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Dual/Quad Low Power, High Speed JFET Operational Amplifiers AD8682/AD8684
FEATURES
Low supply current: 250 A/amp maximum High slew rate: 9 V/s Bandwidth: 3.5 MHz typical Low offset voltage: 1 mV maximum @ 25C Low input bias current: 20 pA maximum @ 25C CMRR: 90 dB typical Fast settling time Unity gain stable
PIN CONFIGURATIONS
OUT A 1 -IN A 2 +IN A 3 V- 4
8
V+ OUT B
06278-001
06278-002
AD8682
TOP VIEW (Not to Scale)
7 6 5
-IN B +IN B
Figure 1. 8-Lead SOIC_N and 8-Lead MSOP
OUT A 1 -IN A 2 +IN A 3 V+ 4 +IN B 5 -IN B 6 OUT B 7 TOP VIEW (Not to Scale)
14 OUT D 13 -IN D 12 +IN D
APPLICATIONS
Portable telecommunication Low power industrial and instrumentation Loop filters Active and precision filters Integrators Strain gauge amplifiers Portable medical instrumentation Supply current monitoring
AD8684
11 V- 10 +IN C 9 8
-IN C OUT C
Figure 2. 14-Lead SOIC_N and 14-Lead TSSOP
GENERAL DESCRIPTION
The AD8682 and AD8684 are dual and quad low power, precision (1 mV) JFET amplifiers featuring excellent speed at low supply currents. The slew rate is typically 9 V/s with a supply current under 250 A per amplifier. These unity-gain stable amplifiers have a typical gain bandwidth of 3.5 MHz. The JFET input stage ensures bias current is typically a few picoamps and below 125 pA maximum over the full temperature operating range. The devices are ideal for portable, low power applications, especially with high source impedance. The devices are unity gain stable and can drive higher capacity loads (G = 1, noninverting), as an example of their excellent dynamic response over a wide range of conditions, delivering dc precision performance at low quiescent currents.
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: 781.461.3113 (c)2006 Analog Devices, Inc. All rights reserved.
AD8682/AD8684 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 Pin Configurations ........................................................................... 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Electrical Characteristics............................................................. 3 Absolute Maximum Ratings............................................................ 4 Thermal Resistance ...................................................................... 4 ESD Caution...................................................................................4 Typical Performance Characteristic................................................5 Applications Information .............................................................. 10 High-Side Signal Conditioning ................................................ 10 Phase Inversion........................................................................... 10 Active Filters ............................................................................... 10 Programmable State Variable Filter ......................................... 11 Outline Dimensions ....................................................................... 12 Ordering Guide .......................................................................... 13
REVISION HISTORY
10/06--Revision 0: Initial Version
Rev. 0 | Page 2 of 16
AD8682/AD8684 SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
VS = 15.0 V, TA = 25C, VCM = 0 V, unless otherwise noted. Table 1.
Parameter INPUT CHARACTERISTICS Offset Voltage Symbol VOS AD8682: +25C TA +85C AD8684: +25C TA +85C AD8682: -40C TA +25C AD8684: -40C TA +25C Input Bias Current Input Offset Current Input Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain Offset Voltage Drift Bias Current Drift OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low Short-Circuit Limit Open-Loop Output Impedance POWER SUPPLY Power Supply Rejection Ratio Supply Current/Amplifier Supply Voltage Range DYNAMIC PERFORMANCE Slew Rate Full-Power Bandwidth Settling Time Gain Bandwidth Product Phase Margin NOISE PERFORMANCE Voltage Noise Voltage Noise Density Current Noise Density IB -40C TA +85C IOS -40C TA +85C CMRR AVO VOS/T IB/T VOH VOL ISC ZOUT PSRR ISY VS SR BWP tS GBP OO en p-p en in RL = 10 k RL = 10 k Source Sink f = 1 MHz VS = 4.5 V to 18 V, -40C TA +85C VO = 0 V, -40C TA +85C +13.5 3 -11 V VCM +15 V, -40C TA +85C RL = 10 k RL = 10 k, -40C TA +85C -11 70 20 15 90 6 Conditions Min Typ 0.35 Max 1 2.5 3.5 3 4 20 125 20 100 +15 Unit mV mV mV mV mV pA pA pA pA V dB V/mV V/mV V/C pA/C V V mA mA dB A V V/s kHz s MHz Degrees V p-p nV/Hz pA/Hz
10 8 +13.9 -13.9 10 -12 200 114 210
-13.5 -8
92 4.5
250 18
RL = 10 k 1% distortion To 0.01%
7
9 125 1.6 3.5 55 1.3 36 0.01
0.1 Hz to 10 Hz f = 1 kHz
Rev. 0 | Page 3 of 16
AD8682/AD8684 ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Supply Voltage Input Voltage Differential Input Voltage1 Output Short-Circuit Duration Storage Temperature Range Operating Temperature Range Junction Temperature Range Lead Temperature (Soldering, 60 sec)
1
Rating 18 V 18 V 36 V Indefinite -65C to +150C -40C to +85C -65C to +150C 300C
THERMAL RESISTANCE
Table 3.
