AD8638

16 V Auto-Zero, Rail-to-Rail Output Operational Amplifiers AD8638/AD8639 FEATURES Low offset voltage: 9 μV maximum Offset drift: 0.04 μV/°C maximum Rail-to-rail output swing 5 V to 16 V single-supply or ±2.5 V to ±8 V dual-supply operation High gain: 136 dB typical High CMRR: 133 dB typical High PSRR: 143 dB typical Very low input bias current: 40 pA maximum Low supply current: 1.3 mA maximum PIN CONFIGURATIONS OUT 1 V– 2 +IN 3 AD8638 TOP VIEW (Not to Scale) 5 V+ 4 –IN Figure 1. 5-Lead SOT-23 (RJ-5) NC 1 –IN 2 +IN 3 8 NC V+ AD8638 7 APPLICATIONS Pressure and position sensors Strain gage amplifiers Medical instrumentation Thermocouple amplifiers Automotive sensors Precision references Precision current sensing NC = NO CONNECT Figure 2. 8-Lead SOIC_N (R-8) OUT A 1 –IN A 2 +IN A 3 V– 4 8 AD8639 TOP VIEW (Not to Scale) V+ OUT B +IN B 06895-203 06895-204 7 6 5 –IN B Figure 3. 8-Lead MSOP (RM-8) 8-Lead SOIC_N (R-8) PIN 1 INDICATOR GENERAL DESCRIPTION The AD8638/AD8639 are single and dual wide bandwidth, auto-zero amplifiers featuring rail-to-rail output swing and low noise. These amplifiers have very low offset, drift, and bias current. Operation is fully specified from 5 V to 16 V single supply (±2.5 V to ±8 V dual supply). The AD8638/AD8639 provide benefits previously found only in expensive zero-drift or chopper-stabilized amplifiers. Using the Analog Devices, Inc., topology, these auto-zero amplifiers combine low cost with high accuracy and low noise. No external capacitors are required. In addition, the AD8638/AD8639 greatly reduce the digital switching noise found in most chopperstabilized amplifiers. With a typical offset voltage of only 3 μV, drift of 0.01 μV/°C, and noise of 1.2 μV p-p (0.1 Hz to 10 Hz), the AD8638/AD8639 are suited for applications in which error sources cannot be tolerated. Position and pressure sensors, medical equipment, and strain gage amplifiers benefit greatly from nearly zero drift over their operating temperature ranges. Many systems can take advantage of the rail-to-rail output swing provided by the AD8638/AD8639 to maximize signal-to-noise ratio (SNR). OUT A –IN A +IN A v– 1 2 3 4 8 V+ 7 OUT B 6 –IN B 5 +IN B AD8639 TOP VIEW (Not to Scale) NOTES 1. EXPOSED PAD SOLDERED TO APPLICATION BOARD. Figure 4. 8-Lead LFCSP_WD (CP-8-5) The AD8638/AD8639 are specified for the extended industrial temperature range (−40°C to +125°C). The single AD8638 is available in tiny 5-lead SOT-23 and 8-lead SOIC packages. The dual AD8639 is available in 8-lead MSOP, 8-lead SOIC, and 8-lead LFCSP packages. The AD8638/AD8639 are members of a growing series of autozero op amps offered by Analog Devices (see Table 1). Table 1. Auto-Zero Op Amps Supply Single Dual Quad 2.7 V to 5 V AD8628 AD8629 AD8630 2.7 V to 5 V Low Power AD8538 AD8539 5 V to 16 V AD8638 AD8639 Rev. C Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2007–2008 Analog Devices, Inc. All rights reserved. 06895-002 6 OUT TOP VIEW V– 4 (Not to Scale) 5 NC 06895-001 AD8638/AD8639 TABLE OF CONTENTS Features .............................................................................................. 1  Applications ....................................................................................... 1  General Description ......................................................................... 1  Pin Configurations ........................................................................... 1  Revision History ............................................................................... 2  Specifications..................................................................................... 3  Electrical Characteristics—5 V Operation................................ 3  Electrical Characteristics—16 V Operation ............................. 4  Absolute Maximum Ratings............................................................ 5  Thermal Resistance ...................................................................... 5  ESD Caution .................................................................................. 5  Typical Performance Characteristics ..............................................6  Theory of Operation ...................................................................... 