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 OUT A 1 OUT B 6 –IN B 5 +IN B +IN A 3 8 V+ AD8657 TOP VIEW (Not to Scale) V– 4 7 OUT B 6 –IN B 5 +IN B NOTES 1. IT IS RECOMMENDED TO CONNECT THE EXPOSED PAD TO V–. 08804-061 –IN A 2 Portable operating systems Current monitors 4 mA to 20 mA loop drivers Buffer/level shifting Multipole filters Remote/wireless sensors Low power transimpedance amplifiers Figure 2. 8-Lead LFCSP GENERAL DESCRIPTION Table 1. Micropower Op Amps The AD8657 is a dual, micropower, precision, rail-to-rail input/output amplifier optimized for low power and wide operating supply voltage range applications. Supply Voltage Single 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. V+ 7 Figure 1. 8-Lead MSOP APPLICATIONS 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. 8 08804-001 FEATURES 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 The AD8657 is specified over the extended industrial temperature range (−40°C to +125°C) and is available in an 8-lead MSOP package and an 8-lead LFCSP package. Rev. A 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 ©2011 Analog Devices, Inc. All rights reserved. AD8657 TABLE OF CONTENTS Features .............................................................................................. 1 Applications Information .............................................................. 17 Applications ....................................................................................... 1 Input Stage ................................................................................... 17 Pin Configuration ............................................................................. 1 Output Stage................................................................................ 17 General Description ......................................................................... 1 Rail to Rail ................................................................................... 18 Revision History ............................................................................... 2 Resistive Load ............................................................................. 18 Specifications..................................................................................... 3 Comparator Operation .............................................................. 19 Electrical Characteristics—2.7 V Operation ............................ 3 EMI Rejection Ratio .................................................................. 20 Electrical Characteristics—10 V Operation ............................. 4 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 Typical Performance Characteristics ............................................. 7 REVISION HISTORY 3/11—Rev. 0 to Rev. A Added LFCSP Package Information ........................... Throughout Added Figure 2, Renumbered Subsequent Figures ................... 1 Changes to Table 2, Introductory Text; Input Characteristics, Offset Voltage and Common-Mode Rejection Ratio Test Conditions/Comments; and Dynamic Performance, Phase Margin Values ................................................................................... 3 Changes to Table 3, Introductory Text; Input Characteristics, Offset Voltage and Common-Mode Rejection Ratio Test Conditions/Comments .................................................................... 4 Changes to Table 4, Introductory Text; Input Characteristics, Offset Voltage and Common-Mode Rejection Ratio Test Conditions/Comments .................................................................... 5 Changes to Thermal Resistance Section and Table 5................... 6 Updated Outline Dimensions ....................................................... 21 Changes to Ordering Guide .......................................................... 21 1/11—Revision 0: Initial Version Rev. A | Page 2 of 24 AD8657 SPECIFICATIONS ELECTRICAL CHARACTERISTICS—2.7 V OPERATION VSY = 2.7 V, VCM = VSY/2 V, 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 = 0.3 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 Max Unit 1 350 1 2.5 4 10 2.6 20 500 2.7 µV mV mV mV pA nA pA pA V dB dB dB dB dB dB dB μV/°C GΩ pF pF −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 = 0.3 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 63 60 94 75 65 ΔVOS/ΔT RIN CINDM CINCM 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 95 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 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 6 60 56 0.1 µV p-p nV/√Hz nV/√Hz pA/√Hz Current Noise Density in Rev. A | Page 3 of 24 AD8657 ELECTRICAL CHARACTERISTICS—10 V OPERATION VSY = 10 V, VCM = VSY/2 V, 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 ≤ +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 ≤ +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 64 105 95 67 ΔVOS/ΔT RIN CINDM CINCM VOH VOL ISC ZOUT PSRR ISY Max Unit 350 9 15 2.6 30 500 10 µV mV pA nA pA pA V dB dB dB dB