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low power, wide supply range, low cost difference amplifiers, g = ?, 2 ad8278/ad8279 rev. c 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 ?2009C2011 analog devices, inc. all rights reserved. features wide input range beyond supplies rugged input overvoltage protection low supply current: 200 a maximum (per amplifier) low power dissipation: 0.5 mw at v s = 2.5 v bandwidth: 1 mhz (g = ?) cmrr: 80 db minimum, dc to 20 khz (g = ?, b grade) low offset voltage drift: 1 v/c maximum (b grade) low gain drift: 1 ppm/c maximum (b grade) enhanced slew rate: 1.4 v/s wide power supply range single supply: 2 v to 36 v dual supplies: 2 v to 18 v 8-lead soic, 14-lead soic, and 8-lead msop packages applications voltage measurement and monitoring current measurement and monitoring instrumentation amplifier building block portable, battery-powered equipment test and measurement general description the ad8278 and ad8279 are general-purpose difference amplifiers intended for precision signal conditioning in power critical applications that require both high performance and low power. the ad8278 and ad8279 provide exceptional common- mode rejection ratio (80 db) and high bandwidth while amplifying input signals that are well beyond the supply rails. the on-chip resistors are laser trimmed for excellent gain accuracy and high cmrr. they also have extremely low gain drift vs. temperature. the common-mode range of the amplifier extends to almost triple the supply voltage (for g = ?), making the amplifer ideal for single-supply applications that require a high common- mode voltage range. the internal resistors and esd circuitry at the inputs also provide overvoltage protection to the op amp. the ad8278 and ad8279 can be used as difference amplifiers with g = ? or g = 2. they can also be connected in a high precision, single-ended configuration for non inverting and inverting gains of ??, ?2, +3, +2, +1?, +1, or +?. the ad8278 and ad8279 provide an integrated precision solution that has a smaller size, lower cost, and better performance than a discrete alternative. the ad8278 and ad8279 operate on single supplies (2.0 v to 36 v) or dual supplies (2 v to 18 v). the maximum quiescent supply current is 200 a, which is ideal for battery-operated and portable systems. for unity-gain difference amplifiers with similar performance, refer to the ad8276 and ad8277 data sheets. functional block diagrams 2 5 3 1 6 7 4 40k ? 20k ? 40k ? ?vs +vs ?in +in sense out ref 20k ? ad8278 08308-001 figure 1. ad8278 2 12 3 14 13 11 40k ? 20k ? 40k ? +vs ?ina +ina sensea outa refa 20k ? 6 10 5 8 9 40k ? 20k ? 40k ? ?inb +inb senseb outb refb 20k ? ad8279 4 ?vs 08308-058 figure 2. ad8279 table 1. difference amplifiers by category low distortion high voltage current sensing 1 low power ad8270 ad628 ad8202 (u) ad8276 ad8271 ad629 ad8203 (u) ad8277 ad8273 ad8205 (b) ad8274 ad8206 (b) amp03 ad8216 (b) 1 u = unidirectional, b = bidirectional. the ad8278 is available in the space-saving 8-lead msop and soic packages, and the ad8279 is offered in a 14-lead soic package. both are specified for performance over the industrial temperature range of ?40c to +85c and are fully rohs compliant.
ad8278/ad8279 rev. c | page 2 of 24 table of contents features .............................................................................................. 1 ? applications....................................................................................... 1 ? general description ......................................................................... 1 ? functional block diagrams............................................................. 1 ? revision history ............................................................................... 2 ? specifications..................................................................................... 3 ? absolute maximum ratings............................................................ 7 ? thermal resistance ...................................................................... 7 ? maximum power dissipation ..................................................... 7 ? short-circuit current .................................................................. 7 ? esd caution.................................................................................. 7 ? pin configurations and function descriptions ........................... 8 ? typical performance characteristics ..............................................9 ? theory of operation ...................................................................... 16 ? circuit information.................................................................... 16 ? driving the ad8278 and ad8279 ........................................... 16 ? input voltage range................................................................... 16 ? power supplies ............................................................................ 17 ? applications information .............................................................. 18 ? configurations............................................................................ 18 ? differential output .................................................................... 19 ? instrumentation amplifier........................................................ 19 ? outline dimensions ....................................................................... 20 ? ordering guide .......................................................................... 21 ? revision history 1/11rev. b to rev. c change to impedance/differential parameter, table 3 ............... 4 change to impedance/differential parameter, table 5 ............... 6 4/10rev. a to rev. b changed supply current parameters to ad8278 supply current parameter and ad8279 supply current parameter, table 5 ...... 6 updated outline dimensions ....................................................... 20 10/09rev. 0 to rev. a added ad8279 and 14-lead soic model .....................universal changes to features.......................................................................... 