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precision instrumentation amplifier ad8221 rev. a information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent ri ghts of analog devices. trademarks and registered trademarks are the prop erty of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781.329.4700 www.analog.com fax: 781.326.8703 ? 2003 analog devices, inc. all rights reserved. features available in space-saving msop package gain set with 1 external resistor (gain range 1 to 1000) wide power supply range: 2.3 v to 18 v temperature range for specified performance: C40c to +85c operational up to 125c 1 excellent ac specificatons 80 db min cmrr to 10 khz ( g = 1) 825 khz C3 db bandwidth (g = 1) 2 v/s slew rate low noise 8 nv/hz, @ 1 khz, max input voltage noise 0.25 v p-p input noise (0.1 hz to 10 hz) high accuracy dc performance (ad8221br) 90 db min cmrr (g = 1) 25 v max input offset voltage 0.3 v/c max input offset drift 0.4 na max input bias current applications weigh scales industrial process controls bridge amplifiers precision data acquisition systems medical instrumentation strain gages transducer interfaces general description the ad8221 is a gain programmable, high performance instru- mentation amplifier that delivers the industrys highest cmrr over frequency. the cmrr of instrumentation amplifiers on the market today falls off at 200 hz. in contrast, the ad8221 maintains a minimum cmrr of 80 db to 10 khz for all grades at g = 1. high cmrr over frequency allows the ad8221 to reject wideband interference and line harmonics, greatly simplifying filter requirements. possible applications include precision data acquisition, biomedical analysis, and aerospace instrumentation. low voltage offset, low offset drift, low gain drift, high gain accuracy, and high cmrr make this part an excellent choice in applications that demand the best dc performance possible, such as bridge signal conditioning. connection diagram 8 7 6 5 1 2 3 4 ?in r g r g +v s v out ref ?v s + in top view ad8221 03149-0-001 figure 1. soic and msop connection diagram 40 50 60 70 80 90 cmrr (db) 100 110 120 frequency (hz) 100 10 1k 10k 100k 03149-0-002 ad8221 competitor 1 competitor 2 figure 2. typical cmrr vs. frequency for g = 1 programmable gain affords the user design flexibility. a single resistor sets the gain from 1 to 1000. the ad8221 operates on both single and dual supplies, and is well suited for applications where 10 v input voltages are encountered. the ad8221 is available in low cost 8-lead soic and msop packages, both of which offer the industrys best performance. the msop requires half the board space of the soic, making it ideal for multichannel or space-constrained applications. performance is specified over the entire industrial temperature range of C40c to +85c for all grades. furthermore, the ad8221 is operational from C40c to +125c 1 . 1 see typical performance curves for expected oper ation from 85c to 125c.
ad8221 rev. a | page 2 of 20 table of contents specifications..................................................................................... 3 absolute maximum ratings............................................................ 5 esd caution.................................................................................. 5 typical performance characteristics ............................................. 6 theory of operation ...................................................................... 13 gain selection ............................................................................. 14 layout........................................................................................... 14 reference terminal .................................................................... 15 power supply regulation and bypassing ................................ 15 input bias current return path................................................ 15 input protection ......................................................................... 15 rf interference ........................................................................... 16 precision strain gage................................................................. 16 conditioning 10 v signals for a +5 v differential input adc ............................................................................................. 17 ac-coupled instrumentation amplifier ................................ 17 outline dimensions ....................................................................... 18 ordering guide .......................................................................... 18 revision history revision a 11/03data sheet changed from rev. 0 to rev. a change page changes to features...............................................................................1 changes to specifications section .......................................................4 change to theory of operation section...........................................13 change to gain selection section......................................................14
