18 V, Precision, Micropower CMOS RRIO Operational Amplifier AD8657 PIN CONFIGURATION Micropower at high voltage (18 V): 18 μA typical Low offset voltage: 350 µV maximum Single-supply operation: 2.7 V to 18 V Dual-supply operation: ±1.35 V to ±9 V Low input bias current: 20 pA Gain bandwidth: 200 kHz Unity-gain stable Excellent electromagnetic interference immunity OUT A 1 –IN A 2 AD8657 +IN A 3 TOP VIEW (Not to Scale) V– 4 8 V+ 7 OUT B 6 –IN B 5 +IN B 08804-001 FEATURES Figure 1. 8-Lead MSOP APPLICATIONS Portable operating systems Current monitors 4 mA to 20 mA loop drivers Buffer/level shifting Multipole filters Remote/wireless sensors Low power transimpedance amplifiers GENERAL DESCRIPTION Table 1. Micropower Op Amps The AD8657 is a dual, precision, micropower, rail-to-rail input/output (RRIO) amplifier optimized for low power and wide operating supply voltage range applications. Supply Voltage Single The AD8657 operates from 2.7 V up to 18 V with a typical quiescent supply current of 18 μA. It uses the Analog Devices, Inc., patented DigiTrim® trimming technique, which achieves low offset voltage. The AD8657 also has high immunity to electromagnetic interference. The combination of low supply current, low offset voltage, very low input bias current, wide supply range, and rail-to-rail input and output makes the AD8657 ideal for current monitoring and current loops in process and motor control applications. The combination of precision specifications makes this device ideal for dc gain and buffering of sensor front ends or high impedance input sources in wireless or remote sensors or transmitters. The AD8657 is specified over the extended industrial temperature range ( −40°C to +125°C) and is available in an 8-lead MSOP package. Dual Quad 5V AD8500 ADA4505-1 AD8505 AD8541 AD8603 AD8502 ADA4505-2 AD8506 AD8542 AD8607 AD8504 ADA4505-4 AD8508 AD8544 AD8609 12 V to 16 V AD8663 36 V AD8667 OP281 OP295 ADA4062-2 AD8669 OP481 OP495 ADA4062-4 Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. www.analog.com Tel: 781.329.4700 Fax: 781.461.3113 ©2011 Analog Devices, Inc. All rights reserved. AD8657 TABLE OF CONTENTS Features .............................................................................................. 1 Typical Performance Characteristics ..............................................7 Applications ....................................................................................... 1 Applications Information .............................................................. 17 Pin Configuration ............................................................................. 1 Input Stage ................................................................................... 17 General Description ......................................................................... 1 Output Stage................................................................................ 17 Revision History ............................................................................... 2 Rail to Rail ................................................................................... 18 Specifications..................................................................................... 3 Resistive Load ............................................................................. 18 Electrical Characteristics—2.7 V Operation ............................ 3 Comparator Operation .............................................................. 19 Electrical Characteristics—10 V Operation ............................. 4 EMI Rejection Ratio .................................................................. 20 Electrical Characteristics—18 V Operation ............................. 5 4 mA to 20 mA Process Control Current Loop Transmitter 20 Absolute Maximum Ratings............................................................ 6 Outline Dimensions ....................................................................... 21 Thermal Resistance ...................................................................... 6 Ordering Guide .......................................................................... 21 ESD Caution .................................................................................. 