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programmable gain precision difference amplifier AD8271 rev. 0 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 rights of analog devices. trademarks and registered trademarks are the property 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: 781.461.3113 ?2009 analog devices, inc. all rights reserved. features with no external resistors difference amplifier, gains of ?, 1, or 2 single-ended amplifier: over 40 different gains set reference voltage at midsupply excellent ac specifications 15 mhz bandwidth 30 v/s slew rate high accuracy dc performance 0.08% maximum gain error 10 ppm/c maximum gain drift 80 db minimum cmrr (gain of 2) 10-lead msop package supply current: 2.6 ma supply range: 2.5 v to 18 v applications adc driver instrumentation amplifier building blocks level translators automatic test equipment high performance audio sine/cosine encoders functional block diagram 1 7 6 10k? AD8271 10k? 10k? 10k? 20k? 20k? 10k? ?v s p4 p3 p2 p1 +v s out n1 n2 n3 07363-001 10 9 8 2 3 4 5 figure 1. general description the AD8271 is a low distortion, precision difference amplifier with internal gain setting resistors. with no external components, it can be configured as a high performance difference amplifier with gains of ?, 1, or 2. it can also be configured in over 40 single- ended configurations, with gains ranging from ?2 to +3. the AD8271 comes in a 10-lead msop package. the AD8271 operates on both single and dual supplies and requires only a 2.6 ma maximum supply current. it is specified over the industrial temperature range of ?40c to +85c and is fully rohs compliant. for a dual channel version of the AD8271, see the ad8270 data sheet. table 1. difference amplifiers by category high speed high voltage single-supply unidirectional single-supply bidirectional ad8270 ad628 ad8202 ad8205 ad8273 ad629 ad8203 ad8206 ad8274 ad8216 amp03
AD8271 rev. 0 | page 2 of 20 table of contents features .............................................................................................. 1 ? applications ....................................................................................... 1 ? functional block diagram .............................................................. 1 ? general description ......................................................................... 1 ? revision history ............................................................................... 2 ? specifications ..................................................................................... 3 ? difference amplifier configurations ........................................ 3 ? absolute maximum ratings ............................................................ 6 ? thermal resistance ...................................................................... 6 ? maximum power dissipation ..................................................... 6 ? esd caution .................................................................................. 6 ? pin configuration and function description .............................. 7 ? typical performance characteristics ............................................. 8 ? operational amplifier plots ...................................................... 14 ? theory of operation ...................................................................... 15 ? circuit information .................................................................... 15 ? driving the AD8271 ................................................................... 15 ? power supplies ............................................................................ 15 ? input voltage range ................................................................... 15 ? applications information .............................................................. 16 ? difference amplifier configurations ...................................... 16 ? single-ended configurations ................................................... 17 ? kelvin measurement .................................................................. 18 ? instrumentation amplifier........................................................ 18 ? driving cabling .......................................................................... 19 ? driving an adc ......................................................................... 19 ? outline dimensions ....................................................................... 20 ? ordering guide .......................................................................... 20 ? revision history 1/09revision 0: initial version
AD8271 rev. 0 | page 3 of 20 specifications difference amplifier configurations v s = 5 to 15 v, v ref = 0 v, g = 1, r load = 2 k, t a = 25c, specifications referred to input (rti), unless otherwise noted. table 2. b grade a grade parameter conditions min typ max min typ max unit dynamic performance bandwidth 15 15 mhz slew rate 30 30 v/s settling time to 0.01% v s = 15, 10 v step on output 700 800 700 800 ns v s = 5, 5 v step on output 550 650 550 650 ns settling time to 0.001% v s = 15, 10 v step on output 750 900 750 900 ns v s = 5, 5 v step on output 600 750 600 750 ns noise/distortion harmonic distortion + noise v s = 15, f = 1 khz, v out = 10 v p-p, r load = 600 110 110 db v s = 5, f = 1 khz, v out = 10 v p-p, r load = 600 141 141 db voltage noise 1 f = 0.1 hz to 10 hz 1.5 1.5 v p-p f = 1 khz 38 38 nv/hz gain gain error v out = 10 v p-p 0.02 0.05 % gain drift t a = ?40c to +85c 1 2 1 10 ppm/c gain nonlinearity v out = 10 v p-p, r load = 10 k, 2 k, 600 1 1 ppm input characteristics offset 2 300 600 300 1000 v average temperature drift t a = ?40c to +85c 2 2 v/c common-mode rejection ratio dc to 1 khz 80 92 74 92 db power supply rejection ratio 2 10 2 10 v/v input voltage range 3 ?v s ? 0.4 +v s + 0.4 ?v s ? 0.4 +v s + 0.4 v common-mode resistance 4 10 10 k bias current inputs grounded 500 500 na output characteristics output swing v s = 15 ?13.8 +13.8 ?13.8 +13.8 v v s = 15, t a = ?40c to +85c ?13.7 +13.7 ?13.7 +13.7 v v s = 5 ?4 +4 ?4 +4 v v s = 5, t a = ?40c to +85c ?3.9 +3.9 ?3.9 +3.9 v short-circuit current limit sourcing 100 100 ma sinking 60 60 ma power supply supply current 2.3 2.6 2.3 2.6 ma t a = ?40c to +85c 3.2 3.2 ma 1 includes amplifier vo ltage and current noise, as well as noise of inte rnal resistors. 2 includes input bias and offset errors. 3 at voltages beyond the rails, internal esd diodes begin to turn on. in some configurations, the input voltage range may be lim ited by the internal op amp (see the se ction for details). input voltage range 4 internal resistors, trimmed to be ratio matched, have 20% absolute accurac y. common-mode resistance was calculated with both inputs in parallel. the common- mode impedance at only one input is 2 the resistance listed.
