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| Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifier AD8628/AD8629 FEATURES Lowest auto-zero amplifier noise Low offset voltage: 1 V Input offset drift: 0.002 V/C Rail-to-rail input and output swing 5 V single-supply operation High gain, CMRR, and PSRR: 120 dB Very low input bias current: 100 pA max Low supply current: 1.0 mA Overload recovery time: 10 s No external components required PIN CONFIGURATIONS OUT 1 AD8628 TOP VIEW (Not to Scale) 5 V+ V- 2 +IN 3 4 -IN Figure 1. 5-Lead TSOT (UJ-5) and 5-Lead SOT-23 (RT-5) NC 1 -IN 2 +IN 3 8 NC V+ OUT 02735-002 02735-064 AD8628 7 6 5 TOP VIEW V- 4 (Not to Scale) NC APPLICATIONS Automotive sensors Pressure and position sensors Strain gage amplifiers Medical instrumentation Thermocouple amplifiers Precision current sensing Photodiode amplifier NC = NO CONNECT Figure 2. 8-Lead SOIC (R-8) OUT A 1 -IN A 2 +IN A 3 8 V+ OUT B 02735-063 AD8629 7 6 -IN B TOP VIEW V- 4 (Not to Scale) 5 +IN B Figure 3. 8-Lead SOIC (R-8) OUT A 1 -IN A 2 +IN A 3 V- 4 8 V+ OUT B -IN B +IN B AD8629 TOP VIEW (Not to Scale) 7 6 5 Figure 4. 8-Lead MSOP (RM-8) GENERAL DESCRIPTION This new breed of amplifier has ultralow offset, drift, and bias current. The AD8628/AD8629 are wide bandwidth auto-zero amplifiers featuring rail-to-rail input and output swings and low noise. Operation is fully specified from 2.7 V to 5 V single supply (1.35 V to 2.5 V dual supply). The AD8628/AD8629 provide benefits previously found only in expensive auto-zeroing or chopper-stabilized amplifiers. Using Analog Devices' new topology, these zero-drift amplifiers combine low cost with high accuracy and low noise. (No external capacitor is required.) In addition, the AD8628/AD8629 greatly reduce the digital switching noise found in most chopper-stabilized amplifiers. With an offset voltage of only 1 V, drift of less than 0.005 V/C, and noise of only 0.5 V p-p (0 Hz to 10 Hz), the AD8628/AD8629 are perfectly 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 range. Many systems can take advantage of the rail-to-rail input and output swings provided by the AD8628/AD8629 to reduce input biasing complexity and maximize SNR. The AD8628/AD8629 are specified for the extended industrial temperature range (-40C to +125C). The AD8628 is available in tiny TSOT-23, SOT-23, and the popular 8-lead narrow SOIC plastic packages. The AD8629 is available in the standard 8-lead narrow SOIC and MSOP plastic packages. 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: 781.326.8703 (c) 2004 Analog Devices, Inc. All rights reserved. 02735-001 AD8628/AD8629 TABLE OF CONTENTS Specifications..................................................................................... 3 Electrical Characteristics ............................................................. 3 Absolute Maximum Ratings............................................................ 5 ESD Caution.................................................................................. 5 Typical Performance Characteristics ............................................. 6 Functional Description .................................................................. 14 1/f Noise....................................................................................... 14 Peak-to-Peak Noise .................................................................... 15 Noise Behavior with First-Order Low-Pass Filter.................. 15 Total Integrated Input-Referred Noise for First-Order Filter15 Input Overvoltage Protection ................................................... 16 Output Phase Reversal............................................................... 16 Overload Recovery Time .......................................................... 16 Infrared Sensors.......................................................................... 