r e m u s t be tak e n t o e n s u r e tha t th e a n alog in p u t sig n als ne v e r exce e d t h e su p p l y ra ils b y m o r e t h a n 300 mv . this c a us es th es e dio d es t o become f o r w a r d-b i as ed and s t a r t s co n d uctin g i n t o t h e s u b s tra t e . t h ese d i od es ca n co n d uct u p t o 10 ma wi t h o u t ca usin g ir r e v e rsi b le da mage t o t h e p a r t . the c1 c a p a ci t ors, in f i gur e 23, a r e typ i cal l y 4 p f a n d can p r i m a r i l y b e a t tri b u t ed t o p i n ca pa c i ta n c e . t h e r e s i s t o r s a r e lu m p e d c o m p o n e n t s m a d e up of t h e on re s i st a n c e of t h e swi t ch es. th e va l u e o f th es e r e sis t o r s is typ i cal l y a b o u t 100 ?. the c2 c a p a ci t ors a r e t h e ad c s s a m p li n g c a p a ci t o rs an d ha v e a ca p a c i tan c e o f 1 6 pf typ i cal l y . f i gur e 2 1 . ad79 38 /ad7 93 9 idea l t r a n s f e r cha r a c t e r i stic with t w os c o mple ment o u tput coding typical connection diagram f i gur e 2 2 f i g u re 22. t y pic a l conne c t io n d i ag r a m s h o w s a typ i cal co nn e c tio n dia g ram f o r th e ad7938/ad79 39. th e a g nd a nd d g nd p i ns a r e co nn ec t e d t o g e t h er a t t h e de vice fo r g o o d n o is e s u p p r es si o n . th e v refin /v refo ut p i n is de cou p le d to a g n d w i t h a 0.47 f c a p a c i tor to a v oi d noi s e pi c k up i f t h e i n te r n a l re fe re nc e i s u s e d . a l te r n a t iv ely , v refin /v refo ut ca n b e co nn ec ted t o a n ext e r n al re f e re nc e s o u r c e , an d i n t h i s c a s e , t h e re f e re nc e pi n s h ou l d b e deco u p led wi th a 0.1 f ca p a c i to r . i n bo th cas e s , th e a n alog in p u t ra n g e c a n ei t h er b e 0 v t o v ref (ran ge b i t = 0) o r 0 v t o 2 v ref (r an ge b i t = 1). th e a n a l og in p u t conf igura t io n ca n b e e i t h er eig h t sin g le-e n d e d i n pu ts, fo ur dif f er e n t i al p a irs, fo ur ps eudo-dif fer e n t ia l p a irs, o r s e ven ps eudo-d if fer e n t ia l in pu ts (s e e ) . th e v dd p i n is conn e c te d to ei t h e r a 3 v o r 5 v s u p p ly . th e v o l t a g e a p plie d t o t h e v dr iv e in p u t co n t r o ls t h e vol t a g e o f t h e di g i t a l i n ter f ace and her e , i t is conn e c te d to t h e s a m e 3 v suppl y of t h e m i c ropro c e ss or to a l l o w a 3 v l o g i c i n t e rf a c e ( s ee th e d s e ct i o n ) . f o r a c a p pl i c a t i o ns , re mov i ng h i g h f r e q u e nc y c o m p o n e n t s f rom t h e a n alog in p u t sig n al is r e co mmende d b y t h e us e o f a n r c lo w-p a s s f i l t er on t h e r e le v a n t analog in p u t pins. i n a p pli c a t io ns w h er e ha r m oni c dis t o r t i o n and sig n al-t o- n o is e ra t i o a r e cr i t ical, t h e a n alog in p u t s h o u l d b e dr i v en f r o m a lo w i m p e dance s o urce . l a r g e so ur ce im pe d a n c e s s i gn i f ica n tl y a f f e ct th e a c pe rf o r m a n c e o f t h e a d c. thi s ma y ne ces s i t a te t h e us e o f an i n p u t b u f f er am pl i f i e r . t h e c h oi c e of t h e op am p w i l l b e a f u nc t i o n of t h e p a r t ic u l a r a p plica t ion. r1 c2 v in + v dd c1 d d 03715-0-028 r1 c2 v in v dd c1 d d t a b l e 9 i g i ta l i n p u t s 03715-0-027 0.1 f1 0 f 3v/5v supply 3v supply c/ p ad7938/AD7939 0.1 f 0.1 f external v ref 0.47 f internal v ref 0 to v ref / 0 to 2 v ref agnd dgnd w/b clkin cs v drive v in 0 v dd v refin /v refout v in 7 10 f 2.5v v ref rd convst wr busy db0 db11/db9 f i g u re 23. equiv a le nt a n al og input c i rcuit , convers i on p h as e switc h es o p e n , t r ack phas e sw itc h es cl os ed w h en n o am pli f ier is us e d t o dr i v e t h e a n alog in p u t, t h e s o ur ce im p e dan c e sh ou ld b e li mi t e d to lo w val u es. the maxim u m s o ur ce im p e dance w i l l dep e nd o n t h e am o u n t o f thd t h a t can be t o le ra t e d . th e t h d in cr ea ses a s th e so ur ce im pe d a n c e in cr e a s e s an d p e r f o r ma n c e deg r ades. f s h o w s a g r a p h o f t h e thd v e rs us t h e a n alog in p u t sig n al f r e q uenc y fo r dif f e r en t s o ur ce im p e dances fo r b o t h v dd = 5 v a nd 3 v . i gur e 2 4 r e v. prn pa ge 19 of 32
ad7938/AD7939 prelim inary technical data 0.47 ' f +1.25v v in r r 3r 0v ?1.25v +2.5v 0v v in0 v in7 v refout ad7938/ AD7939* *additional pins omitted for clarity 03715-0-031 f i g u re 24. th d v s . a n al og input f r equ e nc y f o r v a ri ous s o ur c e impeda nc es f i g u re 2 5 f i g u re 25. th d v s . a n al og input f r equ e nc y f o r v a ri ous su p p ly v o lt ag es show s a g r a p h of t h e t h d ve r s u s t h e an a l o g i n put f r eq uen c y f o r va r i o u s s u p p lies while s a m p ling a t 1.5 m h z wi th a n sclk o f 20 mh z. i n this c a s e , th e s o ur ce im p e dance is 10 ?. analog inputs the ad7938/AD7939 ha v e s o f t wa r e s e lec t ab le a n alog in p u t co nf igura t io n s . the us er can cho o s e ei t h er eig h t sin g le-e n d e d in p u ts, fo ur f u l l y dif f er en t i al p a irs, fo ur ps eudo-dif fer e n t ial p a irs, o r s e v e n p s eudo-dif fer e n t i a l in p u ts. th e ana l og in p u t co nf igura t io n is ch os en b y s e t t i n g t h e mo d e 0/ mo d e 1 b i t s i n t h e i n t e r n al con t r o l r e g i s t er (s e e ) . t a b l e 9 single-ended mode the ad7938/AD7939 can ha ve eig h t sin g le-ended a n alog in p u t cha n n e ls b y s e t t in g t h e mo d e 0 a nd mo d e 1 b i ts in t h e con t r o l r e g i s t er t o 0. i n a p plic a t ion s w h er e t h e sig n al s o ur ce has a hig h im p e dan c e , i t is r e co mme n d e d to b u f f er t h e a n a l og in p u t b e fo r e a p plyi n g i t t o t h e ad c. th e a n a l og in p u t ra n g e ca n b e p r ogra m m e d t o be ei t h er 0 t o v ref o r 0 t o 2 v ref . i f t h e a n alog i n p u t sig n al t o b e s a m p le d is b i p o l a r , t h e in t e r n al r e f e r e n c e o f th e a d c ca n be us ed t o e x t e rn all y b i a s u p th i s sig n al t o ma k e i t o f t h e co r r e c t fo r m a t fo r t h e a d c. f i g u re 2 6 f i gure 26. sing le -ended mod e conn e c t ion d i agr a m differenti a l m o de the ad7938/AD7939 can ha ve f o ur dif f er en tia l a n alog in p u t p a i r s by s e tt i n g t h e m o d e 0 a n d m o d e 1 bit s i n t h e c o n t ro l r e g i s t er t o 0 an d 1, r e s p ec ti v e l y . dif f er en t i al sig n als ha v e s o m e b e n e f i t s o v er sin g le-e n d e d sig n a l s, in cl udi n g n o is e imm u ni ty b a s e d o n t h e de vice s c o m m on - m o d e re j e c t i o n a n d i m prove m e n t s i n d i s t or t i on p e r f o r ma n c e . f d e f i n e s t h e f