AD8271 rev. 0 | page 4 of 20 v s = 5 to 15 v, v ref = 0 v, g = ?, r load = 2 k, t a = 25c, specifications referred to input (rti), unless otherwise noted. table 3. b grade a grade parameter conditions min typ max min typ max unit dynamic performance bandwidth 20 20 mhz slew rate 30 30 v/s settling time to 0.01% v s = 15, 10 v step on output 700 800 700 800 ns v s = 5, 5 v step on output 550 650 550 650 ns settling time to 0.001% v s = 15, 10 v step on output 750 900 750 900 ns v s = 5, 5 v step on output 600 750 600 750 ns noise/distortion harmonic distortion + noise v s = 15, f = 1 khz, v out = 10 v p-p, r load = 600 74 74 db v s = 5, f = 1 khz, v out = 10 v p-p, r load = 600 101 101 db voltage noise 1 f = 0.1 hz to 10 hz 2 2 v p-p f = 1 khz 52 52 nv/hz gain gain error v out = 10 v p-p 0.04 0.08 % gain drift t a = ?40c to +85c 0.5 2 1 10 ppm/c gain nonlinearity v out = 10 v p-p, r load = 10 k, 2 k, 600 200 200 ppm input characteristics offset 2 450 1000 450 1500 v average temperature drift t a = ?40c to +85c 3 3 v/c common-mode rejection ratio dc to 1 khz 74 86 70 86 db power supply rejection ratio 2 10 2 10 v/v input voltage range 3 ?v s ? 0.4 +v s + 0.4 ?v s ? 0.4 +v s + 0.4 v common-mode resistance 4 7.5 7.5 k bias current inputs grounded 500 500 na output characteristics output swing v s = 15 ?13.8 +13.8 ?13.8 +13.8 v v s = 15, t a = ?40c to +85c ?13.7 +13.7 ?13.7 +13.7 v v s = 5 ?4 +4 ?4 +4 v v s = 5, t a = ?40c to +85c ?3.9 +3.9 ?3.9 +3.9 v short-circuit current limit sourcing 100 100 ma sinking 60 60 ma power supply supply current 2.3 2.6 2.3 2.6 ma t a = ?40c to +85c 3.2 3.2 ma 1 includes amplifier vo ltage and current noise, as well as noise of inte rnal resistors. 2 includes input bias and offset errors. 3 at voltages beyond the rails, internal esd diodes begin to turn on. in some configurations, the input voltage range may be lim ited by the internal op amp (see the se ction for details). input voltage range 4 internal resistors, trimmed to be ratio matched, have 20% absolute accurac y. common-mode resistance was calculated with both inputs in parallel. the common- mode impedance at only one input is 2 the resistance listed.
AD8271 rev. 0 | page 5 of 20 v s = 5 to 15 v, v ref = 0 v, g = 2, r load = 2 k, t a = 25c, specifications referred to input (rti), unless otherwise noted. table 4. b grade a grade parameter conditions min typ max min typ max unit dynamic performance bandwidth 10 10 mhz slew rate 30 30 v/s settling time to 0.01% v s = 15, 10 v step on output 700 800 700 800 ns v s = 5, 5 v step on output 550 650 550 650 ns settling time to 0.001% v s = 15, 10 v step on output 750 900 750 900 ns v s = 5, 5 v step on output 600 750 600 750 ns noise/distortion harmonic distortion + noise v s = 15, f = 1 khz, v out = 10 v p-p, r load = 600 86 86 db v s = 5, f = 1 khz, v out = 10 v p-p, r load = 600 112 112 db voltage noise 1 f = 0.1 hz to 10 hz 1 1 v p-p f = 1 khz 26 26 nv/hz gain gain error v out = 10 v p-p 0.04 0.08 % gain drift t a = ?40c to +85c 0.5 2 1 10 ppm/c gain nonlinearity v out = 10 v p-p, r load = 10 k, 2 k, 600 50 50 ppm input characteristics offset 2 225 500 225 750 v average temperature drift t a = ?40c to +85c 1.5 1.5 v/c common-mode rejection ratio dc to 1 khz 84 98 78 98 db power supply rejection ratio 2 10 2 10 v/v input voltage range 3 ?v s ? 0.4 +v s + 0.4 ?v s ? 0.4 +v s + 0.4 v common-mode resistance 4 7.5 7.5 k bias current inputs grounded 500 500 na output characteristics output swing v s = 15 ?13.8 +13.8 ?13.8 +13.8 v v s = 15, t a = ?40c to +85c ?13.7 +13.7 ?13.7 +13.7 v v s = 5 ?4 +4 ?4 +4 v v s = 5, t a = ?40c to +85c ?3.9 +3.9 ?3.9 +3.9 v short-circuit current limit sourcing 100 100 ma sinking 60 60 ma power supply supply current 2.3 2.6 2.3 2.6 ma t a = ?40c to +85c 3.2 3.2 ma 1 includes amplifier vo ltage and current noise, as well as noise of inte rnal resistors. 2 includes input bias and offset errors. 3 at voltages beyond the rails, internal esd diodes begin to turn on. in some configurations, the input voltage range may be lim ited by the internal op amp (see the se ction for details). input voltage range 4 internal resistors, trimmed to be ratio matched, have 20% absolute accurac y. common-mode resistance was calculated with both inputs in parallel. the common- mode impedance at only one input is 2 the resistance listed.