dB μV/°C GΩ pF pF 105 120 2 10 3.5 3.5 RL = 100 kΩ to VCM; −40°C ≤ TA ≤ +125°C RL = 100 kΩ to VCM; −40°C ≤ TA ≤ +125°C 9.98 20 ±11 15 f = 1 kHz, AV = 1 VSY = 2.7 V to 18 V −40°C ≤ TA ≤ +125°C IO = 0 mA −40°C ≤ TA ≤ +125°C 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. A | Page 4 of 24 AD8657 ELECTRICAL CHARACTERISTICS—18 V OPERATION VSY = 18 V, VCM = VSY/2 V, 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 = 0.3 V to 17.7 V; −40°C ≤ TA ≤ +125°C VCM = 0 V to 18 V; −40°C ≤ TA ≤ +125°C Min IB Typ Max Unit 5 350 1.2 2 11 20 2.9 40 500 18 µV mV mV mV pA nA pA pA V dB dB dB dB dB dB dB μV/°C GΩ pF pF −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 = 0.3 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 80 67 110 105 73 ΔVOS/ΔT RIN CINDM CINCM 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 110 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. A | 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 JEDEC board. The exposed pad is soldered to the board. Table 5. Thermal Resistance Package Type 8-Lead MSOP (RM-8) 8-Lead LFCSP (CP-8-11) 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. A | Page 6 of 24 θJA 142 75 θJC 45 12 Unit °C/W °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 6. 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 4. Input Offset Voltage Drift Distribution Figure 7. 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 5. Input Offset Voltage vs. Common-Mode Voltage Figure 8. Input Offset Voltage vs. Common-Mode Voltage Rev. A | Page 7 of 24 18 08804-007 NUMBER OF AMPLIFIERS 40 VOS (µV) Figure 3. 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 12. Input Offset Voltage vs. Common-Mode Voltage Figure 9. 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 1 1 50 75 100 TEMPERATURE (°C) 125 08804-008 10 0.1 25 4 Figure 13. Input Offset Voltage vs. Common-Mode Voltage Figure 10. Input Offset Voltage vs. Common-Mode Voltage 100 2 Figure 11. Input Bias Current vs. Temperature 0.1 25 IB+ IB– 50 75 100 TEMPERATURE (°C) Figure 14. Input Bias Current vs. Temperature Rev. A | 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 18. Input Bias Current vs. Common-Mode Voltage 10 10 OUTPUT VOLTAGE (VOH) TO SUPPLY RAIL (V) Figure 15. 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 16. 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 19. 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 17. 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 20. Output Voltage (VOL) to Supply Rail vs. Load Current Rev. A | Page 9 of 24 08804-017 IB (nA) VSY = 2.7V AD8657 2.700 18.000 RL = 1MΩ RL = 1MΩ OUTPUT VOLTAGE, VOH (V) 2.698 2.697 RL = 100kΩ 17.995 17.990 17.985 RL = 100kΩ 17.980 2.696 VSY = 2.7V 0 –25 25 50 75 100 125 TEMPERATURE (°C) 08804-015 2.695 –50 VSY = 18V 17.975 –50 0 25 50 75 100 125 TEMPERATURE (°C) Figure 24. Output Voltage (VOH) vs. Temperature Figure 21. Output Voltage (VOH) vs. Temperature 12 12 VSY = 18V VSY = 2.7V RL = 100kΩ 10 OUTPUT VOLTAGE, VOL (mV) 10 OUTPUT VOLTAGE, VOL (mV) –25 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 0 25 50 75 100 125 TEMPERATURE (°C) Figure 25. Output Voltage (VOL) vs. Temperature Figure 22. 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 10 –40°C +25°C +85°C +125°C 5 –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 VCM (V) 2.7 0 3 6 9 12 15 VCM (V) Figure 26. Supply Current vs. Common-Mode Voltage Figure 23. Supply Current vs. Common-Mode Voltage Rev. A | Page 10 of 24 18 08804-123 0 0 08804-120 ISY PER AMP (µA) –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 27. Supply Current vs. Supply Voltage 135 GAIN 0 –45 –20 CL = 10pF OPEN-LOOP GAIN (dB) 45 PHASE (Degrees) 20 –90 CL = 100pF –135 1M 100k FREQUENCY (Hz) 90 20 45 0 0 GAIN –45 –20 CL = 10pF 10k Figure 31. 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 32. Closed-Loop Gain vs. Frequency Figure 29. Closed-Loop Gain vs. Frequency Rev. A | Page 11 of 24 1M 08804-025 –40 08804-022 –60 100 –135 1M 100k FREQUENCY (Hz) CLOSED-LOOP GAIN (dB) 0 –90 CL = 100pF –60 1k 60 20 VSY = 18V RL = 1MΩ 40 Figure 28. Open-Loop Gain and Phase vs. Frequency 40 125 135 –40 08804-021 10k 100 75 60 PHASE 90 CLOSED-LOOP GAIN (dB) OPEN-LOOP GAIN (dB) PHASE –60 1k 25 50 TEMPERATURE (°C) VSY = 2.7V RL = 1MΩ 40 –40 0 Figure 30. Supply Current vs. Temperature 60 0 –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 33. 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 34. 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 35. PSRR vs. Frequency 0 100 1k 10k 100k FREQUENCY (Hz) Figure 38. PSRR vs. Frequency Rev. A | Page 12 of 24 1M 08804-031 20 08804-028 PSRR (dB) 1M Figure 37. CMRR vs. Frequency 100 0 100 100k FREQUENCY (Hz) 08804-030 CMRR (dB) 100 08804-027 CMRR (dB) 100 0 100 100k Figure 36. 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 39. Small Signal Overshoot vs. Load Capacitance Figure 42. Small Signal Overshoot vs. Load Capacitance VSY = ±1.35V AV = 1 RL = 1MΩ CL = 100pF TIME (100µs/DIV) TIME (100µs/DIV) Figure 40. Large Signal Transient Response Figure 43. 