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low power, wide supply range, low cost unity-gain difference amplifiers ad8276/ad8277 rev. b 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 ?2009C2010 analog devices, inc. all rights reserved. features wide input range beyond supplies rugged input overvoltage protection low supply current: 200 a maximum per channel low power dissipation: 0.5 mw at v s = 2.5 v bandwidth: 550 khz cmrr: 86 db minimum, dc to 10 khz low offset voltage drift: 2 v/c maximum (b grade) low gain drift: 1 ppm/c maximum (b grade) enhanced slew rate: 1.1 v/s wide power supply range: single supply: 2 v to 36 v dual supplies: 2 v to 18 v applications voltage measurement and monitoring current measurement and monitoring differential output instrumentation amplifier portable, battery-powered equipment test and measurement general description the ad8276/ad8277 are general-purpose, unity-gain difference amplifiers intended for precision signal conditioning in power critical applications that require both high performance and low power. they provide exceptional common-mode rejection ratio (86 db) and high bandwidth while amplifying signals 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 amplifiers extends to almost double the supply voltage, making these amplifiers 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 amps. the ad8276/ad8277 are unity-gain stable. while they are optimized for use as difference amplifiers, they can also be connected in high precision, single-ended configurations with g = ?1, +1, +2. the ad8276/ad8277 provide an integrated precision solution that has smaller size, lower cost, and better performance than a discrete alternative. the ad8276/ad8277 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 per channel, which is ideal for battery- operated and portable systems. functional block diagram 07692-001 2 5 3 1 6 7 4 40k ? 40k? 40k ? ?vs +vs ?in +in sense out ref 40k? ad8276 figure 1. ad8276 07692-052 2 12 3 14 13 11 40k ? 40k? 40k ? +vs ?ina +ina sensea outa refa 40k? ad8277 6 10 5 8 9 4 40k ? 40k? 40k ? ?vs ?inb +inb senseb outb refb 40k? figure 2. ad8277 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) ad8278 ad8274 ad8206 (b) amp03 ad8216 (b) 1 u = unidirectional, b = bidirectional. the ad8276 is available in the space-saving 8-lead msop and soic packages, and the ad8277 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.
ad8276/ad8277 rev. b | page 2 of 20 table of contents features .............................................................................................. 1 ? applications ....................................................................................... 1 ? general description ......................................................................... 1 ? functional block diagram .............................................................. 1 ? revision history ............................................................................... 2 ? specifications ..................................................................................... 3 ? absolute maximum ratings ............................................................ 5 ? thermal resistance ...................................................................... 5 ? maximum power dissipation ..................................................... 5 ? short-circuit current .................................................................. 5 ? esd caution .................................................................................. 5 ? pin configurations and function descriptions ........................... 6 ? typical performance characteristics ............................................. 8 ? theory of operation ...................................................................... 14 ? circuit information .................................................................... 14 ? driving the ad8276/ad8277 .................................................. 14 ? input voltage range ................................................................... 14 ? power supplies ............................................................................ 15 ? applications information .............................................................. 16 ? configurations ............................................................................ 16 ? differential output .................................................................... 16 ? current source ............................................................................ 17 ? voltage and current monitoring .............................................. 17 ? instrumentation amplifier........................................................ 18 ? rtd .............................................................................................. 18 ? outline dimensions ....................................................................... 19 ? ordering guide .......................................................................... 20 ? revision history 4/10rev. a to rev. b changes to figure 53 ...................................................................... 18 updated outline dimensions ....................................................... 19 7/09rev. 0 to rev. a added ad8277 ................................................................... universal changes to features section............................................................ 1 changes to general description section ...................................... 1 added figure 2; renumbered sequentially .................................. 