u l l y dif f er en t i al a n alog in p u t o f th e ad7938/AD7939. i gur e 2 7 f i g u re 27. d i f f e r e nt ia l input d e f i nit i on 03715-0-032 v ref p-p v in+ v in v ref p-p additional pins omitted for clarity ad7938/ AD7939 common-mode voltage the am pli t ude o f t h e dif f er en t i al sig n al is t h e dif f er en ce b e tw e e n t h e sig n als a p plie d t o t h e v in+ and v in? p i n s in eac h dif f er en t i al p a ir (i .e ., v in+ ? v in ? ). v in+ a nd v in ? shou l d b e sim u l t an e o us l y dr i v en b y tw o sig n als e a c h o f a m p l i t ude v ref tha t a r e 180 o u t o f p h as e (as s u min g t h e 0 t o v ref ra n g e is s e le c t e d ). th e am pli t ude o f t h e dif f er en t i al sig n al is t h er efo r e ?v ref to + v ref peak -t o- peak ( i .e . , 2 v ref ) . t h i s i s re g a rd l e ss of t h e comm o n mo de (cm). th e co mm o n m o de is t h e a v era g e o f t h e tw o sig n als, i . e . (v in+ + v in? ) / 2 an d is t h er efo r e t h e v o l t a g e t h a t t h e tw o in pu ts a r e cen t er e d o n . this r e s u l t s in t h e s p an o f ea c h in p u t bei n g c m v ref / 2 . t h i s v o l t a g e h a s t o be set u p ext e r n al ly a n d i t s ra n g e va r i es w i t h v ref . a s t h e val u e o f v ref in cr e a s e s, t h e comm on- m o d e ran g e de cr e a s e s. w h en dr i v i n g t h e i n p u ts wi t h a n am plif ier , t h e ac t u al comm o n -mo d e ra n g e is det e r m i n e d b y t h e am plif ier s ou t p ut v o l t a g e s w i n g. f i gur e 2 8 a n d s h o w ho w th e co mm on-m o d e ra n g e typ i cal l y va r i es wi t h v ref f o r a 5 v p o w e r s u p p l y usin g th e 0 t o v ref ra n g e o r 2 v ref ra n g e , r e s p ecti v e l y . t h e co m m o n m o de m u s t be in th i s ra n g e t o g u a r a n t e e t h e fun c ti o n ali t y o f th e ad7938/ad79 39. f i gur e 2 9 show s a t y pi c a l c o n n e c t i on d i ag r a m w h e n o p e r a t i n g t h e ad c in si ng le-e n d e d m o de. r e v. prn pa ge 20 of 32
prelim inary technical data ad7938/AD7939 using an op a m p p a ir w h en a con v ersio n t a k e s pl ace , t h e comm o n mo de is r e je c t e d r e su l t in g i n a vi r t ua l l y n o is e f r e e sig n a l o f a m pl i t ud e ?v ref to +v ref co r r es p o n d in g t o t h e dig i tal co des o f 0 t o 4096 f o r th e ad7938 an d 0 to 1024 f o r th e AD7939. i f th e 2 v ref ra n g e was us e d t h en t h e i n p u t sig n al am pli t ude w o u l d ext e nd f r o m ?2v ref to + 2 v ref af te r c o n v e r s i on . an o p a m p p a ir ca n be us e d t o dir e c t l y co u p le a dif f er en t i al sig n al t o o n e o f th e a n alog in p u t p a irs o f th e ad7938/AD7939. the cir c ui t conf igur a t io n s sh ow n i n a n d sh o w h o w a d u a l o p a m p can b e us e d to con v er t a sin g le-e nde d sig n al in t o a dif f er en t i a l sig n al fo r b o t h a b i p o lar a n d u n i p ola r i n p u t s i gn al , r e s p ecti v e l y . f i gur e 3 0 f i gur e 3 0 f i gur e 3 0 f i gure 3 0 . dua l o p a m p cir c ui t to co nv er t a single-ended uni p ol ar si gnal i n to a di ffer e nt i a l si g n a l f i gur e 3 1 f i gur e 3 1 f i gur e 3 1 f i gure 3 1 . dua l o p a m p cir c ui t to co nv er t a single-ended bipo l a r s i g n a l int o a d i f f e r e nt ia l u n ipol ar sig n al v ref (v) common-mode range (v ) 3.5 3.0 2.0 1.5 2.5 1.0 0.5 0 0 0.5 1.5 1.0 2.0 2.5 3.0 03715-0-033 the v o l t a g e a p plie d t o p o i n t a s ets u p t h e co mm on- m o d e vol t a g e. i n b o t h di a g r a m s , i t is c o nn e c te d in s o m e wa y to t h e r e fer e n c e , b u t an y val u e i n t h e co mm o n - m o d e ra n g e can b e in p u t her e t o s e t u p th e co mm o n m o de . a s u i t ab le d u al o p a m p t h a t co u l d b e us e d i n t h is co nf ig ur a t io n to p r o v i d e dif f er en t i a l dr i v e t o the ad7938/AD7939 is th e ad8022. t a k e ca r e w h en ch o o sin g t h e o p a m p; t h e s e le c t i o n dep e nds o n t h e r e q u ir e d p o w e r s u p p ly a nd sys t em p e r f o r m a n c e ob je c t i v es. the dr i v er cir c ui ts i n a n d a r e o p t i mi ze d fo r d c c o upl i ng a p p l i c a t i o ns re qu i r i n g b e st d i s t or t i on p e r f or m a nc e . the cir c ui t conf igura t io n s h ow n i n c o n v er ts a uni p ol a r , sin g le- e n d e d sig n al in to a dif f er en t i al sig n al. f i gure 28. input common-m ode r a ng e vs . v ref (0 t o v ref ra nge , v dd = 5 v ) the dif f er en t i al o p a m p dr i v er c i r c ui t i n i s c o nf igur e d to c o n v e r t a n d l e vel sh i f t a s i ng l e - e nd e d , g rou n d - re f e re nc e d (b i p ola r ) sig n al t o a dif f er en t i al sig n al cen ter e d a t t h e v ref leve l o f t h e a d c. v ref (v) common-mode range (v ) 4.5 4.0 3.0 1.5 2.0 2.5 3.5 1.0 0.5 0 0.1 0.6 1.6 1.1 2.1 2.6 03715-0-034 2 v ref p-p g nd 390 ( 220 ( 220 ( 220 ( 20k ( 220 ( 10k ( 27 ( 27 ( v+ v v+ v a v in+ v in v ref ad7938/ AD7939 0.47 f 03715- 0- 035 3.75v 2.5v 1.25v 3.75v 2.5v 1.25v f i gure 29. input common-m ode r a ng e vs . v ref (2 v ref ra nge , v dd = 5 v ) driv in g differen tial in p u ts dif f er en t i al op e r a t io n r e q u ir es t h a t v in + an d v in ? be sim u l t an eo us l y dr i v en wi t h tw o eq ual sig n als tha t a r e 180 o u t o f phas e . th e comm on m o de m u s t b e s et u p exter nal l y a n d has a ra n g e tha t i s de t e rm in ed b y v ref , t h e p o w e r s u p p l y , a n d t h e p a r t ic u l a r a m pli f ier us e d t o dr i v e t h e a n alog in pu ts. dif f er en t i al m o de s o f o p era t io n wi t h ei t h er a n ac o r dc i n p u t p r o v ide t h e b e st t h d p e r f or m a nc e ove r a w i d e f r e q u e nc y r a nge. si nc e not all a p p l i c a t i o n s h a v e a s i g n al p r eco n d i ti o n ed f o r d i f f e r e n ti al o p er a t ion, t h er e is o f ten a ne e d to p e r f o r m sin g le-ende d-to - dif f er en t i al co n v ersio n . 2 v ref p-p v ref gnd 390 ( 220 ( 220 ( 20k ( 220 ( 10k ( 27 ( 27 ( v+ v v+ v a v in+ v in v ref ad7938/ AD7939 0.47 f 03715- 0- 036 3.75v 2.5v 1.25v 3.75v 2.5v 1.25v r e v. prn pa ge 21 of 32