17 Precision Current Shunts .......................................................... 18 Output Amplifier for High Precision DACs ........................... 18 Outline Dimensions ....................................................................... 19 Ordering Guide .......................................................................... 20 REVISION HISTORY 10/04--Data Sheet Changed from Rev. B to Rev. C Updated Formatting ...........................................................Universal Added AD8629....................................................................Universal Added SOIC and MSOP Pin Configurations ............................... 1 Added Figure 48.............................................................................. 13 Changes to Figure 62...................................................................... 17 Added MSOP Package ................................................................... 19 Changes to Ordering Guide .......................................................... 20 10/03--Data Sheet Changed from Rev. A to Rev. B Changes to General Description .................................................... 1 Changes to Absolute Maximum Ratings ....................................... 4 Changes to Ordering Guide ............................................................ 4 Added TSOT-23 Package............................................................... 15 6/03--Data Sheet Changed from Rev. 0 to Rev. A Changes to Specifications ................................................................ 3 Changes to Ordering Guide ............................................................ 4 Change to Functional Description ............................................... 10 Updated Outline Dimensions ....................................................... 15 10/02--Revision 0: Initial Version Rev. C | Page 2 of 20 AD8628/AD8629 SPECIFICATIONS ELECTRICAL CHARACTERISTICS VS = 5.0 V, VCM = 2.5 V, TA = 25C, unless otherwise noted. Table 1. Parameter INPUT CHARACTERISTICS Offset Voltage Input Bias Current Input Offset Current Input Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain1 Offset Voltage Drift OUTPUT CHARACTERISTICS Output Voltage High Symbol VOS -40C TA +125C IB -40C TA +125C IOS -40C TA +125C CMRR AVO VOS/T VOH VCM = 0 V to 5 V -40C TA +125C RL = 10 k, VO = 0.3 V to 4.7 V -40C TA +125C -40C TA +125C RL = 100 k to ground -40C TA +125C RL = 10 k to ground -40C TA +125C RL = 100 k to V+ -40C TA +125C RL = 10 k to V+ -40C TA +125C -40C TA +125C Output Current POWER SUPPLY Power Supply Rejection Ratio Supply Current/Amplifier INPUT CAPACITANCE Differential Common-Mode DYNAMIC PERFORMANCE Slew Rate Overload Recovery Time Gain Bandwidth Product NOISE PERFORMANCE Voltage Noise Voltage Noise Density Current Noise Density IO -40C TA +125C PSRR ISY VS = 2.7 V to 5.5 V -40C TA +125C VO = 0 V -40C TA +125C 0 120 115 125 120 140 130 145 135 0.002 4.996 4.995 4.98 4.97 1 2 10 15 50 40 30 15 50 30 Conditions Min Typ 1 Max 5 10 100 1.5 200 250 5 Unit V V pA nA pA pA V dB dB dB dB V/C V V V V mV mV mV mV mA mA mA mA 0.02 4.99 4.99 4.95 4.95 Output Voltage Low VOL 5 5 20 20 Short-Circuit Limit ISC 25 115 130 0.85 1.0 1.5 10 1.1 1.2 dB mA mA pF pF V/s ms MHz V p-p mV p-p nV/Hz fA/Hz CIN SR GBP en p-p en p-p en in RL = 10 k 1.0 0.05 2.5 0.5 0.16 22 5 0.1 Hz to 10 Hz 0.1 Hz to 1.0 Hz f = 1 kHz f = 10 Hz 1 Gain testing is highly dependent upon test bandwidth. Rev. C | Page 3 of 20 AD8628/AD8629 VS = 2.7 V, VCM = 1.35 V, VO = 1.4 V, TA = 25C, unless otherwise noted. Table 2. Parameter INPUT CHARACTERISTICS Offset Voltage Input Bias Current Input Offset Current Input Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain Offset Voltage Drift OUTPUT CHARACTERISTICS Output Voltage High Symbol VOS -40C TA +125C IB -40C TA +125C IOS -40C TA +125C CMRR AVO VOS/T VOH VCM = 0 V to 2.7 V -40C TA +125C RL = 10 k , VO = 0.3 V to 2.4 V -40C TA +125C -40C TA +125C RL = 100 k to ground -40C TA +125C RL = 10 k to ground -40C TA +125C RL = 100 k to V+ -40C TA +125C RL = 10 k to V+ -40C TA +125C -40C TA +125C Output Current POWER SUPPLY Power Supply Rejection Ratio Supply Current/Amplifier INPUT CAPACITANCE Differential Common-Mode DYNAMIC PERFORMANCE Slew Rate Overload Recovery Time Gain Bandwidth Product NOISE PERFORMANCE Voltage Noise Voltage Noise Density Current Noise Density IO -40C TA +125C PSRR ISY VS = 2.7 V to 5.5 V -40C TA +125C VO = 0 V -40C TA +125C 0 115 110 110 105 130 120 140 130 0.002 2.695 2.695 2.68 2.675 1 2 10 15 15 10 10 5 30 1.0 50 Conditions Min Typ 1 Max 5 10 100 1.5 200 250 5 Unit V V pA nA pA pA V dB dB dB dB V/C V V V V mV mV mV mV mA mA mA mA 0.02 2.68 2.68 2.67 2.67 Output Voltage Low VOL 5 5 20 20 Short-Circuit Limit ISC 10 115 130 0.75 0.9 1.5 10 1.0 1.2 dB mA mA pF pF V/s ms MHz V p-p nV/Hz fA/Hz CIN SR GBP en p-p en in RL = 10 k 1 0.05 2 0.5 22 5 0.1 Hz to 10 Hz f = 1 kHz f = 10 Hz Rev. C | Page 4 of 20 AD8628/AD8629 ABSOLUTE MAXIMUM RATINGS Table 3. Parameters Supply Voltage Input Voltage Differential Input Voltage1 Output Short-Circuit Duration to GND Storage Temperature Range R, RM, RT, UJ Packages Operating Temperature Range Junction Temperature Range R, RM, RT, UJ Packages Lead Temperature Range (Soldering, 60 s) Ratings 6V GND - 0.3 V to VS- + 0.3 V 5.0 V Indefinite -65C to +150C -40C to +125C -65C to +150C 300C 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 listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Table 4. Thermal Characteristics Package Type 5-Lead TSOT-23 (UJ-5) 5-Lead SOT-23 (RT-5) 8-Lead SOIC (R-8) 8-Lead MSOP (RM-8) JA1 207 230 158 190 JC 61 146 43 44 Unit C/W C/W C/W C/W 1 Differential input voltage is limited to 5 V or the supply voltage, whichever is less. 1 JA is specified for worst-case conditions, that is, JA is specified for the device soldered in a circuit board for surface-mount packages. ESD CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. Rev. C | Page 5 of 20 AD8628/AD8629 TYPICAL PERFORMANCE CHARACTERISTICS 180 160 VS = 2.7V TA = 25C 100 90 80 VS = 5V VCM = 2.5V TA = 25C 140 120 100 80 60 40 02735-003 NUMBER OF AMPLIFIERS NUMBER OF AMPLIFIERS 70 60 50 40 30 20 10 0 -2.5 -1.5 -0.5 0.5 INPUT OFFSET VOLTAGE (V) 1.5 02735-006 20 0 -2.5 -1.5 -0.5 0.5 INPUT OFFSET VOLTAGE (V) 1.5 2.5 2.5 Figure 5. Input Offset Voltage Distribution at 2.7 V Figure 8. Input Offset Voltage Distribution at 5 V 60 VS = 5V 50 +85C 7 VS = 5V TA = -40C TO +125C 6 INPUT BIAS CURRENT (pA) NUMBER OF AMPLIFIERS 5 40 4 3 2 30 20 +25C 10 02735-004 0 0 1 2 3 4 5 INPUT COMMON-MODE VOLTAGE (V) 6 0 0 2 4 6 TCVOS (nV/C) 8 10 Figure 6. Input Bias Current vs. Input Common-Mode Voltage at 5 V Figure 9. Input Offset Voltage Drift 1500 VS = 5V 1000 150C 1k VS = 5V TA = 25C 100 INPUT BIAS CURRENT (pA) 500 OUTPUT VOLTAGE (mV) 125C 10 SOURCE SINK 1 0 -500 -1000 02735-005 0.1 02735-008 -1500 0 1 2 3 4 5 INPUT COMMON-MODE VOLTAGE (V) 6 0.01 0.0001 0.001 0.01 0.1 LOAD CURRENT (mA) 1 10 Figure 7. Input Bias Current vs. Input Common-Mode Voltage at 5 V Figure 10. Output Voltage to Supply Rail vs. Load Current at 5 V Rev. C | Page 6 of 20 02735-007 -40C 1 AD8628/AD8629 1k VS = 2.7V 100 800 1000 TA = 25C OUTPUT VOLTAGE (mV) 10 SOURCE SINK 1 SUPPLY CURRENT (A) 02735-009 600 400 0.1 200 02735-012 0.01 0.0001 0.001 0.01 0.1 LOAD CURRENT (mA) 1 10 0 0 1 2 3 4 SUPPLY VOLTAGE (V) 5 6 Figure 11. Output Voltage to Supply Rail vs. Load Current at 2.7 V Figure 14. Supply Current vs. Supply Voltage 1500 VS = 5V VCM = 2.5V TA = -40C TO +150C 70 60 50 VS = 2.7V CL = 20pF RL = M = 52.1 0 45 90 135 180 225 02735-013 1150 INPUT BIAS CURRENT (pA) 40 30 20 10 0 -10 900 450 100 02735-010 -20 -30 10k 100k 1M FREQUENCY (Hz) 10M 0 -50 -25 0 25 50 75 100 TEMPERATURE (C) 125 150 175 Figure 12. Input Bias Current vs. Temperature