ad8221 rev. a | page 3 of 20 specifications table 1. v s = 15 v, v ref = 0 v, t a = +25c, g = 1, r l = 2 k, unless otherwise noted ar grade br grade arm grade parameter conditions min typ ma x min typ max min typ max unit common-mode rejection ratio (cmrr) cmrr dc to 60 hz with 1 k? source imbalance v cm = C10 v to +10 v g = 1 80 90 80 db g = 10 100 110 100 db g = 100 120 130 120 db g = 1000 130 140 130 db cmrr at 10 khz v cm = C10 v to +10 v g = 1 80 80 80 db g = 10 90 100 90 db g = 100 100 110 100 db g = 1000 100 110 100 db noise rti noise = e ni 2 + (e no /g) 2 voltage noise, 1 khz input voltage noise, e ni v in+ , v inC , v ref = 0 8 8 8 nv/hz output voltage noise, e no 75 75 75 nv/hz rti f = 0.1 hz to 10 hz g = 1 2 2 2 v p-p g = 10 0.5 0.5 0.5 v p-p g = 100 to 1000 0.25 0.25 0.25 v p-p current noise f = 1 khz 40 40 40 fa/hz f = 0.1 hz to 10 hz 6 6 6 pa p-p voltage offset 1 input offset, v osi v s = 5 v to 15 v 60 25 70 v over temperature t = C40c to +85c 86 45 135 v average tc 0.4 0.3 0.9 v/c output offset, v oso v s = 5 v to 15 v 300 200 600 v over temperature t = C40c to +85c 0.66 0.45 1.00 mv average tc 6 5 9 v/c offset rti vs. supply (psr) v s = 2.3 v to 18 v g = 1 90 110 94 110 90 100 db g = 10 110 120 114 130 100 120 db g = 100 124 130 130 140 120 140 db g = 1000 130 140 140 150 120 140 db input current input bias current 0.5 1.5 0.2 0.4 0.5 2 na over temperature t = C40c to +85c 2.0 1 3 na average tc 1 1 3 pa/c input offset current 0.2 0.6 0.1 0.4 0.3 1 na over temperature t = C40c to +85c 0.8 0.6 1.5 na average tc 1 1 3 pa/c reference input r in 20 20 20 k? i in v in+ , v inC , v ref = 0 50 60 50 60 50 60 a voltage range Cv s +v s Cv s +v s Cv s +v s v gain to output 1 0.0001 1 0.0001 1 0.0001 v/v power supply operating range v s = 2.3 v to 18 v 2.3 18 2.3 18 2.3 18 v quiescent current 0.9 1 0.9 1 0.9 1 ma over temperature t = C40c to +85c 1 1.2 1 1.2 1 1.2 ma
ad8221 rev. a | page 4 of 20 ar grade br grade arm grade parameter conditions min typ max min typ max min typ max unit dynamic response small signal C3 db bandwidth g = 1 825 825 825 khz g = 10 562 562 562 khz g = 100 100 100 100 khz g = 1000 14.7 14.7 14.7 khz settling time 0.01% 10 v step g = 1 to 100 10 10 10 s g = 1000 80 80 80 s settling time 0.001% 10 v step g = 1 to 100 13 13 13 s g = 1000 110 110 110 s slew rate g = 1 1.5 2 1.5 2 1.5 2 v/s g = 5C100 2 2.5 2 2.5 2 2.5 v/s gain g = 1 + (49.4 k?/r g ) gain range 1 1000 1 1000 1 1000 v/v gain error v out 10 v g = 1 0.03 0.02 0.1 % g = 10 0.3 0.15 0.3 % g = 100 0.3 0.15 0.3 % g = 1000 0.3 0.15 0.3 % gain nonlinearity v out = C10 v to +10 v g = 1 to 10 r l = 10 k? 3 10 3 10 5 15 ppm g = 100 r l = 10 k? 5 15 5 15 7 20 ppm g = 1000 r l = 10 k? 10 40 10 40 10 50 ppm g = 1 to 100 r l = 2 k? 10 95 10 95 15 100 ppm gain vs. temperature g = 1 3 10 2 5 3 10 ppm/c g > 1 2 C50 C50 C50 ppm/c input input impedance differential 100||2 100||2 100||2 g?||pf common mode 100||2 100||2 100||2 g?||pf input operating voltage range 3 v s = 2.3 v to 5 v Cv s + 1.9 +v s C 1.1 Cv s + 1.9 +v s C 1.1 Cv s + 1.9 +v s C 1.1 v over temperature t = C40c to +85c Cv s + 2.0 +v s C 1.2 Cv s + 2.0 +v s C 1.2 Cv s + 2.0 +v s C 1.2 v input operating voltage range v s = 5 v to 18 v Cv s + 1.9 +v s C 1.2 Cv s + 1.9 +v s C 1.2 Cv s + 1.9 +v s C 1.2 v over temperature t = C40c to +85c Cv s + 2.0 +v s C 1.2 Cv s + 2.0 +v s C 1.2 Cv s + 2.0 +v s C 1.2 v output r l = 10 k? output swing v s = 2.3 v to 5 v Cv s + 1.1 +v s C 1.2 Cv s + 1.1 +v s C 1.2 Cv s + 1.1 +v s C 1.2 v over temperature t = C40c to +85c Cv s + 1.4 +vs C 1.3 Cv s + 1.4 +vs C 1.3 Cv s + 1.4 +vs C 1.3 v output swing v s = 5 v to 18 v Cv s + 1.2 +v s C 1.4 Cv s + 1.2 +v s C 1.4 Cv s + 1.2 +v s C 1.4 v over temperature t = C40c to +85c Cv s + 1.6 +v s C 1.5 Cv s + 1.6 +v s C 1.5 Cv s + 1.6 +v s C 1.5 v short-circuit current 18 18 18 ma temperature range specified performance C40 +85 C40 +85 C40 +85 c operational 4 C40 +125 C40 +125 C40 +125 c 1 total rti v os = (v osi ) + (v oso /g). 2 does not include the effects of external resistor r g . 3 one input grounded. g = 1. 4 see typical performance curves for expe cted operation between 85c to 125c.
ad8221 r e v. a | pa ge 5 o f 2 0 absolute maximum ratings table 2. ad82 21 absolute maximum ratings p a r a m e t e r r a t i n g supply voltage 18 v internal power dissipation 200 mw output short ci rcuit current indefinite input vol t age (c ommon-mode) v s differential input voltage vs storage temperature C65c to +150c operational* te mperature range C40c to +125c *temperature rang e for specifi e d perfor mance is C40c to +85c. see typica l per f ormance curves for expected oper ation fr om +85c t o +125c. s t r e s s es a b o v e t h os e lis t e d u n de r a b s o l u t e m a xi m u m r a t i n g s ma y c a us e p e r m a n en t dama ge t o t h e de vice . this is a s t r e s s ra t i n g onl y ; f u n c t i o n al o p era t ion o f t h e de vice a t t h es e o r an y o t h e r con d i t io ns a b o v e t h o s e i ndic a te d i n t h e op er a t io na l s e c t io n o f t h is sp e c if ic a t io n is no t im plie d . e x p o sur e t o a b s o l u te max i m u m r a t i ng co ndi t i on s m a y a f fe c t de vic e r e liab i l i t y . s p e c if ic a t io n is fo r de vic e in f r e e a i r : so i c ja (4 l a yer jed e c b o a r d) = 121c/w. mso p ja (4 l a yer jed e c b o a r d) = 135c/w. esd caution esd (electrostatic discharge) sensitive device. ele c trostatic charg e s as high as 4000 v readily accumu- late on the human body and test eq uipment and ca n discharge without detecti o n. although this product feature s propri e tary esd protection cir c uitry, permanent damage may occur on devices subjected to high energy electro s tatic discharg e s . therefore, pro p er esd precautions are re com- mended to avoid performance degradation or l o ss of functiona l ity.