ad7938/AD7939 prelim inary technical data power on write to the control register to set up operating mode, analog input and output configuration set seq = shdw = 0. select the desired channel to convert (add2 to add0). issue convst pulse to initiate a conversion on the selected channel. initiate a read cycle to read the data from the selected channel. initiate a write cycle to select the next channel to be converted by changing the values of bits add2 to add0 in the control register. seq = shdw = 0. 03715-0-038 pseudo -differential mode the ad7938/AD7939 can ha ve f o ur ps eudo-dif f e r e n t ial p a irs ( p s e udo m o de 1) o r s e ven ps eu do dif f er en t i a l i n p u ts ( p s e udo m o de 2) b y s e t t in g th e m o d e 0 a nd m o d e 1 b i ts in t h e con t r o l r e g i s t er t o 1, 0 a nd 1, 1, r e s p ec tiv e l y . i n t h e c a s e o f th e f o ur ps eudo-dif fer e n t ia l p a irs, v in + i s c o n n e ct ed t o th e s i g n a l s o u r c e whic h m u s t ha ve a n am p l i t ude o f v ref t o mak e us e o f t h e f u l l d y na mic ran g e o f t h e p a r t . a dc in p u t is a p pli e d t o t h e v in ? pi n . the v o l t a g e a p plie d t o t h is i n p u t p r o v ides an o f fs et f r o m g r o u n d or a p s e u d o g rou nd f o r t h e v in+ in p u t. i n t h e cas e o f t h e s e v e n ps eudo-dif fer e n t ial i n p u ts, t h e s e v e n a n alog in pu t sig n als in p u t s are re fe r r e d to a d c volt age a p pl i e d to v in 7. the b e n e f i t o f ps eudo-dif fer e n t ial i n p u ts is t h a t t h e y s e p a ra te t h e analog in p u t s i g n a l g rou nd f rom t h e a d c s g rou nd a l l o w i ng d c c o m m on - m o de v o l t a g es to be cance l le d . f s h o w s a co nn ec tio n d i a g ra m f o r pseud o -d if f e r e n t ial m o de . i gur e 3 2 f i g u re 32. p s eud o -d if f e r e nt ia l m o de conne c t io n d i ag r a m v in+ v in v ref ad7938/ AD7939 additional pins omitted for clarity 03715-0-037 v ref p-p 0.47 f dc input voltage analog input selection a s sh o w n i n , t h e us er c a n s et u p t h e i r analog in p u t co nf igura t io n b y s e t t in g t h e va lues in t h e mo d e 0 a nd mo d e 1 b i ts in t h e co n t rol r e g i s t er . a s s u min g t h e co nf ig ura t io n has b e e n ch os en, t h er e a r e dif f er en t w a ys o f s e le c t in g t h e a n alog in p u t t o b e con v er te d de p e ndi n g o n t h e st a t e o f t h e s e q a nd s h d w b i t s i n t h e c o n t ro l re g i ste r . t a b l e 9 t a b l e 9 traditional m u ltichannel operation (seq = sh dw = 0) an y o n e o f eig h t a n alog in p u t cha n n e ls o r fo ur p a irs o f cha nne ls ma y b e s e le c t e d fo r co n v ersio n in an y o r d er b y s e t t i n g t h e s e q an d sh dw bit s i n t h e c o n t ro l re g i ste r to 0 . t h e ch an nel to b e co n v er t e d is s e l e c t e d b y wr i t ing t o t h e addr es s b i ts, ad d2 t o ad d0, in t h e c o n t r o l r e g i s t er to p r og ra m t h e m u l t i p lexer p r io r t o t h e con v ersion. this m o d e o f o p era t ion is o f a t r adi t io na l m u l t icha nne l a d c w h er e e a ch da t a wr i te s e le c t s t h e n e xt ch an nel f o r c o n v e r s i on . f show s a f l ow ch ar t of t h i s m o d e o f o p er a t i o n. t h e channel co nf igur a t io n s a r e sh own i n . i g u re 3 3 f i g u re 33. t r adit io n a l m u lt i c ha nne l o p er at ion f l o w ch a r t using the sequ e n c e r progra mmab le sequ e n c e (seq = 0, shdw = 1 ) the ad7938/AD7939 ma y be c o nf igur ed t o a u to ma tic a l l y c y c l e t h rou g h a n u mb e r of s e l e c t e d c h an nel s u s i n g t h e o n - c h i p p r ogra m m a b l e seq u en cer b y set t in g s e q = 0 a n d s h d w = 1 in t h e con t r o l r e g i s t er . the a n alog in p u t cha n n e ls t o b e con v er t e d a r e s e le c t e d b y s e t t i n g t h e r e le v a n t b i t s in t h e s h ado w r e g i s t er t o 1, s e e . t a b l e 1 1 on ce t h e s h adow r e g i s t er has b e en p r og ra mm e d w i t h t h e r e q u ir e d s e q u ence , t h e n e xt con v ersio n exe c u t e d is o n t h e lo w e s t cha nne l p r og ra mm e d in t h e shd w r e g i s t er . the n e xt co n v ersio n exe c u t e d wi l l b e on t h e n e xt hig h e s t cha n n e l i n t h e seq u en ce a n d s o o n . w h en t h e la s t c h a n n e l i n t h e s e q u en ce i s co n v er t e d , t h e i n t e r n al m u l t i p le xer r e t u r n s t o th e f i rs t cha n n e l se lect e d in th e s h a d o w r e gi s t e r a n d co mm en ces th e s e q u en ce ag ai n . i t is n o t n e ces s ar y t o wr i t e t o t h e co n t r o l r e g i s t e r a g a i n on ce a seq u en ce r o p e r a t i o n ha s been in i t i a t e d . th e wr in p u t m u st b e k e pt hig h t o en sur e t h a t t h e co n t r o l r e g i s t er is no t accide n t al ly ove r w r itte n or t h a t a s e qu e n c e op e r a t i o n i s not i n te r r upte d. i f th e co n t r o l r e gi s t e r i s w r i t t e n t o a t a n y tim e d u ri n g th e s e q u e n ce , t h en en s u r e t h a t t h e s e q a nd s h d w b i ts a r e s et t o 1, 0 t o a v o i d in t e r r u p t in g t h e con v ersio n s e q u e n ce. th e s e q u e n ce pro g r a m re m a i n s i n f orc e u n t i l su ch t i me a s t h e ad7938/ad79 39 is wr i t t e n t o a nd t h e s e q and s h d w b i ts a r e co nf igur e d wi t h a n y b i t com b in a t io n excep t 1, 0 . f s h o w s a f l o w cha r t o f t h e p r og ra mma b l e s e q u e n ce op era t ion. i gur e 3 4 r e v. prn pa ge 22 of 32
prelim inary technical data ad7938/AD7939 power on write to the control register to set up operating mode, analog input and output configuration set seq = 0 shdw = 1. initiate a write cycle. this write cycle is to the shadow register. set relevant bits to select the channels to be included in the sequence. seq bit = 1 shdw bit = 0 continuously convert consecutive channels selected with each convst pulse but allows the range, coding, analog input type, etc bits in the control register to be changed without interrupting the sequence. continuously convert consecutive channels selected in the shadow register with each convst pulse. 03715-0-039 wr = high seq bit = 0 shdw bit = 1 reference section the ad7938/AD7939 can o p er a t e wi th ei t h er th e on-c hi p o r e x te r n a l re f e re nc e. t h e i n te r n a l re f e re nc e i s s e l e c t e d by s e tt i n g t h e ref b i t in t h e i n t e r n al con t r o l r e g i s t er t o 1. a b l o c k di a g ram of t h e i n te r n a l re f e re nc e c i rc u i t r y i s show n i n fi . t h e i n te r n a l re f e re n c e c i rc u i t r y i n clu d e s an on - c h i p 2 . 