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Low Power, Rail-to-Rail Output Precision JFET Amplifier AD8641
FEATURES
Low supply current: 250 A max Very low input bias current: 1 pA max Low offset voltage: 750 V max Single-supply operation: 5 V to 26 V Dual-supply operation: 2.5 V to 13 V Rail-to-rail output Unity gain stable No phase reversal SC70 package
OUT 1
5
VCC
AD8641
VEE 2 +IN 3
4
-IN
Figure 1. 5-Lead SC70 (KS-5)
NC 1 -IN 2
8
NC VCC OUT
05072-102
AD8641
TOP VIEW (Not to Scale)
7 6 5
APPLICATIONS
Line-/battery-powered instruments Photodiode amplifiers Precision current sensing Medical instrumentation Industrial controls Precision filters Portable audio ATE
+IN 3 VEE 4
NC
NC = NO CONNECT
Figure 2. 8-Lead SOIC (R-8)
GENERAL DESCRIPTION
The AD8641 is a low power, precision JFET input amplifier featuring extremely low input bias current and rail-to-rail output. The ability to swing nearly rail-to-rail at the input and rail-to-rail at the output enables designers to buffer CMOS DACs, ASICs, and other wide output swing devices in singlesupply systems. The outputs remain stable with capacitive loads of more than 500 pF. The AD8641 is suitable for applications utilizing multichannel boards that require low power to manage heat. Other applications include photodiodes, ATE reference level drivers, battery management, and industrial controls. The AD8641 is fully specified over the extended industrial temperature range of -40 to +125C. The AD8641 is available in 5-lead SC70 and 8-lead SOIC lead-free packages.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 (c) 2004 Analog Devices, Inc. All rights reserved.
05072-101
TOP VIEW (Not to Scale)
AD8641 TABLE OF CONTENTS
Specifications..................................................................................... 3 Electrical Characteristics ............................................................. 3 Absolute Maximum Ratings............................................................ 5 Typical Performance Characteristics ............................................. 6 Outline Dimensions ....................................................................... 12 Ordering Guide .......................................................................... 12
REVISION HISTORY
10/04--Initial Version: Revision 0
Rev. 0 | Page 2 of 12
AD8641 SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
@ VS =5.0 V, VCM = 2.5 V, TA =25C, unless otherwise noted. Table 1.