AD8271 rev. 0 | page 6 of 20 absolute maximum ratings table 5. parameter rating supply voltage 18 v output short-circuit current see derating curve in figure 2 input voltage range +v s + 0.4 v to ?v s ? 0.4 v storage temperature range ?65c to +130c specified temperature range ?40c to +85c package glass transition temperature (t g ) 150c esd human body model 1 kv charge device model 1 kv machine model 0.1 kv stresses above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. thermal resistance table 6. thermal resistance package type ja jc unit 10-lead msop 141.9 43.7 c/w the ja values in table 6 assume a 4-layer jedec standard board with zero airflow. maximum power dissipation the maximum safe power dissipation for the AD8271 is limited by the associated rise in junction temperature (t j ) on the die. at approximately 150c, which is the glass transition temperature, the properties of the plastic change. even temporarily exceeding this temperature limit may change the stresses that the package exerts on the die, permanently shifting the parametric perfor- mance of the amplifiers. exceeding a temperature of 150c for an extended period of time can cause changes in silicon devices, potentially resulting in a loss of functionality. the AD8271 has built-in short-circuit protection that limits the output current to approximately 100 ma (see figure 22 for more information). although the short-circuit condition itself does not damage the part, the heat generated by the condition can cause the part to exceed its maximum junction temperature, with corresponding negative effects on reliability. 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 ?50 ?25 0 25 50 75 100 125 maximum power dissipation (w) ambient temperature (c) t j max = 150c 07363-102 figure 2. maximum power dissipation vs. ambient temperature esd caution
AD8271 rev. 0 | page 7 of 20 pin configuration and function description 1 2 3 4 5 10 9 8 7 6 AD8271 top view (not to scale) 07363-002 ?v s p4 p3 p2 p1 +v s out n1 n2 n3 figure 3. table 7. pin function descriptions pin no. mnemonic description 1 p1 noninverting input. a 10 k resistor is connect ed to the noninverting (+) terminal of the op amp. 2 p2 noninverting input. a 10 k resistor is connect ed to the noninverting (+) terminal of the op amp. 3 p3 noninverting input. a 20 k resistor is connected to the noninverting (+) terminal of the op amp. this pin is used as a reference voltage input in many configurations. 4 p4 noninverting input. a 20 k resistor is connected to the noninverting (+) terminal of the op amp. this pin is used as a reference voltage input in many configurations. 5 ?v s negative supply. 6 +v s positive supply. 7 out output. 8 n1 inverting input. a 10 k resistor is connected to the inverting (?) terminal of the op amp. 9 n2 inverting input. a 10 k resistor is connected to the inverting (?) terminal of the op amp. 10 n3 inverting input. a 10 k resistor is connected to the inverting (?) terminal of the op amp.
AD8271 rev. 0 | page 8 of 20 typical performance characteristics v s = 15 v, t a = 25c, difference amplifier configuration, unless otherwise noted. 180 150 120 90 60 30 0 ?200 ?100 0 100 200 07363-107 number of units cmmr (v/v) n = 989 mean = ?29 sd = 43 figure 4. typical distribution of cmrr, gain = 1 180 150 120 90 60 30 0 ?1000 ?500 0 500 1000 07363-108 number of units system offset voltage (v) n = 989 mean = ?306 sd = 229 figure 5. typical distribution of system offset, gain = 1 240 180 120 210 150 90 60 30 0 ?0.04 ?0.02 0 0.02 0.04 07363-109 number of units gain error (%) n = 1006 mean = 0.003 sd = 0.005 figure 6. typical distribution of gain error, gain = 1 ?40 ?30 ?20 ?10 0 10 20 30 40 50 60 70 ?50 ?30 ?10 10 30 50 70 90 110 130 cmrr ( v/v) temperature (c) gain = 1 representative samples 07363-004 +0.6v/v/c ?0.1v/v/c figure 7. cmrr vs. temperature, normalized at 25c, gain = 1 ?300 ?200 ?100 200 300 0 100 ?50?30?10103050 7090110130 system offset voltage ( v) temperature (c) gain = 1 representative samples 07363-005 2.2v/c 2.8v/c figure 8. system offset vs. temp erature, normalized at 25c, referred to output, gain = 1 ?150 ?100 ?50 100 150 200 0 50 ?50 ?30 ?10 10 30 50 70 90 110 130 gain error ( v/v) temperature (c) gain = 1 representative samples 07363-006 1.7ppm/c 0.5ppm/c figure 9. gain error vs. temperature, normalized at 25c, gain = 1