5 v b a nd g a p r e fer e n c e an d a r e fer e n c e b u f f er . w h e n usin g t h e in ter nal re f e re nc e, t h e v refin /v refo ut p i n sh o u ld b e de cou p le d to a g nd wi t h a 0.47 f c a p a ci t o r . this in t e r n al r e f e r e n c e n o t onl y p r o v ides t h e r e fer e n c e fo r t h e analog-t o-dig i t a l co n v ersio n , b u t i t can als o b e us e d ext e r n al ly in t h e sys tem. i t is r e co mme n d e d t h a t t h e r e fer e nce o u t p u t is b u f f er e d usin g a n ex t e r n al p r e c isio n op am p b e f ore apply i ng it a n y w he re i n t h e s y ste m . g u re 3 6 f i gure 36. inte rn al r e fer e n c e c i rcuit bl ock d i agr a m reference ad7938/ AD7939 adc buffer 03715-0-041 v refin / v refout f i gure 34. p r ogr a m m ab le s e qu ence f l o w ch a r t consecuti v e s e que n c e (seq = 1, shdw = 1 ) a s e q u en ce o f c o n s ec u t i v e c h a n n e ls ca n be co n v er t e d b e g i nning wi t h chann e l 0 a nd en din g wi t h a f i nal c h ann e l s e lec t e d b y wr i t i n g t o t h e a d d2 t o ad d0 b i ts in t h e co n t rol r e g i s t er . this is do ne b y s e t t i n g t h e s e q an d s h d w b i ts i n t h e con t r o l r e g i s t er t o 1. i n t h is m o de , t h e s e q u encer can b e us e d w i t h o u t ha vin g t o wr i te t o t h e s h ado w r e g i s t er . once t h e co n t r o l r e g i s t e r is wr i t t e n t o , t o s et t h is m o de up , t h e n e xt con v ersio n is o n cha n n e l 0, t h en cha n n e l 1, and s o o n un til t h e cha n n e l s e lec t e d b y t h e addr es s b i ts (ad d 2 t o a d d0) is r e ach e d . th e c y cle be gin s a g a i n p r o v i d ed t h e wr i n p u t i s ti ed h i gh . i f lo w , th e s e q a nd s h d w b i t s m u s t b e s et t o 1, 0 t o al lo w t h e ad c t o co n t in ue i t s p r ep r o g r a m m e d s e q u en c e unin t e r r u p t e d . f s h o w s t h e f l o w cha r t o f t h e co ns e c u t i v e s e q u e n ce mo de . a l te r n a t iv ely , an e x te r n a l re fe renc e c a n b e a p pl i e d to t h e v refin /v refo ut p i n o f th e ad7938/AD7939. an ext e r n al r e fer e n c e i n p u t is s e le c t e d b y s e t t in g t h e ref b i t in t h e i n t e r n al c o n t ro l re g i ste r to 0 . w h e n u s i n g an e x te r n a l re f e re nc e, t h e v refin /v refo ut p i n sh o u ld b e de co u p le d to a g nd wi t h a 0.1 f ca p a c i t o r . w h en o p era t i n g in dif f er en t i al m o de , t h e ext e r n al r e f e r e n c e in p u t ra n g e is 0.1 v t o 3.5 v , a nd in al l o t h e r a n alog in p u t m o des, t h e ext e r n al r e fer e n c e in pu t ra n g e is 0.1 v t o v dd . i n a l l c a s e s, t h e sp e c if ie d r e fer e n c e is 2.5 v . i gur e 3 5 f i gure 35. cons ecu tive s e qu ence m o d e f l o w ch a r t i t is im p o r t an t to en s u r e t h a t , w h e n ch o o sin g t h e r e fer e n c e val u e , t h e maxi m u m analog in p u t ra n g e ( v in ma x ) is n e v e r gr ea t e r th a n v dd + 0.3 v t o co m p l y wi th t h e maxim u m ra tings o f t h e de vi ce . i n t h e ps eudo- d if fer e n t ia l m o des, t h e us er m u st en s u r e t h a t v ref + v in v dd w h en us i n g th e 0 t o v ref ra n g e , o r w h en usin g t h e 2 v ref ra n g e tha t 2 v ref + v in v dd . power on write to the control register to set up operating mode, analog input and output configuration select final channel (add2 to add0) in consecutive sequence. set seq = 1 shdw = 1. continuously convert a consecutive sequence of channels from channel 0 up to and including the previously selected final channel on add2 to add0 with each convst pulse. seq bit = 1 shdw bit = 0 continuously convert consecutive channels selected with each convst pulse but allows the range, coding, analog input type, etc bits in the control register to be changed without interrupting the sequence. 03715-0-040 the fol l o w in g t w o exa m ples cal c u l a t e t h e maxi m u m v ref in p u t tha t c a n be us e d when o p era t ing th e ad7938 /AD7939 in dif f er en t i al mo de , usin g t h e 0 to v ref ra n g e wi t h a v dd of 5 v a nd 3 v , r e sp e c t i vely . ex a m p l e 1 v in ma x = v dd + 0.3 v in ma x = v ref + v ref /2 if v dd = 5 v , th en v in ma x = 5.3 v . ther efo r e , 3 v ref /2 = 5.3 v . v ref ma x = 3.5 v r e v. prn | pa ge 23 of 32
ad7938/AD7939 prelim inary technical data ther efo r e , w h e n o p era t in g a t v dd = 5 v , t e ale o f v ref a n ra n g e f r o 1 v t o a ai al e o f 3.5 v . en v dd = 4.5 v , v ref ma x = 3.1 v . 315--42 1 ad nc 2 +v in nc 3 nd 6 4 temp 5 /pseect trim v t v ref 2.5v nc nc v dd nc = n cnnect 1nf .1 f .1 f .1 f additina pins mitted fr carit ad3/ ad3 e a l e 2 v in ma x = v dd + .3 v in ma x = v ref + v ref /2 if v dd = 3.6 v , t en v in ma x = 3. v . ter efo r e , 3 v ref /2 = 3.6 v . v ref ma x = 2.6 v ter efo r e , e n o era t in g i t a t v dd = 3 v , t e a l e o f v ref a n ran g e f r o 1 v t o a ai a l e o f 2.4 v . en v dd = 2. v , v re f ma x = 2 v . t es e ea l es s o t a t t e a i r e fer e n e a li e t o t e ad3/ad 3 is ir e t l e e n a n t o n t e al e a l ie t o v dd . te e r f o r a ne o f t e a r t a t if f er en t r e fer e n e a l es is s on i n f i gr e s td t o t d . te al e o f t e r e fer e n e s ets t e a n alog in t s a n an t e o on- o e o l t a g e ra n g e . e r ror s i n t e re f e re n e s o r e re s lt i n g a i n e r ror s i n t e ad3/ad 3 tra n sf er f n tio n an a t o s eif ie f l l - s ale er r o r s o n t e a r t . t a l e 1 2 tale 12. e a les of sit ale voltage re fere nes l i s t s e a les o f s i t ale o l t a g e r e fer e n es t a t o l e s e t a t are a ai l a l e f ro a n a l o g d e i e s an f s o s a t i a l o nne t io n i a g r a fo r a n e ter n a l r e fer e n e. i g re 3 f i g re 3. t i a l v ref c o nne t ion d i agr a digital ints te ig i tal in ts a l ie t o t e ad3/ad 3 a r e n o t lii te t e ai ra t i ngs t a t lii t t e a n alog in ts. i n s t e a , t e ig i t a l in ts a lie an g o t o v a n a r e n o t r e s t ri t e t e a v dd + .3 v lii t as o n t e a n alog in ts. an o t e r a a n t a g e o f t e ig i t a l in ts n o t e i n g r e s t r i t e t e a v dd + .3 v lii t is t e fa t t a t o e r s l s e en i n g is s es a r e a o i e . i f an o f t e s e in ts a r e a lie e fo r e av dd , t en t er e is n o r i s o f l a t - as t er e o l e on t e a n a l og in t s if a sig n a l g r e a t e r t a n .3 v a s a lie r io r t o av dd . v drive int te ad3/ad3 as a v dr i v e fe a t r e. v dr iv e o n t r o ls t e o l t a g e a t i t e a ral l e l i n t e r f ae o era t es. v dr iv e allo s t e a d c to e a s i l i n te r f a e to 3 v an 5 v ro e s s o rs . referene t t voltage initial a ra ma erating crrent a ad780 2.5/3 0.04 1000 a d r 4 2 1 2 . 5 0 . 0 4 5 0 0 a d r 4 2 0 2 . 0 4 8 0 . 0 5 5 0 0 f o r exa m p l e , if th e ad7938 /AD7939 o p era t e wi th a n a v dd of 5 v a nd t h e v dr i v e pi n i s p o we re d f rom a 3 v supply , t h e ad7938/ad79 39 has bet ter d y na mic p e r f o r ma n c e wi th an av dd o f 5v while s t il l bein g ab le t o in ter face dir e c t l y t o 3 v pro c e s s o r s . c a re shou l d b e t a ke n to e n su re v dr i v e do es n o t e x ceed a v dd b y m o r e th a n 0. 3 v (see th e s e c t i o n ) . a b so l u t e m a xim u m ra t i n g s r e v. prn | pa ge 24 of 32