14  1/f Noise ....................................................................................... 14  Input Voltage Range ................................................................... 14  Output Phase Reversal ............................................................... 14  Overload Recovery Time .......................................................... 14  Infrared Sensors.......................................................................... 15  Precision Current Shunt Sensor ............................................... 15  Output Amplifier for High Precision DACs ........................... 15  Outline Dimensions ....................................................................... 16  Ordering Guide .......................................................................... 17  REVISION HISTORY 5/08—Rev. B to Rev. C Added LFCSP_WD Package ............................................. Universal Inserted Figure 4; Renumbered Sequentially ................................ 1 Changes to Layout ............................................................................ 1 Changes to General Description .................................................... 1 Changes to Offset Voltage Drift for All Packages Except SOT-23 Parameter in Table 2 ......................................................................... 3 Changes to Table 5 ............................................................................ 5 Updated Outline Dimensions ....................................................... 16 Changes to Ordering Guide .......................................................... 17 4/08—Rev. A to Rev. B Added AD8639 ................................................................... Universal Added 8-lead MSOP Package ........................................... Universal Changes to Features.......................................................................... 1 Changes to General Description .................................................... 1 Changes Table 2 ................................................................................ 3 Changes to Table 3 ............................................................................ 4 Changes to Table 4, Added Endnote 1 and Endnote 2 .................5 Changes to Figure 4 through Figure 9 ............................................6 Changes to Figure 11, Figure 12, Figure 14, and Figure 15..........7 Changes to Figure 16 through Figure 27 ........................................8 Changes to Figure 28 through Figure 33 ..................................... 10 Changes to Figure 34 through Figure 39 ..................................... 11 Changes to Figure 41 and Figure 44............................................. 12 Inserted Figure 46, Figure 47, Figure 49, and Figure 50; Renumbered Sequentially ............................................................. 13 Changes to Figure 51, Figure 52, and Figure 53 ......................... 15 Updated Outline Dimensions ....................................................... 16 Changes to Ordering Guide .......................................................... 17 11/07—Rev. 0 to Rev. A Change to Large Signal Voltage Gain Specification ......................4 11/07—Revision 0: Initial Version Rev. C | Page 2 of 20 AD8638/AD8639 SPECIFICATIONS ELECTRICAL CHARACTERISTICS—5 V OPERATION VSY = 5 V, VCM = VSY/2, TA = 25°C, unless otherwise noted. Table 2. Parameter INPUT CHARACTERISTICS Offset Voltage Symbol VOS −40°C ≤ TA ≤ +125°C −0.1 V ≤ VCM ≤ +3.0 V −40°C ≤ TA ≤ +125°C Input Bias Current IB −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C Input Offset Current IOS −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C VCM = 0 V to 3 V −40°C ≤ TA ≤ +125°C RL = 10 kΩ, VO = 0.5 V to 4.5 V −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C Conditions Min Typ 3 3 1.5 7 45 7 7 16.5 −0.1 118 118 120 119 133 136 0.01 0.04 22.5 4 1.7 4.97 4.97 4.90 4.86 4.985 4.93 7.5 32 ±19 4.2 127 125 143 1.0 1.3 1.5 10 15 40 55 0.06 0.15 Max 9 23 9 23 40 40 105 40 40 60 +3 Unit μV μV μV μV pA pA pA pA pA pA V dB dB dB dB μV/°C μV/°C TΩ pF pF V V V V mV mV mV mV mA Ω dB dB mA mA V/μs μs μs MHz Degrees μV p-p