Parameter INPUT CHARACTERISTICS Offset Voltage Symbol VOS -40C < TA < +85C +85C < TA < +125C, VCM = 1.5 V 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 Output Voltage Low Output Current POWER SUPPLY Power Supply Rejection Ratio Supply Current/Amplifier DYNAMIC PERFORMANCE Slew Rate Gain Bandwidth Product Phase Margin NOISE PERFORMANCE Voltage Noise Voltage Noise Density Current Noise Density IB -40C < TA < +125C IOS -40C < TA < +125C CMRR AVO VOS/T VOH IL = 2 mA, -40C to +125C VOL IL = 2 mA, -40C to +125C IOUT PSRR ISY VS = 5 V to 26 V -40C < TA < +125C SR GBP OO eN p-p eN iN f = 0.1 Hz to 10 Hz f = 1 kHz f = 1 kHz 2 3 50 4.0 28.5 0.5 90 0.01 6 107 195 VCM = 0 V to 2.5 V RL = 10 k, VO = 0.5 to 4.5 V -40C < TA < +125C 0 74 80 93 140 2.5 0.25 Conditions Min Typ 50 Max 750 1.5 1.6 1 180 0.5 50 3 Unit V mV mV pA pA pA pA V dB V/mV V/C V V V V mA dB A A V/s MHz Degrees V p-p nV/Hz fA/Hz
4.94 4.93 0.05 0.05
250 270
Rev. 0 | Page 3 of 12
AD8641
@ VS= 13 V, VCM = 0 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 Output Voltage Low Output Current POWER SUPPLY Power Supply Rejection Ratio Supply Current/Amplifier DYNAMIC PERFORMANCE Slew Rate Gain Bandwidth Product Phase Margin NOISE PERFORMANCE Voltage Noise Voltage Noise Density Current Noise Density Symbol VOS -40 < TA < +125C IB -40C < TA < +125C IOS -40C < TA < +125C CMRR AVO VOS/T VOH IL = 2 mA, -40C to +125C VOL IL = 2 mA, -40C to +125C IOUT PSRR ISY VS = 2.5 V to 13 V -40C < TA < +125C SR GBP OO eN p-p eN iN f = 0.1 Hz to 10 Hz f = 1 kHz f = 1 kHz 3 3.5 60 4.2 27.5 0.5 90 12 107 200 VCM = -13 V to +10 V RL = 10 k, VO = -11 V to +11 V -40C < TA < +125C -13 90 215 107 290 2.5 0.25 Conditions Min Typ 70 Max 750 1.5 1 260 0.5 35 +10 Unit V mV pA pA pA pA V dB V/mV V/C V V V V mA dB A A V/s MHz Degrees V p-p nV/Hz fA/Hz
+12.94 +12.93 +12.94 -12.93
290 330
Rev. 0 | Page 4 of 12
AD8641 ABSOLUTE MAXIMUM RATINGS
Table 3. Absolute Maximum Ratings1
Parameter Supply Voltage Input Voltage Differential Input Voltage Output Short-Circuit Duration Storage Temperature Range KS-5, R-8 Packages Operating Temperature Range Junction Temperature Range KS-5, R-8 Packages Lead Temperature Range (Soldering, 60 Sec) Rating 27.3 V VS- to VS+ Supply Voltage Indefinite -65C to +150C -40C to +125C -65C to +150C 300C
Table 4.
Package Type 5-Lead SC70 (KS-5) 8-Lead SOIC (R-8) JA2 331.4 157 JC 223.9 56 Units C/W C/W
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.
1 2
Absolute maximum ratings apply at 25C, unless otherwise noted. JA is specified for the worst-case conditions, i.e., JA is specified for devices soldered on circuit boards for surface-mounted 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. 0 | Page 5 of 12
AD8641 TYPICAL PERFORMANCE CHARACTERISTICS
80
20
VSY = 13V
70
NUMBER OF AMPLIFIERS
18 16
VSY = 5V VCM = 1.5V
60
FREQUENCY
14 12 10 8 6 4
50 40 30 20 10 0
2
05072-002 05072-005
05072-007
05072-006