ad8221 r e v. a | pa ge 6 o f 2 0 typical perf orm ance cha r acte ristics (@+25c, v s = 15 v, r l = 10 k?, un less otherw i se not ed.) 0 200 400 600 800 1000 units 1200 1400 1600 0 ?5 0 ?1 00 ? 150 5 0 10 0 150 cmr ( v/v) 03149-0-003 figure 3. typic a l d i s t ributio n fo r cmr (g = 1) 0 300 600 900 1200 1500 units 1800 2100 2400 0 ?2 0 ?4 0 ? 6 0 2 04 06 0 input offset voltage ( v) 03149-0-004 figure 4. typic a l d i s t ributi o n of i n put of f s et v o lt ag e 0 500 1000 1500 2000 2500 3000 units 0 ?0 . 5 ?1 . 0 ? 1 .5 0 . 5 1 .0 1 . 5 input bias current (na) 03149-0-005 figure 5. typic a l d i s t ributi o n of i n put bias cu rr ent 0 500 1000 1500 2000 2500 3000 3500 units 0 ?0 . 3 ?0 . 6 ? 0 . 9 0. 3 0 . 6 0. 9 input offset current (na) 03149-0-006 figure 6. typic a l d i s t ributio n of i n put offs et current ?1 5 ?1 0 ?5 0 5 10 15 inp u t common-mode v o ltage (v ) ?5 0 ?15 ? 10 5 1 0 1 5 output voltage (v) 03149-0-007 v s = 5v v s = 15v fig u re 7. input c o mm on-m ode r a ng e v s . out p ut v o lt ag e, g = 1 ?1 5 ?1 0 ?5 0 5 10 15 inp u t common-mode v o ltage (v ) ?5 0 ? 1 5 ? 10 5 1 0 1 5 output voltage (v) 03149-0-008 v s = 5v v s = 15v fig u re 8. input c o mm on-m ode r a ng e v s . out p ut v o lt ag e, g = 1 0 0
ad8221 r e v. a | pa ge 7 o f 2 0 0.40 0.45 0.50 0.55 0.60 0.65 inp u t bias curre nt (na) 0.70 0.75 0.80 ?5 0 ? 1 5 ? 10 5 1 0 1 5 common-mode voltage (v) 03149-0-009 v s = 5v v s = 15v figure 9. i bi as vs. cmv 0 0.25 0.50 0.75 1.00 1.25 change in inp u t offs e t v o ltage ( v) 1.50 1.75 2.00 0.1 0.01 1 1 0 warm-up time (min) 03149-0-010 fi gure 10 . ch a n ge in input o ffset volt age v s . w a r m -up t i m e ?5.0 ?4.0 ?3.0 ?2.0 ?1.0 0 1.0 2.0 3.0 4.0 5.0 inp u t curre nt (na) ? 4 0 ? 20 0 2 0 4 0 6 0 8 0 100 120 140 temperature ( c) 03149-0-011 input bias current v s = 15v input offset current figure 1 1 . inp u t bi a s curre nt and offs et curre nt v s . te mpe r atur e 20 40 60 80 100 120 p s rr (db) 140 160 180 0.1 1 1 0 100 1k 10k 100k 1m frequency (hz) 03149-0-012 gain = 1 gain = 10 gain = 100 gain = 1000 gain = 1000 fig u re 1 2 . pos it iv e psr r v s . frequ e ncy , r t i (g = 1 t o 10 00) 20 40 60 80 100 120 p s rr (db) 140 160 180 0.1 1 1 0 100 1k 10k 100k 1m frequency (hz) 03149-0-013 gain = 1 gain = 10 gain = 100 gain = 1000 fi gur e 13 . ne ga t i ve p s rr vs. fr e q ue ncy, rti (g = 1 t o 1000 ) total drift 25 c? 8 5 c rti ( v) 10 100 1k 10k 100k 1k 10k 10 100 100k 1m 10m source resistance ( ? ) 03149-0-014 best available fet input in-amp gain = 1 best available fet input in-amp gain = 1000 ad8221 gain = 1 ad8221 gain = 1000 fi gure 14 . to tal drift vs. so urce resi stance
ad8221 r e v. a | pa ge 8 o f 2 0 ?3 0 ?2 0 ?1 0 0 10 20 30 40 50 60 70 100 1k 10k 100k 1m 10m frequency (hz) gain ( d b) 03149-0-015 gain = 1000 gain = 100 gain = 10 gain = 1 figure 15. g a in vs. freque ncy 40 60 80 100 cmrr (db) 120 140 160 0.1 1 1 0 100 1k 10k 100k 1m frequency (hz) 03149-0-016 gain = 1000 gain = 1000 gain = 100 gain = 100 gain = 10 gain = 10 gain = 1 fi gur e 16 . cmrr vs. fr e q ue nc y, rti 40 60 80 100 cmrr (db) 120 140 160 0.1 1 1 0 100 1k 10k 100k 1m frequency (hz) 03149-0-017 gain = 1000 gain = 1000 gain = 100 gain = 100 gain = 10 gain = 10 gain = 1 figure 1 7 . cmr r v s . frequ e ncy, r t i, 1 k? s o ur ce i m b a l a nc e ? 100 ?80 ?60 ?40 ?20 0 20 40 60 80 100 cmr ( v/v) ?40 ? 20 0 2 0 4 0 6 0 8 0 100 120 140 temperature ( c) 03149-0-041 figure 18. cmr vs. temp er ature ?v s +0.0 +0.4 +0.8 +1.2 +1.6 +2.0 +2.4 ?1.6 ?2.0 ?2.4 ?1.2 ?0.8 ?0.4 +v s ?0.0 input voltage limit (v) r e fer r e d to su pply volta ges supply voltage (v) 5 01 0 1 5 03149-0-018 2 0 fig u re 1 9 . inp u t v o lt ag e l i mit v s . sup p ly v o lt ag e, g = 1 ?v s +0.0 +0.4 +0.8 +1.2 +1.6 +2.0 ?1.6 ?2.0 ?1.2 ?0.8 ?0.4 +v s ?0.0 output voltage sw ing (v) r e fer r e d to su pply volta ges supply voltage (v) 5 01 0 1 5 03149-0-019 2 0 r l = 10k ? r l = 2k ? r l = 10k ? r l = 2k ? fig u re 2 0 . out p ut v o lt ag e sw ing v s . su pply v o lt ag e, g = 1