6 REVISION HISTORY 1/11—Revision 0: Initial Version Rev. 0 | Page 2 of 24 AD8657 SPECIFICATIONS ELECTRICAL CHARACTERISTICS—2.7 V OPERATION VSY = 2.7 V, VCM = VSY/2, TA = 25°C, unless otherwise specified. Table 2. Parameter INPUT CHARACTERISTICS Offset Voltage Input Bias Current Symbol Test Conditions/Comments VOS VCM = 0 V to 2.7 V VCM = 0.3 V to 2.4 V; −40°C ≤ TA ≤ +85°C VCM = 0 V to 2.7 V; −40°C ≤ TA ≤ +85°C VCM = 0.3 V to 2.4 V; −40°C ≤ TA ≤ +125°C VCM = 0 V to 2.7 V; −40°C ≤ TA ≤ +125°C Min IB Typ 1 −40°C ≤ TA ≤ +125°C Input Offset Current IOS −40°C ≤ TA ≤ +125°C Input Voltage Range Common-Mode Rejection Ratio CMRR Large Signal Voltage Gain AVO Offset Voltage Drift Input Resistance Input Capacitance, Differential Mode Input Capacitance, Common Mode OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low Short-Circuit Current Closed-Loop Output Impedance POWER SUPPLY Power Supply Rejection Ratio Supply Current per Amplifier VCM = 0 V to 2.7 V VCM = 0.3 V to 2.4 V, −40°C ≤ TA ≤ +85°C VCM = 0 V to 2.7 V, −40°C ≤ TA ≤ +85°C VCM = 0.3 V to 2.4 V, −40°C ≤ TA ≤ +125°C VCM = 0 V to 2.7 V, −40°C ≤ TA ≤ +125°C RL = 100 kΩ, VO = 0.5 V to 2.2 V −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C 0 79 70 64 63 60 94 75 65 ΔVOS/ΔT RIN CINDM CINCM Unit 350 1 2.2 2.5 4 10 2.6 20 500 2.7 µV mV mV mV mV pA nA pA pA V dB dB dB dB dB dB dB dB μV/°C GΩ pF pF 95 105 2 10 3.5 3.5 VOH VOL ISC ZOUT RL = 100 kΩ to VCM, −40°C ≤ TA ≤ +125°C RL = 100 kΩ to VCM, −40°C ≤ TA ≤ +125°C PSRR VSY = 2.7 V to 18 V −40°C ≤ TA ≤ +125°C IO = 0 mA −40°C ≤ TA ≤ +125°C ISY Max 2.69 10 ±4 20 f = 1 kHz, AV = 1 105 70 125 18 22 33 V mV mA Ω dB dB µA µA DYNAMIC PERFORMANCE Slew Rate Settling Time to 0.1% Gain Bandwidth Product Phase Margin Channel Separation EMI Rejection Ratio of +IN x SR ts GBP ΦM CS EMIRR RL = 1 MΩ, CL = 10 pF, AV = 1 VIN = 1 V step, RL = 100 kΩ, CL = 10 pF RL = 1 MΩ, CL = 10 pF, AV = 1 RL = 1 MΩ, CL = 10 pF, AV = 1 f = 10 kHz, RL = 1 MΩ VIN = 100 mVPEAK, f = 400 MHz, 900 MHz, 1800 MHz, 2400 MHz 38 14 170 69 105 90 V/ms µs kHz Degrees dB dB NOISE PERFORMANCE Voltage Noise Voltage Noise Density en p-p en f = 0.1 Hz to 10 Hz f = 1 kHz f = 10 kHz f = 1 kHz 6 60 56 0.1 µV p-p nV/√Hz nV/√Hz pA/√Hz Current Noise Density in Rev. 0 | Page 3 of 24 AD8657 ELECTRICAL CHARACTERISTICS—10 V OPERATION VSY = 10 V, VCM = VSY/2, TA = 25°C, unless otherwise specified. Table 3. Parameter INPUT CHARACTERISTICS Offset Voltage Input Bias Current Symbol Test Conditions/Comments VOS VCM = 0 V to 10 V VCM = 0 V to 10 V, −40°C ≤ TA ≤ +85°C VCM = 0 V to 10 V, −40°C ≤ TA ≤ +125°C Min IB Typ 2 −40°C ≤ TA ≤ +125°C Input Offset Current IOS −40°C ≤ TA ≤ +125°C Input Voltage Range Common-Mode Rejection Ratio CMRR Large Signal Voltage Gain AVO Offset Voltage Drift Input Resistance Input Capacitance, Differential Mode Input Capacitance, Common Mode OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low Short-Circuit Current Closed-Loop Output Impedance POWER SUPPLY Power Supply Rejection Ratio Supply Current per Amplifier VCM = 0 V to 10 V VCM = 0 V to 10 V, −40°C ≤ TA ≤ +85°C VCM = 0 V to 10 V, −40°C ≤ TA ≤ +125°C RL = 100 kΩ, VO = 0.5 V to 9.5 V −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C 0 90 72 64 105 95 67 ΔVOS/ΔT RIN CINDM CINCM Unit 350 2.7 9 15 2.6 30 500 10 µV mV mV pA nA pA pA V dB dB dB dB dB dB μV/°C GΩ pF pF 105 120 2 10 3.5 3.5 VOH VOL ISC ZOUT RL = 100 kΩ to VCM, −40°C ≤ TA ≤ +125°C RL = 100 kΩ to VCM, −40°C ≤ TA ≤ +125°C PSRR VSY = 2.7 V to 18 V −40°C ≤ TA ≤ +125°C IO = 0 mA −40°C ≤ TA ≤ +125°C ISY Max 9.98 20 ±11 15 f = 1 kHz, AV = 1 105 70 125 18 22 33 V mV mA Ω dB dB µA µA DYNAMIC PERFORMANCE Slew Rate Settling Time to 0.1% Gain Bandwidth Product Phase Margin Channel Separation EMI Rejection Ratio of +IN x SR ts GBP ΦM CS EMIRR RL = 1 MΩ, CL = 10 pF, AV = 1 VIN = 1 V step, RL = 100 kΩ, CL = 10 pF RL = 1 MΩ, CL = 10 pF, AV = 1 RL = 1 MΩ, CL = 10 pF, AV = 1 f = 10 kHz, RL = 1 MΩ VIN = 100 mVPEAK, f = 400 MHz, 900 MHz, 1800 MHz, 2400 MHz 60 13 200 60 105 90 V/ms µs kHz Degrees dB dB NOISE PERFORMANCE Voltage Noise Voltage Noise Density en p-p en f = 0.1 Hz to 10 Hz f = 1 kHz f = 10 kHz f = 1 kHz 5 50 45 0.1 µV p-p nV/√Hz nV/√Hz pA/√Hz Current Noise Density in Rev. 0 | Page 4 of 24 AD8657 ELECTRICAL CHARACTERISTICS—18 V OPERATION VSY = 18 V, VCM = VSY/2, TA = 25°C, unless otherwise specified. Table 4. Parameter INPUT CHARACTERISTICS Offset Voltage Input Bias Current Symbol Test Conditions/Comments VOS VCM = 0 V to 18 V VCM = 0.3 V to 17.7 V, −40°C ≤ TA ≤ +85°C VCM = 0 V to 18 V, −40°C ≤ TA ≤ +85°C VCM = 0.3 V to 17.7 V, −40°C ≤ TA ≤ +125°C VCM = 0 V to 18 V, −40°C ≤ TA ≤ +125°C Min IB Typ 5 −40°C ≤ TA ≤ +125°C Input Offset Current IOS −40°C ≤ TA ≤ +125°C Input Voltage Range Common-Mode Rejection Ratio CMRR Large Signal Voltage Gain AVO Offset Voltage Drift Input Resistance Input