Package Type 8-Lead MSOP [RM-8] 8-Lead SOIC_N [R-8] 14-Lead TSSOP [RU-14] 14-Lead SOIC [R-14] JA 210 158 180 120 JC 45 43 35 36 Unit C/W C/W C/W C/W
For supply voltages less than 18 V, the absolute maximum input voltage is equal to the supply voltage.
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. 0 | Page 4 of 16
AD8682/AD8684 TYPICAL PERFORMANCE CHARACTERISTIC
80 VS = 15V TA = 25C 180 70 60 135 50 VS = 15V TA = 25C 60
AVCL = 100
CLOSED-LOOP GAIN (dB)
OPEN-LOOP GAIN (dB)
40
90
40 30 20 10 0 -10 -20
PHASE (Degree)
20
45
AVCL = 10
0
0
AVCL = 1
-20
-45
06278-003
10k
100k FREQUENCY (Hz)
1M
10k
100k FREQUENCY (Hz)
1M
10M
Figure 3. AD8682 Open-Loop Gain and Phase vs. Frequency
45 40 35 VS = 15V RL = 10k
30
Figure 6. AD8682 Closed-Loop Gain vs. Frequency
25
VS = 15V RL = 10k CL = 50pF -SR
OPEN-LOOP GAIN (V/mV)
25 20 15 10
SLEW RATE (V/s)
30
20
15
10 +SR 5
5
06278-004
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
100
125
TEMPERATURE (C)
TEMPERATURE (C)
Figure 4. AD8682 Open-Loop Gain vs. Temperature
Figure 7. Slew Rate vs. Temperature
OVERSHOOT (%)
+OS 50 40 30 20 10
06278-005
-OS
INPUT BIAS CURRENT (pA)
VS = 15V RL = 2k 70 V = 100mV p-p IN AVCL = 1 60 TA = 25C
80
1000
VS = 15V VCM = 0V
100
10
1
0
100
200
300
400
500
-50
-25
0
25
50
75
100
125
LOAD CAPACITANCE (pF)
TEMPERATURE (C)
Figure 5. Small Signal Overshoot vs. Load Capacitance
Figure 8. AD8682 Input Bias Current vs. Temperature
Rev. 0 | Page 5 of 16
06278-008
0
0.1 -75
06278-007
0 -75
0 -75
06278-006
-40 1k
-90 10M
-30 1k
AD8682/AD8684
1000 VS = 15V TA = 25C
OUTPUT VOLTAGE SWING (V) 20 15 10 5 0 -5 -10 VOL -15
06278-009
06278-012 06278-014
TA = 25C RL = 10k VOH
VOLTAGE NOISE DENSITY (nV/Hz)
100
10
1 10
100 1k FREQUENCY (Hz)
10k
-20
0
5
10 SUPPLY VOLTAGE (V)
15
20
Figure 9. Voltage Noise Density vs. Frequency
Figure 12. Output Voltage Swing vs. Supply Voltage
1000
VS = 15V TA = 25C
1000
VS = 15V TA = 25C
INPUT BIAS CURRENT (pA)
100
100
OUTPUT IMPEDANCE ()
AVCL = 100 10 AVCL = 10 1 AVCL = 1
10
1
06278-010
-10
-5
0
5
10
15
1k
COMMON-MODE VOLTAGE (V)
10k FREQUENCY (Hz)
100k
1M
Figure 10. Input Bias Current vs. Common-Mode Voltage
Figure 13. Closed-Loop Output Impedance vs. Frequency
480
TA = 25C
480
475
475 SUPPLY CURRENT (A)
SUPPLY CURRENT (A)
470
470
465
465
460
460
455
455
0
5
10 SUPPLY VOLTAGE (V)
15
20
06278-011
450
450 -50
-25
0
25
50
75
100
125
TEMPERATURE (C)
Figure 11. AD8682 Supply Current vs. Supply Voltage
Figure 14. AD8682 Supply Current vs. Temperature
Rev. 0 | Page 6 of 16
06278-013
0.1 -15
0.1 100
AD8682/AD8684
16 14 VS = 15V TA = 25C
30
ABSOLUTE OUTPUT VOLTAGE (V)
12 10 VOH 8 6 4 2
06278-015
MAXIMUM OUTPUT SWING (V p-p)
VOL
25