prelim inary technical data ad7938/AD7939 parallel interf ace the ad7938/AD7939 ha v e a f l exi b le , hig h s p e e d , p a ral l e l in t e r f ace . this in t e r f ace is 12-b i ts (ad7938) o r 10-b i ts (AD7939) wide a nd is c a p a b l e of o p era t in g in ei th er w o r d ( w / b ti ed h i gh ) o r b y t e (w/ b ti ed lo w ) m o de . th e co n v s t sig n al is us e d t o ini t ia t e co n v ersio n s on t h e ad c, and w h e n o p era t in g i n a u to - s h u tdow n or a u to - s t a ndb y mo d e , i t i s u s e d to p o we r up t h e de vice. a fa l l in g e d ge on t h e co n v s t sig n al is u s ed t o ini t ia t e co n v ersio n s and i t als o p u ts t h e ad c t r ack-and-h o ld in t o t r ack. on ce t h e co n v s t sig n al g o es lo w , th e b u s y sig n al go es hig h fo r t h e d u ra t i o n o f t h e con v ersio n . i n b e tw e e n co n v ersio n s, co n v s t mu s t b e b r o u g h t h i g h f o r a m i n i mu m t i m e o f t 1 . t h i s m u s t ha p p e n a f ter t h e 14 th r i sing edg e o f clki n; o t h e r w is e , t h e co n v ersio n is ab o r te d an d t h e t r ack-and- h o ld go es b a ck i n to t r ack. a t t h e e nd o f t h e con v ers i o n , b u s y g o es lo w a n d can b e us e d t o ac t i v a te a n i n t e r r u p t s e r v ice r o u t i ne . the cs a nd rd lin e s a r e t h en ac ti va t e d in p a ral l e l t o r e ad t h e 12 - o r 10- b i ts o f co n v ersio n da t a . w h e n p o w e r su p p lies a r e f i rs t a p plie d t o t h e de vice, a r i sin g e d ge o n co n v s t p u ts t h e t r ack-and- h o l d in t o trac k. th e ac q u isi t io n time o f 135 n s minim u m m u s t be al lo w e d b e f ore co n v s t is b r o u g h t lo w t o ini t i a te a con v ersio n . the a d c t h en g o e s i n t o h o ld o n t h e falli n g ed g e o f co n v s t a nd ba c k in t o tra c k o n th e 13 th r i sing edg e o f clki n a f t e r this (s e e ) . w h e n op e r at i n g t h e d e v i c e i n a u to - s h u td o w n or a u t o - s t a nd b y mo de , w h er e t h e ad c p o w e rs do w n a t t h e e n d o f ea c h co n v e r s i o n , a ri s i n g ed g e o n th e co n v s t sig n al is u s ed t o po w e r u p th e dev i c e . f i g u re 3 8 f i gur e 3 8 . ad79 38 /ad7 93 9 p a r a l l e l inte r f a c e co n v e r s i on a n d re a d c y c l e in w o r d m o de ( w / b = 1) t 2 t 3 t 20 t 14 t 11 t 9 t 13 t 12 t 10 t convert t aquisition t quiet t 1 12 3 4 5 1 2 1 3 1 4 b a data data old data db0 to db11 db0 to db11 rd cs internal trac/hold bus clin convst three-state three-state with cs and rd tied low 03715-0-004 r e v. prn pa ge 25 of 32
ad7938/AD7939 prelim inary technical data reading data from the a d 7 938/AD7939 w i th th e w / b p i n tie d log i c hig h , th e ad7938 /AD7939 in t e r f ace op era tes in w o r d m o de . i n t h is c a s e , a sin g le r e ad o p era t ion f r o m t h e de vice access es t h e con v ersio n da t a -w o r d on pi ns db 0 to db 1 1 . the db 8 / h b e n pi n a ssu me s i t s db 8 fu n c t i o n . w i th th e w / b p i n tied t o logi c l o w , th e ad7938/ad79 39 in t e r f ace op era t es in b y t e m o de . i n this cas e , t h e d b 8/ hb e n p i n as s u m e s i t s hb en f u n c t i on. c o n v ersio n da ta f r o m t h e ad7938/ ad793 9 m u s t be access ed in tw o r e ad o p e r a t i o n s wi th 8 b i t s o f da ta p r o v i d ed o n d b 0 t o d b 7 f o r ea c h o f t h e r e ad o p era t io n s . the hben p i n det e r m i n es w h et her t h e r e ad o p era t io n acces s es t h e hig h b y t e o r t h e lo w b y t e o f t h e12- or 1 0 - bit word. f o r a l o w by te r e a d , db 0 to db 7 prov i d e t h e eig h t l s bs o f t h e 12-b i t w o rd . f o r 10-b i t o p era t io n, t h e tw o l s b s of t h e l o w by t e a r e 0 s a n d a r e f o l l ow e d by 6 bit s of c o n v e r s i on d a t a . f o r a h i g h by te re a d , db 0 to db 4 prov i d e t h e f o ur ms bs o f th e 12-/10-b i t w o rd . d b 5 t o d b 7 o f th e hig h b y t e prov i d e t h e c h a n n e l i d . f show s t h e re a d c y cl e t i m i ng di a g ra m fo r a 1 2 -/10- b i t t r a n sfer . w h en op era t e d i n w o r d m o de , t h e h b en in put do es n o t exis t, a nd o n ly t h e f i rs t r e ad o p era t ion is r e q u ir ed t o ac ces s da t a f r o m t h e de vice . w h en o p era t e d in by te m o d e , t h e t w o re a d c y cl e s show n i n f are re qu i r e d to a c c e ss t h e f u l l d a t a - w ord f rom t h e d e v i c e . i g u re 3 8 i g u re 3 9 f i gur e 3 9 . ad79 38 /ad7 93 9 p a r a l l e l inte r f a c erea d c y c l e ti mi ng for byte m o de ope r a t i o n ( w / b = 0) the cs and rd sig n a l s a r e ga te d i n ter n a l ly a n d l e vel t r ig ger e d ac ti v e lo w . i n ei t h er w o r d m o de o r b y t e m o de , cs a nd rd ma y be tied t o g e t h e r a s th e t i m i n g s p eci f i c a t i o n s f o r t 10 a nd t 11 are 0 n s mini m u m. this w o u l d m e an t h e b u s w o u l d b e co nst a n t ly dr i v en b y the ad7938/AD7939. t h e d a t a i s p l aced o n t o th e da t a - b us a tim e t 13 af ter b o t h cs an d rd g o lo w . th e rd ri s i n g ed g e ca n be used t o la t c h da ta o u t o f th e de v i ce . a f t e r a tim e , t 14 , th e da ta lin e s will b e co m e th r e e - st a t e d . a l te r n a t iv ely , cs a nd rd ca n be ti e d pe rm a n en tl y lo w a n d t h e co n v e r s i o n da t a i s v a li d a n d p l aced o n t o th e da t a -b us a tim e , t 9 , b e f ore t h e f a l l i n g e d ge of b u s . t 11 t 10 t 13 t 15 t 15 t 16 t 16 t 14 t 12 t 17 low bte hih bte db0 to db7 hben/db8 rd cs 03715-0-005 r e v. prn pa ge 26 of 32
prelim inary technical data ad7938/AD7939 writing data to the a d 7938/AD7939 wi t h w / b t i e d log i c hig h , a sing le wr i te o p er a t ion t r a n sfers t h e f u l l d a t a - w ord o n db 0 to db 1 1 to t h e c o n t ro l re g i ste r on t h e ad7938/ad79 39. th e d b 8 / hb en p i n as s u mes i t s d b 8 f u n c tion. da t a wr i t t e n t o the ad7938/AD7939 s h o u ld be p r o v i d ed o n t h e d b 0 t o d b 11 i n p u t s wi th d b 0 be in g th e l s b o f th e da ta- w o r d . w i t h w/ b tied log i c lo w , th e ad7938/AD7939 r e q u ir es tw o wr i t e o p era t ion s to t r a n sfer a f u l l 12-b i t w o r d . d b 8/hb e n assum e s i t s h b en f u n c t i on. da t a wr i t t e n t o t h e ad7938/ad79 39 s h o u ld be p r o v ided on t h e db0 t o d b 7 in p u ts. hb e n det e r m i n es w h et h e r t h e b y t e wr i t t e n is hig h b y t e o r lo w b y te da t a . th e lo w b y te of t h e da t a -w o r d sh o u ld b e wr i t t e n f i rs t wi t h d b 0 b e in g t h e ls b o f t h e f u l l da t a -w o r d . f o r t h e hig h b y te w r i t e , hb e n sh ou ld b e hig h and t h e da t a on t h e d b 