1 changes to general description .................................................... 1 change to table 2 ............................................................................. 3 change to table 3 ..............................................................................4 change to table 4 ..............................................................................5 change to table 5 ..............................................................................6 added figure 6 and table 9 .............................................................8 changes to figure 31 and figure 32............................................. 13 changes to figure 40, figure 41, and figure 42 ......................... 14 added figure 47; renumbered sequentially .............................. 15 changes to figure 51 to figure 57................................................ 18 added differential output section.............................................. 19 changes to figure 59...................................................................... 19 updated outline dimensions....................................................... 21 changes to ordering guide .......................................................... 21 7/09revision 0: initial version
ad8278/ad8279 rev. c | page 3 of 24 specifications v s = 5 v to 15 v, v ref = 0 v, t a = 25c, r l = 10 k connected to ground, g = ? difference amplifier configuration, unless otherwise noted. table 2. g = ? grade b grade a parameter conditions min typ max min typ max unit input characteristics system offset 1 50 100 50 250 v over temperature t a = ?40c to +85c 100 250 v vs. power supply v s = 5 v to 18 v 2.5 5 v/v average temperature coefficient t a = ?40c to +85c 0.3 1 2 5 v/c common-mode rejection ratio (rti) v s = 15 v, v cm = 27 v, r s = 0 80 74 db input voltage range 2 ?3 (v s + 0.1) +3 (v s ? 1.5) ?3 (v s + 0.1) +3 (v s ? 1.5) v impedance 3 differential 120 120 k common mode 30 30 k dynamic performance bandwidth 1 1 mhz slew rate 1.1 1.4 1.1 1.4 v/s channel separation f = 1 khz 130 130 db settling time to 0.01% 10 v step on output, c l = 100 pf 9 9 s settling time to 0.001% 10 10 s gain gain error 0.005 0.02 0.01 0.05 % gain drift t a = ?40c to +85c 1 5 ppm/c gain nonlinearity v out = 20 v p-p 7 12 ppm output characteristics output voltage swing 4 v s = 15 v, r l = 10 k t a = ?40c to +85c ?v s + 0.2 +v s ? 0.2 ?v s + 0.2 +v s ? 0.2 v short-circuit current limit 15 15 ma capacitive load drive 200 200 pf noise 5 output voltage noise f = 0.1 hz to 10 hz 1.4 1.4 v p-p f = 1 khz 47 50 47 50 nv/hz power supply 6 ad8278 supply current 200 200 a over temperature t a = ?40c to +85c 250 250 a ad8279 supply current 300 350 300 350 a over temperature t a = ?40c to +85c 400 400 a operating voltage range 7 2 18 2 18 v temperature range operating range ?40 +125 ?40 +125 c 1 includes input bias and offset curre nt errors, rto (referred to output). 2 the input voltage range may also be limit ed by absolute maximum input voltage or by the output swing. see the for details. input voltage ra nge 3 internal resistors are trimme d to be ratio matched and have 20% absolute accuracy. 4 output voltage swing varies with supply voltage and temperature. see figur through for details. e 22 figure 25 5 includes amplifier voltage and current noise, as well as noise from inte rnal resistors. 6 supply current varies with supply voltage and temp erature. see figure and for details. 26 figure 28 7 unbalanced dual supplies can be used, such as ?v s = ?0.5 v and +v s = +2 v. the positive supply rail must be at least 2 v above the negative supply and reference voltage.
ad8278/ad8279 rev. c | page 4 of 24 v s = 5 v to 15 v, v ref = 0 v, t a = 25c, r l = 10 k connected to ground, g = 2 difference amplifier configuration, unless otherwise noted. table 3. g = 2 grade b grade a parameter conditions min typ max min typ max unit input characteristics system offset 1 100 200 100 500 v over temperature t a = ?40c to +85c 200 500 v vs. power supply v s = 5 v to 18 v 5 10 v/v average temperature coefficient t a = ?40c to +85c 0.6 2 2 5 v/c common-mode rejection ratio (rti) v s = 15 v, v cm = 27 v, r s = 0 86 80 db input voltage range 2 ?1.5 (v s + 0.1) +1.5 (v s ? 1.5) ?1.5 (v s + 0.1) +1.5 (v s ? 1.5) v impedance 3 differential 30 30 k common mode 30 30 k dynamic performance bandwidth 550 550 khz slew rate 1.1 1.4 1.1 1.4 v/s channel separation f = 1 khz 130 130 db settling time to 0.01% 10 v step on output, c l = 100 pf 10 10 s settling time to 0.001% 11 11 s gain gain error 0.005 0.02 0.01 0.05 % gain drift t a = ?40c to +85c 1 5 ppm/c gain nonlinearity v out = 20 v p-p 7 12 ppm output characteristics output voltage swing 4 v s = 15 v, r l = 10 k, t a = ?40c to +85c ?v s + 0.2 +v s ? 0.2 ?v s + 0.2 +v s ? 0.2 v short-circuit current limit 15 15 ma capacitive load drive 350 350 pf noise 5 output voltage noise f = 0.1 hz to 10 hz 2.8 2.8 v p-p f = 1 khz 90 95 90 95 nv/hz power supply 6 ad8278 supply current 200 200 a over temperature t a = ?40c to +85c 250 250 a ad8279 supply current 300 350 300 350 a over temperature t a = ?40c to +85c 400 400 a operating voltage range 7 2 18 2 18 v temperature range operating range ?40 +125 ?40 +125 c 1 includes input bias and offset curre nt errors, rto (referred to output). 2 the input voltage range may also be limit ed by absolute maximum input voltage or by the output swing. see the section for details. input voltage ra nge 3 internal resistors are trimme d to be ratio matched and have 20% absolute accuracy. 4 output voltage swing varies with supply voltage and temperature. see figur through for details. e 22 figure 25 5 includes amplifier voltage and current noise, as well as noise from inte rnal resistors. 6 supply current varies with supply voltage and temp erature. see figure and for details. 26 figure 28 7 unbalanced dual supplies can be used, such as ?v s = ?0.5 v and +v s = +2 v. the positive supply rail must be at least 2 v above the negative supply and reference voltage.