nV/√Hz Input Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain Offset Voltage Drift for All Packages Except SOT-23 Offset Voltage Drift for SOT-23 Input Resistance Input Capacitance, Differential Mode Input Capacitance, Common Mode OUTPUT CHARACTERISTICS Output Voltage High CMRR AVO ∆VOS/∆T ∆VOS/∆T RIN CINDM CINCM VOH Output Voltage Low VOL Short-Circuit Current Closed-Loop Output Impedance POWER SUPPLY Power Supply Rejection Ratio Supply Current per Amplifier DYNAMIC PERFORMANCE Slew Rate Settling Time to 0.1% Overload Recovery Time Gain Bandwidth Product Phase Margin NOISE PERFORMANCE Voltage Noise Voltage Noise Density ISC ZOUT PSRR ISY RL = 10 kΩ to VCM −40°C ≤ TA ≤ +125°C RL = 2 kΩ to VCM −40°C ≤ TA ≤ +125°C RL = 10 kΩ to VCM −40°C ≤ TA ≤ +125°C RL = 2 kΩ to VCM −40°C ≤ TA ≤ +125°C TA = 25°C f = 100 kHz, AV = 1 VSY = 4.5 V to 16 V −40°C ≤ TA ≤ +125°C IO = 0 mA −40°C ≤ TA ≤ +125°C RL = 10 kΩ, CL = 20 pF, AV = 1 VIN = 2 V step, CL = 20 pF, RL = 1 kΩ, AV = 1 RL = 2 kΩ, CL = 20 pF, AV = 1 RL = 2 kΩ, CL = 20 pF, AV = 1 0.1 Hz to 10 Hz f = 1 kHz Rev. C | Page 3 of 20 SR tS GBP ΦM en p-p en 2.5 3 50 1.35 70 1.2 60 AD8638/AD8639 ELECTRICAL CHARACTERISTICS—16 V OPERATION VSY = 16 V, VCM = VSY/2, TA = 25°C, unless otherwise noted. Table 3. Parameter INPUT CHARACTERISTICS Offset Voltage Symbol VOS −40°C ≤ TA ≤ +125°C −0.1 V ≤ VCM ≤ +14 V −40°C ≤ TA ≤ +125°C Input Bias Current IB −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C Input Offset Current IOS −40°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C VCM = 0 V to 14 V −40°C ≤ TA ≤ +125°C RL = 10 kΩ, VO = 0.5 V to 15.5 V −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C −40°C ≤ TA ≤ +125°C Conditions Min Typ 3 3 1 4 85 20 20 50 −0.1 127 127 130 130 142 147 0.03 0.04 22.5 4 1.7 15.94 15.93 15.77 15.70 15.96 15.82 30 120 ±37 3.0 127 125 143 1.25 1.5 1.7 40 60 140 200 0.06 0.15 Max 9 23 9 23 75 75 250 70 75 150 +14 Unit μV μV μV μV pA pA pA pA pA pA V dB dB dB dB μV/°C μV/°C TΩ pF pF V V V V mV mV mV mV mA Ω dB dB mA mA V/μs μs μs MHz Degrees μV p-p nV/√Hz Input Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain Offset Voltage Drift for All Packages Except SOT-23 Offset Voltage Drift for SOT-23 Input Resistance Input Capacitance, Differential Mode Input Capacitance, Common Mode OUTPUT CHARACTERISTICS Output Voltage High CMRR AVO ∆VOS/∆T ∆VOS/∆T RIN CINDM CINCM VOH Output Voltage Low VOL Short-Circuit Current Closed-Loop Output Impedance POWER SUPPLY Power Supply Rejection Ratio Supply Current per Amplifier DYNAMIC PERFORMANCE Slew Rate Settling Time to 0.1% Overload Recovery Time Gain Bandwidth Product Phase Margin NOISE PERFORMANCE Voltage Noise Voltage Noise Density ISC ZOUT PSRR ISY RL = 10 kΩ to VCM −40°C ≤ TA ≤ +125°C RL = 2 kΩ to VCM −40°C ≤ TA ≤ +125°C RL = 10 kΩ to VCM −40°C ≤ TA ≤ +125°C RL = 2 kΩ to VCM −40°C ≤ TA ≤ +125°C TA = 25°C f = 100 kHz, AV = 1 VSY = 4.5 V to 16 V −40°C ≤ TA ≤ +125°C IO = 0 mA −40°C ≤ TA ≤ +125°C RL = 10 kΩ, CL = 20 pF, AV = 1 VIN = 4 V step, CL = 20 pF, RL = 1 kΩ, AV = 1 RL = 2 kΩ, CL = 20 pF, AV = 1 RL = 2 kΩ, CL = 20 pF, AV = 1 0.1 Hz to 10 Hz f = 1 kHz SR tS GBP ΦM en p-p en 2 4 50 1.5 74 1.2 60 Rev. C | Page 4 of 20 AD8638/AD8639 ABSOLUTE MAXIMUM RATINGS Table 4. Parameter Supply Voltage Input Voltage Input Current1 Differential Input Voltage2 Output Short-Circuit Duration to GND Storage Temperature Range Operating Temperature Range Junction Temperature Range Lead Temperature (Soldering, 60 sec) 1 Rating 16 V GND − 0.3 V to VSY+ + 0.3 V ±10 mA ±VSY Indefinite −65°C to +150°C −40°C to +125°C −65°C to +150°C 300°C THERMAL RESISTANCE Table 5. Thermal Resistance Package Type 5-Lead SOT-23 (RJ-5) 8-Lead SOIC_N (R-8) 8-Lead MSOP (RM-8) 8-Lead LFCSP_WD (CP-8-5)2 1 θJA1 230 158 206 75 θJC 146 43 44 18 Unit °C/W °C/W °C/W °C/W Input pin has clamp diodes to power the supply pins. Input current should be limited to 10 mA or less whenever input signals exceed the power supply rail by 0.5 V. 2 Differential input voltage is limited to 5 V or the supply voltage, whichever is less. θJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages. This was measured using a standard two-layer board. 