0 in p u t sh o u ld be da t a b i t 8 o f th e 12-b i t w o r d . i n bo th w o rd a nd b y t e m o de , a sin g le wr i t e op era t ion t o t h e s h ado w r e g i s t er is alwa ys s u f f i cien t sin c e i t is only 8-b i ts wide . f i gur e 4 0 f i g u re 40. a d 7 9 3 8 / a d79 3 9 p a r a lle l i n t e r f ace w r it e c y c l e tim i ng f o r w o r d m o de o p er at io n ( w / b = 1) s h o w s t h e wr i t e c y cle t i min g dia g ram o f t h e ad7938/ad79 39. w h en o p er a t ed in w o r d mo de , th e hb e n in p u t do es n o t e x is t a nd o n ly t h e o n e wr i t e o p er a t io n is r e q u ir e d to w r ite t h e word of d a t a to t h e d e v i c e . d a t a s h ou l d b e prov i d e d o n d b 0 t o d b 1 1 . w h e n o p er a t e d i n b y t e m o de, t h e tw o wr i te c y cles s h o w n i n f a r e r e q u ir e d t o wr i t e t h e f u l l da t a - w o r d t o the ad7938/AD7939. i n f , th e f i rs t wr i te tra n s f e r s th e lo w e r 8 b i t s o f th e da ta- w o r d f r o m d b 0 t o d b 7, a nd t h e s e cond w r i t e t r a n s f e r s th e u p pe r 4 b i t s o f th e d a ta - w o r d . w h en wr i t ing to t h e ad793 8 / ad79 39, t h e to p 4 b i t s in t h e hig h b y te m u s t b e 0s. i gur e 4 1 i gur e 4 1 f i g u re 41. a d 7 9 3 8 / a d79 3 9 p a r a lle l i n t e r f ace w r it e c y c l e tim i ng f o r b y t e m o de o p er at io n ( w / b = 0) the da t a is l a t c h e d in t o the device o n t h e r i sin g edg e o f wr . t h e d a t a n eeds t o be set u p a tim e , t 7 , b e f ore t h e wr ri s i n g ed g e a nd h e ld fo r a t i m e , t 8 , a f ter t h e wr ri s i n g ed g e . th e cs a nd wr sig n als a r e ga t e d in t e r n al l y . cs a nd wr m a y be ti e d t o g e th e r a s th e tim i n g s p ecif i c a t i o n s f o r t 4 and t 5 are 0 ns m i n i m u m ( a ssu mi ng cs and rd ha v e n o t alr e ady b e en t i e d t o g e t h er). t 8 t 5 t 7 t 6 t 4 data db0 to db11 wr cs 03715-0-002 t 5 t 4 t 7 t 18 t 18 t 19 t 19 t 8 t 6 t 17 low bte hih bte db0 to db11 hben/db8 wr cs 03715-0-003 r e v. prn pa ge 27 of 32
ad7938/AD7939 prelim inary technical data power modes of operation the ad7938/AD7939 ha v e f o u r dif f er en t p o w e r m o des o f o p era t ion. th es e m o des a r e des i g n e d t o p r o v ide f l exi b le p o w e r m a n a ge me n t opt i ons . d i f f e r e n t opt i ons c a n b e c h o s e n to o p tim i ze t h e po w e r d i s s i p a t io n/th r o u gh p u t ra t e ra tio f o r dif f er in g a p plic a t io n s . the m o d e o f o p era t io n is s e le c t e d b y t h e p o w e r ma na ge m e n t b i t s, pm1 a nd pm0, in t h e co n t r o l r e g i ster , as det a i l e d i n . w h en p o w e r is f i rs t a p pli e d t o t h e ad7938/ad79 39 a n o n -c hi p , p o w e r - o n r e s et cir c ui t en s u r e s t h a t t h e def a u l t p o w e r - u p con d i t io n is n o r m al m o de . t a b l e 8 n o te t h a t , af te r p o we r - on, t h e t r ack- and- hol d i s i n hol d mo d e a nd t h e f i rs t r i sin g e d g e o f co n v s t places t h e t r ack-and - h o ld in t o t r ack mo de. normal mode (pm1 = pm0 = 0) this m o de is in t e nde d fo r t h e f a s t est t h r o u g h pu t ra t e p e r f o r ma n c e b e ca us e t h e us er do es n o t ha v e t o w o r r y a b o u t a n y p o w e r - u p tim e s as s o c i a t e d wi th th e ad7938/AD7939 be ca us e i t re m a i n s f u l l y p o we re d up a t a l l t i me s a t p o we r - on re s e t , t h i s m o de is t h e def a u l t s e t t i n g i n t h e con t r o l r e g i st er auto-shutdo w n (pm1 = 0; pm0 = 1) i n this m o de o f o p era t ion, th e ad7938/AD7939 a u t o ma tical l y en t e r s f u l l s h u t do wn a t t h e en d o f eac h co n v er sio n , which is sh own a t p o i n t a i n i n sh u t do w n m o de, a l l in ter na l c i rc u i t r y on t h e d e v i c e i s p o we re d d o w n t h e p a r t re t a i n s info r m a t io n i n t h e con t r o l r e g i st er d u r i n g sh u t do wn th e t r ac- a nd- h o ld a l s o go es in t o h o ld a t t h is p o in t an d rema in s i n h o ld as lo n g as t h e device is in sh u t do wn th e ad79 38/AD7939 r e ma in s in sh u t do wn m o de un t i l t h e n e xt r i sing e d g e o f co n v s t (s e e p o in t i n ) i n o r d er t o e ep t h e de vice in sh u t do wn f o r as lo n g as p o s s ib le , co n v s t s h o u l d idle lo w be tw e e n con v ersio n s as sh o w n in e r ro r ref e renc e s o u r c e not f o und on th i s ri s i n g ed g e , th e pa r t be gi n s t o p o w e r - u p a n d tra c - a n d - h o ld r e t u rn s t o tra c m o de th e po w e r - u p tim e r e q u ir e d de p e nds o n w h et h e r t h e us er is o p er a t in g wi t h t h e i n te r n a l or e x te r n a l re f e re nc e w i t h t h e i n te r n a l re f e re nc e, t h e p o w e r - u p t i m e i s typ i cal l y t d , a nd wi t h a n exter nal r e fer e n c e , t h e p o w e r - u p t i m e is typ i c a l l y t d the us er s h o u ld e n s u r e t h a t th e po w e r - u p tim e ha s e l a p se d be f o r e i n i t ia tin g a co n v e r s i o n f i gur e 3 8 f i gur e 3 8 f i gur e 3 8 auto-st a ndby (pm1 = 1; pm0 = 0) i n this m o de o f o p era t ion, th e ad7938/AD7939 a u t o ma tical l y e n t e r s s t a n d b y m o de a t th e en d o f ea c h co n v e r s i o n , wh i c h i s s h o w n as p o in t a i n w h en this m o de is en t e r e d , al l cir c ui tr y o n th e ad7938/ad79 39 is p o w e r e d do wn excep t f o r t h e r e fer e n c e and r e fer e n c e b u f f er th e t r ac-and- h o ld g o es i n to h o ld a t this p o in t als o an d r e ma in s in h o ld as l o n g as t h e de vic e is in st an d b y th e p a r t r e ma i n s in st an d b y un t i l t h e n e xt r i sin g ed g e o f co n v s t po w e r s u p th e de v i ce , w h i c h ta e s a t leas t t d the us er s h o u ld en s u r e this p o w e r - u p time has ela p s e d b e f ore i n it i a t i ng anot he r c o n v e r s i on a s s h ow n i n er r o r ref e ren c e s o urce not f o u nd this r i sin g edg e o f co nv s t al s o places t r ac - and- h o ld b a c i n to t r ac m o de full shutdow n mode (pm1 =1; pm0 = 1) w h e n th i s m o de i s p r ogra m m e d , all ci r c ui tr y o n th e ad7938/ad79 39 is p o w e r e d do wn u p on com p letio n o f th e wr i t e op era t io n, i e , o n r i sin g e d g e o f wr the p a r t r e t a in s t h e info r m a t io n i n t h e con t r o l r e g i st er w h i l e t h e p a r t is in sh u t do w n a l s o , t r ac-and- h o ld go es in to h o ld m o d e a t t h is p o in t th e ad7 938/AD7939 r e ma in s in f u l l s h u t do wn m o de a nd t r ac - an d - h o ld i n h o ld m o de, un t i l t h e p o w e r ma na ge m e n t b i ts (pm1 an d p m 0) in t h e co n t r o l r e g i s t er a r e cha n g e d i f a wr i t e t o t h e co n t r o l r e g i s t er o c c u rs w h i l e t h e p a r t is in f u l l sh u t do w n m o de, a n d t h e p o w e r ma na ge m e n t b i ts a r e cha n ge d t o pm0 = pm1 = 0, i e , n o r m al m o de , the p a r t beg i n s t o p o w e r - up on t h e wr r i sin g e d ge and t h e t r ac-and- h o ld ret u r n s to t r a c t o e n su re t h e p a r t i s f u l l y p o we re d up b e f ore a c o n v e r s i on i s i n i t ia t e d , th e po w e r - u p tim e , t d , sh o u ld be allo w e d be f o r e th e n e xt co n v s t fa l l in g e d ge; o t her w is e , in va li d d a t a wi l l b e re a d t power-up 1 1 1 1 us clin convst 03715-0-09 a f i gure 2 a u to -sh u t d o w n/ a u to -sta nd b y mo de r e v prn pa ge 28 of 32