ad8278/ad8279 rev. c | page 5 of 24 v s = +2.7 v to <5 v, v ref = midsupply, t a = 25c, r l = 10 k connected to midsupply, g = ? difference amplifier configuration, unless otherwise noted. table 4. g = ? grade b grade a parameter conditions min typ max min typ max unit input characteristics system offset 1 75 150 75 250 v over temperature t a = ?40c to +85c 150 250 v vs. power supply v s = 5 v to 18 v 2.5 5 v/v average temperature coefficient t a = ?40c to +85c 0.3 1 2 5 v/c common-mode rejection ratio (rti) v s = 2.7 v, v cm = 0 v to 2.4 v, r s = 0 80 74 db v s = 5 v, v cm = ?10 v to +7 v, r s = 0 80 74 db input voltage range 2 ?3 (v s + 0.1) +3 (v s ? 1.5) ?3 (v s + 0.1) +3 (v s ? 1.5) v impedance 3 differential 120 120 k common mode 30 30 k dynamic performance bandwidth 870 870 khz slew rate 1.3 1.3 v/s channel separation f = 1 khz 130 130 db settling time to 0.01% 2 v step on output, c l = 100 pf, v s = 2.7 v 7 7 s gain gain error 0.005 0.02 0.01 0.05 % gain drift t a = ?40c to +85c 1 5 ppm/c output characteristics output swing 4 r l = 10 k, t a = ?40c to +85c ?v s + 0.1 +v s ? 0.15 ?v s + 0.1 +v s ? 0.15 v short-circuit current limit 10 10 ma capacitive load drive 200 200 pf noise 5 output voltage noise f = 0.1 hz to 10 hz 1.4 1.4 v p-p f = 1 khz 47 50 47 50 nv/hz power supply 6 ad8278 supply current t a = ?40c to +85c 200 200 a ad8279 supply current t a = ?40c to +85c 375 375 a operating voltage range 2.0 36 2.0 36 v temperature range operating range ?40 +125 ?40 +125 c 1 includes input bias and offset curre nt errors, rto (referred to output). 2 the input voltage range may also be limited by absolute maximum input voltage or by the output swing. see the section for details. input voltage ra nge 3 internal resistors are trimme d to be ratio matched and have 20% absolute accuracy. 4 output voltage swing varies with supply voltage and temperature. see figur through for details. e 22 figure 25 5 includes amplifier voltage and current noise, as well as noise from inte rnal resistors. 6 supply current varies with supply voltage and temp erature. see figure and for details. 27 figure 28
ad8278/ad8279 rev. c | page 6 of 24 v s = +2.7 v to <5 v, v ref = midsupply, t a = 25c, r l = 10 k connected to midsupply, g = 2 difference amplifier configuration, unless otherwise noted. table 5. g = 2 grade b grade a parameter conditions min typ max min typ max unit input characteristics system offset 1 150 300 150 500 v over temperature t a = ?40c to +85c 300 500 v vs. power supply v s = 5 v to 18 v 5 10 v/v average temperature coefficient t a = ?40c to +85c 0.6 2 3 5 v/c common-mode rejection ratio (rti) v s = 2.7 v, v cm = 0 v to 2.4 v, r s = 0 86 80 db v s = 5 v, v cm = ?10 v to +7 v, r s = 0 86 80 db input voltage range 2 ?1.5 (v s + 0.1) +1.5 (v s ? 1.5) ?1.5 (v s + 0.1) +1.5 (v s ? 1.5) v impedance 3 differential 30 30 k common mode 30 30 k dynamic performance bandwidth 450 450 khz slew rate 1.3 1.3 v/s channel separation f = 1 khz 130 130 db settling time to 0.01% 2 v step on output, c l = 100 pf, v s = 2.7 v 9 9 s gain gain error 0.005 0.02 0.01 0.05 % gain drift t a = ?40c to +85c 1 5 ppm/c output characteristics output swing 4 r l = 10 k, t a = ?40c to +85c ?v s + 0.1 +v s ? 0.15 ?v s + 0.1 +v s ? 0.15 v short-circuit current limit 10 10 ma capacitive load drive 200 200 pf noise 5 output voltage noise f = 0.1 hz to 10 hz 2.8 2.8 v p-p f = 1 khz 94 100 94 100 nv/hz power supply 6 ad8278 supply current t a = ?40c to +85c 200 200 a ad8279 supply current t a = ?40c to +85c 375 375 a operating voltage range 2.0 36 2.0 36 v temperature range operating range ?40 +125 ?40 +125 c 1 includes input bias and offset curre nt errors, rto (referred to output). 2 the input voltage range may also be limited by absolute maximum input voltage or by the output swing. see the section for details. input voltage ra nge 3 internal resistors are trimme d to be ratio matched and have 20% absolute accuracy. 4 output voltage swing varies with supply voltage and temperature. see figur through for details. e 22 figure 25 5 includes amplifier voltage and current noise, as well as noise from inte rnal resistors. 6 supply current varies with supply voltage and temp erature. see figure and for details. 27 figure 28