Capacitance, Differential Mode Input Capacitance, Common Mode OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low Short-Circuit Current Closed-Loop Output Impedance POWER SUPPLY Power Supply Rejection Ratio Supply Current per Amplifier VCM = 0 V to 18 V VCM = 0.3 V to 17.7 V, −40°C ≤ TA ≤ +85°C VCM = 0 V to 18 V, −40°C ≤ TA ≤ +85°C VCM = 0.3 V to 17.7 V, −40°C ≤ TA ≤ +125°C VCM = 0 V to 18 V, −40°C ≤ TA ≤ +125°C RL = 100 kΩ, VO = 0.5 V to 17.5 V −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C 0 95 83 74 80 67 110 105 73 ΔVOS/ΔT RIN CINDM CINCM Unit 350 1.2 4 2 11 20 2.9 40 500 18 µV mV mV mV mV pA nA pA pA V dB dB dB dB dB dB dB dB μV/°C GΩ pF pF 110 120 2 10 3.5 10.5 VOH VOL ISC ZOUT RL = 100 kΩ to VCM, −40°C ≤ TA ≤ +125°C RL = 100 kΩ to VCM, −40°C ≤ TA ≤ +125°C PSRR VSY = 2.7 V to 18 V −40°C ≤ TA ≤ +125°C IO = 0 mA −40°C ≤ TA ≤ +125°C ISY Max 17.97 30 ±12 15 f = 1 kHz, AV = 1 105 70 125 18 22 33 V mV mA Ω dB dB µA µA DYNAMIC PERFORMANCE Slew Rate Settling Time to 0.1% Gain Bandwidth Product Phase Margin Channel Separation EMI Rejection Ratio of +IN x SR ts GBP ΦM CS EMIRR RL = 1 MΩ, CL = 10 pF, AV = 1 VIN = 1 V step, RL = 100 kΩ, CL = 10 pF RL = 1 MΩ, CL = 10 pF, AV = 1 RL = 1 MΩ, CL = 10 pF, AV = 1 f = 10 kHz, RL = 1 MΩ VIN = 100 mVPEAK, f = 400 MHz, 900 MHz, 1800 MHz, 2400 MHz 70 12 200 60 105 90 V/ms µs kHz Degrees dB dB NOISE PERFORMANCE Voltage Noise Voltage Noise Density en p-p en f = 0.1 Hz to 10 Hz f = 1 kHz f = 10 kHz f = 1 kHz 5 50 45 0.1 µV p-p nV/√Hz nV/√Hz pA/√Hz Current Noise Density in Rev. 0 | Page 5 of 24 AD8657 ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Table 4. Parameter Supply Voltage Input Voltage Input Current1 Differential Input Voltage Output Short-Circuit Duration to GND Temperature Range Storage Operating Junction Lead Temperature (Soldering, 60 sec) 1 Rating 20.5 V (V−) − 300 mV to (V+) + 300 mV ±10 mA ±VSY Indefinite −65°C to +150°C −40°C to +125°C −65°C to +150°C 300°C θJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages using a standard 4-layer board. Table 5. Thermal Resistance Package Type 8-Lead MSOP (RM-8) ESD CAUTION The input pins have clamp diodes to the power supply pins. Limit the input current to 10 mA or less whenever input signals exceed the power supply rail by 0.3 V. 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. Rev. 0 | Page 6 of 24 θJA 142 θJC 45 Unit °C/W AD8657 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. 160 160 VSY = 2.7V VCM = VSY/2 120 NUMBER OF AMPLIFIERS 140 08804-005 120 80 100 60 Figure 5. Input Offset Voltage Distribution 18 20 VSY = 2.7V –40°C ≤ TA ≤ +125°C 16 VSY = 18V –40°C ≤ TA ≤ +125°C 18 16 14 NUMBER OF AMPLIFIERS 12 10 8 6 4 14 12 10 8 6 4 2 2 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 TCVOS (µV/°C) 0 TCVOS (µV/°C) Figure 3. Input Offset Voltage Drift Distribution Figure 6. Input Offset Voltage Drift Distribution 300 300 VSY = 2.7V VSY = 18V 200 100 100 VOS (µV) 200 0 0 –100 –100 –200 –200 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 VCM (V) 2.7 –300 08804-004 –300 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 08804-006 0 0 08804-003 0 0 2 4 6 8 10 12 14 16 VCM (V) Figure 4. Input Offset Voltage vs. Common-Mode Voltage Figure 7. Input Offset Voltage vs. Common-Mode Voltage Rev. 0 | Page 7 of 24 18 08804-007 NUMBER OF AMPLIFIERS 40 VOS (µV) Figure 2. Input Offset Voltage Distribution VOS (µV) 0 –140 140 VOS (µV) 08804-002 120 80 100 60 40 0 20 –20 –40 –60 –80 0 –100 0 –120 20 –140 20 20 40 –20 40 60 –40 60 80 –60 80 100 –80 100 –100 120 NUMBER OF AMPLIFIERS VSY = 18V VCM = VSY/2 140 –120 140 AD8657 4 VSY = 2.7V –40°C ≤ TA ≤ +85°C 2 0.5 1 VOS (mV) 1.0 0 0 –0.5 –1 –1.0 –2 –1.5 –3 –2.0 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 VSY = 18V –40°C ≤ TA ≤ +85°C 3 2.7 VCM (V) –4 08804-108 VOS (mV) 1.5 0 2 4 6 8 10 VCM (V) 12 14 16 18 08804-111 2.0 Figure 11. Input Offset Voltage vs. Common-Mode Voltage Figure 8. Input Offset Voltage vs. Common-Mode Voltage 6 2.0 VSY = 2.7V –40°C ≤ TA ≤ +125°C 1.5 VSY = 18V –40°C ≤ TA ≤ +125°C 4 1.0 2 VOS (mV) VOS (mV) 0.5 0 –0.5 0 –2 –1.0 –4 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 VCM (V) –6 0 8 10 VCM (V) 12 14 16 18 VSY = 18V VSY = 2.7V 1000 1000 100 IB+ IB– IB (pA) IB (pA) 6 10000 10000 10 10 1 1 50 75 100 TEMPERATURE (°C) 125 0.1 25 08804-008 0.1 25 4 Figure 12. Input Offset Voltage vs. Common-Mode Voltage Figure 9. Input Offset Voltage vs. Common-Mode Voltage 100 2 IB+ IB– 50 75 100 TEMPERATURE (°C) Figure 10. Input Bias Current vs. Temperature Figure 13. Input Bias Current