2 Exposed pad is soldered to the application board. ESD CAUTION 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. C | Page 5 of 20 AD8638/AD8639 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. 1400 1200 NUMBER OF AMPLIFIERS VSY = 5V 0V ≤ VCM ≤ +3V 6000 VSY = 16V 0V ≤ VCM ≤ +14V 5000 NUMBER OF AMPLIFIERS 1000 800 600 400 200 06895-003 4000 3000 2000 1000 –5 0 VOS (µV) 5 10 –5 0 VOS (µV) 5 10 Figure 5. Input Offset Voltage Distribution 25 VSY = ±2.5V –40°C ≤ TA ≤ +125°C SOIC PACKAGE 20 NUMBER OF AMPLIFIERS Figure 8. Input Offset Voltage Distribution 12 VSY = ±8V –40°C ≤ TA ≤ +125°C SOIC PACKAGE 10 NUMBER OF AMPLIFIERS 8 15 6 10 4 5 2 06895-004 0 4 8 12 16 20 24 28 32 36 40 0 4 8 12 16 20 24 28 32 36 40 TCVOS (nV/°C) TCVOS (nV/°C) Figure 6. Input Offset Voltage Drift Distribution 10.0 7.5 5.0 2.5 10.0 7.5 5.0 2.5 Figure 9. Input Offset Voltage Drift Distribution VSY = 5V –0.5V ≤ VCM ≤ +3.9V VOS (µV) 0 –2.5 –5.0 –7.5 06895-005 VOS (µV) 0 –2.5 –5.0 –7.5 –10.0 –0.5 VSY = 16V –0.5V ≤ VCM ≤ +14.5V 1.0 2.5 4.0 5.5 7.0 VCM (V) 8.5 10.0 11.5 13.0 14.5 06895-008 –10.0 –0.5 0 0.5 1 1.5 2.0 VCM (V) 2.5 3.0 3.5 4 Figure 7. Input Offset Voltage vs. Common-Mode Voltage Figure 10. Input Offset Voltage vs. Common-Mode Voltage Rev. C | Page 6 of 20 06895-007 0 0 06895-006 0 –10 0 –10 AD8638/AD8639 TA = 25°C, unless otherwise noted. 100 VSY = ±2.5V 100 VSY = ±8V 10 10 IB (pA) 1 0.1 25 IB (pA) 1 0.1 50 75 TEMPERATURE (°C) 100 125 50 75 TEMPERATURE (°C) 100 125 Figure 11. Input Bias Current vs. Temperature 10k 10k Figure 14. Input Bias Current vs. Temperature OUTPUT VOLTAGE TO SUPPLY RAIL (mV) 1k OUTPUT VOLTAGE TO SUPPLY RAIL (mV) VSY = ±2.5V VSY = ±8V 1k VDD – VOH 100 100 VDD – VOH 10 VOL – VSS VOL – VSS 10 1 06895-009 0.01 0.1 1 LOAD CURRENT (mA) 10 100 0.01 0.1 1 LOAD CURRENT (mA) 10 100 Figure 12. Output Voltage to Supply Rail vs. Load Current 120 Figure 15. Output Voltage to Supply Rail vs. Load Current 250 OUTPUT VOLTAGE TO SUPPLY RAIL (mV) 100 VDD – VOH OUTPUT VOLTAGE TO SUPPLY RAIL (mV) VSY = 5V RL = 2kΩ VSY = 16V RL = 2kΩ 200 80 150 VDD – VOH 60 100 VOL 40 20 VOL 50 06895-010 –25 0 25 50 75 TEMPERATURE (°C) 100 125 –25 0 25 50 TEMPERATURE (°C) 75 100 125 Figure 13. Output Voltage to Supply Rail vs. Temperature Figure 16. Output Voltage to Supply Rail vs. Temperature Rev. C | Page 7 of 20 06895-013 0 –40 0 –40 06895-012 0.1 0.001 1 0.001 06895-118 06895-117 0.01 25 AD8638/AD8639 TA = 25°C, unless otherwise noted. 120 100 80 60 40 GAIN CL = 20pF PHASE 120 100 80 60 120 100 80 60 PHASE 120 100 80 60 PHASE (Degrees) GAIN (dB) 0 –20 –40 –60 –80 –100 –120 1k VSY = ±2.5V RL = 2kΩ 10k 100k FREQUENCY (Hz) 1M CL = 200pF 0 –20 –40 –60 –80 –100 GAIN (dB) 20 20 20 0 –20 –40 –60 –80 –100 VSY = ±8V RL = 2kΩ 10k 100k FREQUENCY (Hz) CL = 20pF 20 0 –20 CL = 200pF –40 –60 –80 –100 06895-016 1M Figure 17. Open-Loop Gain and Phase vs. Frequency 60 VSY = ±2.5V RL = 2kΩ CL = 20pF Figure 20. Open-Loop Gain and Phase vs. Frequency 60 VSY = ±8V RL = 2kΩ CL = 20pF 40 AV = +100 40 CLOSED-LOOP GAIN (dB) AV = +100 CLOSED-LOOP GAIN (dB) 20 AV = +10 20 AV = +10 0 AV = +1 0 AV = +1 –20 –20 06895-018 10k 100k FREQUENCY (Hz) 1M 10M 10k 100k FREQUENCY (Hz) 1M 10M Figure 18. Closed-Loop Gain vs. Frequency 1k VSY = ±2.5V Figure 21. Closed-Loop Gain vs. Frequency 1k VSY = ±8V 100 AV = –10 100 AV = –10 ZOUT (Ω) ZOUT (Ω) 10 AV = –100 AV = +1 1 10 AV = –100 AV = +1 1 1k 10k 100k FREQUENCY (Hz) 1M 10M 06895-100 1k 10k 100k FREQUENCY (Hz) 1M 10M Figure 19. Output Impedance vs. Frequency Figure 22. Output Impedance vs. Frequency Rev. C | Page 8 of 20 06895-119 0.1 100 0.1 100 06895-019 –40 1k –40 1k 06895-017 –120 10M –120 1k –120 10M PHASE (Degrees) 40 40 GAIN 40 AD8638/AD8639 TA = 25°C, unless otherwise noted. 