AD8271 rev. 0 | page 9 of 20 v s = 15 v, t a = 25c, difference amplifier configuration, unless otherwise noted. 20 15 10 5 0 ?5 ?10 ?15 ?20 ?10 ?5 0 5 10 output voltage (v) common-mode input voltage (v) (?7.5, +7.5) (+7.5, +7.5) (?7.5, ?7.5) (+7.5, ?7.5) (0, +15) (0, ?15) 07363-007 figure 10. common-mode input vo ltage vs. output voltage, gain = ?, 15 v supplies 6 4 2 0 ?2 ?4 ?6 ?3 ?2 ?1 0 1 2 3 output voltage (v) common-mode input voltage (v) (?1.25, ?1.25) (+1.25, +1.25) (?2.5, +2.5) (+2.5, +2.5) (?2.5, ?2.5) (+2.5, ?2.5) (?1.25, ?1.25) (+1.25, ?1.25) (0, +2.5) (0, ?2.5) (0, +5) (0, ?5) v s = 2.5 v s = 5 0 7363-008 figure 11. common-mode input vo ltage vs. output voltage, gain = ?, 5 v and 2.5 v supplies 20 15 10 5 0 ?5 ?10 ?15 ?20 ?20 ?15 ?10 ?5 0 5 10 15 20 output voltage (v) common-mode input voltage (v) (0, +15) (0, ?15) (?14.3, +7.85) (+14.3, +7.85) (?14.3, ?7.85) (+14.3, ?7.85) 07363-009 figure 12. common-mode input vo ltage vs. output voltage, gain =1, 15 v supplies 6 4 2 0 ?2 ?4 ?6 ?5 ?4 ?3 ?2 ?1 0 1 2 3 4 5 output voltage (v) common-mode input voltage (v) (0, +5) (0, ?5) (?4.3, +2.85) (+4.3, +2.85) (?4.3, +2.85) (?4.3, ?2.85) (+4.3, ?2.85) (?1.6, ?1.7) (+1.6, ?1.7) (?1.6, +1.7) (+1.6, +1.7) (0, +2.5) (0, ?2.5) v s = 2.5 v s = 5 07363-010 figure 13. common-mode input voltage vs. output voltage, gain = 1, 5 v and 2.5 v supplies 20 15 10 5 0 ?5 ?10 ?15 ?20 ?20 ?15 ?10 ?5 0 5 10 15 20 output voltage (v) common-mode input voltage (v) (0, +15) (0, ?15) (+14.3, +11.4) (+14.3, ?11.4) (?14.3, ?11.4) (?14.3, +11.4) 0 7363-011 figure 14. common-mode input voltage vs. output voltage, gain = 2, 15 v supplies 6 4 2 0 ?2 ?4 ?6 ?5 ?4 ?3 ?2 ?1 0 1 2 3 4 5 output voltage (v) common-mode input voltage (v) (0, +5) (0, ?5) (?4, +4) (+4, +4) (?4, ?4) (+4, ?4) (?1.6, ?2.1) (+1.6, ?2.1) (?1.6, +2.1) (+1.6, +2.1) (0, +2.5) (0, ?2.5) v s = 2.5 v s = 5 07363-012 figure 15. common-mode input voltage vs. output voltage, gain = 2, 5 v and 2.5 v supplies
AD8271 rev. 0 | page 10 of 20 v s = 15 v, t a = 25c, difference amplifier configuration, unless otherwise noted. 10 5 0 ?5 ?10 ?15 ?20 100 1k 10k 100k 1m 10m 100m frequency (hz) gain (db) gain = ? gain = 1 gain = 2 07363-018 figure 16. gain vs. frequency 100 90 80 70 60 50 40 30 20 10 0 10 100 1k 10k 100k 1m 10m frequency (hz) cmrr (db) gain = 2, ? gain = 1 07363-019 figure 17. cmrr vs. frequency 32 28 24 20 16 12 8 4 0 100 1k 10k 100k 1m 10m frequency (hz) output voltage swing (v p-p) v s = 15v v s = 5v 07363-017 figure 18. output voltage swing vs. large-signal frequency response 140 120 100 80 60 40 20 0 10 100 1k 10k 100k 1m frequency (hz) positive psrr (db) gain = 2, ? gain = 1 07363-015 figure 19. positive psrr vs. frequency 140 120 100 80 60 40 20 0 10 100 1k 10k 100k 1m frequency (hz) negative psrr (db) gain = 2, ? gain = 1 07363-016 figure 20. negative psrr vs. frequency 4 3 2 1 0 ?1 ?2 ?3 ?4 ?10 ?8 ?6 ?4 ?2 0 2 4 8 61 nonlinearity (1ppm/div) temperature (c) 0 10v p-p input gain = 1 r load = 10k ? , 2k ? , 600 ? 07363-136 figure 21. gain nonlinearity, gain = 1
AD8271 rev. 0 | page 11 of 20 v s = 15 v, t a = 25c, difference amplifier configuration, unless otherwise noted. ?100 ?80 ?60 40 80 120 ?40 0 60 100 ?20 20 ?50 ?30 ?10 10 30 50 70 90 110 130 short-circuit current (ma) temperature (c) 07363-118 i short+ i short? figure 22. short-circuit current vs. temperature + v s +v s ? 2 +v s ? 4 0 ?v s + 4 ?v s + 2 ?v s output voltage swing (v) 1k 200 10k r load ( ? ) +85c +125c +25c +25c ?40c ?40c +85c +125c 07363-022 figure 23. output voltage swing vs. r load 0 2040608010 ?v s + 3 ?v s ?v s + 6 +v s ? 6 0 + 0 v s +v s ? 3 ?40c ?40c +85c +125c +25c +25c current (ma) output voltage swing (v) +85c +125c 07363-023 figure 24. output voltage swing vs. current (i out ) 1s/div 50mv/di v 0pf 18pf 100pf v s = 15v 07363-024 figure 25. small-signal step response, gain = ? 1s/div 50mv/di v 0pf 33pf 220pf v s = 15v 07363-025 figure 26. small-signal step response, gain = 1 1s/div 50ms/di v 0pf 100pf 470pf v s = 15v 07363-026 figure 27. small-signal step response, gain = 2