ad8221 r e v. a | pa ge 9 o f 2 0 output voltage sw ing (v p-p) 0 20 10 30 load resistance ( ? ) 10 1 100 1k 10k 03149-0-020 v s = 15v fig u re 2 1 . out p ut v o lt ag e sw ing v s . l o ad r e s i s t an ce ?v s +0 +1 +2 +3 ?3 ?2 ?1 +v s ?0 output voltage sw ing ( v ) re fe rre d to s u p p l y v o ltage s 0123456789 1 0 1 1 1 2 output current (ma) 03149-0-021 sourcing sinking figure 2 2 . output v o ltag e sw ing v s . o u tput current, g = 1 ? 1 0 ? 8? 6? 4? 2 0 2 4 6 8 1 0 v s = 15v 03149-0-022 e rror (1 ppm/div ) output voltage (v) figure 2 3 . g a i n n o nlin ea rity, g = 1, r l = 1 0 k ? v s = 15v 03149-0-023 ? 1 0 ? 8? 6? 4? 2 0 2 4 6 8 1 0 e r ror (1 0 p pm/div ) output voltage (v) figure 2 4 . g a i n n o nlin ea rity, g = 1 00, r l = 1 0 k? v s = 15v 03149-0-024 ? 1 0 ? 8? 6? 4? 2 0 2 4 6 8 1 0 er r o r ( 100ppm/d iv) output voltage (v) fi gur e 25 . ga in nonl i n e a r i ty, g = 10 00 , r l = 1 0 k? volta ge n o ise r t i ( n v/ h z ) 1 100 10 1k 1 1 0 100 1k 10k 100k frequency (hz) 03149-0-025 gain = 1 gain = 1000 bw limit gain = 10 gain = 100 gain = 1000 fig u re 2 6 . v o lt ag e nois e spe c t r a l d e n s it y v s . frequen c y ( g = 1 t o 1 0 0 0 )
ad8221 rev. a | page 10 of 20 1s/div 2 v/div 03149-0-026 fig u re 2 7 . 0.1 h z t o 10 h z r t i v o lt ag e nois e (g = 1) 1s/div 0.1 v/div 03149-0-027 fi gur e 28 . 0 . 1 hz to 1 0 hz rti v o l t a g e no i s e (g = 10 00 ) curre nt nois e (fa/ hz) 10 100 1k frequency (hz) 10 1 100 1k 10k 03149-0-028 figure 2 9 . cu rre nt nois e spe c tra l d e n s ity v s . frequen c y 1s/div 5pa/div 03149-0-029 figure 3 0 . 0.1 h z to 10 h z cur r ent no is e 0 5 10 15 20 25 30 output voltage (v p-p) frequency (hz) 1k 100k 10k 1m 03149-0-030 gain = 1 gain = 10, 100, 1000 v s = 15v figure 3 1 . l a rge si gnal f r equ e ncy r e s p ons e 20 s/div 10mv/div 7.9 s to 0.01% 8.5 s to 0.001% 5v/div 03149-0-031 fig u re 3 2 . l a rg e si g n al pu ls e r e s p ons e and set t l ing t i me (g = 1), 0.0 0 2 %/d i v
ad8221 rev. a | page 11 of 20 20 s/div 10mv/div 4.9 s to 0.01% 5.6 s to 0.001% 5v/div 03149-0-032 fig u re 3 3 . l a rg e si g n al pu ls e r e s p ons e and set t l ing t i me (g = 10), 0 . 002 %/ di v 20 s/div 10mv/div 10.3 s to 0.01% 13.4 s to 0.001% 5v/div 03149-0-033 fig u re 3 4 . l a rg e si g n al pu ls e r e s p ons e and set t l ing t i me (g = 10 0), 0 . 002 %/ di v 20 s/div 10mv/div 83 s to 0.01% 112 s to 0.001% 5v/div 03149-0-034 fig u re 3 5 . l a rg e si g n al pu ls e r e s p ons e and set t l ing t i me (g = 10 0 0 ), 0 . 002 %/ di v 4 s/div 20mv/div 03149-0-035 fig u re 3 6 . s m al l s i g n al r e s p ons e , g = 1, r l = 2 k? , c l = 1 00 pf 4 s/div 20mv/div 03149-0-036 fig u re 3 7 . s m al l s i g n al r e s p ons e , g = 10 , r l = 2 k ? , c l = 10 0 pf 10 s/div 20mv/div 03149-0-037 fig u re 3 8 . s m al l s i g n al r e s p ons e , g = 10 0, r l = 2 k ? , c l = 10 0 pf
ad8221 rev. a | page 12 of 20 2 100 s/div 20mv/div 03149-0-038 fig u re 3 9 . s m al l s i g n al r e s p ons e , g = 10 0 0 , r l = 2 k ? , c l = 100 pf settling time ( s) 0 10 5 15 output voltage step size (v) 5 01 0 1 5 03149-0-039 2 0 settled to 0.01% settled to 0.001% figure 40. s e ttling time vs. step siz e ( g = 1) settling time ( s) 1 100 10 1k gain 1 100 10 1k 03149-0-040 settled to 0.001% settled to 0.01% fig u re 4 1 . s e t t ling tim e v s . g a in f o r a 10 v st ep
ad8221 rev. a | page 13 of 20 theory of operation c1 c2 +v s +v s +in ?in ?v s ?v s 10k ? 10k ? 10k ? 400 ? 400 ? 10k ? ref output i b compensation i b compensation +v s ?v s +v s ?v s +v s v b ii r1 24.7k ? 24.7k ? r g q1 r2 q2 ?v s +v s ?v s a2 a1 a3 03149-0-042 figure 42. simpli fied schematic the ad8221 is a monolithic instrumentation amplifier based on the classic 3-op amp topology. input transistors q1 and q2 are biased at a fixed current, so that any differential input signal will force the output voltages of a1 and a2 to change accor- dingly. a signal applied to the input creates a current through r g , r1, and r2, such that the outputs of a1 and a2 deliver the correct voltage. topologically, q1, a1, r1 and q2, a2, r2 can be viewed as precision current feedback amplifiers. the amplified differential and common-mode signals are applied to a dif- ference amplifier that rejects the common-mode voltage but amplifies the differential voltage. the difference amplifier employs innovations that result in low output offset voltage as well as low output offset voltage drift. laser-trimmed resistors allow for a highly accurate in-amp with gain error typically less than 20 ppm and cmrr that exceeds 90 db (g = 1). using superbeta input transistors and an i b compensation scheme, the ad8221 offers extremely high input impedance, low i b , low i b drift, low i os , low input bias current noise, and extremely low voltage noise of 8 nv/hz. the transfer function of the ad8221 is g r g k 4 . 