-0.60 -0.55 -0.50 -0.45 -0.40 -0.35 -0.30 -0.25 -0.20 -0.15 -0.10 -0.05 0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60
0
0
VOS (mV)
TCVOS (V/C)
Figure 3. Input Offset Voltage
Figure 6. Offset Voltage Drift
16
4.5
VSY = 13V
14
NUMBER OF AMPLIFIERS
4.0 3.5
VSY = 13V TA = 25C
12
3.0
10 8 6 4
INPUT BIAS (pA)
2.5 2.0 1.5 1.0 0.5
2 0
0 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 7.5 8.0 8.5 9.0 9.5
0
05072-003
-0.5
-15 -13 -11 -9 -7 -5 -3 -1 1 3 5 7 9 11 13 15
OFFSET VOLTAGE (V/C)
10.0
VCM (V)
Figure 4. Offset Voltage Drift
Figure 7. Input Bias Current vs. VCM
70
0.5
VSY = 2.5V
60
0.4 0.3
VSY = 13V TA = 25C
50
INPUT BIAS (pA)
0.2 0.1
FREQUENCY
40
0 -0.1 -0.2 -0.3
30
20
10
-0.4
05072-004
-0.60 -0.55 -0.50 -0.45 -0.40 -0.35 -0.30 -0.25 -0.20 -0.15 -0.10 -0.05 0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60
0
-0.5
-15.0 -12.5 -10.0 -7.5 -5.0 -2.5 0 2.5 5.0 7.5 10.0 12.5 15.0
VOS (mV)
VCM (V)
Figure 5. Input Offset Voltage
Rev. 0 | Page 6 of 12
Figure 8. Input Bias Current vs. VCM
10.0
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
7.5
8.0
8.5
9.0
9.5
AD8641
1000 VSY = 13V
500 VSY = 5V 400 300
INPUT BIAS CURRENT (pA)
100
200
VOS (V)
05072-008
100 0 -100 -200
10
1
-300 -400
05072-011
0.1 0 25 50 75 100 125 150 TEMPERATURE (C)
-500 0 0.5 1.0 1.5 VCM (V) 2.0 2.5
Figure 9. Input Bias Current vs. Temperature
Figure 12. Input Offset Voltage vs. VCM
1.0 0.8 0.6 0.4
INPUT BIAS (pA) OPEN-LOOP GAIN (V/V)
10M VSY = +5V OR 5V
1M VSY = 13V
0.2 0 -0.2 -0.4 -0.6 -0.8
05072-009
100k
VSY = 2.5V
-5
-4
-3
-2
-1
0 VCM (V)
1
2
3
4
5
1
10
100
LOAD RESISTANCE (k)
Figure 10. Input Bias Current vs. VCM
Figure 13. Open-Loop Gain vs. Load Resistance
1000 900 800 700 600 500 400 300 200 100 0
VSY = 13V
1000 A B C 100
AVO (V/mV)
D E
VOS (V)
10 A. VSY = 13V, VO = 11V, RL = 10k B. VSY = 13V, VO = 11V, RL = 2k C. VSY = +5V, VO = +0.5V/+4.5V, RL = 10k D. VSY = +5V, VO = +0.5V/+4.5V, RL = 2k E. VSY = +5V, VO = +0.5V/+4.5V, RL = 600
05072-010
-15 -13 -11
-9
-7
-5
-3
-1 0 1
3
5
7
9
11
13
15
-30
-10
10
30
50
70
90
110
130
150
VCM (V)
TEMPERATURE (C)
Figure 11. Input Offset Voltage vs. VCM
Figure 14. Open-Loop Gain vs. Temperature
Rev. 0 | Page 7 of 12
05072-013
-100
1 -50
05072-012
-1.0
10k 0.1
AD8641
600 500 400
SATURATION VOLTAGE (mV)
OFFSET VOLTAGE (V)
10000
VSY = 13V
VSY = 13V VSY - VOH
1000
300 200 100 0 -100 -200 -300 -400 -500
05072-014
100k
100 -VSY - VOL
10k 1k
10
-10
-5
0
5
10
15
0.01
0.1
1
10
100
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
Figure 15. Input Error Voltage vs. Output Voltage for Resistive Loads
Figure 18. Output Saturation Voltage vs. Load Current
250 200 150 100
INPUT VOLTAGE (V)
10000
VSY = 5V
POS RAIL
SATURATION VOLTAGE (mV)
VSY = 5V VSY - VOH