Figure 15. Open-Loop Gain and Phase vs. Frequency 1250 TA = 25C 70 60 VS = 5V CL = 20pF RL = M = 52.1 0 45 90 135 180 225 02735-014 5V 1000 SUPPLY CURRENT (A) OPEN-LOOP GAIN (dB) 50 40 30 20 10 0 -10 02735-011 2.7V 750 500 250 -20 -30 10k 100k 1M FREQUENCY (Hz) 10M 0 -50 0 50 100 TEMPERATURE (C) 150 200 Figure 13. Supply Current vs. Temperature Figure 16. Open-Loop Gain and Phase vs. Frequency Rev. C | Page 7 of 20 PHASE SHIFT (Degrees) PHASE SHIFT (Degrees) OPEN-LOOP GAIN (dB) AD8628/AD8629 70 60 50 VS = 2.7V CL = 20pF RL = 2k 300 VS = 5V 270 240 CLOSED-LOOP GAIN (dB) 40 30 20 10 0 -10 -20 -30 1k 10k 100k 1M FREQUENCY (Hz) 10M AV = 1 02735-015 OUTPUT IMPEDANCE () 210 180 150 120 90 60 30 0 100 1k 10k 100k 1M FREQUENCY (Hz) AV = 100 AV = 100 AV = 1 AV = 10 AV = 10 02735-018 10M 100M Figure 17. Closed-Loop Gain vs. Frequency at 2.7 V Figure 20. Output Impedance vs. Frequency at 5 V 70 60 50 VS = 5V CL = 20pF RL = 2k CLOSED-LOOP GAIN (dB) 40 30 VOLTAGE (500mV/DIV) AV = 100 AV = 10 20 10 AV = 1 0 -10 -20 -30 1k 10k 100k 1M FREQUENCY (Hz) 10M 02735-016 VS = 1.35V CL = 300pF RL = AV = 1 TIME (4s/DIV) Figure 18. Closed-Loop Gain vs. Frequency at 5 V Figure 21. Large Signal Transient Response at 2.7 V 300 VS = 2.7V 270 240 OUTPUT IMPEDANCE () 210 180 VOLTAGE (1V/DIV) AV = 1 AV = 100 150 120 90 60 30 0 100 1k 10k 100k 1M FREQUENCY (Hz) 10M AV = 10 02735-017 VS = 2.5V CL = 300pF RL = AV = 1 100M TIME (5s/DIV) Figure 19. Output Impedance vs. Frequency at 2.7 V Figure 22. Large Signal Transient Response at 5 V Rev. C | Page 8 of 20 02735-020 02735-019 AD8628/AD8629 VS = 1.35V CL = 50pF RL = AV = 1 80 70 60 VS = 2.5V RL = 2k TA = 25C VOLTAGE (50mV/DIV) OVERSHOOT (%) 50 40 30 OS- 20 OS+ 02735-021 0 1 10 100 CAPACITIVE LOAD (pF) TIME (4s/DIV) 1k Figure 23. Small Signal Transient Response at 2.7 V Figure 26. Small Signal Overshoot vs. Load Capacitance at 5 V VS = 2.5V CL = 50pF RL = AV = 1 VIN VOLTAGE (50mV/DIV) VS = 2.5V AV = -50 RL = 10k CL = 0 CH1 = 50mV/DIV CH2 = 1V/DIV VOLTAGE (V) 0V 0V 02735-022 VOUT TIME (2s/DIV) TIME (4s/DIV) Figure 24. Small Signal Transient Response at 5 V Figure 27. Positive Overvoltage Recovery 100 90 80 70 VS = 1.35V RL = 2k TA = 25C 0V VS = 2.5V AV = -50 RL = 10k CL = 0 CH1 = 50mV/DIV CH2 = 1V/DIV OVERSHOOT (%) 60 50 40 30 20 10 0 1 10 100 CAPACITIVE LOAD (pF) 02735-023 OS- VOLTAGE (V) VIN VOUT OS+ 1k TIME (10s/DIV) Figure 25. Small Signal Overshoot vs. Load Capacitance at 2.7 V Figure 28. Negative Overvoltage Recovery Rev. C | Page 9 of 20 02735-026 0V 02735-025 02735-024 10 AD8628/AD8629 VS = 2.5V VIN = 1kHz @ 3V p-p CL = 0pF RL = 10k AV = 1 VOLTAGE (1V/DIV) 140 120 100 80 VS = 1.35V PSRR (dB) 60 +PSRR 40 20 0 -20 -PSRR 02735-027 -40 -60 100 1k 10k 100k FREQUENCY (Hz) 1M TIME (200s/DIV) 10M Figure 29. No Phase Reversal Figure 32. PSRR vs. Frequency 140 VS = 2.7V 120 100 80 140 120 100 80 VS = 2.5V CMRR (dB) 60 40 20 0 -20 02735-028 PSRR (dB) 60 +PSRR 40 20 0 -20 -40 -60 100 1k 10k 100k FREQUENCY (Hz) 1M 02735-031 -PSRR -40 -60 100 1k 10k 100k FREQUENCY (Hz) 1M 10M 10M Figure 30. CMRR vs. Frequency at 2.7 V Figure 33. PSRR vs. Frequency 140 120 100 80 VS = 5V 3.0 VS = 2.7V RL = 10k TA = 25C AV = 1 2.5 OUTPUT SWING (V p-p) 2.0 CMRR (dB) 60 40 20 0 -20 -40 -60 100 1k 10k 100k FREQUENCY (Hz) 1M 02735-029 1.5 1.0 0.5 02735-032 10M 0 100 1k 10k FREQUENCY (Hz) 100k 1M Figure 31. CMRR vs. Frequency at 5 V Figure 34. Maximum Output Swing vs. Frequency Rev. C | Page 10 of 20 02735-030 AD8628/AD8629 5.5 5.0 4.5 VS = 5V RL = 10k TA = 25C AV = 1 120 105 90 75 60 45 30 02735-036 VS = 2.7V NOISE AT 1kHz = 21.3nV OUTPUT SWING (V p-p) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 100 VOLTAGE NOISE DENSITY (nV/Hz) 02735-033 15 0 0 0.5 1.0 1.5 FREQUENCY (kHz) 2.0 1k 10k FREQUENCY (Hz) 100k 1M 2.5 Figure 35. Maximum Output Swing vs. Frequency at 5 V Figure 38. Voltage Noise Density at 2.7 V from 0 Hz to 2.5 kHz 0.60 VS = 2.7V 0.45 0.30 120 105 90 75 60 45 30 02735-037 VS = 2.7V NOISE AT 10kHz = 42.4nV 0.15 0 -0.15 -0.30 02735-034 -0.45 -0.60 0 1 2 3 4 5 6 TIME (s) 7 8 9 10 VOLTAGE NOISE DENSITY (nV/Hz) VOLTAGE (V) 15 0 0 5 10 15 FREQUENCY (kHz) 20 25 Figure 36. 