1 changes to specifications section .................................................. 3 changes to figure 3 and table 5 ..................................................... 5 added figure 5 and table 7; renumbered sequentially ............. 7 changes to figure 10 ........................................................................ 8 changes to figure 34 ...................................................................... 12 added figure 36 ............................................................................. 13 changes to input voltage range section .................................... 14 changes to power supplies section and added figure 40 ........ 15 added to figure 40 ......................................................................... 15 changes to differential output section ...................................... 16 added figure 47 and changes to current source section ....... 17 added voltage and current monitoring section and figure 49..... 17 moved instrumentation amplifier section and added rtd section ........................................................................................................ 18 changes to ordering guide .......................................................... 20 5/09revision 0: initial version
ad8276/ad8277 rev. b | page 3 of 20 specifications v s = 5 v to 15 v, v ref = 0 v, t a = 25c, r l = 10 k connected to ground, g = 1 difference amplifier configuration, unless otherwise noted. table 2. g = 1 grade b grade a parameter conditions min typ max min typ max unit input characteristics system offset 1 100 200 100 500 v vs. temperature t a = ?40c to +85c 200 500 v average temperature coefficient t a = ?40c to +85c 0.5 2 2 5 v/c vs. power supply v s = 5 v to 18 v 5 10 v/v common-mode rejection ratio (rti) v s = 15 v, v cm = 27 v, r s = 0 86 80 db input voltage range 2 ?2(v s + 0.1) +2(v s ? 1.5) ?2(v s + 0.1) +2(v s ? 1.5) v impedance 3 differential 80 80 k common mode 40 40 k dynamic performance bandwidth 550 550 khz slew rate 0.9 1.1 0.9 1.1 v/s settling time to 0.01% 10 v step on output, c l = 100 pf 15 15 s settling time to 0.001% 16 16 s channel separation f = 1 khz 130 130 db 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 5 10 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 2 2 v p-p f = 1 khz 65 70 65 70 nv/hz power supply supply current 6 200 200 a vs. temperature t a = ?40c to +85c 250 250 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 in the the section for details. input voltage range ory of operation 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 18 figure 21 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. 22 figure 24 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.
ad8276/ad8277 rev. b | page 4 of 20 v s = +2.7 v to <5 v, v ref = midsupply, t a = 25c, r l = 10 k connected to midsupply, g = 1 difference amplifier configuration, unless otherwise noted. table 3. g = 1 grade b grade a parameter conditions min typ max min typ max unit input characteristics system offset 1 100 200 100 500 v vs. temperature t a = ?40c to +85c 200 500 v average temperature coefficient t a = ?40c to +85c 0.5 2 2 5 v/c vs. power supply v s = 5 v to 18 v 5 10 v/v 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 ?2(v s + 0.1) +2(v s ? 1.5) ?2(v s + 0.1) +2(v s ? 1.5) v impedance 3 differential 80 80 k common mode 40 40 k dynamic performance bandwidth 450 450 khz slew rate 1.0 1.0 v/s settling time to 0.01% 8 v step on output, c l = 100 pf, v s = 10 v 5 5 s channel separation f = 1 khz 130 130 db 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 2 v p-p f = 1 khz 65 65 nv/hz power supply supply current 6 t a = ?40c to +85c 200 200 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 in the section for details. input voltage ra nge theory of operation 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 18 figure 21 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. 23 figure 24
ad8276/ad8277 rev. b | page 5 of 20 absolute maximum ratings table 4. 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 5 assume a 4-layer jedec standard board with zero airflow. table 5. 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 ad8276/ad8277 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 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 25 50 75 100 125 maximum power dissipation (w) ambient temerature (c) t j max = 150c 8-lead msop ja = 135c/w 8-lead soic ja = 121c/w 07692-002 14-lead soic ja = 105c/w figure 3. maximum power dissipation vs. ambient temperature short-circuit current the ad8276/ad8277 have built-in, short-circuit protection that limits the output current (see figure 25 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 25 , 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
ad8276/ad8277 rev. b | page 6 of 20 pin configurations and function descriptions ref 1 ?in 2 +in 3 ?vs 4 nc 8 +vs 7 out 6 sense 5 nc = no connect ad8276 top view (not to scale) 0 7692-003 figure 4. ad8276 8-lead msop pin configuration ref 1 ?in 2 +in 3 ?vs 4 nc 8 +vs 7 out 6 sense 5 nc = no connect ad8276 top view (not to scale) 0 7692-004 figure 5. ad8276 8-lead soic pin configuration table 6. ad8276 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.
ad8276/ad8277 rev. b | page 7 of 20 nc 1 ?ina 2 +ina 3 ?vs 4 refa 14 outa 13 sensea 12 +vs 11 +inb 5 senseb 10 ?inb 6 outb 9 nc 7 refb 8 nc = no connect ad8277 top view (not to scale) 07692-053 figure 6. ad8277 14-lead soic pin configuration table 7. ad8277 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.