vs. Temperature Rev. 0 | Page 8 of 24 125 08804-011 0 08804-109 –2.0 08804-112 –1.5 AD8657 4 4 VSY = 18V 3 3 2 2 1 1 IB (nA) 0 125°C 85°C 25°C –1 –2 –2 –3 –3 0.9 1.2 1.5 1.8 2.1 2.4 2.7 VCM (V) 0 2 4 6 8 10 12 14 16 Figure 17. Input Bias Current vs. Common-Mode Voltage 10 10 OUTPUT VOLTAGE (VOH) TO SUPPLY RAIL (V) Figure 14. Input Bias Current vs. Common-Mode Voltage VSY = 2.7V 1 –40°C +25°C +85°C +125°C 100m 10m 1m 0.01 0.1 1 LOAD CURRENT (mA) 10 100 VSY = 18V 1 –40°C +25°C +85°C +125°C 100m 10m 1m 0.1m 0.01m 0.001 08804-010 0.1m 0.01m 0.001 18 VCM (V) Figure 15. Output Voltage (VOH) to Supply Rail vs. Load Current 08804-012 0.6 0.01 0.1 1 LOAD CURRENT (mA) 10 100 08804-013 0.3 08804-009 –4 0 OUTPUT VOLTAGE (VOH) TO SUPPLY RAIL (V) 125°C 85°C 25°C –1 –4 Figure 18. Output Voltage (VOH) to Supply Rail vs. Load Current 10 OUTPUT VOLTAGE (VOL) TO SUPPLY RAIL (V) 10 VSY = 2.7V 1 100m 10m –40°C +25°C +85°C +125°C 1m 0.1m 0.01m 0.001 0.01 0.1 1 LOAD CURRENT (mA) 10 100 08804-014 OUTPUT VOLTAGE (VOL) TO SUPPLY RAIL (V) 0 Figure 16. Output Voltage (VOL) to Supply Rail vs. Load Current VSY = 18V 1 100m 10m –40°C +25°C +85°C +125°C 1m 0.1m 0.01m 0.001 0.01 0.1 1 LOAD CURRENT (mA) 10 100 Figure 19. Output Voltage (VOL) to Supply Rail vs. Load Current Rev. 0 | Page 9 of 24 08804-017 IB (nA) VSY = 2.7V AD8657 18.000 2.700 RL = 1MΩ RL = 1MΩ OUTPUT VOLTAGE, VOH (V) 2.698 2.697 RL = 100kΩ 2.696 17.995 17.990 17.985 17.980 VSY = 2.7V VSY = 18V –25 0 25 50 75 100 125 TEMPERATURE (°C) 17.975 –50 08804-015 2.695 –50 –25 0 25 50 75 100 125 TEMPERATURE (°C) Figure 23. Output Voltage (VOH) vs. Temperature Figure 20. Output Voltage (VOH) vs. Temperature 12 12 VSY = 2.7V VSY = 18V RL = 100kΩ 10 OUTPUT VOLTAGE, VOL (mV) 10 OUTPUT VOLTAGE, VOL (mV) RL = 100kΩ 08804-018 OUTPUT VOLTAGE, VOH (V) 2.699 8 6 4 RL = 100kΩ 8 6 4 2 2 RL = 1MΩ –25 0 25 50 75 100 125 TEMPERATURE (°C) 0 –50 08804-016 0 –50 25 50 75 100 125 Figure 24. Output Voltage (VOL) vs. Temperature 35 35 VSY = 18V VSY = 2.7V 30 25 25 ISY PER AMP (µA) 30 20 15 20 15 10 –40°C +25°C +85°C +125°C 5 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 –40°C +25°C +85°C +125°C 5 2.7 VCM (V) 0 0 3 6 9 12 15 18 VCM (V) Figure 25. Supply Current per Amp vs. Common-Mode Voltage Figure 22. Supply Current per Amp vs. Common-Mode Voltage Rev. 0 | Page 10 of 24 08804-123 10 08804-120 ISY PER AMP (µA) 0 TEMPERATURE (°C) Figure 21. Output Voltage (VOL) vs. Temperature 0 –25 08804-019 RL = 1MΩ AD8657 60 35 30 50 VSY = 2.7V VSY = 18V ISY PER AMP (µA) ISY PER AMP (µA) 25 20 15 40 30 20 10 –40°C +25°C 5 10 +85°C 9 12 15 18 VSY (V) 0 –50 Figure 26. Supply Current per Amp vs. Supply Voltage 0 –45 –20 CL = 10pF –90 CL = 100pF 10k –135 1M 100k FREQUENCY (Hz) 20 45 0 0 GAIN –45 –20 CL = 10pF 10k –135 1M 100k FREQUENCY (Hz) Figure 30. Open-Loop Gain and Phase vs. Frequency 60 VSY = 2.7V AV = 100 40 AV = 10 AV = 1 –20 –40 20 0 VSY = 18V AV = 100 AV = 10 AV = 1 –20 1k 10k 100k FREQUENCY (Hz) 1M –60 100 1k 10k 100k FREQUENCY (Hz) Figure 31. Closed-Loop Gain vs. Frequency Figure 28. Closed-Loop Gain vs. Frequency Rev. 0 | Page 11 of 24 1M 08804-025 –40 08804-022 –60 100 –90 CL = 100pF –60 1k CLOSED-LOOP GAIN (dB) 0 VSY = 18V RL = 1MΩ 90 60 20 125 40 Figure 27. Open-Loop Gain and Phase vs. Frequency 40 100 135 –40 08804-021 –60 1k OPEN-LOOP GAIN (dB) 45 PHASE (Degrees) 20 GAIN 75 60 PHASE 90 CLOSED-LOOP GAIN (dB) OPEN-LOOP GAIN (dB) PHASE –40 25 50 TEMPERATURE (°C) VSY = 2.7V RL = 1MΩ 40 0 0 Figure 29. Supply Current per Amp vs. Temperature 135 60 –25 PHASE (Degrees) 6 08804-024 3 08804-020 0 08804-023 +125°C 0 AD8657 1000 1000 AV = 100 AV = 100 AV = 10 AV = 10 100 100 AV = 1 ZOUT (Ω) ZOUT (Ω) AV = 1 10 10 1k 10k FREQUENCY (Hz) 100k 08804-026 100 1 100 Figure 32. Output Impedance vs. Frequency 140 VSY = 2.7V VCM = 2.4V 120 VSY = 18V VCM = VSY/2 80 60 80 60 40 40 20 20 1k 10k 100k 1M FREQUENCY (Hz) 0 100 1k 10k Figure 33. CMRR vs. Frequency 100 VSY = 2.7V VSY = 18V 80 60 60 PSRR (dB) 80 PSRR+ PSRR– 40 20 PSRR+ PSRR– 40 1k 10k 100k FREQUENCY (Hz) 1M Figure 34. PSRR vs. Frequency 0 100 1k 10k 100k FREQUENCY (Hz) Figure 37. PSRR vs. Frequency Rev. 0 | Page 12 of 24 1M 08804-031 20 08804-028 PSRR (dB) 1M Figure 36. CMRR vs. Frequency 100 0 100 100k FREQUENCY (Hz) 08804-030 CMRR (dB) 100 08804-027 CMRR (dB) 100 0 100 100k Figure 35. Output Impedance vs. Frequency 140 120 1k 10k FREQUENCY (Hz) 08804-029 VSY = 18V VSY = 2.7V 1 AD8657 70 70 VSY = 2.7V VIN = 10mV p-p RL = 1MΩ 60 OS+ OS– OS+ OS– 50 40 30 40 30 20 20 10 10 100 1000 CAPACITANCE (pF) 0 10 08804-032 100 1000 CAPACITANCE (pF) Figure 38. Small Signal Overshoot vs. Load Capacitance Figure 41. Small Signal Overshoot vs. Load Capacitance VSY = ±1.35V AV = 1 RL = 1MΩ CL = 100pF TIME (100µs/DIV) TIME (100µs/DIV) Figure 39. Large Signal Transient Response Figure 42. Large Signal Transient Response VSY = ±9V AV = 1 RL = 1MΩ CL = 100pF VOLTAGE (5mV/DIV) 08804-034 VOLTAGE (5mV/DIV) VSY = ±1.35V AV = 1 RL = 1MΩ CL = 100pF TIME (100µs/DIV) 08804-036 08804-033 VOLTAGE (5V/DIV) VOLTAGE (500mV/DIV) VSY = ±9V AV = 1 RL = 1MΩ CL = 100pF TIME (100µs/DIV) Figure 40. Small Signal Transient Response Figure 43. Small Signal Transient Response Rev. 0 | Page 13 of 24 08804-037 0 10 08804-035 OVERSHOOT (%) 50 OVERSHOOT (%) VSY = 18V VIN = 10mV p-p RL = 1MΩ 60 AD8657 INPUT 2 INPUT VOLTAGE (V) VSY = ±1.35 AV = –10 RL = 1MΩ –0.4 OUTPUT VOLTAGE (V) –1 –2 10 1 5 OUTPUT OUTPUT 0 TIME (40µs/DIV) TIME (40µs/DIV) Figure 44. Positive Overload Recovery Figure 47. Positive Overload Recovery VSY = ±9V AV = –10 RL = 1MΩ 2 0.4 0 OUTPUT 0 –1 –5 –2 –10 08804-038 VSY = ±1.35V AV = –10 RL = 1MΩ INPUT 0 TIME (40µs/DIV) TIME (40µs/DIV) Figure 45. Negative Overload Recovery Figure 48. Negative Overload Recovery INPUT VOLTAGE (500mV/DIV) VOLTAGE (500mV/DIV) INPUT VSY = 2.7V RL = 100kΩ CL = 10pF +5mV 0 ERROR BAND 08804-041 OUTPUT INPUT VOLTAGE (V) 0 OUTPUT VOLTAGE (V) INPUT VSY = 18V RL = 100kΩ CL = 10pF +5mV 0 ERROR BAND OUTPUT OUTPUT –5mV –5mV 08804-040 TIME (10µs/DIV) OUTPUT VOLTAGE (V) 1 0.2 INPUT VOLTAGE (V) 08804-042 08804-039 0 Figure 46. Positive Settling Time to 0.1% TIME (10µs/DIV) Figure 49. Positive Settling Time to 0.1% Rev. 0 | Page 14 of 24 08804-043 INPUT VOLTAGE (V) INPUT 0 –0.2 VSY = ±9V AV = –10 RL = 1MΩ OUTPUT VOLTAGE (V) 0 AD8657 VSY =18V RL = 100kΩ CL = 10pF VOLTAGE (500mV/DIV) VOLTAGE (500mV/DIV) VSY = 2.7V RL = 100kΩ CL = 10pF INPUT +5mV OUTPUT 0 ERROR BAND INPUT +5mV OUTPUT –5mV TIME (10µs/DIV) Figure 50. Negative Settling Time to 0.1% Figure 53. Negative Settling Time to 0.1% 1000 1000 VSY = 18V 100 1 100 1k 10k FREQUENCY (Hz) 100k 1M 1 10 Figure 51. Voltage Noise Density vs. Frequency 100 1k 10k FREQUENCY (Hz) 100k 1M Figure 54. Voltage Noise Density vs. Frequency VSY = 2.7V TIME (2s/DIV) 08804-046 VOLTAGE (2µV/DIV) VOLTAGE (2µV/DIV) VSY = 18V TIME (2s/DIV) Figure 52. 0.1 Hz to 10 Hz Noise Figure 55. 0.1 Hz to 10 Hz Noise Rev. 0 | Page 15 of 24 08804-049 10 10 08804-045 10 100 08804-048 VOLTAGE NOISE DENSITY (nV/√Hz) VSY = 2.7V VOLTAGE NOISE DENSITY (nV/√Hz) 08804-047 08804-044 –5mV TIME (10µs/DIV) 0 ERROR BAND AD8657 20 3.0 VSY = 2.7V VIN = 2.6V RL = 1MΩ AV = 1 VSY = 18V VIN = 17.9V RL = 1MΩ AV = 1 18 16 OUTPUT SWING (V) OUTPUT SWING (V) 2.5 2.0 1.5 1.0 14 12 10 8 6 4 0.5 0 100 1k 10k 100k 1M FREQUENCY (Hz) 08804-050 0 10 10 10k 100k 1M Figure 59. Output Swing vs. Frequency 100 100 VSY = 2.7V VIN = 0.2V rms RL = 1MΩ AV = 1 VSY = 18V VIN = 0.2V rms RL = 1MΩ AV = 1 10 THD + N (%) 10 1 0.1 100 1k 10k 100k FREQUENCY (Hz) 0.01 10 08804-051 0.01 10 100 1k 10k 100k 08804-054 0.1 1 100k 08804-055 THD + N (%) 1k FREQUENCY (Hz) Figure 56. Output Swing vs. Frequency FREQUENCY (Hz) Figure 57. THD + N vs. Frequency Figure 60. THD + N vs. Frequency 0 0 1MΩ 1MΩ VSY = 2.7V RL = 1MΩ AV = –100 10kΩ RL –40 –60 VIN = 0.5V p-p –80 VIN = 1.5V p-p VIN = 2.6V p-p –100 10kΩ VSY = 18V RL = 1MΩ AV = –100 –20 CHANNEL SEPARATION (dB) –20 RL –40 VIN = 1V p-p VIN = 5V p-p VIN = 10V p-p VIN = 15V p-p VIN = 17V p-p –60 –80 –100 –120 –120 –140 –140 100 1k 10k FREQUENCY (Hz) 100k 08804-052 CHANNEL SEPARATION (dB) 100 08804-053 2 Figure 58. Channel Separation vs. Frequency 100 1k 10k FREQUENCY (Hz) Figure 61. Channel Separation vs. Frequency Rev. 0 | Page 16 of 24 AD8657 APPLICATIONS INFORMATION The AD8657 is a low power, rail-to-rail input and output precision CMOS amplifier that operates over a wide supply voltage range of 2.7 V to 18 V. This amplifier uses the Analog Devices DigiTrim technique to achieve a higher degree of precision than is available from other CMOS amplifiers. The DigiTrim technique is a method of trimming the offset voltage of an amplifier after assembly. The advantage of postpackage trimming is that it corrects any shifts in offset voltage caused by mechanical stresses of assembly. The AD8657 also employs unique input and output stages to achieve a rail-to-rail input and output range with a very low supply current. INPUT STAGE Figure 62 shows the simplified schematic of the AD8657. The input stage comprises two differential transistor pairs, an NMOS pair (M1, M2) and a PMOS pair (M3, M4). The input commonmode