ad8278/ad8279 rev. c | page 7 of 24 absolute maximum ratings table 6. parameter rating supply voltage 18 v maximum voltage at any input pin ?v s + 40 v minimum voltage at any input pin +v s ? 40 v storage temperature range ?65c to +150c specified temperature range ?40c to +85c package glass transition temperature (t g ) 150c 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 the ja values in table 7 assume a 4-layer jedec standard board with zero airflow. table 7. thermal resistance package type ja unit 8-lead msop 135 c/w 8-lead soic 121 c/w 14-lead soic 105 c/w maximum power dissipation the maximum safe power dissipation for the ad8278 and ad8279 are limited by the associated rise in junction tempera- ture (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 performance of the amplifiers. exceeding a temperature of 150c for an extended period may result in a loss of functionality. 2.0 1.6 1.2 0.8 0.4 0 ?50 0 ?25 255075100125 maximum power dissipation (w) ambient temerature (c) t j max = 150c msop ja = 135c/w soic ja = 121c/w 08308-002 figure 3. maximum power dissipation vs. ambient temperature short-circuit current the ad8278 and ad8279 have built-in, short-circuit protection that limits the output current (see figure 29 for more information). while 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. figure 3 and figure 29 , combined with knowledge of the supply voltages and ambient temperature of the part, can be used to determine whether a short circuit will cause the part to exceed its maximum junction temperature. esd caution
ad8278/ad8279 rev. c | page 8 of 24 pin configurations and function descriptions ref 1 ?in 2 +in 3 ?vs 4 nc 8 +vs 7 out 6 sense 5 nc = no connect ad8278 top view (not to scale) 0 8308-003 figure 4. msop pin configuration ref 1 ?in 2 +in 3 ?vs 4 nc 8 +vs 7 out 6 sense 5 nc = no connect ad8278 top view (not to scale) 0 8308-004 figure 5. soic pin configuration table 8. ad8278 pin function descriptions pin no. mnemonic description 1 ref reference voltage input. 2 ?in inverting input. 3 +in noninverting input. 4 ?vs negative supply. 5 sense sense terminal. 6 out output. 7 +vs positive supply. 8 nc no connect. 08308-059 nc 1 ?ina 2 +ina 3 ?vs 4 refa 14 13 12 11 +inb 5 10 ?inb 6 9 nc 7 8 nc = no connect ad8279 top view (not to scale) outa sensea +vs senseb outb refb figure 6. 14-lead soic pin configuration table 9. ad8279 pin function descriptions pin no. mnemonic description 1 nc no connect. 2 ?ina channel a inverting input. 3 +ina channel a noninverting input. 4 ?vs negative supply. 5 +inb channel b noninverting input. 6 ?inb channel b inverting input. 7 nc no connect. 8 refb channel b reference voltage input. 9 outb channel b output. 10 senseb channel b sense terminal. 11 +vs positive supply. 12 sensea channel a sense terminal. 13 outa channel a output. 14 refa channel a reference voltage input.
ad8278/ad8279 rev. c | page 9 of 24 typical performance characteristics v s = 15 v, t a = 25c, r l = 10 k connected to ground, g = ? difference amplifier configuration, unless otherwise noted. 600 500 400 300 200 100 0 ?150 ?100 ?50 0 50 100 150 number of hits system offset voltage (v) 08308-005 n = 3840 mean = ?16.8 sd = 41.7673 figure 7. distribution of typical system offset voltage, g = 2 800 600 700 500 400 300 200 100 0 ?60 ?40 ?20 0 20 40 60 number of hits cmrr (v/v) 08308-006 n = 3837 mean = 7.78 sd = 13.569 figure 8. distribution of typica l common-mode rejection, g = 2 10 ?20 ?15 ?10 ?5 0 5 ?50?35?20?5102540557085 cmrr (v/v) temperature (c) 08308-007 representative data figure 9. cmrr vs. temperature, normalized at 25c, g = ? 80 ?100 ?80 ?60 ?40 ?20 0 20 40 60 ?50 ?35 ?20 ?5 10 25 40 55 70 85 system offset (v) temperature (c) representative data 08308-008 figure 10. system offset vs. temper ature, normalized at 25, g = ? 20 ?30 ?25 ?20 ?15 ?10 ?5 0 5 10 15 ?50 ?35 ?20 ?5 10 25 40 55 70 85 gain error (v/v) temperature (c) representative data 08308-009 figure 11. gain error vs. temperature, normalized at 25c, g = ? 30 ?30 ?20 ?10 0 10 20 ?20 ?15 ?10 ?5 0 5 10 15 20 common-mode voltage (v) output voltage (v) v s = 15v v s = 5v 08308-010 figure 12. input common-mode voltage vs. output voltage, 15 v and 5 v supplies, g = ?