0.1 Hz to 10 Hz Noise at 2.7 V Figure 39. Voltage Noise Density at 2.7 V from 0 Hz to 25 kHz 0.60 VS = 5V 0.45 0.30 120 105 90 75 60 45 30 02735-038 VS = 5V NOISE AT 1kHz = 22.1nV 0.15 0 -0.15 -0.30 02735-035 -0.45 -0.60 0 1 2 3 4 5 6 TIME (s) 7 8 9 10 VOLTAGE NOISE DENSITY (nV/Hz) VOLTAGE (V) 15 0 0 0.5 1.0 1.5 FREQUENCY (kHz) 2.0 2.5 Figure 37. 0.1 Hz to 10 Hz Noise at 5 V Figure 40. Voltage Noise Density at 5 V from 0 Hz to 2.5 kHz Rev. C | Page 11 of 20 AD8628/AD8629 120 105 90 75 60 45 30 02735-039 150 OUTPUT SHORT-CIRCUIT CURRENT (mA) VS = 5V NOISE AT 10kHz = 36.4nV VS = 2.7V TA = -40C TO +150C 100 VOLTAGE NOISE DENSITY (nV/Hz) 50 ISC- 0 ISC+ -50 02735-042 15 0 0 5 10 15 FREQUENCY (kHz) 20 25 -100 -50 -25 0 25 50 75 100 TEMPERATURE (C) 125 150 175 Figure 41. Voltage Noise Density at 5 V from 0 Hz to 25 kHz Figure 44. Output Short-Circuit Current vs. Temperature 120 VS = 5V 105 90 75 60 45 30 02735-040 150 OUTPUT SHORT-CIRCUIT CURRENT (mA) VOLTAGE NOISE DENSITY (nV/Hz) VS = 5V TA = -40C TO +150C 100 ISC- 50 0 -50 ISC+ -100 -50 -25 0 25 50 75 100 TEMPERATURE (C) 125 150 02735-043 15 0 0 5 FREQUENCY (kHz) 10 175 Figure 42. Voltage Noise Figure 45. Output Short-Circuit Current vs. Temperature 150 140 1k VS = 5V POWER SUPPLY REJECTION (dB) 130 120 110 100 90 80 70 60 50 -50 -25 0 25 50 TEMPERATURE (C) 75 100 02735-041 OUTPUT-TO-RAIL VOLTAGE (mV) VCC - VOH @ 1k 100 VOL - VEE @ 1k VCC - VOH @ 10k 10 VOL - VEE @ 10k VCC - VOH @ 100k 1 VOL - VEE @ 100k 02735-044 VS = 2.7V TO 5V TA = -40C TO +125C 125 0.10 -50 -25 0 25 50 75 100 TEMPERATURE (C) 125 150 175 Figure 43. Power Supply Rejection vs. Temperature Figure 46. Output-to-Rail Voltage vs. Temperature Rev. C | Page 12 of 20 AD8628/AD8629 1k VS = 2.7V OUTPUT-TO-RAIL VOLTAGE (mV) 140 VSY = 2.5V 100 VOL - VEE @ 1k VCC - VOH @ 10k 10 VOL - VEE @ 10k VCC - VOH @ 100k 1 VOL - VEE @ 100k 02735-045 CHANNEL SEPARATION (dB) VCC - VOH @ 1k 120 100 80 R1 10k V- R2 100 60 40 +2.5V + - V+ VIN 28mV p-p A V- -2.5V VOUT V+ B 02735-062 20 0 1k 0.10 -50 -25 0 25 50 75 100 TEMPERATURE (C) 125 150 175 10k 100k FREQUENCY (Hz) 1M 10M Figure 47. Output-to-Rail Voltage vs. Temperature Figure 48. AD8629 Channel Separation Rev. C | Page 13 of 20 AD8628/AD8629 FUNCTIONAL DESCRIPTION The AD8628/AD8629 are single-supply, ultrahigh precision rail-to-rail input and output operational amplifiers. The typical offset voltage of less than 1 V allows these amplifiers to be easily configured for high gains without risk of excessive output voltage errors. The extremely small temperature drift of 2 nV/C ensures a minimum of offset voltage error over their entire temperature range of -40C to +125C, making these amplifiers ideal for a variety of sensitive measurement applications in harsh operating environments. The AD8628/AD8629 achieve a high degree of precision through a patented combination of auto-zeroing and chopping. This unique topology allows the AD8628/AD8629 to maintain their low offset voltage over a wide temperature range and over their operating lifetime. The AD8628/AD8629 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 AD8628/AD8629 family use both auto-zeroing and chopping in a patented pingpong arrangement to obtain lower low-frequency noise together with lower energy at the chopping and auto-zeroing frequencies, maximizing the signal-to-noise ratio (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 AD8628 is among the few auto-zero amplifiers offered in the 5-lead TSOT-23 package. This provides a significant improvement over the ac parameters of the previous auto-zero amplifiers. The AD8628/AD8629 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 of from 5 kHz to 10 kHz, the AD8628/ AD8629 provide true 16-bit accuracy, making them the best choice for very high resolution systems. 