49 1 + = users can easily and accurately set the gain using a single, standard resistor. since the input amplifiers employ a current feedback architec- ture, the ad8221s gain-bandwidth product increases with gain, resulting in a system that does not suffer from the expected bandwidth loss of voltage feedback architectures at higher gains. in order to maintain precision even at low input levels, special attention was given to the ad8221s design and layout, resulting in an in-amp whose performance satisfies the most demanding applications. a unique pinout enables the ad8221 to meet a cmrr specification of 80 db at 10 khz (g = 1) and 110 db at 1 khz (g = 1000). the balanced pinout, shown in figure 43, reduces the parasitics that had, in the past, adversely affected cmrr performance. in addition, the new pinout simplifies board layout because associated traces are grouped together. for example, the gain setting resistor pins are adjacent to the inputs, and the reference pin is next to the output. 8 7 6 5 1 2 3 4 ?in r g r g +v s v out ref ?v s + in top view ad8221 03149-0-001 figure 43. pinout diagram
ad8221 rev. a | page 14 of 20 gain selec t io n placin g a r e sistor acr o ss t h e r g ter m inals wil l s e t th e ad8221 s ga in, which ma y b e ca lc u l a t e d b y r e ferr in g t o t a b l e 3 o r b y usin g t h e ga in e q ua t i o n 1 k 4 . 49 ? = g r g tab l e 3. gain s achiev ed using 1% resistors 1% std t a ble v a lue of r g (?) calculate d g a i n 49.9 k 1.990 12.4 k 4.984 5.49 k 9.998 2.61 k 19.93 1.00 k 50.40 4 9 9 1 0 0 . 0 2 4 9 1 9 9 . 4 1 0 0 4 9 5 . 0 4 9 . 9 9 9 1 . 0 the ad8221 defa u l ts t o g = 1 when n o ga in r e sis t o r is us ed . ga in acc u rac y is det e r m i n e d b y t h e a b s o l u t e t o lera n c e o f r g . t h e tc of t h e e x te r n a l g a i n re s i stor w i l l i n c r e a s e t h e g a i n d r i f t o f t h e inst r u m e n t a t io n am plif ie r . ga in er r o r a n d ga in dr if t a r e k e p t t o a min i m u m w h en the gain r e sis t o r is n o t used . layout c a r e f u l b o ar d l a yo u t max i mi zes sy stem p e r f o r manc e. t r ac es f r o m t h e ga in s e t t in g r e sis t o r t o t h e r g pi ns s h o u l d b e ke pt a s sho r t as p o ssibl e to mini mi ze p a r a si t i c i n d u c t anc e . t o ensur e t h e m o st acc u ra t e o u t p u t , t h e t r ace f r o m t h e re f p i n sh o u ld ei ther be co nn e c t e d t o t h e ad8 221 s lo cal g r o u nd as sh o w n in f i gur e 47, o r co n n ec t e d t o a v o l t a g e tha t is r e f e r e n c e d t o t h e ad8221 s lo cal g r o u n d . common-mo d e rejection on e ben e f i t o f th e ad8221 s hig h cmrr o v er f r eq uen c y is tha t it h a s g r e a te r i m m u n i t y to d i s t u r b a nc e s su ch a s l i ne noi s e a n d i t s as s o c i a t ed har m o n ics t h an do typ i cal in-a m p s. th es e , typ i cal l y , ha v e cmrr fal l -o f f a t 200 h z ; co mm on-m o d e f i l t ers a r e o f t e n us e d to co m p en s a te fo r this s h o r t c om ing. th e ad8 221 is a b le t o r e j e c t cmrr o v er a g r e a t e r f r e q uen c y ra n g e , r e d u cing t h e n e e d fo r f i l t er in g. a w e l l im p l em en t e d l a yo u t he l p s t o m a in ta in the ad8221 s hig h cmrr o v er f r e q uen c y . i n p u t s o ur ce im p e dan c e a n d c a p a c i t a nce sh o u ld b e clo s ely ma tch e d . i n a ddi t i on, s o ur ce r e sist a n c e an d ca p a c i t a n c e sh ou ld b e place d as clos e t o t h e i n pu ts as pe rm i s s i b l e . grou nd ing the ad8221 s ou t p u t v o l t a g e is deve lo p e d wi th r e s p ec t t o t h e p o te n t i a l o n t h e re f e re nc e te r m i n a l . c a re shou l d b e t a k e n to t i e r e f t o t h e ap p r o p r i at e l o c a l g r o u n d . i n mi x e d - si gn al en v i r o nm en ts, lo w lev e l a n alog si gn als n e e d t o b e is ol a t e d f r o m t h e n o isy dig i t a l en vir o nm e n t. m a n y ad cs h a v e se pa ra t e a n al og a n d d i gi tal gr o u n d p i n s . al th o u gh i t i s co n v en ien t t o tie bo t h gr o u n d s t o a sin g le gr o u n d p l an e , t h e cu rr e n t tra v e l i n g th r o u g h th e g r o u n d w i r e s a n d p c boa r d ma y ca us e h u n d r e ds o f mi l l i v ol ts o f er r o r . th er efo r e , s e p a ra t e analog a n d d i g i tal gr o u n d r e t u r n s sh o u ld be use d t o min i m i ze t h e c u r r en t f l o w f r o m s e n s i t i v e p o i n ts t o t h e syste m g r o u nd . an exa m p l e l a yo u t is s h own in f i g u r e 44 a n d f i gu r e 45. 