ad8278/ad8279 rev. c | page 10 of 24 10 ?10 ?8 ?6 ?4 ?2 0 2 4 6 8 ?0.5 0.5 1.5 2.5 3.5 4.5 5.5 common-mode voltage (v) output voltage (v) v s = 5v v ref = midsupply v s = 2.7v 08308-011 figure 13. input common-mode voltage vs. output voltage, 5 v and 2.7 v supplies, v ref = midsupply, g = ? 12 ?6 ?4 ?2 0 2 4 6 8 10 ?0.5 0.5 1.5 2.5 3.5 4.5 5.5 common-mode voltage (v) output voltage (v) v s = 5v v s = 2.7v 08308-012 v ref = 0v figure 14. input common-mode voltage vs. output voltage, 5 v and 2.7 v supplies, v ref = 0 v, g = ? 30 ?30 ?20 ?10 0 10 20 ?20 ?15 ?10 ?5 0 10 20 51 5 common-mode voltage (v) output voltage (v) v s = 5v v s = 15v 08308-013 figure 15. input common-mode voltage vs. output voltage, 15 v and 5 v supplies, g = 2 5 ?3 ?2 ?1 0 1 2 3 4 ?0.5 0.5 1.5 2.5 3.5 4.5 5.5 common-mode voltage (v) output voltage (v) v s = 5v v s = 2.7v 08308-014 v ref = midsupply figure 16. input common-mode voltage vs. output voltage, 5 v and 2.7 v supplies, v ref = midsupply, g = 2 6 5 ?2 ?1 0 1 2 3 4 ?0.5 0.5 1.5 2.5 3.5 4.5 5.5 common-mode voltage (v) output voltage (v) v s = 5v v s = 2.7v 08308-015 v ref = 0v figure 17. input common-mode voltage vs. output voltage, 5 v and 2.7 v supplies, v ref = 0 v, g = 2 18 ?36 ?30 ?24 ?18 ?12 ?6 0 6 12 100 10m 1m 100k 10k 1k gain (db) frequency (hz) gain = 2 gain = ? 08308-016 figure 18. gain vs. frequency, 15 v supplies
ad8278/ad8279 rev. c | page 11 of 24 18 ?36 ?30 ?24 ?18 ?12 ?6 0 6 12 100 10m 1m 100k 10k 1k gain (db) frequency (hz) gain = 2 gain = ? 08308-017 figure 19. gain vs. frequenc y, +2.7 v single supply 120 100 80 60 40 20 0 11 m 100k 10k 1k 100 10 cmrr (db) frequency (hz) gain = 2 gain = ? 08308-018 figure 20. cmrr vs. frequency 120 100 80 60 40 20 0 11 m 100k 10k 1k 100 10 psrr (db) frequency (hz) ?psrr +psrr 08308-019 figure 21. psrr vs. frequency + v s ?0.1 ?0.2 ?0.3 ?0.4 ?v s +0.1 +0.2 +0.3 +0.4 21 16141210 864 output voltage swing (v) referred to supply voltages supply voltage (v s ) 8 t a = ?40c t a = +25c t a = +85c t a = +125c 08308-020 figure 22. output voltage swing vs. supply voltage and temperature, r l = 10 k + v s ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 ?1.2 ?v s +0.2 +0.4 +0.6 +0.8 +1.0 +1.2 output voltage swing (v) referred to supply voltages supply voltage (v s ) t a = ?40c t a = +25c t a = +85c t a = +125c 21 16141210 864 08308-021 8 figure 23. output voltage swing vs. supply voltage and temperature, r l = 2 k + v s ?4 ?8 ?v s +4 +8 output voltage swing (v) referred to supply voltages load resistance ( ? ) 1k 100k 10k t a = ?40c t a = +25c t a = +85c t a = +125c 08308-022 figure 24. output voltage swing vs. r l and temperature, v s = 15 v
ad8278/ad8279 rev. c | page 12 of 24 + v s ?0.5 ?1.0 ?1.5 ?2.0 ?v s +0.5 +1.0 +1.5 +2.0 output voltage swing (v) referred to supply voltages output current (ma) 01 987654321 0 t a = ?40c t a = +25c t a = +85c t a = +125c 08308-023 figure 25. output voltage swing vs. i out and temperature, v s = 15 v 180 160 170 150 140 130 120 01 16 1412 10 8642 supply current (a) supply voltage (v) 8 08308-024 figure 26. supply current per ch annel vs. dual-supply voltage, v in = 0 v 180 160 170 150 140 130 120 04 353025201510 5 supply current (a) supply voltage (v) 0 08308-025 figure 27. supply current per cha nnel vs. single-supply voltage, v in = 0 v, v ref = 0 v 250 150 200 100 50 0 ?50 ?30 ?10 10 30 50 70 90 110 130 supply current (a) temperature (c) v s = 15v v s = +2.7v v ref = midsupply 08308-026 figure 28. supply current per channel vs. temperature 30 25 20 15 10 5 0 ?5 ?10 ?15 ?20 ?50 ?30 ?10 10 30 50 70 90 110 130 short-circuit current (ma) temperature (c) i short+ i short? 08308-027 figure 29. short-circuit current per channel vs. temperature 2.0 1.6 1.8 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 ?50 ?30 ?10 10 30 50 70 90 110 130 slew rate (v/s) temperature (c) ?slew rate +slew rate 08308-028 figure 30. slew rate vs. temperature, v in = 20 v p-p, 1 khz
ad8278/ad8279 rev. c | page 13 of 24 08308-029 ?10 ?8 ?6 ?4 ?2 0 2 4 6 8 10 ?5 ?4 ?3 ?2 ?1 0 1 2 3 4 5 nonlinearity (2ppm/div) output voltage (v) figure 31. gain nonlinearity, v s = 15 v, r l 2 k, g = ? 08308-030 ?20 ?12 ?16 ?8 ?4 0 4 8 12 16 20 ?5 ?4 ?3 ?2 ?1 0 1 2 3 4 5 nonlinearity (2ppm/div) output voltage (v) figure 32. gain nonlinearity, v s = 15 v, r l 2 k, g = 2 time (s) 5v/div 40s/div 0.002%/div 6.24s to 0.01% 7.92s to 0.001% 0 8308-031 figure 33. large signal pulse response and settling time, 10 v step, v s = 15 v, g = ? time (s) 1v/div 0.002%/div 3.64s to 0.01% 4.12s to 0.001% 4s/div 0 8308-032 figure 34. large signal pulse response and settling time, 2 v step, v s = 2.7 v, g = ? time (s) 5v/div 0.002%/div 7.6s to 0.01% 9.68s to 0.001% 40s/div 0 8308-033 figure 35. large signal pulse response and settling time, 10 v step, v s = 15 v, g = 2 time (s) 1v/div 0.002%/div 4.34s to 0.01% 5.12s to 0.001% 4s/div 08308-034 figure 36. large signal pulse response and settling time, 2 v step, v s = 2.7 v