AD8271 rev. 0 | page 12 of 20 v s = 15 v, t a = 25c, difference amplifier configuration, unless otherwise noted. 160 140 120 100 80 60 40 20 0 0 102030405060708090100 capacitive load (pf) overshoot (%) v s = 15v v s = 18v v s = 10v v s = 5v v s = 2.5v 07363-030 figure 28. small-signal overshoot vs. capacitive load, gain = ? 80 70 60 50 40 30 20 10 0 0 50 100 150 200 capacitive load (pf) overshoot (%) v s = 15v v s = 18v v s = 10v v s = 5v v s = 2.5v 07363-031 figure 29. small-signal overshoot vs. capacitive load, gain = 1 80 70 60 50 40 30 20 10 0 250 300 350 400 450 0 50 100 150 200 capacitive load (pf) overshoot (%) v s = 15v v s = 18v v s = 10v v s = 5v v s = 2.5v 07363-132 figure 30. small-signal overshoot vs. capacitive load, gain = 2 07363-127 gain = ? 2v/di v 1s/div figure 31. large-signal pulse response, gain = ? 07363-128 gain = 1 2v/di v 1s/div figure 32. large-signal pulse response, gain = 1 07363-129 gain = 2 2v/di v 1s/div figure 33. large-signal pulse response, gain = 2
AD8271 rev. 0 | page 13 of 20 v s = 15 v, t a = 25c, difference amplifier configuration, unless otherwise noted. 45 40 35 30 25 20 15 10 5 0 ?45 output slew rate (v/s) temperature (c) +sr ?sr 07363-130 ?35 ?25 ?15 ?5 5 15 25 35 45 55 65 75 85 95 105 115 125 figure 34. output slew rate vs. temperature 1k 100 10 1 10 100 1k 10k 100k frequency (hz) voltage noise spectral density (nv/ hz) gain = ? gain = 1 gain = 2 07363-041 figure 35. voltage noise spectral density vs. frequency, referred to output 1v/div 1s/div gain = ? gain = 1 gain = 2 07363-042 figure 36. 0.1 hz to 10 hz voltage noise, referred to output 0.1 0.01 0.001 0.0001 10 100 1k 10k 100k 07363-133 thd + n (%) frequency (hz) r load = 100k ? r load = 2k ? r load = 600 ? gain = 1 gain = 2 gain = ? figure 37. thd + n vs. frequency 1 0.1 0.01 0.001 0.0001 0 25 5 thdn + n (%) 10 15 20 output amplitude (dbu) 0 7363-134 gain = 1 f = 1khz r load = 600 ? r load = 2k ? r load = 100k ? figure 38. thd + n vs. output amplitude, gain = 1 10 100 1k 10k 100k frequency (hz) 0.1 0.01 0.001 0.0001 0.00001 amplitude (% of fundamental) 07363-135 gain = 1 v out = 10v p-p hd2, r load = 100k ? hd2, r load = 2k ? hd2, r load = 600 ? hd3, r load = 100k ? hd3, r load = 2k ? hd3, r load = 600 ? figure 39. harmonic distortion products vs. frequency, gain = 1
AD8271 rev. 0 | page 14 of 20 operational amplifier plots v s = 15 v, t a = 25c, unless otherwise noted. 012345678 910 time (sec) offset (10v/div) 07363-044 figure 40. change in op amp o ffset voltage vs. warm-up time 50pa/div 1s/div 07363-028 figure 41. 0.1 hz to 10 hz current noise 10 1 0.1 1 10 100 1k 10k 100k frequency (hz) current noise spectral density (pa/ hz) 0 7363-029 figure 42. current noise spectral density vs. frequency
AD8271 rev. 0 | page 15 of 20 theory of operation 1 7 6 10k? AD8271 10k? 10k ? 10k ? 20k ? 20k ? 10k ? ?v s p4 p3 p2 p1 +v s out n1 n2 n3 07363-032 10 9 8 2 3 4 5 figure 43. functional block diagram circuit information the AD8271 consists of a high precision, low distortion op amp and seven trimmed resistors. these resistors can be connected to create a wide variety of amplifier configurations, including difference, noninverting, and inverting configurations. the resistors on the chip can be connected in parallel for a wider range of options. using the on-chip resistors of the AD8271 provides the designer with several advantages over a discrete design. dc performance much of the dc performance of op amp circuits depends on the accuracy of the surrounding resistors. the resistors on the AD8271 are laid out to be tightly matched. the resistors of each part are laser trimmed and tested for th eir matching a ccuracy. because of this trimming and testing, the AD8271 can guarantee high accuracy for specifications, such as gain drift, common-mode rejection, and gain error. ac performance because feature size is much smaller in an integrated circuit than on a printed circuit