ANALOG DEVICES AD8277

Low Power, Wide Supply Range, Low Cost Unity-Gain Difference Amplifiers Data Sheet AD8276/AD8277 FEATURES FUNCTIONAL BLOCK DIAGRAM +VS Wide input range beyond supplies 7 Rugged input overvoltage protection AD8276 40kΩ 40kΩ Low supply current: 200 μA maximum per channel 2 –IN 5 SENSE Low power dissipation: 0.5 mW at V = 2.5 V S Bandwidth: 550 kHz 6 OUT CMRR: 86 dB minimum, dc to 10 kHz Low offset voltage drift: ±2 μV/°C maximum (B Grade) 40kΩ 40kΩ Low gain drift: 1 ppm/°C maximum (B Grade) 3 1 +IN REF Enhanced slew rate: 1.1 V/μs 4 Wide power supply range: –VS Single supply: 2 V to 36 V Figure 1. AD8276 Dual supplies: ±2 V to ±18 V +VS 11 APPLICATIONS AD8277 40kΩ 40kΩ Voltage measurement and monitoring 2 –INA 12 SENSEA Current measurement and monitoring Differential output instrumentation amplifier 13 OUTA Portable, battery-powered equipment Test and measurement 40kΩ 40kΩ 3 14 +INA REFA GENERAL DESCRIPTION 40kΩ 40kΩ The AD8276/AD8277 are general-purpose, unity-gain difference 6 –INB 10 SENSEB amplifiers intended for precision signal conditioning in power critical applications that require both high performance and low 9 OUTB power. They provide exceptional common-mode rejection ratio (86 dB) and high bandwidth while amplifying signals well beyond 40kΩ 40kΩ 5 8 +INB REFB the supply rails. The on-chip resistors are laser-trimmed for excellent gain accuracy and high CMRR. They also have extremely 4 low gain drift vs. temperature. –VS Figure 2. AD8277 The common-mode range of the amplifiers extends to almost double the supply voltage, making these amplifiers ideal for single- Table 1. Difference Amplifiers by Category supply applications that require a high common-mode voltage Low High Current 1 range. The internal resistors and ESD circuitry at the inputs also Distortion Voltage Sensing Low Power provide overvoltage protection to the op amps. AD8270 AD628 AD8202 (U) AD8276 AD8271 AD629 AD8203 (U) AD8277 The AD8276/AD8277 are unity-gain stable. While they are AD8273 AD8205 (B) AD8278 optimized for use as difference amplifiers, they can also be AD8274 AD8206 (B) connected in high precision, single-ended configurations with AMP03 AD8216 (B) G = −1, +1, +2. The AD8276/AD8277 provide an integrated precision solution that has smaller size, lower cost, and better 1 U = unidirectional, B = bidirectional. performance than a discrete alternative. The AD8276 is available in the space-saving 8-lead MSOP and The AD8276/AD8277 operate on single supplies (2.0 V to 36 V) SOIC packages, and the AD8277 is offered in a 14-lead SOIC or dual supplies (±2 V to ±18 V). The maximum quiescent package. Both are specified for performance over the industrial supply current is 200 μA per channel, which is ideal for battery- temperature range of −40°C to +85°C and are fully RoHS operated and portable systems. compliant. 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. No Tel: 781.329.4700 www.analog.com license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Fax: 781.461.3113 ©2009–2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 07692-052 07692-001 AD8276/AD8277 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Circuit Information .................................................................... 14 Applications ....................................................................................... 1 Driving the AD8276/AD8277 .................................................. 14 General Description ......................................................................... 1 Input Voltage Range ................................................................... 14 Functional Block Diagram .............................................................. 1 Power Supplies ............................................................................ 15 Revision History ............................................................................... 2 Applications Information .............................................................. 16 Specifications ..................................................................................... 3 Configurations ............................................................................ 16 Absolute Maximum Ratings ............................................................ 5 Differential Output .................................................................... 16 Thermal Resistance ...................................................................... 5 Current Source ............................................................................ 17 Maximum Power Dissipation ..................................................... 5 Voltage and Current Monitoring .............................................. 