140 VSY = ±2.5V 120 100 CMRR (dB) CMRR (dB) 140 VSY = ±8V 120 100 80 60 40 20 06895-120 06895-127 06895-112 06895-113 80 60 40 20 0 100 1k 10k 100k FREQUENCY (Hz) 1M 10M 0 100 1k 10k 100k FREQUENCY (Hz) 1M 10M Figure 23. CMRR vs. Frequency 120 VSY = ±2.5V 100 80 PSRR (dB) PSRR (dB) Figure 26. CMRR vs. Frequency 120 VSY = ±8V 100 80 PSRR+ PSRR– 60 PSRR– 40 20 0 PSRR+ 60 40 20 0 100 1k 10k 100k FREQUENCY (Hz) 1M 10M 06895-111 –20 10 –20 10 100 1k 10k 100k FREQUENCY (Hz) 1M 10M Figure 24. PSRR vs. Frequency 80 70 60 OVERSHOOT (%) 80 70 60 Figure 27. PSRR vs. Frequency VSY = ±2.5V RL = 10kΩ VSY = ±8V RL = 10kΩ 50 40 30 20 10 0 10 06895-126 OVERSHOOT (%) 50 40 30 20 10 0 10 OS+ OS– OS+ OS– 100 LOAD CAPACITANCE (pF) 1k 100 LOAD CAPACITANCE (pF) 1k Figure 25. Small Signal Overshoot vs. Load Capacitance Figure 28. Small Signal Overshoot vs. Load Capacitance Rev. C | Page 9 of 20 AD8638/AD8639 TA = 25°C, unless otherwise noted. VSY = ±2.5V AV = +1 CL = 200pF RL = 10kΩ VSY = ±8V AV = +1 CL = 200pF RL = 10kΩ VOLTAGE (500mV/DIV) 06895-101 VOLTAGE (2V/DIV) TIME (2µs/DIV) TIME (2µs/DIV) Figure 29. Large Signal Transient Response VSY = ±2.5V AV = +1 CL = 200pF RL = 10kΩ Figure 32. Large Signal Transient Response VSY = ±8V AV = +1 CL = 200pF RL = 10kΩ VOLTAGE (50mV/DIV) VOLTAGE (50mV/DIV) 06895-103 TIME (2µs/DIV) TIME (2µs/DIV) Figure 30. Small Signal Transient Response 0.05 0 INPUT VOLTAGE Figure 33. Small Signal Transient Response 0.05 0 INPUT VOLTAGE (50mV/DIV) OUTPUT VOLTAGE (1V/DIV) INPUT VOLTAGE INPUT VOLTAGE (50mV/DIV) –0.10 –0.15 VSY = ±2.5V AV = –100 –0.10 –0.15 10 5 OUTPUT VOLTAGE 0 –5 TIME (10µs/DIV) 3 2 1 OUTPUT VOLTAGE 0 –1 TIME (10µs/DIV) 06895-132 OUTPUT VOLTAGE (5V/DIV) 06895-133 –0.05 –0.05 VSY = ±8V AV = –100 Figure 31. Negative Overload Recovery Figure 34. Negative Overload Recovery Rev. C | Page 10 of 20 06895-104 06895-102 AD8638/AD8639 TA = 25°C, unless otherwise noted. 0.15 0.10 VSY = ±2.5V AV = –100 0.15 0.10 VSY = ±8V AV = –100 INPUT VOLTAGE (50mV/DIV) INPUT VOLTAGE (50mV/DIV) OUTPUT VOLTAGE (1V/DIV) 0 –0.05 INPUT VOLTAGE 0 –0.05 INPUT VOLTAGE 1 OUTPUT VOLTAGE 0 –1 –2 –3 TIME (10µs/DIV) 5 0 –5 –10 –15 TIME (10µs/DIV) OUTPUT VOLTAGE 06895-134 Figure 35. Positive Overload Recovery Figure 38. Positive Overload Recovery INPUT INPUT 1V/DIV ERROR BAND OUTPUT +2mV 0 06895-136 2V/DIV ERROR BAND OUTPUT +2mV 0 06895-137 06895-139 –2mV VSY = ±2.5V TIME (4µs/DIV) –2mV VSY = ±8V TIME (4µs/DIV) Figure 36. Positive Settling Time to 0.1% Figure 39. Positive Settling Time to 0.1% INPUT INPUT 1V/DIV OUTPUT ERROR BAND VSY = ±2.5V TIME (4µs/DIV) +2mV OUTPUT 0 06895-138 2V/DIV +2mV 0 ERROR BAND VSY = ±8V TIME (4µs/DIV) –2mV –2mV Figure 37. Negative Settling Time to 0.1% Figure 40. Negative Settling Time to 0.1% Rev. C | Page 11 of 20 06895-135 OUTPUT VOLTAGE (5V/DIV) 0.05 0.05 AD8638/AD8639 TA = 25°C, unless otherwise noted. 1k VSY = ±2.5V 1k VSY = ±8V VOLTAGE NOISE DENSITY (nV/ Hz) VOLTAGE NOISE DENSITY (nV/ Hz) 100 100 06895-114 1 10 100 1k FREQUENCY (Hz) 10k 25k 1 10 100 1k FREQUENCY (Hz) 10k 25k Figure 41. Voltage Noise Density vs. Frequency 1.5 VSY = ±2.5V INPUT NOISE VOLTAGE (0.5µV/DIV) Figure 44. Voltage Noise Density vs. Frequency 1.5 VSY = ±8V 1.0 1.0 INPUT NOISE VOLTAGE (µV) 0.5 0.5 0 0 –0.5 –0.5 –1.0 –1.0 06895-043 0 1 2 3 4 5 6 TIME (Seconds) 7 8 9 10 0 1 2 3 4 5 6 TIME (Seconds) 7 8 9 10 Figure 42. 0.1 Hz to 10 Hz Noise 1400 1250 +125°C +85°C +25°C 750 –40°C 500 Figure 45. 0.1 Hz to 10 Hz Noise 1200 VSY = ±8V SUPPLY CURRENT (µA) 1000 800 600 400 200 06895-014 SUPPLY CURRENT (µA) 1000 VSY = ±2.5V 250 0 1 2 3 4 5 6 789 VSY (V) 10 11 12 13 14 15 16 –25 –10 5 20 35 50 65 TEMPERATURE (°C) 80 95 110 125 Figure 43. Supply Current vs. Supply Voltage Figure 46. Supply Current vs. Temperature Rev. C | Page 12 of 20 06895-125 0 0 –40 06895-044 –1.5 –1.5 06895-115 10 10 AD8638/AD8639 TA = 25°C, unless otherwise noted. 0 –20 CHANNEL SEPARATION (dB) VSY = ±8V AV = –10 CHANNEL SEPARATION (dB) 0 –20 –40 –60 RL = 2kΩ –80 –100 –120 –140 100 VSY = ±8V AV = –100 –40 –60 –80 –100 –120 –140 100 RL = 10kΩ RL = 2kΩ RL = 10kΩ 06895-147 1k 10k FREQUENCY (Hz) 100k 1k 10k FREQUENCY (Hz) 100k Figure 47. Channel Separation vs. Frequency 0.1 VSY = ±8V AV = +1 RL = 2kΩ 0.1 Figure 50. Channel Separation vs. Frequency VS = ±8V AV = +1 RL = 10kΩ THD + NOISE (%) THD + NOISE (%) 0.01 VIN = 1V rms 0.01 VIN = 1V rms 0.001 VIN = 3V rms 0.001 VIN = 3V rms 06895-149 100 1k FREQUENCY (Hz) 10k 100k 100 1k FREQUENCY (Hz) 10k 100k Figure 48. THD + Noise vs. Frequency 300 250 200 150 100 50 0 –50 VSY = 16V TA = 125°C Figure 51. THD + Noise vs. Frequency IB (pA) 0 1 2 3 4 5 6 789 VCM (V) 10 11 12 13 14 15 16 Figure 49. Input Bias Current vs. Input Common-Mode Voltage 06895-034 Rev. C | Page 13 of 20 