voltage determines which differential pair turns on and is more active than the other. The PMOS differential pair is active when the input voltage approaches and reaches the lower supply rail. The NMOS pair is needed for input voltages up to and including the upper supply rail. This topology allows the amplifier to maintain a wide dynamic input voltage range and to maximize signal swing to both supply rails. For the majority of the input common-mode voltage range, the PMOS differential pair is active. Differential pairs commonly exhibit different offset voltages. The handoff from one pair to the other creates a step-like characteristic that is visible in the VOS vs. VCM graph (see Figure 4 and Figure 7). This is inherent in all railto-rail amplifiers that use the dual differential pair topology. Therefore, always choose a common-mode voltage that does not include the region of handoff from one input differential pair to the other. Additional steps in the VOS vs. VCM curves are also visible as the input common-mode voltage approaches the power supply rails. These changes are a result of the load transistors (M8, M9, M14, and M15) running out of headroom. As the load transistors are forced into the triode region of operation, the mismatch of their drain impedances contributes to the offset voltage of the amplifier. This problem is exacerbated at high temperatures due to the decrease in the threshold voltage of the input transistors (see Figure 8, Figure 9, Figure 11, and Figure 12 for typical performance data). Current Source I1 drives the PMOS transistor pair. As the input common-mode voltage approaches the upper rail, I1 is steered away from the PMOS differential pair through the M5 transistor. The bias voltage, VB1, controls the point where this transfer occurs. M5 diverts the tail current into a current mirror consisting of the M6 and M7 transistors. The output of the current mirror then drives the NMOS pair. Note that the activation of this current mirror causes a slight increase in supply current at high commonmode voltages (see Figure 22 and Figure 25 for more details). The AD8657 achieves its high performance by using low voltage MOS devices for its differential inputs. These low voltage MOS devices offer excellent noise and bandwidth per unit of current. Each differential input pair is protected by proprietary regulation circuitry (not shown in the simplified schematic). The regulation circuitry consists of a combination of active devices that maintain the proper voltages across the input pairs during normal operation and passive clamping devices that protect the amplifier during fast transients. However, these passive clamping devices begin to forward bias as the common-mode voltage approaches either power supply rail. This causes an increase in the input bias current (see Figure 14 and Figure 17). The input devices are also protected from large differential input voltages by clamp diodes (D1 and D2). These diodes are buffered from the inputs with two 10 kΩ resistors (R1 and R2). The differential diodes turn on whenever the differential voltage exceeds approximately 600 mV; in this condition, the differential input resistance drops to 20 kΩ. OUTPUT STAGE The AD8657 features a complementary output stage consisting of the M16 and M17 transistors. These transistors are configured in Class AB topology and are biased by the voltage source, VB2. This topology allows the output voltage to approach, within millivolts, the supply rails, achieving a rail-to-rail output swing. The output voltage is limited by the output impedance of the transistors, which are low RON MOS devices. The output voltage swing is a function of the load current and can be estimated using the output voltage to the supply rail vs. load current plots (see Figure 15, Figure 16, Figure 18, and Figure 19). Rev. 0 | Page 17 of 24 AD8657 V+ VB1 I1 M5 +IN x R1 –IN x R2 M3 D1 M8 M9 M10 M11 M4 M16 D2 VB2 M1 OUT x M2 M7 M6 M13 M14 M15 08804-056 M17 M12 V– Figure 62. Simplified Schematic RAIL TO RAIL Inverting Configuration The AD8657 features rail-to-rail input and output with a supply voltage from 2.7 V to 18 V. Figure 63 shows the input and output waveforms of the AD8657 configured as a unity-gain buffer with a supply voltage of ±9 V and a resistive load of 1 MΩ. With an input voltage of ±9 V, the AD8657 allows the output to swing very close to both rails. Additionally, it does not exhibit phase reversal. Figure 64 shows AD8657 in an inverting configuration with a resistive load, RL, at the output. The