ad8278/ad8279 rev. c | page 14 of 24 10s/div 2v/di v 08308-035 figure 37. large signal step response, g = ? 10s/div 5v/di v 08308-036 figure 38. large signal step response, g = 2 30 25 20 15 10 5 0 100 1m 100k 10k 1k output voltage (v p-p) frequency (hz) v s = 15v v s = 5v 08308-037 figure 39. maximum output voltage vs. frequency, v s = 15 v, 5 v 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 100 1m 100k 10k 1k output voltage (v p-p) frequency (hz) v s = 5v v s = 2.7v 08308-038 figure 40. maximum output voltage vs. frequency, v s = 5 v, 2.7 v 20mv/di v 40s/div no load c l = 100pf c l = 147pf c l = 247pf 08308-039 figure 41. small signal step response for various capacitive loads, g = ? 20mv/di v 40s/div c l = 100pf c l = 200pf c l = 247pf c l = 347pf 08308-040 figure 42. small signal step response for various capacitive loads, g = 2
ad8278/ad8279 rev. c | page 15 of 24 50 45 40 35 30 25 20 15 10 5 0 02 150 200 100 50 overshoot (%) capacitive load (pf) 5 0 2v 5v 15v 18v 08308-041 figure 43. small signal overshoot vs. capacitive load, r l 2 k, g = ? 35 30 25 20 15 10 5 0 03 5 0 150 250 300 200 100 50 overshoot (%) capacitive load (pf) 2v 5v 15v 18v 08308-042 figure 44. small signal overshoot vs. capacitive load, r l 2 k, g = 2 1k 100 10 0.1 100k 10k 1k 100 10 1 noise (nv/ hz) frequency (hz) gain = 2 gain = ? 08308-043 figure 45. voltage noise density vs. frequency 1v/di v 1s/div gain = 2 gain = ? 08308-044 figure 46. 0.1 hz to 10 hz voltage noise 08308-060 0 20 40 60 80 100 120 140 160 10 100 1k 10k 100k frequency (hz) 2k? load channel separation (db) figure 47. channel separation
ad8278/ad8279 rev. c | page 16 of 24 theory of operation circuit information each channel of the ad8278 and ad8279 consists of a low power, low noise op amp and four laser-trimmed on-chip resistors. these resistors can be externally connected to make a variety of amplifier configurations, including difference, noninverting, and inverting configurations. taking advantage of the integrated resistors of the ad8278 and ad8279 provides the designer with several benefits over a discrete design, including smaller size, lower cost, and better ac and dc performance. 2 5 3 1 6 7 4 40k ? 20k ? 40k ? ?vs +vs ?in +in sense out ref 20k ? ad8278 08308-045 figure 48. functional block diagram dc performance much of the dc performance of op amp circuits depends on the accuracy of the surrounding resistors. using superposition to analyze a typical difference amplifier circuit, as is shown in figure 49 , the output voltage is found to be ? ? ? ? ? ? ? ? ? ? ? ? ? + ? ? ? ? ? ? ? ? + = ? + r3 r4 v r3 r4 r2r1 r2 vv in in out 1 this equation demonstrates that the gain accuracy and common- mode rejection ratio of the ad8278 and ad8279 is determined primarily by the matching of resistor ratios. even a 0.1% mismatch in one resistor degrades the cmrr to 69 db for a g = 2 difference amplifier. the difference amplifier output voltage equation can be reduced to () ? + ? = in in out vv r3 r4 v as long as the following ratio of the resistors is tightly matched: r3 r4 r1 r2 = the resistors on the ad8278 and ad8279 are laser trimmed to match accurately. as a result, the ad8278 and ad8279 provide superior performance over a discrete solution, enabling better cmrr, gain accuracy, and gain drift, even over a wide tempera- ture range. ac performance component sizes and trace lengths are much smaller in an ic than on a pcb; therefore, the corresponding parasitic elements are also smaller. this results in better ac performance of the ad8278 and ad8279. for example, the positive and negative input terminals of the ad8278 and ad8279 op amps are intentionally not pinned out. by not connecting these nodes to the traces on the pcb, their capacitance remains low and balanced, resulting in improved loop stability and excellent common-mode rejection over frequency. driving the ad8278 and ad8279 care should be taken to drive the ad8278 and ad8279 with a low impedance source, for example, another amplifier. source resistance of even a few kilohms (k) can unbalance the resistor ratios and, therefore, significantly degrade the gain accuracy and common-mode rejection of the ad8278 and ad8279. because all configurations present several kilohms (k) of input resistance, the ad8278 and ad8279 do not require a high current drive from the source and are easy to drive. input voltage range the ad8278 and ad8279 are able to measure input voltages beyond the supply rails. the internal resistors divide down the voltage before it reaches the internal op amp and provide protection to the op amp inputs. figure 49 shows an example of how the voltage division works in a difference amplifier configuration. for the ad8278 and ad8279 to measure correctly, the input voltages at the input nodes of the internal op amp must stay below 1.5 v of the positive supply rail and can exceed the negative supply rail by 0.1 v. refer to the power supplies section for more details. 08308-062 r4 v in+ v in? r3 r1 r2 r2 r1 + r2 (v in+ ) r2 r1 + r2 (v in+ ) figure 49. voltage division in the difference amplifier configuration the ad8278 and ad8279 have integrated esd diodes at the inputs that provide overvoltage protection. this feature simplifies system design by eliminating the need for additional external protection circuitry and enables a more robust system. the voltages at any of the inputs of the parts can safely range from +v s ? 40 v up to ?v s + 40 v. for example, on 10 v supplies, input voltages can go as high as 30 v. care should be taken to not exceed the +v s ? 40 v to ?v s + 40 v input limits to avoid damaging the parts.