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 V or more, and, when amplified with the closed-loop gain of the circuit, can show up as a large output offset. For example, when an amplifier with a 5 V p-p 1/f noise is configured for a gain of 1,000, its output has 5 mV of error due to the 1/f noise. But the AD8628/AD8629 eliminate 1/f noise internally, and thereby greatly reduce output errors. The internal elimination of 1/f noise is accomplished as follows. 1/f noise appears as a slowly varying offset to AD8628/AD8629 inputs. Auto-zeroing corrects any dc or low frequency offset. Therefore, the 1/f noise component is essentially removed, leaving the AD8628/AD8629 free of 1/f noise. One of the biggest advantages that the AD8628/AD8629 bring to systems applications over competitive auto-zero amplifiers is their very low noise. The comparison shown in Figure 49 indicates an input-referred noise density of 19.4 nV/Hz at 1 kHz for the AD8628, which is much better than the LTC2050 and LMC2001. The noise is flat from dc to 1.5 kHz, slowly increasing up to 20 kHz. The lower noise at low frequency is desirable where auto-zero amplifiers are widely used. 120 105 90 75 60 45 30 02735-046 VOLTAGE NOISE DENSITY (nV/Hz) LTC2050 (89.7nV/Hz) LMC2001 (31.1nV/Hz) 15 0 0 AD8628 (19.4nV/Hz) 2 MK AT 1kHz FOR ALL 3 GRAPHS 4 6 FREQUENCY (kHz) 8 10 12 Figure 49. Noise Spectral Density of AD8628 vs. Competition Rev. C | Page 14 of 20 AD8628/AD8629 PEAK-TO-PEAK NOISE Because of the ping-pong action between auto-zeroing and chopping, the peak-to-peak noise of the AD8628/AD8629 is much lower than the competition. Figure 50 and Figure 51 show this comparison. en p-p = 0.5V BW = 0.1Hz TO 10Hz 50 45 40 35 NOISE (dB) 30 25 20 15 VOLTAGE (0.5V/DIV) 10 5 0 0 10 20 30 40 50 60 FREQUENCY (Hz) 70 80 90 02735-050 100 Figure 53. Simulation Transfer Function of the Test Circuit 50 02735-047 45 40 35 TIME (1s/DIV) NOISE (dB) Figure 50. AD8628 Peak-to-Peak Noise 30 25 20 15 10 en p-p = 2.3V BW = 0.1Hz TO 10Hz VOLTAGE (0.5V/DIV) 5 0 0 10 20 30 40 50 60 70 FREQUENCY (kHz) 80 90 100 Figure 54. Actual Transfer Function of Test Circuit 02735-048 The measured noise spectrum of the test circuit shows that noise between 5 kHz and 45 kHz is successfully rolled off by the first-order filter. TIME (1s/DIV) TOTAL INTEGRATED INPUT-REFERRED NOISE FOR FIRST-ORDER FILTER For a first-order filter, the total integrated noise from the AD8628 is lower than the LTC2050. 10 Figure 51. LTC2050 Peak-to-Peak Noise NOISE BEHAVIOR WITH FIRST-ORDER LOW-PASS FILTER The AD8628 was simulated as a low-pass filter and then configured as shown in Figure 52. The behavior of the AD8628 matches the simulated data. It was verified that noise is rolled off by first-order filtering. IN OUT 100k 470pF LTC2050 RMS NOISE (V) AD8551 1 AD8628 1k 02735-049 Figure 52. Test Circuit: First-Order Low-Pass Filter--x101 Gain and 3 kHz Corner Frequency 0.1 10 100 1k 3dB FILTER BANDWIDTH (Hz) 10k Figure 55. 3 dB Filter Bandwidth in Hz Rev. C | Page 15 of 20 02735-052 02735-051 AD8628/AD8629 INPUT OVERVOLTAGE PROTECTION Although the AD8628/AD8629 are rail-to-rail input amplifiers, care should be taken to ensure that the potential difference between the inputs does not exceed the supply voltage. 