actual load seen by the amplifier is the parallel combination of the feedback resistor, R2, and load, RL. Having a feedback resistor of 1 kΩ and a load of 1 MΩ results in an equivalent load resistance of 999 Ω at the output. In this condition, the AD8657 is incapable of driving such a heavy load; therefore, its performance degrades greatly. To avoid loading the output, use a larger feedback resistor, but consider the resistor thermal noise effect on the overall circuit. VSY = ±9V RL = 1MΩ R2 VOLTAGE (5V/DIV) INPUT OUTPUT VIN +VSY R1 AD8657 VOUT 1/2 RL 08804-058 –VSY RL, EFF = RL || R2 Figure 64. Inverting Op Amp Noninverting Configuration 08804-057 Figure 65 shows the AD8657 in a noninverting configuration with a resistive load, RL, at the output. The actual load seen by the amplifier is the parallel combination of R1 + R2 and RL. Figure 63. Rail-to-Rail Input and Output RESISTIVE LOAD The feedback resistor alters the load resistance that an amplifier sees. It is, therefore, important to be aware of the value of feedback resistors chosen for use with the AD8657. The AD8657 is capable of driving resistive loads down to 100 kΩ. The following two examples, inverting and noninverting configurations, show how the feedback resistor changes the actual load resistance seen at the output of the amplifier. R2 +VSY R1 AD8657 VIN 1/2 VOUT RL –VSY RL, EFF = RL || (R1 + R2) Figure 65. Noninverting Op Amp Rev. 0 | Page 18 of 24 08804-059 TIME (200µs/DIV) AD8657 COMPARATOR OPERATION Op amps are designed to operate in a closed-loop configuration with feedback from its output to its inverting input. Figure 66 shows the AD8657 configured as a voltage follower with an input voltage that is always kept at midpoint of the power supplies. The same configuration is applied to the unused channel. A1 and A2 indicate the placement of ammeters to measure supply current. ISY+ refers to the current flowing from the upper supply rail to the op amp, and ISY− refers to the current flowing from the op amp to the lower supply rail. As shown in Figure 67, as expected, in normal operating condition, the total current flowing into the op amp is equivalent to the total current flowing out of the op amp, where, ISY+ = ISY− = 36 μA for the dual AD8657 at VSY = 18 V. consist of substrate PNP bipolar transistors, and conduct whenever the differential input voltage exceeds approximately 600 mV; however, these diodes also allow a current path from the input to the lower supply rail, thus resulting in an increase in the total supply current of the system. As shown in Figure 70, both configurations yield the same result. At 18 V of power supply, ISY+ remains at 36 μA per dual amplifier, but ISY− increases to 140 μA in magnitude per dual amplifier. +VSY AD8657 +VSY 100kΩ ISY+ AD8657 ISY– A2 –VSY Figure 68. Comparator A +VSY ISY– 08804-066 A2 100kΩ VOUT 1/2 100kΩ VOUT 1/2 08804-068 A1 ISY+ A1 100kΩ –VSY A1 ISY+ 100kΩ Figure 66. Voltage Follower AD8657 40 VOUT 1/2 100kΩ A2 ISY– 08804-069 30 25 –VSY 20 Figure 69. Comparator B 15 160 ISY– ISY+ 140 0 0 2 4 6 8 10 VSY (V) 12 14 16 18 08804-067 5 Figure 67. Supply Current vs. Supply Voltage (Voltage Follower) In contrast to op amps, comparators are designed to work in an open-loop configuration and to drive logic circuits. Although op amps are different from comparators, occasionally an unused section of a dual op amp is used as a comparator to save board space and cost; however, this is not recommended. Figure 68 and Figure 69 show the AD8657 configured as a comparator, with 100 kΩ resistors in series with the input pins. Any unused channels are configured as buffers with the input voltage kept at the midpoint of the power supplies. The AD8657 has input devices that are protected from large differential input voltages by Diode D1 and Diode D2 (refer to Figure 62). These diodes 120 100 ISY– ISY+ 80 60 40 20 0 0 2 4 6 8 10 VSY (V) 12 14 16 18 08804-070 10 ISY pER DUAL AMPLIFIER (µA) ISY PER DUAL AMPLIFIER (µA) 35 Figure 70. Supply Current vs. Supply Voltage (AD8657 as a Comparator) Note that 100 kΩ resistors are used in series with the input of the op amp. If smaller resistor values are used, the supply current of the system increases much more. For more details on op amps as comparators, refer to the AN-849 Application Note Using Op Amps as Comparators. Rev. 0 | Page 19 of 24 AD8657 EMI REJECTION RATIO Circuit performance is often adversely affected by high frequency electromagnetic interference (EMI). In the event where signal strength is low and transmission