1000 VOL 100
RL = 1k RL = 2k RL = 10k RL = 100k
50 0 -50 -100 -150 -200 -250 -300 -350 0 50
10
RL = 100k RL = 1k RL = 10k NEG RAIL RL = 2k
05072-015
100
150
200
250
300
350
0.01
0.1
1
10
100
OUTPUT VOLTAGE FROM SUPPLY RAIL (mV)
LOAD CURRENT (mA)
Figure 16. Input Error Voltage vs. Output Voltage Within 300 mV of Supply Rails
Figure 19. Output Saturation Voltage vs. Load Current
800 700 600 500
70 60 50 40 GAIN VSY = 13V RL = 2k CL = 40pF
315 270 225
GAIN (dB)
30 20 10 0 -10 -20 PHASE
ISY (A)
135 90 45 0 -45 -90 100k 1M FREQUENCY (Hz) 10M
400 300 200 -55C 100 0 4 8 12 16 VSY (V) 20 24 28 +25C +125C
05072-016
Figure 17. Quiescent Current vs. Supply Voltage at Different Temperatures
Figure 20. Open-Loop Gain and Phase Margin vs. Frequency
Rev. 0 | Page 8 of 12
05072-019
-30 10k
-135
PHASE (Degrees)
180
05072-018
1 0.001
05072-017
-600 -15
1 0.001
AD8641
70 60 50 40 GAIN VSY = 5V RL = 2k CL = 40pF 315 270 225
140 120 100
PHASE (Degrees)
VSY = 13V
180 135 90 PHASE 45 0 -45 -90
80
CMRR (dB)
GAIN (dB)
30 20 10 0 -10 -20 -30 10k 100k 1M FREQUENCY (Hz) 10M
60 40 20 0 -20 -40
05072-020
10k
100k FREQUENCY (Hz)
1M
10M
Figure 21. Open-Loop Gain and Phase Margin vs. Frequency
Figure 24. CMRR vs. Frequency
70 60 50 40 G = +100 GAIN (dB) CMRR (dB) 30 20 G = +10 10 0 G = +1 -10 -20 10k 100k FREQUENCY (Hz) 1M 10M
05072-021
VSY = 13V RL = 2k CL = 40pF
140 120 100 80 60 40 20 0 -20 -40 10k 100k FREQUENCY (Hz) 1M 10M
05072-024 05072-025
VSY = 5V
-30 1k
-60 1k
Figure 22. Closed-Loop Gain vs. Frequency
Figure 25. CMRR vs. Frequency
70 60 50 40 G = +100
GAIN (dB) PSRR (dB)
140 VSY = 5V RL = 2k CL = 40pF 120 100 80 60 40 20 0 -20 -40 10k 100k FREQUENCY (Hz) 1M 10M
05072-022
VSY = 13V
+PSRR
30 20 G = +10 10 0 G = +1 -10 -20 -30 1k
-PSRR
-60 1k
10k
100k FREQUENCY (Hz)
1M
10M
Figure 23. Closed-Loop Gain vs. Frequency
Figure 26. PSRR vs. Frequency
Rev. 0 | Page 9 of 12
05072-023
-135
-60 1k
AD8641
140 120 100 +PSRR 80
PSRR (dB)
1.0
VSY = 5V
T
VSY = 13V
0.8 0.6
1
0.4
INPUT BIAS (pA)
VIN
60 40 20 0 -20 -40 10k 100k FREQUENCY (Hz) 1M 10M
05072-026
0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 CH1 -4 10.0V -3 CH2 -2 10.0V-1 -5 M400s CH1 4 1.00V 0 1 2 A3 5 T 0.00000s VCM (V)
2
-PSRR
VOUT
05072-029
Figure 27. PSRR vs. Frequency
Figure 30. No Phase Reversal
1000
15
VSY = 13V
G = +100 100
OUTPUT SWING (V)
VS = 13V GAIN = +5 10 TS + (1%) 5 TS + (0.1%)
ZOUT ()
10 G = +10 1 G = +1 0.1
0
-5 TS - (0.1%) -10 TS - (1%)
05072-027
10k
100k
1M
10M
100M
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
FREQUENCY (Hz)
SETTLING TIME (s)
Figure 28. Output Impedance vs. Frequency
Figure 31. Output Swing and Error vs. Settling Time
1000
70
VSY = 5V
G = +100 100
60 50