ad8278/ad8279 rev. c | page 17 of 24 power supplies the ad8278 and ad8279 operate extremely well over a very wide range of supply voltages. they can operate on a single supply as low as 2 v and as high as 36 v, under appropriate setup conditions. for best performance, the user should ensure that the internal op amp is biased correctly. the internal input terminals of the op amp must have sufficient voltage headroom to operate properly. proper operation of the part requires at least 1.5 v between the positive supply rail and the op amp input terminals. this relationship is expressed in the following equation: v5.1 ?+< + s ref vv r2r1 r1 for example, when operating on a +v s = 2 v single supply and v ref = 0 v, it can be seen from figure 50 that the op amp input terminals are biased at 0 v, allowing more than the required 1.5 v headroom. however, if v ref = 1 v under the same conditions, the input terminals of the op amp are biased at 0.66 v (g = ?). now the op amp does not have the required 1.5 v headroom and cannot function. therefore, the user must increase the supply voltage or decrease v ref to restore proper operation. the ad8278 and ad8279 are typically specified at single and dual supplies, but they can be used with unbalanced supplies as well; for example, ?v s = ?5 v, +v s = +20 v. the difference between the two supplies must be kept below 36 v. the positive supply rail must be at least 2 v above the negative supply. 08308-046 r4 r3 r1 r2 r1 r1 + r2 (v ref ) r1 r1 + r2 (v ref ) v ref figure 50. ensure sufficient voltage headroom on the internal op amp inputs use a stable dc voltage to power the ad8278 and ad8279. noise on the supply pins can adversely affect performance. place a bypass capacitor of 0.1 f between each supply pin and ground, as close as possible to each supply pin. use a tantalum capacitor of 10 f 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.
ad8278/ad8279 rev. c | page 18 of 24 applications information configurations the ad8278 and ad8279 can be configured in several ways (see figure 51 to figure 57 ). these configurations have excellent gain accuracy and gain drift because they rely on the internal matched resistors. note that figure 53 shows the ad8278 and ad8279 as difference amplifiers with a midsupply reference voltage at the noninverting input. this allows the ad8278 and ad8279 to be used as a level shifter, which is appropriate in single-supply applications that are referenced to midsupply. table 10 lists several single-ended amplifier configurations that are not illustrated. 40k? 2 3 5 1 6 20k ? 40k? 20k ? ?in out +in v out = ? (v in+ ? v in ? ) 08308-047 ad8278 figure 51. difference amplifier, gain = ? 20k? 5 1 2 3 6 40k ? 20k? 40k ? ?in out +in v out = 2(v in+ ? v in ? ) 08308-048 ad8278 figure 52. difference amplifier, gain = 2 40k? 2 3 5 1 v ref = midsupply 6 20k? 40k? 20k? ?in out +in v out = ? (v in+ ? v in ? ) + v ref 08308-049 ad8278 figure 53. difference amplifier, gain = ?, referenced to midsupply 20k? 5 1 2 3 v ref = midsupply 6 40k? 20k? 40k? ?in out +in v out = 2 (v in+ ? v in ? ) + v ref 08308-050 ad8278 figure 54. difference amplifier, ga in = 2, referenced to midsupply 40k? 2 3 5 1 6 20k ? 40k? 20k ? in out v out = ??v in 0 8308-051 ad8278 figure 55. inverting amplifier, gain = ?? 40k? 25 6 20k? in out 3 1 40k? 20k ? v out = 1.5v in 08308-052 ad8278 figure 56. noninverting amplifier, gain = 1.5 20k ? 2 3 5 1 6 40k ? 20k ? 40k ? out in v out = 2v in 0 8308-053 ad8278 figure 57. noninverting amplifier, gain = 2 table 10. ad8278 difference and single-ended amplifier configurations amplifier configuration signal gain pin 1 (ref) pin 2 (vin?) pin 3 (vin+) pin 5 (sense) difference amplifier +? gnd in? in+ out difference amplifier +2 in+ out gnd in? single-ended inverting amplifier ?? gnd in gnd out single-ended inverting amplifier ?2 gnd out gnd in single-ended noninverting amplifier +3?2 in gnd in out single-ended noninverting amplifier +3 in out in gnd single-ended noninverting amplifier +? gnd gnd in out single-ended noninverting amplifier +1 in gnd gnd out single-ended noninverting amplifier +1 gnd out in gnd single-ended noninverting amplifier +2 in out gnd gnd