prelim inary technical data ad7938/AD7939 power vs. throughput rate a b i g ad van t a g e o f p o w e r i n g t h e ad c do w n a f t e r a con v ersio n is t h a t t h e p o w e r co n s um p t ion o f t h e p a r t is sig n if ican t l y r e d u ce d a t lo w e r t h r o u g h p u t ra t e s. w h e n usin g t h e dif f er en t p o w e r m o des, t h e ad7938 /AD7939 is o n l y p o w e r e d u p f o r the d u ra t i on o f t h e co n v ersio n . the r efo r e , t h e a v erag e p o w e r co n s um p t io n p e r c y cle is sig n if ica n t l y r e d u c e d . f a nd show pl ot s of p o we r ve r s u s t h rou g h put w h e n o p er a t i n g i n a u to -sh u tdo w n and a u to -st a n d b y m o de s. i gur e 4 3 f i gure 43. p o wer vs. throu g hput in au to -shutdown m o d e f i g u re 4 4 f i gure 44. p o wer vs. throu g hput in au to -standb y m o de microprocessor interfacing ad7938/AD7939 to adsp-2 1xx interface f i gur e 4 5 f i g u re 45. inte r f a c i n g to t h e a d s p - 21x x s h o w s th e ad7938/AD7939 in ter face d t o the ads p - 21xx s e r i es o f d s p s as a m e m o r y ma p p e d de vic e . a sin g le wa i t s t a t e ma y be ne ces s a r y t o in t e r f ace the ad7938 /AD7939 t o t h e ads p -21xx dep e ndin g on t h e cl o c k s p e e d o f t h e ds p . th e wa i t s t a t e c a n b e p r og r a m m ed v i a th e d a ta m e m o r y w a i t s t a t e co n t r o l r e g i s t er o f t h e a d s p -21 xx (ple as e s e e t h e ad s p -21xx fa mi ly u s er s m a n u a l fo r det a i l s). th e fol l o w in g in st r u c t io n r e ads f r o m th e ad7938/ad79 39 mr = d m (ad c ) wher e ad c is th e addr es s o f the ad7938 /ad7 939. ad7938/ AD7939 adsp-21xx wr rd db0 to db11 d0 to d23 a0 to a15 dms ir q2 busy cs convst optional wr rd additional pins omitted for clarity address bus data bus address decoder 03715-0-045 ad7938/AD7939 to adsp-2 1065l interface f i gur e 4 6 f i gure 4 6 . int e r f acing t o th e ads p - 2 10 65 l s h o w s a typ i cal i n t e r f ace b e tw e e n t h e ad7938/ad79 39 a nd t h e ads p -21065l s h ar c p r o c es s o r . this i n t e r f ace is a n exa m ple o f o n e o f t h r e e d m a han d s h a k e mo d e s . t h e ms x co n t r o l line is ac t u al l y thr e e m e mo r y s e lec t l i ne s . in te r n a l a ddr 25-24 a r e de co de d i n to ms 3-0 , t h es e lin e s a r e th en as s e r t e d as c h i p s e lec t s. the dm a r 1 (d ma r e q u est 1) is us e d in t h is s e t u p as t h e in t e r r u p t t o sig n al t h e end o f c o n v e r s i on . t h e re st of t h e i n te r f a c e i s st a n d a r d h a nd sh a k i n g op e r a t i o n . ad7938/ AD7939 adsp-21065l wr db0 to db11 d0 to d31 addr 0 to addr 23 ms x dm ar 1 busy cs convst optional wr rd rd additional pins removed for clarit y address bus address bus data bus address latch address decoder 03715-0-046 ad7938/AD7939 to tms32020, tms320c 25, and tms320c5x interface p a ral l e l in t e r f ac es betw een t h e ad7938/ad79 39 a nd t h e t m s32020, t m s320c25, a nd tms320c5x fa mil y o f ds p s a r e s h o w n i n . th e m e m o r y ma p p e d addr es s c h os en f o r th e ad7938 /AD7939 sh o u ld b e c h os en t o fal l in the i/o m e m o r y s p ace o f t h e dsp s . the p a ral l e l in ter face o n t h e ad7938/ad79 39 is fas t en o u g h t o in t e r f ace t o th e t m s32020 wi t h n o extra wa i t sta t es. i f hig h s p e e d g l ue log i c, s u c h as 74 a s de vices, a r e us e d t o dr i v e t h e rd a nd t h e wr lin e s w h en in t e r f acing t o the t m s320c25, t h en a g a i n, n o wa i t sta t es a r e n e ces s a r y . h o w e v e r , if s l o w er log i c is us ed , da t a acces s es ma y b e f i gur e 4 7 r e v. prn pa ge 29 of 32
ad7938/AD7939 prelim inary technical data sl owe d su f f i c i e n t l y w h e n re a d i n g f rom an d w r it i n g to t h e p a r t t o r e q u ir e t h e in s e r t io n o f o n e wai t s t a t e . e x t r a wai t s t a t es wi l l b e n e ces s a r y wh en usin g th e t m s 320c5x a t t h eir fas t est c l o c k s p eeds (s ee t h e t m s320c5x u s er ? s g u ide f o r deta ils). d a t a is r e ad f r o m t h e a d c usi n g t h e fol l o w ing in st r u c t io n in d , ad c w h er e d is t e a t a e o r a r ess an t e ad c is t e ad3/ad 3 ar es s. ad3/ ad3 tms322/ tms32c25/ tms32c5 r rd d11 t d dmd t dmd15 a t a15 is read in t x s cs en cnvst ptina tms32c25 n r/ str additina pins mitted fr carit address s data s address decder 315--4 msc f i gr e 4 . int e r f a ing t o te tms3 22 / c 2 5 / c 5 ad7938/AD7939 to 80c18 6 interface f i gur e 8 f i g u re 8 inte r f a c i n g to t h e 80c 18 6 s h o w s th e ad7938/AD7939 in ter face d t o the 80c186 micr o p r o ces s o r the 80c186 d m a co n t r o l l er p r o v ides tw o indep e n d en t hi g h s p e e d d m a cha n n e ls w h er e da t a t r an sfer can occur be tw een m e m o r y a n d i/o s p a c e s e a c h da ta tra n s f e r co n s u m es t w o b u s c y cles , o n e c y cle t o fet c h da t a a nd t h e o t h e r t o s t o r e da t a af t e r th e ad7938 /a d7939 f i nish a con v ersio n , the u s l i ne ge ne r a te s a dm a re qu e s t to c h an n e l 1 ( d rq 1 ) e ca us e o f t h e i n t e r r u p t, t h e p r o c es s o r p e r f o r m s a d m a r e ad o p era t ion t h a t a l s o r e s ets t h e i n ter r u p t la t c h s u f f i cien t p r io r i ty m u s t be as s i gn e d t o th e d m a ch a n n e l t o en s u r e th a t t h e d m a re qu e s t i s s e r v i c e d b e f ore t h e c o m p l e t i on of t h e ne x t co n v ersio n ad7938/ AD7939 80c186 wr d0 to d11 ad0 to ad15 a16 to a19 ale drq 1 us cs qr s convst optional wr rd rd additional pins omitted for clarit address/data us address us data us address latch address decoder 03715- 0- 08 r e v prn pa ge 30 of 32