ad8276/ad8277 rev. b | page 8 of 20 typical performance characteristics v s = 15 v, t a = 25c, r l = 10 k connected to ground, g = 1 difference amplifier configuration, unless otherwise noted. 600 500 400 300 200 100 0 ?300 ?200 ?100 0 100 200 300 number of hits system offset voltage (v) 07692-005 n = 2042 mean = ?2.28 sd = 32.7 figure 7. distribution of typical system offset voltage 400 300 200 100 0 ?90 ?60 ?30 0 30 60 90 number of hits cmrr (v/v) 07692-006 n = 2040 mean = ?0.87 sd = 16.2 figure 8. distribution of ty pical common-mode rejection 4 2 0 ?2 ?4 ?6 ?8 ?50 ?35 ?20 ?5 10 25 40 55 70 85 90 cmrr (v/v) temperature (c) representative data 07692-007 figure 9. cmrr vs. temperature, normalized at 25c 07692-008 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) figure 10. system offset vs. te mperature, normalized at 25c 20 ?30 ?25 ?20 ?15 ?10 ?5 0 5 10 15 gain error (v/v) 07692-009 ?50 ?35 ?20 ?5 10 25 40 55 70 85 90 temperature (c) representative data figure 11. gain error vs. temperature, normalized at 25c 10 0 ?10 ?20 ?30 ?40 ?50 100 10m 1m 100k 10k 1k gain (db) frequency (hz) v s = 15v v s = +2.7v 07692-010 figure 12. gain vs. frequency, v s = 15 v, +2.7 v
ad8276/ad8277 rev. b | page 9 of 20 120 100 80 60 40 20 0 11 m v s = 15v 100k 10k 1k 100 10 cmrr (db) frequency (hz) 07692-011 figure 13. cmrr vs. frequency 120 100 80 60 40 20 0 11 m 100k 10k 1k 100 10 psrr (db) frequency (hz) ?psrr +psrr 07692-012 figure 14. psrr vs. frequency 30 20 10 0 ?10 ?20 ?30 ?20 201510 50 ?5 ?10 ?15 common-mode voltage (v) output voltage (v) v s = 5v v s = 15v 07692-013 figure 15. input common-mode voltage vs. output voltage, 15 v and 5 v supplies 8 4 6 2 0 ?2 ?4 ?6 ?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 07692-014 figure 16. input common-mode voltage vs. output voltage, 5 v and 2.7 v supplies, v ref = midsupply 8 4 6 2 0 ?2 ?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 ref = 0v v s = 2.7v 07692-015 figure 17. input common-mode voltage vs. output voltage, 5 v and 2.7 v supplies, v ref = 0 v + 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 07692-016 figure 18. output voltage swing vs. supply voltage per channel and temperature, r l = 10 k
ad8276/ad8277 rev. b | page 10 of 20 + 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 8 16141210 864 07692-017 figure 19. output voltage swing vs. supply voltage per channel 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 07692-018 figure 20. output voltage swing vs. r l and temperature, v s = 15 v + 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 07692-019 figure 21. 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 07692-020 figure 22. supply current per channel 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 07692-021 figure 23. supply current per channel 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 07692-022 v ref = midsupply figure 24. supply current per channel vs. temperature
ad8276/ad8277 rev. b | page 11 of 20 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? 07692-023 figure 25. short-circuit current per channel vs. temperature 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) ?sr +sr 07692-024 figure 26. slew rate vs. temperature, v in = 20 v p-p, 1 khz 8 6 4 2 0 ?2 ?4 ?6 ?8 ?10?8?6?4?20246810 nonlinearity (2ppm/div) output voltage (v) 07692-025 figure 27. gain nonlinearity, v s = 15 v, r l 2 k 0 7692-026 0.002%/div 5v/div 11.24 s to 0.01% 13.84s to 0.001% 40s/div time (s) figure 28. large-signal pulse response and settling time, 10 v step, v s = 15 v 0 7692-027 0.002%/div 1v/div 4.34 s to 0.01% 5.12s to 0.001% 40s/div time (s) figure 29. large-signal pulse response and settling time, 2 v step, v s = 2.7 v 07692-028 2v/di v 10s/div figure 30. large-signal step response