03149-0-051 figure 4 4 .t op lay e r of th e a d 8 2 21-e v a l 03149-0-052 fi gur e 45 .bo tto m la ye r o f the ad82 21-eval
ad8221 rev. a | page 15 of 20 reference terminal a s sh o w n in f i gur e 42, th e r e f e r e n c e t e r m in al , ref , is a t o n e en d of a 1 0 k re s i stor . t h e i n st r u m e n t a t i o n am pl i f i e r s output i s r e fer e n c e d t o t h e v o l t a g e on t h e ref t e r m ina l ; t h is is us ef u l when t h e o u t p u t sig n al ne e d s t o b e o f fs et t o a p r e c is e midsu p ply lev e l . f o r exa m ple , a v o l t a g e s o u r ce ca n be t i ed to th e ref p i n to lev e l-s h if t t h e o u t p u t s o tha t t h e ad8221 can in t e r f ace wi t h an ad c. th e al lo wa b l e r e fer e n c e vol t a g e ra n g e is a f u n c t i on o f t h e g a i n , i n put a n d s u pp l y vo lt ag e. t h e r e f pi n s h ou l d not e x c e e d ei t h er +v s or C v s b y m o r e than 0.5 v . f o r be s t pe rf o r m a n c e , so u r c e im ped a n c e t o th e r e f t e rm i n al s h o u ld b e k e p t l o w , sin c e p a ras i t i c r e sis t a n c e can ad v e rs e l y a f f e c t cmrr and ga i n acc u rac y . power supply regulation and b y pass ing a st abl e d c volt age s h ou l d b e u s e d to p o we r t h e i n st r u me n t a - t i o n am plif ier . n o is e on t h e sup p ly p i n s ma y ad v e rs e l y a f fe c t p e r f o r m a n c e . b y p a s s ca p a c i t o rs s h o u ld be us e d t o deco u p le t h e a m plif ier . a 0.1 f ca p a c i to r s h o u ld be placed c l os e t o each s u p p l y p i n. a s s h own in f i gur e 47, a 10 f ta n t al um c a p a ci t o r m a y b e us ed f u r t h e r a w a y f r o m the p a r t . i n m o s t cases, i t ma y be s h a r ed b y o t h e r p r e c isio n in teg r a t e d cir c u i ts. figure 46 ad8221 +v s +in ?in load ref 0.1 f 10 f 0.1 f 10 f ?v s v out 03149-0-043 figure 4 7 . supp ly d eco upl i ng,. r e f a n d output r e ferr ed t o lo ca l g r ou nd input bias current return path the ad8221 s in p u t b i as c u r r en t m u st ha ve a ret u r n p a t h t o co mm o n . w h en th e s o ur ce , s u ch as a t h er m o co u p le , ca nn o t prov i d e a re tu r n c u r r e n t p a t h , one shou l d b e c r e a te d, a s s h ow n in f i gur e 48. +v s ref transformer thermocouple ?v s ad8221 +v s ref ?v s ad8221 capacitor coupled +v s ref c r r c ?v s ad8221 1 f high-pass = 2 rc 03149-0-044 figure 48. c r eating an i bias pa th inpu t pro t ectio n al l t e r m inals o f th e ad8221 a r e p r o t ec t e d a g ain s t es d 1 . i n addi t i o n , t h e i n p u t st r u c t ur e al lo ws fo r dc o v er lo ad co ndi t io n s be lo w t h e n e g a t i v e s u p p l y , Cvs. the in t e r n al 40 0 ? r e sis t o r s limi t c u r r en t i n t h e e v e n t o f a nega t i ve fa u l t con d i t ion. h o w e ver , in t h e c a s e o f a dc o v erlo ad v o l t a g e ab o v e t h e p o si t i v e su p p ly , +vs, a la rg e c u r r en t w o u l d f l o w dir e c t ly t h r o ug h t h e es d dio d e t o t h e p o si t i v e r a i l . th er efo r e , a n ext e r n al r e sist o r sh o u ld b e us e d in s e r i es wi t h t h e i n p u t t o limi t c u r r en t fo r v o l t a g es ab o v e +vs. i n ei t h er s c ena r io , th e ad8221 ca n s a fe l y ha ndle a co n t in uo us 6 ma c u r r en t, i = v in /r ext for p o s i t i ve ove r volt age an d i = v in /(40 0 ? + r ext ) f o r n e ga ti ve o v er v o l t a g e . f o r a p p l ica t ion s wher e the ad8 221 en co u n t e rs extr em e o v erlo ad v o l t a g es, as in c a r d i a c def i b r i l l a t o rs, ext e r n al s e r i es r e sis t o r s a n d lo w leaka g e dio d e c l a m ps s u ch as b a v199ls, fjh1100s, o r s p 720s s h o u ld b e us ed . 1 1 k v hum a n bo d y m o de l.