17 Short-Circuit Current .................................................................. 5 Instrumentation Amplifier........................................................ 18 ESD Caution .................................................................................. 5 RTD .............................................................................................. 18 Pin Configurations and Function Descriptions ........................... 6 Outline Dimensions ....................................................................... 19 Typical Performance Characteristics ............................................. 8 Ordering Guide .......................................................................... 20 Theory of Operation ...................................................................... 14 REVISION HISTORY 11/11—Rev. B to Rev. C Changes to Figure 10 ......................................................................... 8 Change to Figure 53 ....................................................................... 18 Changes to Figure 34 ...................................................................... 12 Added Figure 36 ............................................................................. 13 4/10—Rev. A to Rev. B Changes to Input Voltage Range Section .................................... 14 Changes to Figure 53 ...................................................................... 18 Changes to Power Supplies Section and Added Figure 40 ........ 15 Updated Outline Dimensions ....................................................... 19 Added to Figure 40 ......................................................................... 15 Changes to Differential Output Section ...................................... 16 7/09—Rev. 0 to Rev. A Added Figure 47 and Changes to Current Source Section ....... 17 Added AD8277 ................................................................... Universal Added Voltage and Current Monitoring Section and Figure 49..... 17 Changes to Features Section............................................................ 1 Moved Instrumentation Amplifier Section and Added RTD Changes to General Description Section ...................................... 1 Section ........................................................................................................ 18 Added Figure 2; Renumbered Sequentially .................................. 1 Changes to Ordering Guide .......................................................... 20 Changes to Specifications Section .................................................. 3 Changes to Figure 3 and Table 5 ..................................................... 5 5/09—Revision 0: Initial Version Added Figure 5 and Table 7; Renumbered Sequentially ............. 7 Rev. C | Page 2 of 20 Data Sheet AD8276/AD8277 SPECIFICATIONS VS = ±5 V to ±15 V, VREF = 0 V, TA = 25°C, RL = 10 kΩ 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 1 System Offset 100 200 100 500 µV vs. Temperature TA = −40°C to +85°C 200 500 µV Average Temperature Coefficient T = −40°C to +85°C 0.5 2 2 5 µV/°C A vs. Power Supply V = ±5 V to ±18 V 5 10 µV/V S Common-Mode Rejection VS = ±15 V, VCM = ±27 V, Ratio (RTI) RS = 0 Ω 86 80 dB 2 Input Voltage Range −2(VS + 0.1) +2(VS − 1.5) −2(VS + 0.1) +2(VS − 1.5) V 3 Impedance Differential 80 80 kΩ Common Mode 40 40 kΩ DYNAMIC PERFORMANCE Bandwidth 550 550 kHz Slew Rate 0.9 1.1 0.9 1.1 V/µs Settling Time to 0.01% 10 V step on output, CL = 100 pF 15 15 µs Settling Time to 0.001% 16 16 µs Channel Separation f = 1 kHz 130 130 dB GAIN Gain Error 0.005 0.02 0.01 0.05 % Gain Drift T = −40°C to +85°C 1 5 ppm/°C A Gain Nonlinearity V = 20 V p-p 5 10 ppm OUT OUTPUT CHARACTERISTICS 4 Output Voltage Swing V = ±15 V, R = 10 kΩ, S L TA = −40°C to +85°C −VS + 0.2 +VS − 0.2 −VS + 0.2 +VS − 0.2 V Short-Circuit Current Limit ±15 ±15 mA Capacitive Load Drive 200 200 pF 5 NOISE Output Voltage Noise f = 0.1 Hz to 10 Hz 2 2 μV p-p f = 1 kHz 65 70 65 70 nV/√Hz POWER SUPPLY 6 Supply Current 200 200 μA vs. Temperature TA = −40°C to +85°C 250 250 μA 7 Operating Voltage Range ±2 ±18 ±2 ±18 V TEMPERATURE RANGE Operating Range −40 +125 −40 +125 °C 1 Includes input bias and offset current 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 Input Voltage Range section in the Theory of Operation section for details. 3 Internal resistors are trimmed to be ratio matched and have ±20% absolute accuracy. 4 Output voltage swing varies with supply voltage and temperature. See Figure 18 through Figure 21 for details. 5 Includes amplifier voltage and current noise, as well as noise from internal resistors. 6 Supply current varies with supply voltage and temperature. See Figure 22 and Figure 24 for details. 