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 either supply rail by more than 0.3 V, 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 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 could flow through these diodes, causing permanent damage to the device. If inputs are subject to overvoltage, appropriate series resistors should be inserted to limit the diode current to less than 5 mA maximum. VIN CH1 = 50mV/DIV CH2 = 1V/DIV AV = -50 VOLTAGE (V) 0V 0V VOUT TIME (500s/DIV) Figure 56. Positive Input Overload Recovery for the AD8628 VIN CH1 = 50mV/DIV CH2 = 1V/DIV AV = -50 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 of 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 AD8628/AD8629 amplifiers have been carefully designed to prevent any output phase reversal, provided that both inputs are maintained within the supply voltages. If one or both inputs could exceed either supply voltage, a resistor should be placed in series with the input to limit the current to less than 5 mA. This ensures that the output does not reverse its phase. VOLTAGE (V) 0V 0V VOUT TIME (500s/DIV) Figure 57. Positive Input Overload Recovery for LTC2050 VIN CH1 = 50mV/DIV CH2 = 1V/DIV AV = -50 OVERLOAD RECOVERY TIME Many auto-zero amplifiers are plagued by a long overload recovery time, often in ms, due to the complicated settling behavior of the internal nulling loops after saturation of the outputs. The AD8628/AD8629 have been designed so that internal settling occurs within two clock cycles after output saturation happens. This results in a much shorter recovery time, less than 10 s, when compared to other auto-zero amplifiers. The wide bandwidth of the AD8628/AD8629 enhances performance when they 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. VOLTAGE (V) 0V 0V VOUT TIME (500s/DIV) Figure 58. Positive Input Overload Recovery for LMC2001 Rev. C | Page 16 of 20 02735-055 02735-054 02735-053 AD8628/AD8629 0V CH1 = 50mV/DIV CH2 = 1V/DIV AV = -50 VOLTAGE (V) The results shown in Figure 56 to Figure 61 are summarized in Table 5. Table 5. Overload Recovery Time Product AD8628 LTC2050 LMC2001 Positive Overload Recovery (s) 6 650 40,000 Negative Overload Recovery (s) 9 25,000 35,000 VIN VOUT 02735-056 0V INFRARED SENSORS Infrared (IR) sensors, particularly thermopiles, are increasingly being 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 (Figure 62), low offset and drift prevents the input amplifier's output from drifting close to saturation. The low input bias currents generate minimal errors from the sensor's output impedance. As with pressure sensors, the very low amplifier drift with time and temperature eliminates additional errors once the temperature measurement has been calibrated. The low 1/f noise improves SNR for dc measurements taken over periods often exceeding 1/5 s. Figure 64 (shows a circuit that can amplify ac signals from 100 V to 300 V up to the 1 V to 3 V level, with gain of 10,000 for accurate A/D conversion. 10k 100 100k 5V 5V 100k TIME (500s/DIV) Figure 59. Negative Input Overload Recovery for the AD8628 0V CH1 = 50mV/DIV CH2 = 1V/DIV AV = -50 VIN VOUT VOLTAGE (V) 0V TIME (500s/DIV) Figure 60. Negative Input Overload Recovery for LTC2050 0V CH1 = 50mV/DIV CH2 = 1V/DIV AV = -50 VOLTAGE (V) 100V - 300V IR DETECTOR 02735-057 10F VIN VOUT 1/2 AD8629 10k fC 1.6Hz TO BIAS VOLTAGE 1/2 AD8629 Figure 62. AD8629 Used as Preamplifier for Thermopile 02735-058 0V TIME (500s/DIV) Figure 61. Negative Input Overload Recovery for LMC2001 Rev. C | Page 17 of 20 02735-059 AD8628/AD8629 PRECISION CURRENT SHUNTS A precision shunt current sensor benefits from the unique attributes of auto-zero amplifiers when used in a differencing configuration (Figure 63). Shunt current 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 100k e = 1,000 RS I 100mV/mA RS 0.1 RL OUTPUT AMPLIFIER FOR HIGH PRECISION DACs The AD8628/AD8629 are 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 V when operated 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 zero code error when multiplied by the DAC output impedance (approximately 6 k). Rail-to-rail input and output provide full-scale output with very little error. Output impedance of the DAC is constant and codeindependent, but the high input impedance of the AD8628/ AD8629 minimizes gain errors. The amplifiers' wide