06895-150 0.0001 10 0.0001 10 06895-148 AD8638/AD8639 THEORY OF OPERATION The AD8638/AD8639 are single-supply and dual-supply, ultrahigh precision, rail-to-rail output operational amplifiers. The typical offset voltage of 3 μV allows the amplifiers to be easily configured for high gains without risk of excessive output voltage errors. The extremely small temperature drift of 30 nV/°C ensures a minimum offset voltage error over the entire temperature range of −40°C to +125°C, making the amplifiers ideal for a variety of sensitive measurement applications in harsh operating environments. The AD8638/AD8639 achieve a high degree of precision through a patented auto-zeroing topology. This unique topology allows the AD8638/AD8639 to maintain low offset voltage over a wide temperature range and over the operating lifetime. The AD8638/AD8639 also optimize the noise and bandwidth over previous generations of auto-zero amplifiers, offering the lowest voltage noise of any auto-zero amplifier by more than 50%. Previous designs used either auto-zeroing or chopping to add precision to the specifications of an amplifier. Auto-zeroing results in low noise energy at the auto-zeroing frequency, at the expense of higher low frequency noise due to aliasing of wideband noise into the auto-zeroed frequency band. Chopping results in lower low frequency noise at the expense of larger noise energy at the chopping frequency. The AD8638/AD8639 use both auto-zeroing and chopping in a patented ping-pong arrangement to obtain lower low frequency noise together with lower energy at the chopping and auto-zeroing frequencies, maximizing the SNR for the majority of applications without the need for additional filtering. The relatively high clock frequency of 15 kHz simplifies filter requirements for a wide, useful, noise-free bandwidth. The AD8638 is among the few auto-zero amplifiers offered in the 5-lead SOT-23 package. This provides significant improvement over the ac parameters of previous auto-zero amplifiers. The AD8638/AD8639 have low noise over a relatively wide bandwidth (0 Hz to 10 kHz) and can be used where the highest dc precision is required. In systems with signal bandwidths ranging from 5 kHz to 10 kHz, the AD8638/AD8639 provide true 16-bit accuracy, making this device the best choice for very high resolution systems. The internal elimination of 1/f noise is accomplished as follows: 1/f noise appears as a slowly varying offset to AD8638/AD8639 inputs. Auto-zeroing corrects any dc or low frequency offset. Therefore, the 1/f noise component is essentially removed, leaving the AD8638/AD8639 free of 1/f noise. INPUT VOLTAGE RANGE The AD8638/AD8639 are not rail-to-rail input amplifiers; therefore, care is required to ensure that both inputs do not exceed the input voltage range. Under normal negative feedback operating conditions, the amplifier corrects its output to ensure that the two inputs are at the same voltage. However, if either input exceeds the input voltage range, the loop opens and large currents begin to flow through the ESD protection diodes in the amplifier. These diodes are connected between the inputs and each supply rail to protect the input transistors against an electrostatic discharge event, and they are normally reverse-biased. However, if the input voltage exceeds the supply voltage, these ESD diodes can become forward-biased. Without current limiting, excessive amounts of current may flow through these diodes, causing permanent damage to the device. If inputs are subject to overvoltage, insert appropriate series resistors to limit the diode current to less than 5 mA maximum. OUTPUT PHASE REVERSAL Output phase reversal occurs in some amplifiers when the input common-mode voltage range is exceeded. As common-mode voltage is moved outside the common-mode range, the outputs of these amplifiers can suddenly jump in the opposite direction to the supply rail. This is the result of the differential input pair shutting down, causing a radical shifting of internal voltages that results in the erratic output behavior. The AD8638/AD8639 amplifiers have been carefully designed to prevent any output phase reversal if both inputs are maintained within the specified input voltage range. If one or both inputs exceed the input voltage range but remain within the supply rails, an internal loop opens and the output varies. Therefore, the inputs should always be less than at least 2 V below the positive supply. 