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 41. Small Signal Transient Response Figure 44. Small Signal Transient Response Rev. A | 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 45. Positive Overload Recovery Figure 48. 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 46. Negative Overload Recovery Figure 49. 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 47. Positive Settling Time to 0.1% TIME (10µs/DIV) Figure 50. Positive Settling Time to 0.1% Rev. A | 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 51. Negative Settling Time to 0.1% Figure 54. Negative Settling Time to 0.1% 1000 1000 VSY = 18V 100 1 100 1k 10k FREQUENCY (Hz) 100k 1M 1 10 Figure 52. Voltage Noise Density vs. Frequency 100 1k 10k FREQUENCY (Hz) 100k 1M Figure 55. 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 53. 0.1 Hz to 10 Hz Noise Figure 56. 0.1 Hz to 10 Hz Noise Rev. A | 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 60. 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 57. Output Swing vs. Frequency FREQUENCY (Hz) Figure 58. THD + N vs. Frequency Figure 61. 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 59. Channel Separation vs. Frequency 100 1k 10k FREQUENCY (Hz) Figure 62. Channel Separation vs. Frequency Rev. A | 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 63 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 5 and Figure 8). 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 9, Figure 10, Figure 12, and Figure 13 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 23 and Figure 26 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 15 and Figure 18). 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 go within millivolts of 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 diagrams (see Figure 16, Figure 17, Figure 19, and Figure 20). Rev. A | Page 17 of 24 AD8657 V+ I1 VB1 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 63. 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 64 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 65 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 INPUT OUTPUT R2 VOLTAGE (5V/DIV) +VSY R1 VIN AD8657 VOUT 1/2 RL 08804-058 –VSY RL, EFF = RL || R2 Figure 65. Inverting Op Amp Noninverting Configuration 08804-057 Figure 66 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 64. 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 1/2 VIN VOUT RL –VSY RL, EFF = RL || (R1 + R2) Figure 66. Noninverting Op Amp Rev. A | 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 67 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 68, 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 71, 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 69. 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 67. Voltage Follower AD8657 40 VOUT 1/2 100kΩ A2 ISY– 08804-069 30 25 –VSY 20 Figure 70. Comparator B 15 160 ISY– ISY+ 140 0 0 2 4 6 8 10 VSY (V) 12 14 16 18 08804-067 5 Figure 68. 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 69 and Figure 70 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 63). 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 71. 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. A | 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 73 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 73 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 Figure 72. EMIRR vs. Frequency RSPAN 200kΩ 1% R1 68kΩ 1% 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 73 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. A | Page 20 of 24 Figure 73. 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 0.80 0.55 0.40 0.23 0.09 6° 0° 100709-B 0.15 0.05 COPLANARITY 0.10 COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 74. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters 2.44 2.34 2.24 3.10 3.00 SQ 2.90 0.50 BSC 8 5 1.70 1.60 1.50 EXPOSED PAD 0.50 0.40 0.30 0.80 0.75 0.70 SEATING PLANE 0.30 0.25 0.20 1 4 BOTTOM VIEW TOP VIEW 0.05 MAX 0.02 NOM COPLANARITY 0.08 0.203 REF PIN 1 INDICATOR (R 0.15) FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. COMPLIANT TO JEDEC STANDARDS MO-229-WEED 01-24-2011-B PIN 1 INDEX AREA Figure 75. 8-Lead Lead Frame Chip Scale Package [LFCSP_WD] 3 mm × 3 mm Body, Very Very Thin, Dual Lead (CP-8-11) Dimensions shown in millimeters ORDERING GUIDE Model 1 AD8657ARMZ AD8657ARMZ-R7 AD8657ARMZ-RL AD8657ACPZ-R7 AD8657ACPZ-RL 1 Temperature Range −40°C to +125°C −40°C to +125°C −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] 8-Lead Lead Frame Chip Scale Package [LFCSP_WD] 8-Lead Lead Frame Chip Scale Package [LFCSP_WD] Z = RoHS Compliant Part. Rev. A | Page 21 of 24 Package Option RM-8 RM-8 RM-8 CP-8-11 CP-8-11 Branding A2N A2N A2N A2N A2N AD8657 NOTES Rev. A | Page 22 of 24 AD8657 NOTES Rev. A | Page 23 of 24 AD8657 NOTES ©2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 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