board (pcb), the corresponding parasitics are also smaller. the smaller feature size helps the ac performance of the AD8271. for example, the positive and negative input terminals of the AD8271 op amp are not pinned out intentionally. by not connecting these nodes to the traces on the pcb, the capacitance remains low, resulting in both improved loop stability and common-mode rejection over frequency. production costs because one part, rather than several discrete components, is placed on the pcb, the board can be built more quickly and efficiently. size the AD8271 fits an op amp and seven resistors in one msop package. driving the AD8271 the AD8271 is easy to drive, with all configurations presenting at least several kilohms (k) of input resistance. the AD8271 should be driven with a low impedance source: for example, another amplifier. the gain accuracy and common-mode rejection of the AD8271 depend on the matching of its resistors. even source resistance of a few ohms can have a substantial effect on these specifications. power supplies a stable dc voltage should be used to power the AD8271. noise on the supply pins can adversely affect performance. a bypass capacitor of 0.1 f should be placed between each supply pin and ground, as close as possible to each supply pin. a tantalum capacitor of 10 f should also be used between each supply and ground. it can be farther away from the supply pins and, typically, it can be shared by other precision integrated circuits. the AD8271 is specified at 15 v and 5 v, but it can be used with unbalanced supplies, as well. for example, ?v s = 0 v, +v s = 20 v. the difference between the two supplies must be kept below 36 v. input voltage range the AD8271 has a true rail-to-rail input range for the majority of applications. because most AD8271 configurations divide down the voltage before they reach the internal op amp, the op amp sees only a fraction of the input voltage. figure 44 shows an example of how the voltage division works in the difference amplifier configuration. 07363-033 r4 r3 r1 r2 r2 r1 + r2 (v +in ) r2 r1 + r2 (v +in ) figure 44. voltage division in the difference amplifier configuration the internal op amp voltage range may be relevant in the following applications, and calculating the voltage at the internal op amp is advised. ? difference amplifier configurations using supply voltages of less than 4.5 v ? difference amplifier configurations with a reference voltage near the rail ? single-ended amplifier configurations for correct operation, the input voltages at the internal op amp must stay within 1.5 v of either supply rail. voltages beyond the supply rails should not be applied to the part. the part contains esd diodes at the input pins, which conduct if voltages beyond the rails are applied. currents greater than 5 ma may damage these diodes and the part. for a similar part that can operate with voltages beyond the rails, see the ad8274 data sheet.
AD8271 rev. 0 | page 16 of 20 applications information the resistors and connections provided on the AD8271 offer abundant versatility through the variety of configurations that are possible. difference amplifier configurations the AD8271 can be placed in difference amplifier configurations with gains of ?, 1, and 2. figure 45 through figure 47 show sample difference amplifier configurations referenced to ground. = 07363-053 1 7 10k? AD8271 10k? 10k? 10k? 20k? 20k? 10k? p4 p3 p2 p1 +in gnd out out n1 n2 n3 10 9 8 2 3 4 ?in ?in +in 5k ? 5k? 10k? 10k? gnd figure 45. gain = ? difference amplifier, referenced to ground = ?in +in 10k ? 10k? 10k ? 10k ? gnd 07363-054 1 7 10k? AD8271 10k? 10k ? 10k ? 20k ? 20k ? 10k? p4 p3 p2 p1 +in nc nc gnd out out n1 n2 n3 10 9 8 2 3 4 ?in figure 46. gain = 1 difference amplifier, referenced to ground = ?in +in 10k ? 5k ? 5k ? 10k? gnd 07363-055 1 7 10k? AD8271 10k? 10k ? 10k ? 20k ? 20k ? 