1/f NOISE 1/f noise, also known as pink noise, is a major contributor to errors in dc-coupled measurements. This 1/f noise error term can be in the range of several microvolts or more and, when amplified by the closed-loop gain of the circuit, can show up as a large output signal. For example, when an amplifier with 5 μV p-p 1/f noise is configured for a gain of 1000, its output has 5 mV of error due to the 1/f noise. However, the AD8638/AD8639 eliminate 1/f noise internally and thus significantly reduce output errors. OVERLOAD RECOVERY TIME Many auto-zero amplifiers are plagued by a long overload recovery time, often in milliseconds, due to the complicated settling behavior of the internal nulling loops after saturation of the outputs. The AD8638/AD8639 are designed so that internal settling occurs within two clock cycles after output saturation happens. This results in a much shorter recovery time, less than 50 μs, when compared to other auto-zero amplifiers. The wide bandwidth of the AD8638/AD8639 enhances performance when the parts are used to drive loads that inject transients into the outputs. This is a common situation when an amplifier is used to drive the input of switched capacitor ADCs. Rev. C | Page 14 of 20 AD8638/AD8639 INFRARED SENSORS Infrared (IR) sensors, particularly thermopiles, are increasingly used in temperature measurement for applications as wide ranging as automotive climate control, human ear thermometers, home insulation analysis, and automotive repair diagnostics. The relatively small output signal of the sensor demands high gain with very low offset voltage and drift to avoid dc errors. If interstage ac coupling is used, as shown in Figure 52, low offset and drift prevent the output of the input amplifier from drifting close to saturation. The low input bias currents generate minimal errors from the output impedance of the sensor. Similar to pressure sensors, the very low amplifier drift with time and temperature eliminates additional errors once the system is calibrated at room temperature. The low 1/f noise improves SNR for dc measurements taken over periods often exceeding one-fifth of a second. Figure 52 shows a circuit that can amplify ac signals from 100 μV to 300 μV up to the 1 V to 3 V levels, with a gain of 10,000 for accurate analog-to-digital conversions. 10kΩ 100Ω 100kΩ 5V TO 16V 5V TO 16V 100µV TO 300µV IR DETECTOR 10µF 100kΩ In such applications, it is desirable to use a shunt with very low resistance to minimize the series voltage drop; this minimizes wasted power and allows the measurement of high currents while saving power. A typical shunt may be 0.1 Ω. At measured current values of 1 A, the output signal of the shunt is hundreds of millivolts, or even volts, and amplifier error sources are not critical. However, at low measured current values in the 1 mA range, the 100 μV output voltage of the shunt demands a very low offset voltage and drift to maintain absolute accuracy. Low input bias currents are also needed to prevent injected bias current from becoming a significant percentage of the measured current. High open-loop gain, CMRR, and PSRR help to maintain the overall circuit accuracy. With the extremely high CMRR of the AD8638/AD8639, the CMRR is limited by the resistor ratio matching. As long as the rate of change of the current is not too fast, an auto-zero amplifier can be used with excellent results. OUTPUT AMPLIFIER FOR HIGH PRECISION DACS The AD8638/AD8639 can be used as output amplifiers for a 16-bit high precision DAC in a unipolar configuration. In this case, the selected op amp needs to have very low offset voltage (the DAC LSB is 38 μV when operating with a 2.5 V reference) to eliminate the need for output offset trims. Input bias current (typically a few tens of picoamperes) must also be very low because it generates an additional offset error when multiplied by the DAC output impedance (approximately 6 kΩ). Rail-to-rail