prelim inary technical data ad7938/AD7939 appli c ation hints grounding and layout the r in ted cir c ui t a r d tha t h us es th e ad79 38/AD7939 sh u ld e desi n e d s t h a t t h e a n a l a nd di i t a l s e c t i n s a r e s e a r a te d and c n in e d t cer t ain a r e a s t h e a r d . this aci li t a t e s t h e us e r u n d lan es t h a t c a n e e a si ly s e a ra t e d . a minim u m et ch t e chniq u e is en e ral l y e s t r r u n d l an es as i t i e s t h e es t s h ie ldin. di i tal and a n al r u n d l an es s h u ld e in e d in n l y n e l ace , an d t h e c nn ec ti n sh u ld e a s t a r r u nd i n t est a l ish e d as cls e t t h e r u n d in s n th e ad7938 /AD7939 as s s ile . a i d r u nnin di i t a l lin e s un der t h e de ic e as t h is wi l l cu le n is e n t t h e die . th e a n a l r u n d lan e sh u ld e a l l w e d t r u n un der t h e ad7938/ad79 39 t a i d n is e c u lin. th e w e r s u l y lin e s t t h e ad7938/AD7939 sh u ld us e as la r e a trace as s s i l e t r ide l w im e dan c e a t h s and r e d u ce t h e e e c t s l i t ch es n t h e w e r s u ly lin e . f a st s w itchin s i n a l s , su ch as c l c s , shu l d e shiel d e d wi t h d i i t a l ru n d t a i d r a d i a t i n ni s e t t he r s e c t i ns t h e a r d , an d c l c si n als sh u ld ne e r r u n n e a r t h e a n al in u ts. a id cr s s er di i t a l a nd a n a l si n a l s. t r aces n si t e sides t h e a r d sh u ld r u n a t r i h t a n l es t e a c h t he r . t h i s w i l l re d u c e t h e e e c t s e e d t h ru h t h ru h t h e a r d . a micr s t r i t e chniq u e i s y a r t h e e s t u t is n t alwa y s s s i l e wi th a d u le - s id ed a r d . i n t h is te chni q u e , t h e cm n e n t side t h e a r d is de dic a t e d t r u n d l an e s , w h i l e si n als a r e lace d n t h e s lder side . g d dec u lin is als im r t a n t. al l a n al s u lies sh u ld e dec u led wi th 10 f tan t al um ca a c i t r s in a rall e l wi th 0.1 f ca a ci t r s t gnd . t ac hie e t h e es t r m th es e dec u lin cm n en ts, t h ey m u s t e lace d as c l s e as s s i l e t t h e de ice , ide a l l y r i h t u a ain s t t h e de ice . th e 0.1 f ca a ci t rs s h u ld ha e lw e e c t i e s e r i es r e sis t a n c e es r a n d e e c t i e ser i es in d u c t a n ce es i , s u c h as t h e c mm n ceramic ty e s r s u r ace- m un t ty e s, w h ich r ide a l w im e d a n c e a t h t r u nd a t hi h r e q uen c ies t hand le t r a n sien t c u r r en ts d u e t i n t e r n al l i c swi t chin. pcb desig n guideline s for chip scale pac age the lan d s n t h e chi s c ale a ca e c p - 32 a r e r e c t a n u la r . the r in te d cir c ui t a r d a d r t h es e sh u ld e 0.1 mm l n e r th a n th e a c a e la n d len th a n d 0. 05 m m w i d e r th a n t h e a ca e land w i d t h. th e l a nd sh u ld e ce n t er e d n t h e a d . this ens u r e s t h a t t h e s lder i n t si e is mai mie d . th e t t m t h e chi s c ale a ca e has a t h er mal a d . the t h er mal a d n t h e r i n t e d cir c ui t a r d sh u ld e a t le as t as l a r e as t h is e s e d a d . o n t h e r in te d ci r c ui t a r d , t h e r e s h u ld e a cle a ra n c e a t l e as t 0.25 mm e tw e e n t h e t h er mal a d and t h e i n n e r ed e s th e ad a t t e r n . t h i s e n s u r e s th a t s h r ti n i s a i de d . th er mal i as ma y e us e d n t h e r in te d cir c ui t a r d t h er mal a d t i m r e t h er mal e r r ma n c e t h e a ca e . i i a s a r e use d , th ey s h u ld e in c r r a t ed in t h e th e r m a l a d a t 1.2 mm i t c h r id . th e i a diamet er s h u ld e etw e e n 0.3 mm a nd 0.33 mm, and the ia a r r el s h u ld e la t ed wi t h 1 . c er t l u t h e i a . the us er s h u ld cnn e c t t h e r in t e d cir c ui t a r d t h er mal a d t a g nd . ealuating the ad7938/AD7939 performa nce the r e c mm ended l a y u t r th e ad7938 /AD7939 is u tlin e d in t h e e a l u a t i n a r d d c u men t a t i n. t h e e a l ua t i n a r d a c a e i n c l ud es a ull y a s sem led a n d t e s t ed eal ua t i n a r d , d c u m e n t a t in, a nd s t wa r e r c n t r l l in t h e a r d r m t h e p c i a t h e e al ua ti n a r d c n t r lle r . t h e e al ua ti n a r d c n t r l l er ca n e us ed in c n u n c t in wi t h the ad7938/ad79 39 eal u a tin a r d , as w e l l as ma n y t h e r adi e a l ua t i n a r ds endin in t h e cb desi n a t r , t dem n s t r a t e / e a l ua te t h e ac and dc e r r ma nce t h e ad7938/ad79 39. the s t wa r e al l ws t h e us er t e r r m ac as t f ur ier t r ans r m and d c h i s t r am c d e s te st s n t h e ad7938/ad79 39. th e s t wa r e a nd d c u m e n t a t i n a r e n t h e c d th a t s h i s wi th t h e e al ua ti n a r d . r e . prn pa e 31 32
ad7938/AD7939 prelim inary technical data outline dimensions compliant to jedec standards mo-220-vhhd-2 0.30 0.23 0.18 0. 2 0 r e f 0. 80 m a x 0.65 typ 0.05 max 0.02 nom 12 max 1.00 0.85 0.80 seating plane coplanarity 0.08 1 32 8 9 25 24 16 17 bottom view 0.50 0.40 0.30 3.50 ref 0.50 bsc 3.25 3.10 sq 2.95 0.60 max 0.60 max 0. 25 m i n top view pin 1 indicator pin 1 indicator 5.00 bsc sq 4.75 bsc sq f i gure 49. 3 2 -l ead l e ad f r a m e ch ip s c a l e p a ck ag e [ l fcs p ] , (c p - 3 2 ) d i m e ns ions s h o w n in m i ll im ete r s 0. 4 5 0. 3 7 0. 3 0 0. 80 bs c 7. 00 sq 9.00 sq 1 24 25 32 8 9 17 16 1. 20 ma x 0.75 0.60 0.45 1.05 1.00 0.95 0.20 0.09 0.08 max coplanarity seating plane 0 min 7 3. 5 0 0.15 0.05 view a rotated 90 ccw view a pin 1 top v ie w (pins down) compliant to jedec standards ms-026aba f i g u re 50. 3 2 -l ead thin plas t i c q u ad flat p a ck ag e [ t qfp ] , (su - 32) d i m ens i ons s h own in mi ll i m et ers ordering guide model temperature range linearity error (lsb) 1 package option package descri ptions ad7938bcp C40c to +85c 1 cp-32 lfcsp AD7939bcp C40c to +85c 1 cp-32 lfcsp ad7938bsu C40c to +85c 1 su-32 tqfp AD7939bsu C40c to +85c 1 su-32 tqfp eval-adxxxxcb 2 evaluation bo ar d eval-control brd2 3 controll er boar d 1 linearity error here re fer s to integral li nearity error. 2 this can be us ed a s a s t and - al one evaluation board or in c o njunctio n wit h th e e v a l uatio n bo ard c o ntro l l e r fo r e v al uatio n /d e m o n stration purpose s . 3 e v al uation board control ler. this board is a comp l e te unit al lowing a pc to control a n d c o m m u n i ca t e wi t h a ll an a l o g d e vi ces ev a l ua t i o n boa r ds en di n g i n t h e cb designators. the fo llowing nee d s to b e orde red to obtain a complete evaluation kit: the adc evaluation board (eval a dxxxxcb), th e eval-control brd2 and a 12 v ac transformer. s e e the adxxxx evaluation board technica l note fo r mor e det ails. ?2004 a n alo g de vices, inc. all rig h ts reserv ed. tra d ema r ks and registered tra d ema r ks are the prop erty of their respective owners . r e v. prn | pa ge 32 of 32

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