7 Unbalanced dual supplies can be used, such as −V = −0.5 V and +V = +2 V. The positive supply rail must be at least 2 V above the negative supply and reference S S voltage. Rev. C | Page 3 of 20 AD8276/AD8277 Data Sheet V = +2.7 V to <±5 V, V = midsupply, T = 25°C, R = 10 kΩ connected to midsupply, G = 1 difference amplifier configuration, unless S REF A L otherwise noted. Table 3. G = 1 Grade B Grade A Parameter Conditions Min Typ Max Min Typ Max Unit INPUT CHARACTERISTICS 1 System Offset 100 200 100 500 µV vs. Temperature T = −40°C to +85°C 200 500 µV A Average Temperature Coefficient TA = −40°C to +85°C 0.5 2 2 5 µV/°C vs. Power Supply VS = ±5 V to ±18 V 5 10 µV/V Common-Mode Rejection V = 2.7 V, V = 0 V S CM Ratio (RTI) to 2.4 V, R = 0 Ω 86 80 dB S VS = ±5 V, VCM = −10 V to +7 V, RS = 0 Ω 86 80 dB 2 Input Voltage Range −2(VS + 0.1) +2(VS − 1.5) −2(VS + 0.1) +2(VS − 1.5) V 3 Impedance Differential 80 80 kΩ Common Mode 40 40 kΩ DYNAMIC PERFORMANCE Bandwidth 450 450 kHz Slew Rate 1.0 1.0 V/µs Settling Time to 0.01% 8 V step on output, CL = 100 pF, VS = 10 V 5 5 µs Channel Separation f = 1 kHz 130 130 dB GAIN Gain Error 0.005 0.02 0.01 0.05 % Gain Drift T = −40°C to +85°C 1 5 ppm/°C A OUTPUT CHARACTERISTICS 4 Output Swing RL = 10 kΩ , T = −40°C to +85°C −V + 0.1 +V − 0.15 −V + 0.1 +V − 0.15 V A S S S S Short-Circuit Current ±10 ±10 mA Limit Capacitive Load Drive 200 200 pF 5 NOISE Output Voltage Noise f = 0.1 Hz to 10 Hz 2 2 μV p-p f = 1 kHz 65 65 nV/√Hz POWER SUPPLY 6 Supply Current TA = −40°C to +85°C 200 200 μA Operating Voltage 2.0 36 2.0 36 V Range TEMPERATURE RANGE Operating Range −40 +125 −40 +125 °C 1 Includes input bias and offset current 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 Input Voltage Range section in the Theory of Operation section for details. 3 Internal resistors are trimmed to be ratio matched and have ±20% absolute accuracy. 4 Output voltage swing varies with supply voltage and temperature. See Figure 18 through Figure 21 for details. 5 Includes amplifier voltage and current noise, as well as noise from internal resistors. 6 Supply current varies with supply voltage and temperature. See Figure 23 and Figure 24 for details. Rev. C | Page 4 of 20 Data Sheet AD8276/AD8277 ABSOLUTE MAXIMUM RATINGS 2.0 Table 4. T MAX = 150°C J Parameter Rating 1.6 14-LEAD SOIC Supply Voltage ±18 V θ = 105°C/W JA Maximum Voltage at Any Input Pin −V + 40 V S 1.2 8-LEAD SOIC Minimum Voltage at Any Input Pin +V − 40 V S θ = 121°C/W JA Storage Temperature Range −65°C to +150°C Specified Temperature Range −40°C to +85°C 0.8 8-LEAD MSOP θ = 135°C/W Package Glass Transition Temperature (TG) 150°C JA Stresses above those listed under Absolute Maximum Ratings 0.4 may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any 0 –50 –25 0 25 50 75 100 125 other conditions above those indicated in the operational AMBIENT TEMERATURE (°C) section of this specification is not implied. Exposure to absolute Figure 3. Maximum Power Dissipation vs. Ambient Temperature maximum rating conditions for extended periods may affect device reliability. SHORT-CIRCUIT CURRENT THERMAL RESISTANCE The AD8276/AD8277 have built-in, short-circuit protection that limits the output current (see Figure 25 for more information). The θ values in Table 5 assume a 4-layer JEDEC standard JA While the short-circuit condition itself does not damage the board with zero airflow. part, the heat generated by the condition can cause the part to Table 5. exceed its maximum junction temperature, with corresponding Package Type θ Unit negative effects on reliability. Figure 3 and Figure 25, combined JA with knowledge of the supply voltages and ambient temperature of 8-Lead MSOP 135 °C/W 8-Lead SOIC 121 °C/W the part, can be used to determine whether a short circuit will 14-Lead SOIC 105 °C/W cause the part to exceed its maximum junction temperature. ESD CAUTION MAXIMUM POWER DISSIPATION The maximum safe power dissipation for the AD8276/AD8277 is limited by the associated rise in junction temperature (TJ) on the die. At approximately 150°C, 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 150°C for an extended period may result in a loss of functionality. Rev. C | Page 5 of 20 MAXIMUM POWER DISSIPATION (W) 07692-002 AD8276/AD8277 Data Sheet PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS REF 1 8 NC REF 1 8 NC AD8276 AD8276 –IN 2 7 +VS –IN 2 7 +VS TOP VIEW TOP VIEW +IN 3 6 OUT +IN 3 6 OUT (Not to Scale) (Not to Scale) –VS 4 5 SENSE –VS 4 5 SENSE NC = NO CONNECT NC = NO CONNECT Figure 4. AD8276 8-Lead MSOP Pin Configuration 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. Rev. C | Page 6 of 20 07692-003 07692-004 Data Sheet AD8276/AD8277 NC 1 14 REFA –INA 2 13 OUTA +INA 3 12 SENSEA AD8277 –VS 4 TOP VIEW 11 +VS (Not to Scale) +INB 5 10 SENSEB –INB 6 9 OUTB NC 7 8 REFB NC = NO CONNECT 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. Rev. C | Page 7 of 20 07692-053 AD8276/AD8277 Data Sheet TYPICAL PERFORMANCE CHARACTERISTICS VS = ±15 V, TA = 25°C, RL = 10 kΩ connected to ground, G = 1 difference amplifier configuration, unless otherwise noted. 