output provides full-scale output with very little error. Output impedance of the DAC is constant and codeindependent, but the high input impedance of the AD8638/ AD8639 minimizes gain errors. The wide bandwidth of the amplifier also serves well in this case. The amplifier, with a settling time of 4 μs, adds another time constant to the system, increasing the settling time of the output. For example, see Figure 54. The settling time of the AD5541 is 1 μs. The combined settling time is approximately 4.1 μs, as can be derived from the following equation: t S (TOTAL ) = 1/2 AD8639 1/2 AD8639 fC ≈ 1.6Hz TO BIAS VOLTAGE 06895-065 10kΩ Figure 52. AD8639 Used as a Preamplifier for Thermopile PRECISION CURRENT SHUNT SENSOR A precision current shunt sensor benefits from the unique attributes of auto-zero amplifiers when used in a differencing configuration, as shown in Figure 53. Current shunt sensors are used in precision current sources for feedback control systems. They are also used in a variety of other applications, including battery fuel gauging, laser diode power measurement and control, torque feedback controls in electric power steering, and precision power metering. SUPPLY 100kΩ e = 1000 R S I = 100mV/mA C 5V TO 16V 100Ω I RS 0.1Ω RL (t S DAC )2 + (t S AD8638)2 2.5V 6 0.1µF 5V 0.1µF ADR421 4 2 0.1µF 5V TO 16V 5V TO 16V SERIAL INTERFACE VDD CS DIN SCLK REF(REFF*) REFS* AD8638 AD5541/AD5542 DGND AGND VOUT UNIPOLAR OUTPUT 100kΩ C 100Ω 06895-066 *AD5542 ONLY Figure 54. AD8638 Used as an Output Amplifier Figure 53. Low-Side Current Sensing Rev. C | Page 15 of 20 06895-067 AD8638 LDAC* AD8638/AD8639 OUTLINE DIMENSIONS 2.90 BSC 5.00 (0.1968) 4.80 (0.1890) 5 4 1.60 BSC 1 2 3 2.80 BSC 4.00 (0.1574) 3.80 (0.1497) 8 1 5 4 6.20 (0.2441) 5.80 (0.2284) PIN 1 0.95 BSC 1.30 1.15 0.90 1.90 BSC 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) 1.75 (0.0688) 1.35 (0.0532) 0.50 (0.0196) 0.25 (0.0099) 8° 0° 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) 45° 1.45 MAX 0.22 0.08 10° 5° 0° 0.60 0.45 0.30 COPLANARITY 0.10 SEATING PLANE 0.51 (0.0201) 0.31 (0.0122) 0.15 MAX 0.50 0.30 SEATING PLANE COMPLIANT TO JEDEC STANDARDS MO-178-A A COMPLIANT TO JEDEC STANDARDS MS-012-A A 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. 5-Lead Small Outline Transistor Package [SOT-23] (RJ-5) Dimensions shown in millimeters Figure 56. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches) 3.20 3.00 2.80 3.20 3.00 2.80 PIN 1 8 5 1 5.15 4.90 4.65 4 0.65 BSC 0.95 0.85 0.75 0.15 0.00 0.38 0.22 SEATING PLANE 1.10 MAX 8° 0° 0.80 0.60 0.40 0.23 0.08 COPLANARITY 0.10 COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 57. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters Rev. C | Page 16 of 20 012407-A AD8638/AD8639 3.00 BSC SQ 2.48 2.38 2.23 5 EXPOSED PAD 8 INDEX AREA 0.50 0.40 0.30 TOP VIEW 1.74 1.64 1.49 1 4 BOTTOM VIEW PIN 1 INDICATOR (R 0.2) 0.80 0.75 0.70 0.80 MAX 0.55 NOM 0.05 MAX 0.02 NOM COPLANARITY 0.08 0.20 REF 051508-A SEATING PLANE 0.30 0.25 0.18 0.50 BSC COMPLIANT TO JEDEC STANDARDS MO-229-WEED-4 Figure 58. 8-Lead Lead Frame Chip Scale Package [LFCSP_WD] 3 mm × 3 mm Body, Very Very Thin, Dual Lead (CP-8-5) Dimensions shown in millimeters ORDERING GUIDE Model AD8638ARJZ-R21 AD8638ARJZ-REEL1 AD8638ARJZ-REEL71 AD8638ARZ1 AD8638ARZ-REEL1 AD8638ARZ-REEL71 AD8639ACPZ-R21 AD8639ACPZ-REEL1 AD8639ACPZ-REEL71 AD8639ARZ1 AD8639ARZ-REEL1 AD8639ARZ-REEL71 AD8639ARMZ-R21 AD8639ARMZ-REEL1 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 −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 −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C Package Description 5-Lead SOT-23 5-Lead SOT-23 5-Lead SOT-23 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead LFCSP_WD 8-Lead LFCSP_WD 8-Lead LFCSP_WD 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead MSOP 8-Lead MSOP Package Option RJ-5 RJ-5 RJ-5 R-8 R-8 R-8 CP-8-5 CP-8-5 CP-8-5 R-8 R-8 R-8 RM-8 RM-8 Branding A1T A1T A1T A1Y A1Y A1Y A1Y A1Y Z = RoHS Compliant Part. Rev. C | Page 17 of 20 AD8638/AD8639 NOTES Rev. C | Page 18 of 20 AD8638/AD8639 NOTES Rev. C | Page 19 of 20 AD8638/AD8639 NOTES ©2007–2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06895-0-5/08(C) Rev. C | Page 20 of 20