10k ? p4 p3 p2 p1 out out n1 n2 n3 10 9 8 2 3 4 ?in gnd +in out figure 47. gain = 2 difference amplifier, referenced to ground the AD8271 can also be referred to a combination of reference voltages. for example, the reference can be set at 2.5 v, using just 5 v and gnd. some of the possible configurations are shown in figure 48 through figure 50 . note that the output is not internally tied to a feedback path, so any of the 10 k resistors on the inverting input can be used in the feedback network. this flexibility allows for more efficient board lay- out options. +v s + ?v s 2 ?in = +in 5k? 5k? 10k ? 10k ? 07363-056 1 7 10k? AD8271 10k? 10k ? 10k ? 20k ? 20k ? 10k ? p4 p3 p2 p1 +in ?v s +v s out out n1 n2 n3 10 9 8 2 3 4 ?in figure 48. gain = ? difference amplifier, referenced to midsupply = ?in +in 10k? 10k ? 10k? 10k? +v s + ?v s 2 07363-057 1 7 10k? AD8271 10k? 10k? 10k? 20k? 20k? 10k? p4 p3 p2 p1 +in nc nc out out n1 n2 n3 10 9 8 2 3 4 ?in ?v s +v s figure 49. gain = 1 difference amplifier, referenced to midsupply = ?in +in 10k? 5k? 5k? 10k? +v s + ?v s 2 07363-058 1 7 10k? AD8271 10k? 10k ? 10k ? 20k ? 20k ? 10k? p4 p3 p2 p1 +in ?v s + v s out out n1 n2 n3 10 9 8 2 3 4 +in figure 50. gain = 2 difference amplifier, referenced to midsupply table 8. pin connections for difference amplifier configurations configuration gain and reference pin 1 (p1) pin 2 (p2) pin 3 (p3) pin 4 (p4) pin 8 (n1) pin 9 (n2) pin 10 (n3) gain of ?, referenced to ground +in gnd gnd gnd out out ?in gain of ?, referenced to midsupply +in ?v s +v s +v s out out ?in gain of 1, referenced to ground +in nc gnd gnd out nc ?in gain of 1, referenced to midsupply +in nc ?v s +v s out nc ?in gain of 2, referenced to ground +in +in gnd gnd out ?in ?in gain of 2, referenced to midsupply +in +in ?v s +v s out ?in ?in
AD8271 rev. 0 | page 17 of 20 single-ended configurations the AD8271 can be configured for a wide variety of single-ended configurations with gains ranging from ?2 to +3 (see table 9 ). table 9. selected single-ended configurations electrical performance configuration signal gain op amp closed-loop gain input resistance pin 10 1 pin 9 1 pin 8 1 pin 1 2 pin 2 2 pin 3 3 pin 4 3 ?2 3 5 k in in out gnd gnd gnd gnd ?1.5 3 4.8 k in in out gnd gnd gnd in ?1.4 3 5 k in in out gnd gnd nc in ?1.25 3 5.333 k in in out gnd nc gnd in ?1 3 5 k in in out gnd gnd in in ?0.8 3 5.556 k in in out in gnd nc gnd ?0.667 2 8 k in nc out gnd gnd gnd in ?0.6 2 8.333 k in nc out gnd gnd nc in ?0.5 2 8.889 k in nc out gnd nc gnd in ?0.333 2 7.5 k in nc out gnd gnd in in ?0.25 1.5 8 k out in out gnd gnd gnd in ?0.2 1.5 8.333 k out in out gnd gnd nc in ?0.125 1.5 8.889 k out in out gnd nc gnd in +0.1 1.5 8.333 k out in out in gnd nc gnd +0.2 2 10 k in nc out gnd in nc in +0.25 1.5 24 k out gnd out gnd gnd gnd in +0.3 1.5 25 k out gnd out gnd gnd nc in +0.333 2 24 k gnd nc out gnd gnd gnd in +0.375 1.5 26.67 k out gnd out gnd nc gnd in +0.4 2 25 k gnd nc out gnd gnd nc in +0.5 3 24 k gnd gnd out gnd gnd gnd in +0.5 1.5 15 k out gnd out gnd gnd in in +0.6 3 25 k gnd gnd out gnd gnd nc in +0.6 1.5 16.67 k out gnd out in gnd nc gnd +0.625 1.5 16 k out in out nc in in gnd +0.667 2 15 k gnd nc out gnd gnd in in +0.7 1.5 16.67 k out in out in in nc gnd +0.75 3 26.67 k gnd gnd out gnd nc gnd in +0.75 1.5 13.33 k out gnd out gnd in gnd in +0.8 2 16.67 k gnd nc out in gnd nc gnd +0.9 1.5 16.67 k out gnd out gnd in nc in +1 1.5 15 k out gnd out in in gnd gnd +1 1.5 >1 g out in out in in in in +1 3 >1 g in in out in in in in +1.125 1.5 26.67 k out gnd out nc in in gnd +1.2 3 16.67 k gnd gnd out in gnd nc gnd +1.2 1.5 25 k out gnd out in in nc gnd +1.25 1.5 24 k out gnd out in in in gnd +1.333 2 15 k gnd nc out in in gnd gnd +1.5 3 13.33 k gnd gnd out gnd in gnd in +1.5 1.5 >1 g out gnd out in in in in +1.6 2 25 k gnd nc out in in nc gnd +1.667 2 24 k gnd nc out in in in gnd +1.8 3 16.67 k gnd gnd out gnd in nc in +2 2 >1 g gnd nc out in in in in +2.25 3 26.67 k gnd gnd out nc in in gnd +2.4 3 25 k gnd gnd out in in nc gnd +2.5 3 24 k gnd gnd out in in in gnd +3 3 >1 g gnd gnd out in in in in 1 a 10 k resistor is connected to the inverting (?) terminal of the op amp. 2 a 10 k resistor is connected to the noninverting (+) terminal of the op amp. 3 a 20 k resistor is connected to the noninverting (+) terminal of the op amp.