ad8221 rev. a | page 16 of 20 rf interference rf r e c t if ica t ion is o f t e n a p r ob le m w h e n am plif i e rs a r e us e d in a p plic a t ion s w h er e t h er e a r e st ro n g rf sig n als. the dist urb a n c e m a y a p pea r a s a sm all d c o f fset v o l t a g e . h i gh f r eq uen c y si gn als ca n be f i l t er ed wi t h a lo w-p a s s r - c n e tw o r k pl aced a t t h e in p u t o f t h e inst r u m e n t a t io n am plif ie r , as sh o w n i n f i gur e 49. th e f i l t e r li m i ts th e in p u t s i gn al ba n d wi d t h a cco r d in g t o th e f o ll o w i n g r e la tio n s h i p : c d a f fe c t s t h e di f f er en ce sig n al and c c af fe c t s t h e c o m m on - m o de sign al . v a l u es o f r a n d c c s h o u ld be ch o s en t o minimize rfi. m i sma t ch b e tw e e n t h e r c c a t th e po s i t i v e i n p u t a n d th e r c c a t nega tiv e in p u t wil l deg r ade th e ad82 21 s cmrr . b y usin g a val u e o f c d o n e ma g n i t u d e la rg er t h a n c c , t h e ef fe c t o f t h e misma t ch is r e d u ce d , and hen c e , p e r f o r ma n c e is im p r o v e d . precisio n s t rain ga ge ) 2 ( 2 1 c d diff c c r filterfreq + = the ad8221 s l o w o f fs et a n d hig h cmrr o v er f r eq uen c y m a k e i t an exce l l en t c a ndi d a t e fo r b r idg e m e asur e m e n ts. a s sh o w n i n f i gur e 50, th e b r id g e ca n b e d i r e c t l y co n n ec t e d t o th e in p u ts o f t h e am plif ier . c cm r c filterfreq 2 1 = +5v +2.5v 03149-0-049 10 f 0.1 f ad8221 +in ?i n r 350 ? 350 ? 350 ? 350 ? + ? wher e c d 10 c c . r r ad8221 +15v +in ?in 0.1 f 10 f 10 f 0.1 f ref v out ?15v r1 499 ? c d c c c c 10nf 1nf 1nf 03149-0-045 4.02k ? 4.02k ? figure 5 0 . pr ecis i o n stra in g a ge figure 4 9 . r f i supp res s i o n
ad8221 rev. a | page 17 of 20 +12v +in ?in 0.1 f 10 f 0.1 f 10 f ?12v r3 1k ? +2.5v r4 1k ? ref r5 499 ? r2 10k ? r1 10k ? c1 470pf +12v 0.1 f 0.1 f ? 12v +12v +5v +5v 0.1 f 10nf 0.1 f ?12v +12v 0.1 f 0.1 f ?12v r6 27.4 ? r7 27.4 ? c2 220 f 10 f 0.1 f2 2 f +5v 2.5v 220nf 10nf ad8221 ad8022 op27 ad8022 ad7723 v in+ av dd agnd vgnd ref1 ref2 dv dd v in? ad780 gnd v in v out 03149-0-047 (? ) (? ) figure 5 1 . int e rfa c i n g to a d i fferent ia l input a d c conditioni ng 10 v si gnals for a +5 v differential input adc ther e is a n e e d in man y a p plic a t io n s t o con d i t i o n 10 v sig n als. h o we ve r , m a n y of to d a y s a d c s an d d i g i t a l i c s op e r a t e on m u c h lo w e r , sin g le-s u p p l y v o l t ag es. f u r t h e r m o r e , new ad cs ha v e dif f er en t i al in p u t s b e c a us e t h e y p r o v ide b e t t er co mm on- m o de r e j e c t ion, n o is e imm u ni ty , a n d p e r f o r ma nce a t lo w su p p ly v o l t a g es. i n ter f acin g a 10 v , sing le-en d e d in st r u m e n t a t io n a m plif ier t o a + 5 v , dif f er en t i a l ad c ma y b e a cha l len g e . i n t e r f aci n g t h e i n -am p t o t h e ad c r e q u ir es a t ten u a t ion an d a lev e l shif t. a s o l u tio n is sh o w n in f i gur e 51. i n this t o p o log y , a n o p 27 s e ts t h e ad8221 s r e fer e n c e v o l t a g e . the i n -am p s o u t p u t sig n al is t a k e n acr o ss t h e o u t pin and t h e ref p i n. t w o 1 k r e sis t o r s a n d a 499 r e sis t o r a t ten u a t e t h e 10 v sign al t o +4 v . an o p tio n al ca p a c i t o r , c1, m a y ser v e as an a n t al iasin g f i l t er . an ad8022 is us ed t o dr i v e t h e ad c. t h is t o p o log y has f i v e b e n e f i ts. i n add i tio n t o le v e l-s h if tin g an d a t t e n u a t io n, v e r y li t t le n o is e is c o n t r i b u t e d t o t h e syst em. n o is e f r o m r1 a n d r2 is co m m o n t o bo th o f t h e ad c s in p u ts an d is e a si ly r e j e c t e d . r5 adds a t h ir d o f t h e do mina n t n o is e an d t h er e - fo r e mak e s a ne g l ig i b le con t r i b u t i o n t o t h e n o i s e o f t h e system. the a t t e n u a t o r divides