bandwidth also serves well in this case. The amplifiers, with settling time of 1 s, add another time constant to the system, increasing the settling time of the output. The settling time of the AD5541 is 1 s. The combined settling time is approximately 1.4 s, as can be derived from the following equation: 02735-060 I 100 C 5V AD8628 100k 100 C t S (TOTAL ) = (t S DAC )2 + (t S AD8628 )2 2.5V 10F Figure 63. Low-Side Current Sensing 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 without saving power. A typical shunt might be 0.1 . At measured current values of 1 A, the shunt's output signal is hundreds of mV, or even V, and amplifier error sources are not critical. However, at low measured current values in the 1 mA range, the 100 V output voltage of the shunt demands a very low offset voltage and drift to maintain absolute accuracy. Low input bias currents are also needed, so that injected bias current does not become a significant percentage of the measured current. High open-loop gain, CMRR, and PSRR all help to maintain the overall circuit accuracy. As long as the rate of change of the current is not too fast, an auto-zero amplifier can be used with excellent results. 5V 0.1F 0.1F SERIAL INTERFACE VDD CS DIN SCLK LDAC* REF(REF*) REFS* AD5541/AD5542 OUT UNIPOLAR OUTPUT AD8628 DGND AGND 03023-061 *AD5542 ONLY Figure 64. AD8628 Used as an Output Amplifier Rev. C | Page 18 of 20 AD8628/AD8629 OUTLINE DIMENSIONS 2.90 BSC 5.00 (0.1968) 4.80 (0.1890) 5 4 1.60 BSC 1 2 3 2.80 BSC 8 5 4.00 (0.1574) 3.80 (0.1497) 1 6.20 (0.2440) 4 5.80 (0.2284) PIN 1 0.95 BSC 0.90 0.87 0.84 1.90 BSC 0.25 (0.0098) 0.10 (0.0040) 1.27 (0.0500) BSC 1.75 (0.0688) 1.35 (0.0532) 0.50 (0.0196) x 45 0.25 (0.0099) 1.00 MAX 8 4 0.20 0.08 0.51 (0.0201) COPLANARITY SEATING 0.31 (0.0122) 0.10 PLANE 8 0.25 (0.0098) 0 1.27 (0.0500) 0.40 (0.0157) 0.17 (0.0067) 0.10 MAX 0.50 0.30 SEATING PLANE 0.60 0.45 0.30 COMPLIANT TO JEDEC STANDARDS MO-193AB COMPLIANT TO JEDEC STANDARDS MS-012AA 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 65. 5-Lead Thin Small Outline Transistor Package [TSOT] (UJ-5) Dimensions shown in millimeters 2.90 BSC Figure 67. 8-Lead Standard Small Outline Package [SOIC] Narrow Body (R-8) Dimensions shown in millimeters and (inches) 3.00 BSC 5 4 1.60 BSC 1 2.80 BSC 8 5 2 3 3.00 BSC 4 4.90 BSC PIN 1 0.95 BSC 1.30 1.15 0.90 1.90 BSC PIN 1 0.65 BSC 1.10 MAX 8 0 0.80 0.60 0.40 1.45 MAX 0.22 0.08 10 5 0 0.60 0.45 0.30 0.15 0.00 0.38 0.22 COPLANARITY 0.10 0.15 MAX 0.50 0.30 SEATING PLANE 0.23 0.08 SEATING PLANE COMPLIANT TO JEDEC STANDARDS MO-178AA COMPLIANT TO JEDEC STANDARDS MO-187AA Figure 66. 5-Lead Small Outline Transistor Package [SOT-23] (RT-5) Dimensions shown in millimeters Figure 65. 8-Lead Standard Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters Rev. C | Page 19 of 20 AD8628/AD8629 ORDERING GUIDE Model AD8628AUJ-R2 AD8628AUJ-REEL AD8628AUJ-REEL7 AD8628AUJZ-R21 AD8628AUJZ-REEL1 AD8628AUJZ-REEL71 AD8628AR AD8628AR-REEL AD8628AR-REEL7 AD8628ARZ1 AD8628ARZ-REEL1 AD8628ARZ-REEL71 AD8628ART-R2 AD8628ART-REEL7 AD8628ARTZ-R21 AD8628ARTZ-REEL71 AD8629ARZ1 AD8629ARZ-REEL1 AD8629ARZ-REEL71 AD8629ARMZ-R21 AD8629ARMZ-REEL1 Temperature Range -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C Package Description 5-Lead TSOT-23 5-Lead TSOT-23 5-Lead TSOT-23 5-Lead TSOT-23 5-Lead TSOT-23 5-Lead TSOT-23 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 5-Lead SOT-23 5-Lead SOT-23 5-Lead SOT-23 5-Lead SOT-23 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead MSOP 8-Lead MSOP Package Option UJ-5 UJ-5 UJ-5 UJ-5 UJ-5 UJ-5 R-8 R-8 R-8 R-8 R-8 R-8 RT-5 RT-5 RT-5 RT-5 R-8 R-8 R-8 RM-8 RM-8 Branding AYB AYB AYB AYB AYB AYB AYA AYA AYA AYA A06 A06 1 Z = Pb-free part. (c) 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. C02735-0-10/04(C) Rev. C | Page 20 of 20 |
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