80 N = 2042 MEAN = –2.28 600 SD = 32.7 60 40 500 20 400 0 300 –20 –40 200 –60 100 –80 0 –100 –300 –200 –100 0 100 200 300 –50 –35 –20 –5 10 25 40 55 70 85 SYSTEM OFFSET VOLTAGE (µV) TEMPERATURE (°C) Figure 7. Distribution of Typical System Offset Voltage Figure 10. System Offset vs. Temperature, Normalized at 25°C 20 N = 2040 MEAN = –0.87 400 SD = 16.2 15 10 5 300 0 –5 200 –10 –15 100 –20 –25 REPRESENTATIVE DATA 0 –30 –90 –60 –30 0 30 60 90 –50 –35 –20 –5 10 25 40 55 70 85 90 CMRR (µV/V) TEMPERATURE (°C) Figure 11. Gain Error vs. Temperature, Normalized at 25°C Figure 8. Distribution of Typical Common-Mode Rejection 10 4 0 2 V = ±15V S –10 0 –2 –20 V = +2.7V S –30 –4 –40 –6 REPRESENTATIVE DATA –50 –8 –50 –35 –20 –5 10 25 40 55 70 85 90 100 1k 10k 100k 1M 10M FREQUENCY (Hz) TEMPERATURE (°C) Figure 12. Gain vs. Frequency, V = ±15 V, +2.7 V Figure 9. CMRR vs. Temperature, Normalized at 25°C S Rev. C | Page 8 of 20 CMRR (µV/V) NUMBER OF HITS NUMBER OF HITS 07692-007 07692-006 07692-005 GAIN (dB) GAIN ERROR (µV/V) SYSTEM OFFSET (µV) 07692-008 07692-010 07692-009 Data Sheet AD8276/AD8277 120 8 V = ±15V V = MIDSUPPLY S REF 6 100 V = 5V S 4 80 2 60 0 V = 2.7V S 40 –2 20 –4 0 –6 1 10 100 1k 10k 100k 1M –0.5 0.5 1.5 2.5 3.5 4.5 5.5 FREQUENCY (Hz) OUTPUT VOLTAGE (V) Figure 13. CMRR vs. Frequency Figure 16. Input Common-Mode Voltage vs. Output Voltage, 5 V and 2.7 V Supplies, VREF = Midsupply 120 8 V = 0V REF V = 5V S 100 6 80 4 –PSRR 60 2 +PSRR V = 2.7V S 40 0 20 –2 0 –4 1 10 100 1k 10k 100k 1M –0.5 0.5 1.5 2.5 3.5 4.5 5.5 FREQUENCY (Hz) OUTPUT VOLTAGE (V) Figure 14. PSRR vs. Frequency Figure 17. Input Common-Mode Voltage vs. Output Voltage, 5 V and 2.7 V Supplies, VREF = 0 V +V 30 S –0.1 V = ±15V S 20 –0.2 –0.3 10 –0.4 T = –40°C A V = ±5V 0 S T = +25°C A T = +85°C A T = +125°C +0.4 A –10 +0.3 +0.2 –20 +0.1 –V –30 S 2 4 6 8 10 12 14 16 18 –20 –15 –10 –5 0 5 10 15 20 SUPPLY VOLTAGE (±V ) OUTPUT VOLTAGE (V) S Figure 15. Input Common-Mode Voltage vs. Output Voltage, Figure 18. Output Voltage Swing vs. Supply Voltage Per Channel and ±15 V and ±5 V Supplies Temperature, R = 10 kΩ L Rev. C | Page 9 of 20 PSRR (dB) CMRR (dB) COMMON-MODE VOLTAGE (V) 07692-013 07692-012 07692-011 OUTPUT VOLTAGE SWING (V) COMMON-MODE VOLTAGE (V) COMMON-MODE VOLTAGE (V) REFERRED TO SUPPLY VOLTAGES 07692-015 07692-014 07692-016 AD8276/AD8277 Data Sheet +V 180 S –0.2 –0.4 170 –0.6 –0.8 160 –1.0 T = –40°C A –1.2 T = +25°C A T = +85°C 150 A T = +125°C A +1.2 +1.0 140 +0.8 +0.6 130 +0.4 +0.2 –V 120 S 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18 SUPPLY VOLTAGE (±V ) SUPPLY VOLTAGE (±V) S Figure 22. Supply Current Per Channel vs. Dual Supply Voltage, VIN = 0 V Figure 19. Output Voltage Swing vs. Supply Voltage Per Channel and Temperature, R = 2 kΩ L 180 +V S 170 –4 –8 160 T = –40°C A T = +25°C A 150 T = +85°C A T = +125°C A +8 140 +4 130 120 –V S 1k 10k 100k 0 5 10 15 20 25 30 35 40 SUPPLY VOLTAGE (V) LOAD RESISTANCE (Ω) Figure 20. Output Voltage Swing vs. RL and Temperature, VS = ±15 V Figure 23. Supply Current Per Channel vs. Single-Supply Voltage, VIN = 0 V, VREF = 0 V +V 250 S V = MIDSUPPLY REF –0.5 200 –1.0 –1.5 –2.0 150 T = –40°C A V = ±15V S T = +25°C A T = +85°C A T = +125°C A 100 +2.0 V = +2.7V S +1.5 50 +1.0 +0.5 –V 0 S 0 1 2 3 4 5 6 7 8 9 10 –50 –30 –10 10 30 50 70 90 110 130 OUTPUT CURRENT (mA) TEMPERATURE (°C) Figure 21. Output Voltage Swing vs. IOUT and Temperature, VS = ±15 V Figure 24. Supply Current Per Channel vs. Temperature Rev. C | Page 10 of 20 OUTPUT VOLTAGE SWING (V) OUTPUT VOLTAGE SWING (V) OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES REFERRED TO SUPPLY VOLTAGES REFERRED TO SUPPLY VOLTAGES 07692-017 07692-019 07692-018 SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) 07692-021 07692-020 07692-022 Data Sheet AD8276/AD8277 30 25 20 15 5V/DIV I SHORT+ 10 11.24 µs TO 0.01% 5 13.84µs TO 0.001% 0 0.002%/DIV –5 –10 I SHORT– –15 40µs/DIV –20 TIME (µs) –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (°C) Figure 25. Short-Circuit Current Per Channel vs. Temperature Figure 28. Large-Signal Pulse Response and Settling Time, 10 V Step, VS = ±15 V 1.4 1.2 –SR 1.0 1V/DIV +SR 0.8 4.34 µs TO 0.01% 5.12µs TO 0.001% 0.6 0.002%/DIV 0.4 0.2 40µs/DIV 0 TIME (µs) –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (°C) Figure 26. Slew Rate vs. Temperature, VIN = 20 V p-p, 1 kHz Figure 29. Large-Signal Pulse Response and Settling Time, 2 V Step, VS = 2.7 V 8 6 4 2 0 –2 –4 –6 –8 10µs/DIV –10 –8 –6 –4 –2 0 2 4 6 8 10 OUTPUT VOLTAGE (V) Figure 27. Gain Nonlinearity, V = ±15 V, R ≥ 2 kΩ S L Figure 30. Large-Signal Step Response Rev. C | Page 11 of 20 SLEW RATE (V/µs) SHORT-CIRCUIT CURRENT (mA) NONLINEARITY (2ppm/DIV) 07692-025 07692-024 07692-023 2V/DIV 07692-027 07692-026 07692-028 AD8276/AD8277 Data Sheet 30 40 V = ±15V S 35 25 ±2V 30 ±5V 20 25 15 20 ±18V ±15V 15 V = ±5V S 10 10 5 5 0 0 100 1k 10k 100k 1M 100 150 200 250 300 350 400 FREQUENCY (Hz) CAPACITIVE LOAD (pF) Figure 31. Maximum Output Voltage vs. Frequency, VS = ±15 V, ±5 V Figure 34. Small-Signal Overshoot vs. Capacitive Load, RL ≥ 2 kΩ 5.0 1k V = 5V S 4.5 4.0 3.5 3.0 2.5 100 V = 2.7V S 2.0 1.5 1.0 0.5 0 10 100 1k 10k 100k 1M 0.1 1 10 100 1k 10k 100k FREQUENCY (Hz) FREQUENCY (Hz) Figure 32. Maximum Output Voltage vs. Frequency, VS = 5 V, 2.7 V Figure 35. Voltage Noise Density vs. Frequency C = 100pF L C = 200pF L C = 300pF L C = 470pF L 40µs/DIV 1s/DIV Figure 33. Small-Signal Step Response for Various Capacitive Loads Figure 36. 0.1 Hz to 10 Hz Voltage Noise Rev. C | Page 12 of 20 OUTPUT VOLTAGE (V p-p) OUTPUT VOLTAGE (V p-p) 20mV/DIV 07692-050 07692-030 07692-029 NOISE (nV/ Hz) OVERSHOOT (%) 1µV/DIV 07692-035 07692-051 07692-034 Data Sheet AD8276/AD8277 160 NO LOAD 140 10kΩ LOAD 120 2kΩ LOAD 100 1kΩ LOAD 80 60 40 20 0 1 10 100 1k 10k 100k FREQUENCY (Hz) Figure 37. Channel Separation Rev. C | Page 13 of 20 CHANNEL SEPARATION (dB) 07692-055 AD8276/AD8277 Data Sheet THEORY OF OPERATION AC Performance CIRCUIT INFORMATION Component sizes and trace lengths are much smaller in an IC Each channel of the AD8276/AD8277 consists of a low power, low than on a PCB, so the corresponding parasitic elements are also noise op amp and four laser-trimmed on-chip resistors. These smaller. This results in better ac performance of the AD8276/ resistors can be externally connected to make a variety of amplifier AD8277. For example, the positive and negative input terminals configurations, including difference, noninverting, and inverting of the AD8276/AD8277 op amps are intentionally not pinned configurations. Taking advantage of the integrated resistors of out. By not connecting these nodes to the traces on the PCB, the the AD8276/AD8277 provides the designer with several benefits capacitance remains low, resulting in improved loop stability over a discrete design, including smaller size, lower cost, and and excellent common-mode rejection over frequency. better ac and dc performance. +VS DRIVING THE AD8276/AD8277 7 AD8276 Care should be taken to drive the AD8276/AD8277 with a low 40kΩ 40kΩ impedance source: for example, another amplifier. Source 2 5 IN– SENSE resistance of even a few kilohms (kΩ) can unbalance the resistor ratios and, therefore, significantly degrade the gain accuracy and 6 OUT common-mode rejection of the AD8276/AD8277. Because all configurations present several kilohms of input resistance, the 40kΩ 40kΩ 3 1 IN+ REF AD8276/AD8277 do not require a high current drive from the source and so are easy to drive. 4 –VS INPUT VOLTAGE RANGE Figure 38. Functional Block Diagram The AD8276/AD8277 are able to measure input voltages beyond DC Performance the supply rails. The internal resistors divide down the voltage before it reaches the internal op amp and provide protection to Much of the dc performance of op amp circuits depends on the the op amp inputs. Figure 39 shows an example of how the accuracy of the surrounding resistors. Using superposition to voltage division works in a difference amplifier configuration. analyze a typical difference amplifier circuit, as is shown in For the AD8276/AD8277 to measure correctly, the input Figure 39, the output voltage is found to be voltages at the input nodes of the internal op amp must stay   R2 R4 R4     below 1.5 V of the positive supply rail and can exceed the   V = V 1+ − V     OUT IN+ IN−   R1+ R2  R3  R3  negative supply rail by 0.1 V. Refer to the Power Supplies section   for more details. This equation demonstrates that the gain accuracy and common- R2 (V ) IN+ mode rejection ratio of the AD8276/AD8277 is determined R1 + R2 R4 primarily by the matching of resistor ratios. Even a 0.1% mismatch R3 in one resistor degrades the CMRR to 66 dB for a G = 1 difference V IN– amplifier. R1 V IN+ The difference amplifier output voltage equation can be reduced to R2 R4 R2 V = (V − V ) (V ) IN+ OUT IN+ I N− R1 + R2 R3 Figure 39. Voltage Division in the Difference Amplifier Configuration as long as the following ratio of the resistors is tightly matched: The AD8276/AD8277 have integrated ESD diodes at the inputs R2 R4 = that provide overvoltage protection. This feature simplifies R1 R3 system design by eliminating the need for additional external The resistors on the AD8276/AD8277 are laser trimmed to match protection circuitry, and enables a more robust system. accurately. As a result, the AD8276/AD8277 provide superior The voltages at any of the inputs of the parts can safely range performance over a discrete solution, enabling better CMRR, from +V − 40 V up to −V + 40 V. For example, on ±10 V S S gain accuracy, and gain drift, even over a wide temperature range. supplies, input voltages can go as high as ±30 V. Care should be taken to not exceed the +VS − 40 V to −VS + 40 V input limits to avoid risking damage to the parts. Rev. C | Page 14 of 20 07692-031 07692-033 Data Sheet AD8276/AD8277 The AD8276/AD8277 are typically specified at single- and dual- POWER SUPPLIES supplies, but they can be used with unbalanced supplies, as well; The AD8276/AD8277 operate extremely well over a very wide for example, −V = −5 V, +V = 20 V. The difference between the S S range of supply voltages. They can operate on a single supply as two supplies must be kept below 36 V. The positive supply rail low as 2 V and as high as 36 V, under appropriate setup conditions. must be at least 2 V above the negative supply and reference For best performance, the user must exercise care that the setup voltage. conditions ensure that the internal op amp is biased correctly. R1 (V ) REF R1 + R2 The internal input terminals of the op amp must have sufficient R4 voltage headroom to operate properly. Proper operation of the R3 part requires at least 1.5 V between the positive supply rail and the op amp input terminals. This relationship is expressed in R1 the following equation: R2 V R1 REF R1 V <+V − 1.5 V (V ) REF S REF R1 + R2 R1+ R2 Figure 40. Ensure Sufficient Voltage Headroom on the Internal Op Amp For example, when operating on a +V = 2 V single supply and S Inputs V = 0 V, it can be seen from Figure 40 that the input terminals REF Use a stable dc voltage to power the AD8276/AD8277. Noise on of the op amp are biased at 0 V, allowing more than the required the supply pins can adversely affect performance. Place a bypass 1.5 V headroom. However, if V = 1 V under the same conditions, REF capacitor of 0.1 µF between each supply pin and ground, as the input terminals of the op amp are biased at 0.5 V, barely close as possible to each supply pin. Use a tantalum capacitor allowing the required 1.5 V headroom. This setup does not allow of 10 µF between each supply and ground. It can be farther any practical voltage swing on the noninverting input. Therefore, away from the supply pins and, typically, it can be shared by the user needs to increase the supply voltage or decrease VREF to other precision integrated circuits. restore proper operation. Rev. C | Page 15 of 20 07692-032 AD8276/AD8277 Data Sheet APPLICATIONS INFORMATION CONFIGURATIONS 40kΩ 40kΩ 2 5 IN The AD8276/AD8277 can be configured in several ways (see OUT 6 Figure 42 to Figure 46). All of these configurations have excellent 1 40kΩ gain accuracy and gain drift because they rely on the internal 3 40kΩ matched resistors. Note that Figure 43 shows the AD8276/AD8277 as difference amplifiers with a midsupply reference voltage at V = –V OUT IN the noninverting input. This allows the AD8276/AD8277 to be Figure 44. Inverting Amplifier, Gain = −1 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 40kΩ 40kΩ 2 5 low impedance source to maintain the internal resistor ratio. An OUT 6 example using the low power, low noise OP1177 as a reference is shown in Figure 41. 40kΩ 40kΩ 1 3 INCORRECT CORRECT IN V = V OUT IN Figure 45. Noninverting Amplifier, Gain = 1 AD8276 AD8276 REF REF V V 40kΩ 40kΩ 2 5 + OP1177 OUT 6 – 1 40kΩ IN 3 40kΩ Figure 41. Driving the Reference Pin V = 2V OUT IN Figure 46. Noninverting Amplifier, Gain = 2 2 40kΩ 40kΩ 5 –IN DIFFERENTIAL OUTPUT OUT 6 Certain systems require a differential signal for better perfor- mance, such as the inputs to differential analog-to-digital 40kΩ 40kΩ 3 1 +IN converters. Figure 47 shows how the AD8276/AD8277 can be used to convert a single-ended output from an AD8226 V = V − V OUT IN+ IN− instrumentation amplifier into a differential signal. The internal Figure 42. Difference Amplifier, Gain = 1 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 40kΩ 40kΩ 2 5 the common-mode voltage accurately to midsupply, especially –IN OUT when running on a single supply or in an environment where 6 the supply fluctuates. The resistors at the noninverting input can also be shorted and set to any appropriate bias voltage. Note 3 40kΩ 40kΩ 1 +IN that the V = V node indicated in Figure 47 is internal to BIAS CM