ad8278/ad8279 rev. c | page 19 of 24 the reference must be driven with a low impedance source to maintain the internal resistor ratio. an example using the low power, low noise op1177 as a reference is shown in figure 58 . incorrect v correct ad8278 op1177 + ? v ref ad8278 ref 0 8308-054 figure 58. driving the reference pin differential output the two difference amplifiers of the ad8279 can be configured to provide a differential output, as shown in figure 59 . this differential output configuration is suitable for various applications, such as strain gage excitation and single-ended-to-differential conversion. the differential output voltage has a gain twice that of a single ad8279 channel, as shown in the following equation: v diff_out = v +out ? v ?out = 2 g ad8279 ( v in+ C v in? ) if the ad8279 amplifiers are each configured for g = ?, the differential gain is 1; if the ad8279 amplifiers are each configured for g = 2, the differential gain is 4. 08308-061 12 2 14 3 13 11 20k ? 40k ? 20k ? +vs ?in +in +out 40k ? ad8279 10 6 8 5 9 4 20k ? 40k ? 20k ? ?vs 40k ? ?out figure 59. ad8279 differential output g = 4 configuration instrumentation amplifier the ad8278 and ad8279 can be used as building blocks for a low power, low cost instrumentation amplifier. an instrumentation amplifier provides high impedance inputs and delivers high common-mode rejection. combining the ad8278 with an analog devices, inc., low power amplifier (see table 11 ) creates a precise, power efficient voltage measurement solution suitable for power critical systems. r g r f r f ?in +in a1 a2 ad8278/ ad8279 40k? 20k ? 20k ? 40k ? ref v out v out = (1 + 2r f /r g ) (v in+ ? v in? ) 2 08308-056 figure 60. low power precision instrumentation amplifier table 11. low power op amps op amp (a1, a2) features ad8506 dual micropower op amp ad8607 precision dual micropower op amp ad8617 low cost cmos micropower op amp ad8667 dual precision cmos micropower op amp it is preferable to use dual op amps for the high impedance inputs because they have better matched performance and track each other over temperature. the ad8278 and ad8279 difference amplifiers cancel out common-mode errors from the input op amps, if they track each other. the differential gain accuracy of the in-amp is proportional to how well the input feedback resistors (r f ) match each other. the cmrr of the in-amp increases as the differential gain is increased (1 + 2r f /r g ), but a higher gain also reduces the common-mode voltage range. refer to a designers guide to instrumentation amplifiers for more design ideas and considerations at www.analog.com , under technical documentation.
ad8278/ad8279 rev. c | page 20 of 24 outline dimensions 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-012-aa 012407-a 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 (0.1968) 4.80 (0.1890) 4.00 (0.1574) 3.80 (0.1497) 1.27 (0.0500) bsc 6.20 (0.2441) 5.80 (0.2284) 0.51 (0.0201) 0.31 (0.0122) coplanarity 0.10 figure 61. 8-lead standard small outline package [soic_n] narrow body (r-8) dimensions shown in millimeters and (inches) compliant to jedec standards mo-187-aa 6 0 0.80 0.55 0.40 4 8 1 5 0.65 bsc 0.40 0.25 1.10 max 3.20 3.00 2.80 coplanarity 0.10 0.23 0.09 3.20 3.00 2.80 5.15 4.90 4.65 pin 1 identifier 15 max 0.95 0.85 0.75 0.15 0.05 10-07-2009-b figure 62. 8-lead mini small outline package [msop] (rm-8) dimensions shown in millimeters
ad8278/ad8279 rev. c | page 21 of 24 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-012-ab 060606-a 14 8 7 1 6.20 (0.2441) 5.80 (0.2283) 4.00 (0.1575) 3.80 (0.1496) 8.75 (0.3445) 8.55 (0.3366) 1.27 (0.0500) bsc seating plane 0.25 (0.0098) 0.10 (0.0039) 0.51 (0.0201) 0.31 (0.0122) 1.75 (0.0689) 1.35 (0.0531) 0.50 (0.0197) 0.25 (0.0098) 1.27 (0.0500) 0.40 (0.0157) 0.25 (0.0098) 0.17 (0.0067) coplanarity 0.10 8 0 45 figure 63. 14-lead standard small outline package [soic_n] narrow body (r-14) dimensions shown in millimeters and (inches) ordering guide model 1 temperature range package description package option branding ad8278arz ?40c to +85c 8-lead soic_n r-8 ad8278arz-r7 ?40c to +85c 8-lead soic_n, 7" tape and reel r-8 ad8278arz-rl ?40c to +85c 8-lead soic_n, 13" tape and reel r-8 ad8278brz ?40c to +85c 8-lead soic_n r-8 ad8278brz-r7 ?40c to +85c 8-lead soic_n, 7" tape and reel r-8 AD8278BRZ-RL ?40c to +85c 8-lead soic_n, 13" tape and reel r-8 ad8278armz ?40c to +85c 8-lead msop rm-8 y21 ad8278armz-r7 ?40c to +85c 8-lead msop, 7" tape and reel rm-8 y21 ad8278armz-rl ?40c to +85c 8-lead msop, 13" tape and reel rm-8 y21 ad8278brmz ?40c to +85c 8-lead msop rm-8 y22 ad8278brmz-r7 ?40c to +85c 8-lead msop, 7" tape and reel rm-8 y22 ad8278brmz-rl ?40c to +85c 8-lead msop, 13" tape and reel rm-8 y22 ad8279arz ?40c to +85c 14-lead soic_n r-14 ad8279arz-r7 ?40c to +85c 14-lead soic_n, 7" tape and reel r-14 ad8279arz-rl ?40c to +85c 14-lead soic_n, 13" tape and reel r-14 ad8279brz ?40c to +85c 14-lead soic_n r-14 ad8279brz-r7 ?40c to +85c 14-lead soic_n, 7" tape and reel r-14 ad8279brz-rl ?40c to +85c 14-lead soic_n, 13" tape and reel r-14 1 z = rohs compliant part.
ad8278/ad8279 rev. c | page 22 of 24 notes
ad8278/ad8279 rev. c | page 23 of 24 notes
ad8278/ad8279 rev. c | page 24 of 24 notes ?2009C2011 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. d08308-0-1/11(c)

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