t h e n o is e f r o m r3 an d r4. l i k e wis e , i t s n o is e con t r i b u t i o n is n e g l ig i b le . the fo ur t h b e nef i t o f t h is in ter - face cir c ui t is tha t t h e ad8221 s acq u isi t ion tim e is r e d u ce d b y a fac t o r o f 2. w i t h the he l p o f the o p 27, th e ad8221 o n l y n eeds t o de li v e r on e- half o f t h e f u l l swin g; t h er efo r e , si g n als ca n s e t t le m o r e q u ickly . l a st ly , t h e ad802 2 s e t t les q u ickly , which is he l p f u l b e ca us e t h e sh or t e r t h e s e t t lin g t i me , t h e m o r e b i ts t h a t can b e r e s o lv e d w h e n t h e ad c acq u ir e s da t a . this co nf igura t io n p r o- vides a t t e n u a t ion, a le ve l-shif t, and a con v enien t in t e r f ace wi t h a dif f er en t i al in pu t ad c whi l e ma in t a ini n g p e r f o r ma n c e . ac-couple d ins t rum e nta t io n a m plifier m e asur in g sma l l sig n a l s t h a t a r e in t h e am plif ier s n o is e o r o f fs et ca n be a c h al leng e . f i gur e 52 s h o w s a cir c ui t tha t c a n im p r o v e t h e r e s o l u t i on of smal l ac sig n al s. th e la rg e ga in r e d u ces t h e r e fer r e d in p u t no is e o f t h e am pl if ier t o 8 nv/ h z . th us, sma l ler sig n als ca n be m e as ur ed sin c e t h e n o is e f l o o r is lo w e r . d c o f fs ets tha t w o u l d ha v e been ga in e d b y 100 a r e elim ina t e d f r o m th e ad8221 s ou t p u t b y th e in teg r a t o r fee d back netw o r k. a t lo w f r eq uen c ies, th e o p 1177 fo r c es th e ad82 21 s o u t p u t t o 0 v . on ce a sig n al exceeds f hi g h - p as s , th e ad8221 o u t p u t s the a m plif ie d in p u t sig n a l . ad8221 op1177 r 15.8k ? +v s +in ?in 0.1 f 0.1 f 0.1 f 0.1 f 10 f 10 f ref c 1 f ?v s ?v s +v s +v s ?v s r 499 ? 1 2 rc f high-pass = 03149-0-048 figure 5 2 . a c -co u p l ed c i rc uit
ad8221 rev. a | page 18 of 20 outline dimensions 0.80 0.60 0.40 8 0 4 85 4.90 bsc pin 1 0.65 bsc 3.00 bsc seating plane 0.15 0.00 0.38 0.22 1.10 max 3.00 bsc coplanarity 0.10 0.23 0.08 compliant to jedec standards mo-187aa fig u re 5 3 . 8-le ad m i ni sm al l out lin e pa ck ag e [m s o p] (r m - 8) dim e nsio ns sho w n i n mi ll im e t er s 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) 0.50 (0.0196) 0.25 (0.0099) 45 8 0 1.75 (0.0688) 1.35 (0.0532) seating plane 0.25 (0.0098) 0.10 (0.0040) 4 1 85 5 . 00 ( 0 . 1 968) 4 . 80 ( 0 . 1 890) 4.00 (0.1574) 3.80 (0.1497) 1.27 (0.0500) bsc 6.20 (0.2440) 5.80 (0.2284) 0.51 (0.0201) 0.31 (0.0122) coplanarit y 0.10 controlling dimensions are in millimeters; inch dimensions (in parentheses) are rounded-off millimeter equivalents for reference only and are not appropriate for use in design compliant to jedec standards ms-012aa fig u re 5 4 . 8-le ad s h rink sm al l out lin e pa ck ag e [soic] (r - 8 ) ordering guide model temperature r a nge for specified perfo rmance operational 1 temperature range package descri ption package o p t i o n b r a n d i n g ad8221ar C40c to +85c C40c to 125c 8-lead soic r-8 ad8221ar-reel C40c to +85c C40c to 125c 13" tape and re el r-8 ad8221ar-reel 7 C40c to +85c C40c to 125c 7" tape and ree l r-8 ad8221arm C40c to +85c C40c to 125c 8-lead msop rm-8 jla ad8221arm- r e el C40c to +85c C40c to 125c 13" tape and re el rm-8 jla ad8221arm- r e el7 C40c to +85c C40c to 125c 7" tape and ree l rm-8 jla ad8221br C40c to +85c C40c to 125c 8-lead soic r-8 AD8221BR-REEL C40c to +85c C40c to 125c 13" tape and re el r-8 AD8221BR-REEL 7 C40c to +85c C40c to 125c 7" tape and ree l r-8 a d 8 2 2 1 - e v a l e v a l u a t i o n boar d 1 see typical perfor mance curves for expected oper ation from 85c to 125c.
ad8221 rev. a | page 19 of 20 notes
ad8221 rev. a | page 20 of 20 notes ? 2003 analo g de vices, inc. all rights reserve d . tra d em arks and registered tra d ema r ks are the prop erty of their respective owners . c03149C0 C 11/03(a)

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