V = MIDSUPPLY REF the AD8276 because it is not pinned out. V = V − V OUT IN+ IN− V + AD8226 S Figure 43. Difference Amplifier, Gain = 1, Referenced to Midsupply +IN +OUT –IN V REF R R AD8276 R R V = V BIAS CM –OUT V – S Figure 47. Differential Output With Supply Tracking on Common-Mode Voltage Reference Rev. C | Page 16 of 20 07692-038 07692-039 07692-037 07692-040 07692-041 07692-042 07692-043 Data Sheet AD8276/AD8277 V+ The differential output voltage and common-mode voltage of V+ –2.5V 7 1 10 the AD8226 is shown in the following equations: 40kΩ 5 2 9 V = V − V = Gain × (V – V ) DIFF_OUT +OUT −OUT AD8226 +IN −IN 40kΩ 2 3 8 R2 6 2N3904 VCM = (VS+ − VS−)/2 = VBIAS 40kΩ 3 4 7 REF Refer to the AD8226 data sheet for additional information. 5 6 R1 40kΩ 1 +VS ADR821 V– R AD8276 LOAD 11 4 AD8277 I = 2.5V(1/40kΩ + 1/R1) O 40kΩ 40kΩ R1 = R2 2 –IN 12 Figure 49. Constant Current Source 13 +OUT VOLTAGE AND CURRENT MONITORING Voltage and current monitoring is critical in the following 40kΩ 40kΩ +IN 3 14 applications: power line metering, power line protection, motor control applications, and battery monitoring. The AD8276/ 40kΩ 40kΩ AD8277 can be used to monitor voltages and currents in a 6 10 system, as shown in Figure 50. As the signals monitored by the AD8276/AD8277 rise above or drop below critical levels, a 9 –OUT circuit event can be triggered to correct the situation or raise a warning. 40kΩ 40kΩ 5 8 AD8276 4 I 1 R –VS Figure 48. AD8277 Differential Output Configuration AD8276 The two difference amplifiers of the AD8277 can be configured I 3 R to provide a differential output, as shown in Figure 48. This differential output configuration is suitable for various applications, I C such as strain gage excitation and single-ended-to-differential AD8276 ADC OP1177 8:1 conversion. The differential output voltage has a gain of 2 as V 1 R shown in the following equation: VDIFF_OUT = V+OUT − V−OUT = 2 × (V+IN – V−IN) AD8276 CURRENT SOURCE V 3 R The AD8276 difference amplifier can be implemented as part AD8276 of a voltage-to-current converter or a precision constant current V C R source as shown in Figure 49. Using an integrated precision solution such as the AD8276 provides several advantages over Figure 50.Voltage and Current Monitoring in 3-Phase Power Line Protection a discrete solution, including space-saving, improved gain accuracy, Using the AD8276 and temperature drift. The internal resistors are tightly matched to minimize error and temperature drift. If the external resistors, Figure 50 shows an example of how the AD8276 can be used to R1 and R2, are not well-matched, they become a significant monitor voltage and current on a 3-phase power supply. I1 source of error in the system, so precision resistors are recom- through I3 are the currents to be monitored, and V1 through V3 are the voltages to be monitored on each phase. IC and VC are mended to maintain performance. The ADR821 provides a the common or zero lines. Couplers or transformers interface precision voltage reference and integrated op amp that also the power lines to the front-end circuitry and provide reduces error in the signal chain. attenuation, isolation, and protection. The AD8276 has rail-to-rail output capability that allows higher On the current monitoring side, current transformers (CTs) current outputs. 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 Rev. C | Page 17 of 20 07692-056 07692-057 07692-046 AD8276/AD8277 Data Sheet resistor is determined by the characteristics of the coupler or Table 8. Low Power Op Amps transformer and desired input voltage ranges to the AD8276. Op Amp (A1, A2) Features On the voltage monitoring side, potential transformers (PTs) AD8506 Dual micropower op amp AD8607 Precision dual micropower op amp are used to provide coupling and galvanic isolation. The PTs AD8617 Low cost CMOS micropower op amp present a load to the power line and step down the voltage to a AD8667 Dual precision CMOS micropower op amp measureable level. The AD8276 helps to build a robust system because it allows input voltages that are almost double its supply It is preferable to use dual op amps for the high impedance inputs voltage, while providing additional input protection in the form because they have better matched performance and track each of the integrated ESD diodes. other over temperature. The AD8276 difference amplifiers Not only does the AD8276 monitor the voltage and currents on cancel out common-mode errors from the input op amps, if the power lines, it is able to reject very high common-mode they track each other. The differential gain accuracy of the in- amp is proportional to how well the input feedback resistors voltages that may appear at the inputs. The