lines are long, an op amp must accurately amplify the input signals. However, all op amp pins— the noninverting input, inverting input, positive supply, negative supply, and output pins—are susceptible to EMI signals. These high frequency signals are coupled into an op amp by various means such as conduction, near field radiation, or far field radiation. For instance, wires and PCB traces can act as antennas and pick up high frequency EMI signals. Precision op amps, such as the AD8657, do not amplify EMI or RF signals because of their relatively low bandwidth. However, due to the nonlinearities of the input devices, op amps can rectify these out-of-band signals. When these high frequency signals are rectified, they appear as a dc offset at the output. To describe the ability of the AD8657 to perform as intended in the presence of an electromagnetic energy, the electromagnetic interference rejection ratio (EMIRR) of the noninverting pin is specified in Table 2, Table 3, and Table 4 of the Specifications section. A mathematical method of measuring EMIRR is defined as follows: EMIRR = 20 log (VIN_PEAK/ΔVOS) With a zero-scale input, a current of VREF/RNULL flows through R´. This creates a current flowing through the sense resistor, ISENSE, determined by the following equation (see Figure 72 for details): ISENSE, MIN = (VREF × R´)/(RNULL × RSENSE) With a full-scale input voltage, current flowing through R´ is increased by the full-scale change in VIN/RSPAN. This creates an increase in the current flowing through the sense resistor. ISENSE, DELTA = (Full-Scale Change in VIN × R´)/(RSPAN × RSENSE) Therefore ISENSE, MAX = ISENSE, MIN + ISENSE, DELTA When R´ >> RSENSE, the current through the load resistor at the receiver side is almost equivalent to ISENSE. Figure 72 is designed for a full-scale input voltage of 5 V. At 0 V of input, loop current is 3.5 mA, and at a full scale of 5 V, the loop current is 21 mA. This allows software calibration to fine tune the current loop to the 4 mA to 20 mA range. 140 120 The AD8657 and ADR125 both consume only 160 μA quiescent current, making 3.34 mA current available to power additional signal conditioning circuitry or to power a bridge circuit. 80 ADR125 VREF VOUT 60 20 10M VIN = 100mVPEAK VSY = 2.7V TO 18V 100M 1G 10G FREQUENCY (Hz) 08804-071 40 RNULL 1MΩ 1% VIN 0V TO 5V RSPAN 200kΩ 1% R1 68kΩ 1% Figure 71. EMIRR vs. Frequency 4 mA TO 20 mA PROCESS CONTROL CURRENT LOOP TRANSMITTER The 2-wire current transmitters are often used in distributed control systems and process control applications to transmit analog signals between sensors and process controllers. Figure 72 shows a 4 mA to 20 mA current loop transmitter. C2 C3 10µF 0.1µF R2 2kΩ 1% VIN GND C5 C4 0.1µF 10µF 1/2 AD8657 Q1 R4 3.3kΩ R3 1.2kΩ VDD 18V D1 C1 390pF 4mA TO 20mA RSENSE 100Ω 1% NOTES 1. R1 + R2 = R´. The transmitter powers directly from the control loop power supply, and the current in the loop carries signal from 4 mA to 20 mA. Thus, 4 mA establishes the baseline current budget within which the circuit must operate. Using the AD8657 is an excellent Rev. 0 | Page 20 of 24 Figure 72. 4 mA to 20 mA Current Loop Transmitter RL 100Ω 08804-060 100 EMIRR (dB) choice due to its low supply current of 33 μA per amplifier over temperature and supply voltage. The current transmitter controls the current flowing in the loop, where a zero-scale input signal is represented by 4 mA of current and a full-scale input signal is represented by 20 mA. The transmitter also floats from the control loop power supply, VDD, while signal ground is in the receiver. The loop current is measured at the load resistor, RL, at the receiver side. AD8657 OUTLINE DIMENSIONS 3.20 3.00 2.80 8 3.20 3.00 2.80 1 5.15 4.90 4.65 5 4 PIN 1 IDENTIFIER 0.65 BSC 0.95 0.85 0.75 15° MAX 1.10 MAX 0.40 0.25 6° 0° 0.23 0.09 0.80 0.55 0.40 COMPLIANT TO JEDEC STANDARDS MO-187-AA 100709-B 0.15 0.05 COPLANARITY 0.10 Figure 73. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters ORDERING GUIDE Model 1 AD8657ARMZ AD8657ARMZ-R7 AD8657ARMZ-RL 1 Temperature Range −40°C to +125°C −40°C to +125°C −40°C to +125°C Package Description 8-Lead Mini Small Outline Package [MSOP] 8-Lead Mini Small Outline Package [MSOP] 8-Lead Mini Small Outline Package [MSOP] Z = RoHS Compliant Part. Rev. 0 | Page 21 of 24 Package Option RM-8 RM-8 RM-8 Branding A2N A2N A2N AD8657 NOTES Rev. 0 | Page 22 of 24 AD8657 NOTES Rev. 0 | Page 23 of 24 AD8657 NOTES ©2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D08804-0-1/11(0) Rev. 0 | Page 24 of 24