ad8276/ad8277 rev. b | page 12 of 20 30 25 20 15 10 5 0 100 1k 10k 100k 1m output voltage (v p-p) frequency (hz) v s = 15v v s = 5v 07692-029 figure 31. 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 1k 10k 100k 1m output voltage (v p-p) frequency (hz) v s = 5v v s = 2.7v 07692-030 figure 32. maximum output voltage vs. frequency, v s = 5 v, 2.7 v 07692-050 20mv/di v 40s/div c l = 100pf c l = 200pf c l = 300pf c l = 470pf figure 33. small-signal step response for various capacitive loads 40 30 35 25 20 15 10 5 0 100 150 200 250 300 350 400 2v 5v 15v 18v overshoot (%) capacitive load (pf) 07692-051 figure 34. small-signal overshoot vs. capacitive load, r l 2 k 1k 100 10 0.1 100k 10k 1k 100 10 1 noise (nv/ hz) frequency (hz) 07692-034 figure 35. voltage noise density vs. frequency 07692-035 1v/di v 1s/div figure 36. 0.1 hz to 10 hz voltage noise
ad8276/ad8277 rev. b | page 13 of 20 0 0 k 160 0 20 40 60 80 100 120 140 11 10k 1k 100 10 channel separation (db) frequency (hz) 07692-055 no load 10k ? load 2k ? load 1k ? load figure 37. channel separation
ad8276/ad8277 rev. b | page 14 of 20 theory of operation circuit information each channel of the ad8276/ad8277 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 ad8276/ad8277 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 ? 40k ? 40k ? ?vs +vs in? in+ sense out ref ad8276 40k ? 07692-031 figure 38. 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 39 , 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 ad8276/ad8277 is determined primarily by the matching of resistor ratios. even a 0.1% mismatch in one resistor degrades the cmrr to 66 db for a g = 1 difference amplifier. the difference amplifier output voltage equation can be reduced to () ? + ? = n iin 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 ad8276/ad8277 are laser trimmed to match accurately. as a result, the ad8276/ad8277 provide superior performance over a discrete solution, enabling better cmrr, gain accuracy, and gain drift, even over a wide temperature range. ac performance component sizes and trace lengths are much smaller in an ic than on a pcb, so the corresponding parasitic elements are also smaller. this results in better ac performance of the ad8276/ ad8277. for example, the positive and negative input terminals of the ad8276/ad8277 op amps are intentionally not pinned out. by not connecting these nodes to the traces on the pcb, the capacitance remains low, resulting in improved loop stability and excellent common-mode rejection over frequency. driving the ad8276/ad8277 care should be taken to drive the ad8276/ad8277 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 ad8276/ad8277. because all configurations present several kilohms of input resistance, the ad8276/ad8277 do not require a high current drive from the source and so are easy to drive. input voltage range the ad8276/ad8277 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 39 shows an example of how the voltage division works in a difference amplifier configuration. for the ad8276/ad8277 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. r4 v in+ v in? r3 r1 r2 r2 r1 + r2 (v in+ ) r2 r1 + r2 (v in+ ) 0 7692-033 figure 39. voltage division in the difference amplifier configuration the ad8276/ad8277 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 risking damage to the parts.
ad8276/ad8277 rev. b | page 15 of 20 power supplies the ad8276/ad8277 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 must exercise care that the setup conditions 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 40 that the input terminals of the op amp 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 0.5 v, barely allowing the required 1.5 v headroom. this setup does not allow any practical voltage swing on the non inverting input. therefore, the user needs to increase the supply voltage or decrease v ref to restore proper operation. the ad8276/ad8277 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 and reference voltage. r4 v ref r3 r1 r2 r1 r1 + r2 (v ref ) r1 r1 + r2 (v ref ) 07692-032 figure 40. ensure sufficient voltage headroom on the internal op amp inputs use a stable dc voltage to power the ad8276/ad8277. 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.