AD8276 also performs the differential-to-single-ended conversion on the (RF) match each other. The CMRR of the in-amp increases as input voltages. The 80 kΩ differential input impedance that the the differential gain is increased (1 + 2RF/RG), but a higher gain AD8276 presents is high enough that it should not load the also reduces the common-mode voltage range. Note that dual input signals. supplies must be used for proper operation of this configuration. Refer to A Designer’s Guide to Instrumentation Amplifiers for I SH more design ideas and considerations. AD8276 R SH RTD V = I × R OUT SH SH 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 Figure 51. AD8276 Monitoring Current Through a Shunt Resistor cost and resistance errors to the measurement. The AD8276 Figure 51 shows how the AD8276 can be used to monitor the difference amplifier is effective in measuring errors caused by current through a small shunt resistor. This is useful in power wire resistance in remote 3-wire RTD systems, allowing the critical applications such as motor control (current sense) and user to cancel out the errors introduced by the wires. Its battery monitoring. excellent gain drift provides accurate measurements and stable performance over a wide temperature range. INSTRUMENTATION AMPLIFIER I EX The AD8276/AD8277 can be used as building blocks for a low power, low cost instrumentation amplifier. An instrumentation R L1 40kΩ 40kΩ amplifier provides high impedance inputs and delivers high common-mode rejection. Combining the AD8276 with an R V T OUT Σ-Δ Analog Devices, Inc., low power amplifier (see Table 8) creates a ADC R 40kΩ L2 precise, power efficient voltage measurement solution suitable 40kΩ AD8276 for power critical systems. R L3 –IN A1 40kΩ Figure 53. 3-Wire RTD Cable Resistance Error Measurement R F 40kΩ R G V 40kΩ OUT 40kΩ AD8276 R F REF A2 +IN V = (1 + 2R /R ) (V – V ) OUT F G IN+ IN– Figure 52. Low Power Precision Instrumentation Amplifier Rev. C | Page 18 of 20 07692-058 07692-045 07692-059 Data Sheet AD8276/AD8277 OUTLINE DIMENSIONS 3.20 3.00 2.80 8 5 5.15 3.20 4.90 3.00 4.65 1 2.80 4 PIN 1 IDENTIFIER 0.65 BSC 0.95 15° MAX 0.85 1.10 MAX 0.75 0.80 0.15 0.23 6° 0.55 0.40 0.05 0.09 0° 0.40 0.25 COPLANARITY 0.10 COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 54. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters 5.00 (0.1968) 4.80 (0.1890) 8 5 6.20 (0.2441) 4.00 (0.1574) 1 5.80 (0.2284) 3.80 (0.1497) 4 0.50 (0.0196) 1.27 (0.0500) 45° BSC 1.75 (0.0688) 0.25 (0.0099) 1.35 (0.0532) 0.25 (0.0098) 8° 0.10 (0.0040) 0° COPLANARITY 0.51 (0.0201) 1.27 (0.0500) 0.10 0.31 (0.0122) 0.25 (0.0098) SEATING 0.40 (0.0157) PLANE 0.17 (0.0067) COMPLIANT TO JEDEC STANDARDS MS-012-AA 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. Figure 55. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches) Rev. C | Page 19 of 20 10-07-2009-B 012407-A AD8276/AD8277 Data Sheet 8.75 (0.3445) 8.55 (0.3366) 8 14 6.20 (0.2441) 4.00 (0.1575) 1 5.80 (0.2283) 3.80 (0.1496) 7 1.27 (0.0500) 0.50 (0.0197) 45° BSC 0.25 (0.0098) 1.75 (0.0689) 0.25 (0.0098) 1.35 (0.0531) 8° 0.10 (0.0039) 0° COPLANARITY SEATING 1.27 (0.0500) 0.51 (0.0201) 0.10 PLANE 0.25 (0.0098) 0.40 (0.0157) 0.31 (0.0122) 0.17 (0.0067) COMPLIANT TO JEDEC STANDARDS MS-012-AB 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. Figure 56. 14-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-14) Dimensions shown in millimeters and (inches) ORDERING GUIDE 1 Model Temperature Range Package Description Package Option Branding AD8276ARMZ −40°C to +85°C 8-Lead MSOP RM-8 H1P AD8276ARMZ-R7 −40°C to +85°C 8-Lead MSOP, 7" Tape and Reel RM-8 H1P AD8276ARMZ-RL −40°C to +85°C 8-Lead MSOP, 13" Tape and Reel RM-8 H1P AD8276ARZ −40°C to +85°C 8-Lead SOIC_N R-8 AD8276ARZ-R7 −40°C to +85°C 8-Lead SOIC_N, 7" Tape and Reel R-8 AD8276ARZ-RL −40°C to +85°C 8-Lead SOIC_N, 13" Tape and Reel R-8 AD8276BRMZ −40°C to +85°C 8-Lead MSOP RM-8 H1Q AD8276BRMZ-R7 −40°C to +85°C 8-Lead MSOP, 7" Tape and Reel RM-8 H1Q AD8276BRMZ-RL −40°C to +85°C 8-Lead MSOP, 13" Tape and Reel RM-8 H1Q AD8276BRZ −40°C to +85°C 8-Lead SOIC_N R-8 AD8276BRZ-R7 −40°C to +85°C 8-Lead SOIC_N, 7" Tape and Reel R-8 AD8276BRZ-RL −40°C to +85°C 8-Lead SOIC_N, 13" Tape and Reel R-8 AD8277ARZ −40°C to +85°C 14-Lead SOIC_N R-14 AD8277ARZ-R7 −40°C to +85°C 14-Lead SOIC_N, 7" Tape and Reel R-14 AD8277ARZ-RL −40°C to +85°C 14-Lead SOIC_N, 13" Tape and Reel R-14 AD8277BRZ −40°C to +85°C 14-Lead SOIC_N R-14 AD8277BRZ-R7 −40°C to +85°C 14-Lead SOIC_N, 7" Tape and Reel R-14 AD8277BRZ-RL −40°C to +85°C 14-Lead SOIC_N, 13" Tape and Reel R-14 1 Z = RoHS Compliant Part. ©2009–2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D07692-0-11/11(C) Rev. C | Page 20 of 20 060606-A