VS = 13V RL = 10k VIN = 100mV p-p AV = +1
ZOUT ()
10 G = +10 1
OVERSHOOT (%)
40 30 OS- OS+ 20
G = +1
0.1
10
0.01 1k
05072-028
10k
100k
1M
10M
100M
1
10
100
1000
FREQUENCY (Hz)
CAPACITANCE (pF)
Figure 29. Output Impedance vs. Frequency
Figure 32. Small Signal Overshoot vs. Load Capacitance
Rev. 0 | Page 10 of 12
05072-031
0
05072-030
0.01 1k
-15
05072-009
-60 1k
AD8641
70 VS = 2.5V RL = 10k VIN = 100mV p-p AV = +1 1k VSY = 13V 60 50
OVERSHOOT (%)
VOLTAGE NOISE DENSITY (nV/ Hz)
05072-032
100
40 30 20
OS-
OS+
10
10 0 1 10 100 1000 CAPACITANCE (pF)
10
100 FREQUENCY (Hz)
1k
10k
Figure 33. Small Signal Overshoot vs. Load Capacitance
Figure 36. Voltage Noise Density
1.0 0.8 0.6 0.4
INPUT BIAS (pA)
1k
VS = 13V G = +1M CH1 p-p = 4.26V
VSY = 5V
VOLTAGE NOISE DENSITY (nV/ Hz)
100
0.2
1 0
-0.2 -0.4 -0.6 -0.8 -1.0 CH1 -4 1.00V -3 -5 -2 -1 M1.00s 0 1 VCM (V) 2 A CH1 3 -20.0V 4 5
05072-033
10
05072-009
10
100 FREQUENCY (Hz)
1k
10k
Figure 34. 0.1 Hz to 10 Hz Noise
Figure 37. Voltage Noise Density
1.0 0.8 0.6
0.004
VS = 2.5V G = +1M CH1 p-p = 4.06V
0.001
VSY = 13V LOAD = 100k GAIN = +1
8V p-p INPUT
INPUT BIAS (pA)
0.2
1 0
THD + NOISE (%)
0.4
1V p-p INPUT
0.0001
2V p-p INPUT 4V p-p INPUT
-0.2 -0.4 -0.6 -0.8 -1.0 CH1 -4 1.00V -3 -5 -2 -1 M1.00s 0 1 VCM (V) 2 A CH1 3 -20.0V 4 5
05072-034
0.00001
05072-009
1
100
1k FREQUENCY (Hz)
10k
20k
Figure 35. 0.1 Hz to 10 Hz Noise
Figure 38. Total Harmonic Distortion + Noise vs. Frequency
Rev. 0 | Page 11 of 12
05072-037
0.000001
05072-036
1
05072-035
1
AD8641 OUTLINE DIMENSIONS
2.00 BSC
5
4
1.25 BSC
1 2 3
2.10 BSC
PIN 1 1.00 0.90 0.70 0.65 BSC 1.10 MAX 0.22 0.08 0.30 0.15 0.10 COPLANARITY COMPLIANT TO JEDEC STANDARDS MO-203AA SEATING PLANE
0.10 MAX
0.46 0.36 0.26
Figure 39. 5-Lead Thin Shrink Small Outline Transistor Package [SC70] (KS-5) Dimensions shown in millimeters
5.00 (0.1968) 4.80 (0.1890)
8 5 4
4.00 (0.1574) 3.80 (0.1497) 1
6.20 (0.2440) 5.80 (0.2284)
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) x 45 0.25 (0.0099)
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)
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 40. 8-Lead Standard Small Outline Package [SOIC] (R-8) Dimensions shown in millimeters
ORDERING GUIDE
Model AD8641AKSZ-R21 AD8641AKSZ-Reel71 AD8641AKSZ-Reel1 AD8641ARZ1 AD8641ARZ-Reel71 AD8641ARZ-Reel1
1
Temperature Range -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C
Package Description 5-Lead SC70 5-Lead SC70 5-Lead SC70 8-lead SOIC 8-lead SOIC 8-lead SOIC
Package Option KS-5 KS-5 KS-5 R-8 R-8 R-8
Branding A07 A07 A07
Z = Pb-free part.
(c) 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05072-0-10/04(0)
Rev. 0 | Page 12 of 12

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