ad8276/ad8277 rev. b | page 16 of 20 applications information configurations the ad8276/ad8277 can be configured in several ways (see figure 42 to figure 46 ). all of these configurations have excellent gain accuracy and gain drift because they rely on the internal matched resistors. note that figure 43 shows the ad8276/ad8277 as difference amplifiers with a midsupply reference voltage at the noninverting input. this allows the ad8276/ad8277 to be used as a level shifter, which is appropriate in single-supply applications that are referenced to midsupply. as with the other inputs, 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 41 . incorrect v correct ad8276 op1177 + ? v ref ad8276 ref 0 7692-037 figure 41. driving the reference pin 40k? 2 3 5 1 6 40k ? 40k? 40k ? ?in out +in v out = v in+ ? v in ? 07692-038 figure 42. difference amplifier, gain = 1 40k? 2 3 5 1 v ref = midsupply 6 40k ? 40k? 40k ? ?in out +in v out = v in+ ? v in ? 07692-039 figure 43. difference amplifier, ga in = 1, referenced to midsupply 40k? 2 3 5 1 6 40k ? 40k? 40k ? in out v out = ?v in 0 7692-040 figure 44. inverting amplifier, gain = ?1 40k ? 5 1 2 3 6 40k ? 40k ? 40k ? out in v out = v in 0 7692-041 figure 45. noninverting amplifier, gain = 1 40k? 25 6 40k? in out 3 1 40k? 40k ? v out = 2v in 07692-042 figure 46. noninverting amplifier, gain = 2 differential output certain systems require a differential signal for better perfor- mance, such as the inputs to differential analog-to-digital converters. figure 47 shows how the ad8276/ad8277 can be used to convert a single-ended output from an ad8226 instrumentation amplifier into a differential signal. the internal matched resistors of the ad8276 at the inverting input maximize gain accuracy while generating a differential signal. the resistors at the noninverting input can be used as a divider to set and track the common-mode voltage accurately to midsupply, especially when running on a single supply or in an environment where the supply fluctuates. the resistors at the noninverting input can also be shorted and set to any appropriate bias voltage. note that the v bias = v cm node indicated in figure 47 is internal to the ad8276 because it is not pinned out. 07692-043 ad8276 a d8226 v ref +in ?in r r r r v s ? v s + ?out +out v bias = v cm figure 47. differential output with supply tracking on common-mode voltage reference
ad8276/ad8277 rev. b | page 17 of 20 the differential output voltage and common-mode voltage of the ad8226 is shown in the following equations: v diff_out = v +out ? v ?out = gain ad8226 ( v +in C v ?in ) v cm = ( v s+ ? v s? )/2 = v bias refer to the ad8226 data sheet for additional information. 0 7692-056 2 12 3 14 13 11 40k? 40k ? 40k? +vs ?in +in +out 40k ? ad8277 6 10 5 8 9 4 40k? 40k ? 40k? ?vs 40k ? ?out figure 48. ad8277 differential output configuration the two difference amplifiers of the ad8277 can be configured to provide a differential output, as shown in figure 48 . 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 of 2 as shown in the following equation: v diff_out = v +out ? v ?out = 2 ( v +in C v ?in ) current source the ad8276 difference amplifier can be implemented as part of a voltage-to-current converter or a precision constant current source as shown in figure 49 . using an integrated precision solution such as the ad8276 provides several advantages over a discrete solution, including space-saving, improved gain accuracy, and temperature drift. the internal resistors are tightly matched to minimize error and temperature drift. if the external resistors, r1 and r2, are not well-matched, they become a significant source of error in the system, so precision resistors are recom- mended to maintain performance. the adr821 provides a precision voltage reference and integrated op amp that also reduces error in the signal chain. the ad8276 has rail-to-rail output capability that allows higher current outputs. ref 1 2 3 4 5 10 9 8 7 6 v? v+ adr821 40k ? 40k ? r load r1 r2 2n3904 40k ? 40k ? v + 7 4 5 6 2 3 1 ad8276 ?2.5v i o = 2.5v(1/40k ? + 1/r1) r1 = r2 07692-046 figure 49. constant current source voltage and current monitoring voltage and current monitoring is critical in the following applications: power line metering, power line protection, motor control applications, and battery monitoring. the ad8276/ ad8277 can be used to monitor voltages and currents in a system, as shown in figure 50 . as the signals monitored by the ad8276/ad8277 rise above or drop below critical levels, a circuit event can be triggered to correct the situation or raise a warning. op1177 07692-057 i 1 r ad8276 i 3 i c r ad8276 v 1 r ad8276 v 3 r ad8276 v c r ad8276 8:1 adc figure 50.voltage and current monitoring in 3-phase power line protection using the ad8276 figure 50 shows an example of how the ad8276 can be used to monitor voltage and current on a 3-phase power supply. i 1 through i 3 are the currents to be monitored, and v 1 through v 3 are the voltages to be monitored on each phase. i c and v c are the common or zero lines. couplers or transformers interface the power lines to the front-end circuitry and provide attenuation, isolation, and protection. on the current monitoring side, current transformers (cts) step down the power-line current and isolate the front-end circuitry from the high voltage and high current lines. across the inputs of each difference amplifier is a shunt resistor that converts the coupled current into a voltage. the value of the