AD8271 rev. 0 | page 18 of 20 many signal gains have more than one configuration choice, which allows freedom in choosing the op amp closed-loop gain. in general, for designs that need to be stable with a large capacitive load on the output, choose a configuration with high loop gain. otherwise, choose a configuration with low loop gain, because these configurations typically have lower noise, lower offset, and higher bandwidth. the AD8271 specifications section and typical performance characteristics section show the performance of the part primarily when it is in the difference amplifier configuration. to estimate the performance of the part in a single-ended configuration, refer to the difference amplifier configuration with the corresponding closed-loop gain (see table 10 ). table 10. closed-loop gain of the difference amplifiers difference amplifier gain closed-loop gain 0.5 1.5 1 2 2 3 gain of 1 configuration the AD8271 is designed to be stable for loop gains of 1.5 and greater. because a typical voltage follower configuration has a loop gain of 1, it may be unstable. several stable configurations for gain of 1 are listed in table 9 . kelvin measurement in the case where the output load is located remotely or at a distance from the AD8271, as shown in figure 51 , wire resistance can actually cause significant errors at the load. 07363-149 ?in 10k ? 10k ? 10k ? 10k ? +in r w (wire resistance) r l 1k? since the output of the AD8271 is not internally tied to any of the feedback resistors, kelvin type measurements are possible because the op amp output and feedback can both be connected closer to the load ( figure 52 ). the kelvin sensing on the feedback minimizes error at the load caused by voltage drops across the wire resistance. this technique is most effective in reducing errors for loads less than 10 k. as the load resistance increases, the error due to the wire resistance becomes less significant. because it adds the sense wire resistance to the feedback resistor, a trade-off of the kelvin connection is that it can degrade common- mode rejection, especially over temperature. for sense wire resistance less than 1 , it is typically not an issue. if common- mode performance is critical, two amplifier stages can be used: the first stage removes common-mode interference, and the second stage performs the kelvin drive. 10k ? r w r w sense force 07363-150 ?in 10k ? 10k ? 10k ? +in r l 1k? instrumentation amplifier the AD8271 can be used as a building block for high performance instrumentation amplifiers. for example, figure 53 shows how to build an ultralow noise instrumentation amplifier using the ad8599 dual op amp. external resistors r g and r fx provide gain; therefore, the output is () () 8271 2 1 ad g fx in in out g r r vvv ? ? ? ? ? ? ? ? +?= ?+ ?in +in 10k? 10k ? 10k ? 10k ? ref ad8599 a2 a d8599 a2 r g 20? r f1 r f2 2k? AD8271 out 2k? v s = 15v 07363-153 figure 53.ultralow noise instrumentation amplifier using ad8599 configured for gain = 201 for optimal noise performance, it is desirable to have a high gain at the input stage using low value gain-setting resistors, as shown in this particular example. with less than 2 nv/hz input-referred noise (see figure 54 ) at ~10 ma supply current, the AD8271 and ad8599 combination offers an in-amp with a fine balance of critical specifications: a gain bandwidth product of 10 mhz, low bias current, low offset drift, high cmrr, and high slew rate. 0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 1 10 100 1k 10k 100k voltage noise spectral density (nv/ hz) frequency (hz) 07363-151 g = 201 bandwidth limit figure 54. ultralow noise in-amp voltage noise spectral density vs. frequency, referred to input
AD8271 rev. 0 | page 19 of 20 driving cabling driving an adc because the AD8271 can drive large voltages at high output currents and slew rates, it makes an excellent cable driver. it is good practice to put a small value resistor between the AD8271 output and cable, since capacitance in the cable can cause peaking or instability in the output response. a resistance of 20 or higher is recommended. the ad271 high slew rate and drive capability, combined with its dc accuracy, make it a good adc driver. the AD8271 can drive single-ended input adcs. many converters require the output to be buffered with a small value resistor combined with a high quality ceramic capacitor. see the relevant converter data sheet for more details. AD8271 (single out) 07363-148 figure 55. driving cabling
AD8271 rev. 0 | page 20 of 20 outline dimensions compliant to jedec standards mo-187-ba 0.23 0.08 0.80 0.60 0.40 8 0 0.15 0.05 0.33 0.17 0.95 0.85 0.75 seating plane 1.10 max 10 6 5 1 0.50 bsc pin 1 coplanarity 0.10 3.10 3.00 2.90 3.10 3.00 2.90 5.15 4.90 4.65 figure 56. 10-lead mini small outline package [msop] (rm-10) dimensions are shown in millimeters ordering guide model temperature range package desc ription package option branding AD8271armz 1 ?40c to +85c 10-lead msop rm-10 y1e AD8271armz-r7 1 ?40c to +85c 10-lead msop, 7 tape and reel rm-10 y1e AD8271armz-rl 1 ?40c to +85c 10-lead msop, 13 tape and reel rm-10 y1e AD8271brmz 1 ?40c to +85c 10-lead msop rm-10 y1g AD8271brmz-r7 1 ?40c to +85c 10-lead msop, 7 tape and reel rm-10 y1g AD8271brmz-rl 1 ?40c to +85c 10-lead msop, 13 tape and reel rm-10 y1g 1 z = rohs compliant part. ?2009 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. d07363-0-1/09(0)

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