ad8276/ad8277 rev. b | page 18 of 20 resistor is determined by the characteristics of the coupler or transformer and desired input voltage ranges to the ad8276. table 8. 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 on the voltage monitoring side, potential transformers (pts) are used to provide coupling and galvanic isolation. the pts present a load to the power line and also step down the voltage to a measureable level. the ad8276 helps to build a robust system because it allows input voltages that are almost double its supply voltage, while providing additional input protection in the form of the integrated esd diodes. 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 ad8276 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. note that dual supplies must be used for proper operation of this configuration. not only does the ad8276 monitor the voltage and currents on the power lines, it is able to reject very high common-mode voltages that may appear at the inputs. the ad8276 also performs the differential-to-single-ended conversion on the input voltages. the 80 k differential input impedance that the ad8276 presents is high enough that it should not load the input signals. 07692-058 r sh i sh ad8276 v out = i sh r sh refer to a designers guide to instrumentation amplifiers for more design ideas and considerations. rtd resistive temperature detectors (rtds) are often measured remotely in industrial control systems. the wire lengths needed to connect the rtd to a controller add significant cost and resistance errors to the measurement. the ad8276 difference amplifier is effective in measuring errors caused by wire resistance in remote 3-wire rtd systems, allowing the user to cancel out the errors introduced by the wires. its excellent gain drift provides accurate measurements and stable performance over a wide temperature range. figure 51. ad8276 monitoring cu rrent through a shunt resistor figure 51 shows how the ad8276 can be used to monitor the current through a small shunt resistor. this is useful in power critical applications such as motor control (current sense) and battery monitoring. instrumentation amplifier 0 7692-059 ad8276 r l2 r l1 v out - adc r l3 r t i ex 40k ? 40k ? 40k ? 40k ? the ad8276/ad8277 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 ad8276 with an analog devices, inc. low power amplifier (see table 8 ) creates a precise, power efficient voltage measurement solution suitable for power critical systems. r g r f r f ?in +in a1 a2 ad8276 40k ? 40k ? 40k ? 40k ? ref v out v out = (1 + 2r f /r g ) (v in+ ? v in? ) 07692-045 figure 53. 3-wire rtd cable resistance error measurement figure 52. low power precision instrumentation amplifier
ad8276/ad8277 rev. b | page 19 of 20 outline dimensions compliant to jedec standards mo-187-aa 100709-b 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 figure 54. 8-lead mini small outline package [msop] (rm-8) dimensions shown in millimeters 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 55. 8-lead standard small outline package [soic_n] narrow body (r-8) dimensions shown in millimeters and (inches)
ad8276/ad8277 rev. b | page 20 of 20 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 56. 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 ad8276armz ?40c to +85c 8-lead msop rm-8 h1p ad8276armz-r7 ?40c to +85c 8-lead msop, 7" tape and reel rm-8 h1p ad8276armz-rl ?40c to +85c 8-lead msop, 13" tape and reel rm-8 h1p ad8276arz ?40c to +85c 8-lead soic_n r-8 ad8276arz-r7 ?40c to +85c 8-lead soic_n, 7" tape and reel r-8 ad8276arz-rl ?40c to +85c 8-lead soic_n, 13" tape and reel r-8 ad8276brmz ?40c to +85c 8-lead msop rm-8 h1q ad8276brmz-r7 ?40c to +85c 8-lead msop, 7" tape and reel rm-8 h1q ad8276brmz-rl ?40c to +85c 8-lead msop, 13" tape and reel rm-8 h1q ad8276brz ?40c to +85c 8-lead soic_n r-8 ad8276brz-r7 ?40c to +85c 8-lead soic_n, 7" tape and reel r-8 ad8276brz-rl ?40c to +85c 8-lead soic_n, 13" tape and reel r-8 ad8277arz ?40c to +85c 14-lead soic_n r-14 ad8277arz-r7 ?40c to +85c 14-lead soic_n, 7" tape and reel r-14 ad8277arz-rl ?40c to +85c 14-lead soic_n, 13" tape and reel r-14 ad8277brz ?40c to +85c 14-lead soic_n r-14 ad8277brz-r7 ?40c to +85c 14-lead soic_n, 7" tape and reel r-14 AD8277BRZ-RL ?40c to +85c 14-lead soic_n, 13" tape and reel r-14 1 z = rohs compliant part. ?2009C2010 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. d07692-0-4/10(b)

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