VS = 15V TA = 25C RL = 10k AVCL = 1
20
15
10
5
1k LOAD RESISTANCE ()
10k
1k
10k FREQUENCY (Hz)
100k
1M
Figure 15. Absolute Output Voltage vs. Load Resistance
140
Figure 18. Maximum Output Swing vs. Frequency
140 120 100 VS = 15V TA = 25C
VS = 15V 120 TA = 25C 100 80
+PSRR
80 CMRR (dB) 60 40 20 0 -20 -40
PSRR (dB)
60 40 20 0 -20 -40 1k 10k 100k FREQUENCY (Hz) 1M
06278-016
-PSRR
1k
10k 100k FREQUENCY (Hz)
1M
Figure 16. AD8682 PSRR vs. Frequency
Figure 19. AD8682 CMRR vs. Frequency
14 12
VS = 15V TA = 25C
20 18 16 VS = 15V TA = 25C 100 xAD8682 (200 OP AMPS)
SHORT-CIRCUIT CURRENT (mA)
10 8 6 4 2 0 -50
SINK
14 12
UNITS
SOURCE
10 8 6 4 2
-25
0
25
50
75
100
125
06278-017
TEMPERATURE (C)
-0.4 -0.2 0 0.2 VOS (V)
0.4
0.6
0.8
1.0
Figure 17. AD8682 Short-Circuit Current vs. Temperature
Figure 20. AD8682 VOS Distribution
Rev. 0 | Page 7 of 16
06278-020
0 -1.0 -0.8 -0.6
06278-019
-60 100
-60 100
06278-018
0 100
0 100
AD8682/AD8684
400 360 320 280 240 UNITS 200 160 120 80 40
06278-021
1000
VS = 15V 300 x OP282 (600 OP AMPS)
INPUT BIAS CURRENT (pA)
100
10
1
0
4
8
12
16
20
24
28
32
36
-50
-25
0
25
50
75
100
125
TCVOS (V/C)
TEMPERATURE (C)
Figure 21. AD8682 TCVOS Distribution SOIC_N Package
50 45 40 950 945 940 935 930 925 920 915
06278-022
Figure 24. AD8684 Input Bias Current vs. Temperature
OPEN-LOOP GAIN (V/mV)
35 30 25 20 15 10 5 0 -50 -25 0 25 50 75 100 125
SUPPLY CURRENT (A)
0
10
20 SUPPLY VOLTAGE (V)
30
40
TEMPERATURE (C)
Figure 22. AD8684 Open-Loop Gain vs. Temperature
Figure 25. AD8684 Relative Supply Current vs. Supply Voltage
950 945 940 935 930 925 920 915 910 -50
60 50 AVCL = 100
VS = 15V TA = 25C
CLOSED-LOOP GAIN (dB)
30 AVCL = 10 20 10 AVCL = 1 0 -10
06278-023
1k
10k
100k
1M
10M
100M
-25
0
25
50
75
100
125
FREQUENCY (Hz)
TEMPERATURE (C)
Figure 23. AD8684 Closed-Loop Gain vs. Frequency
Figure 26. AD8684 Supply Current vs. Temperature
Rev. 0 | Page 8 of 16
06278-026
-20
SUPPLY CURRENT (A)
40
06278-025
910
06278-024
0
0.1 -75
AD8682/AD8684
140 VS = 15V 120 100 PSRR+
40 35 30 25
VS = 15V TA = 25C 100 x AD8684 (400 OP AMPS)
PSRR (dB)
PSRR- 60 40 20 0 1k
UNITS
06278-027
80
20 15 10 5
06278-030 06278-031
10k
100k FREQUENCY (Hz)
1M
10M
0 -1.0
-0.8 -0.6 -0.4 -0.2
0 VOS (V)
0.2
0.4
0.6
0.8
1.0
Figure 27. AD8684 PSRR vs. Frequency
14 12
Figure 30. AD8684 VOS Distribution Package
800 700 VS = 15V 300 x OP282 (1200 OP AMPS)
SHORT-CIRCUIT CURRENT (mA)
SINK
10 SOURCE 8 6 4 2 0 -50
600 500
UNITS
-25 0 25 50 75 100 125
06278-028
400 300 200 100 0
0
4
8
12 16 20 24 28 32 36 40 44 48 52 56 60 TCVOS (V/C)
TEMPERATURE (C)
Figure 28. AD8684 Short-Circuit Current vs. Temperature
140 VS = 15V 120 100
Figure 31. AD8684 TCVOS Distribution Package
CMRR (dB)
80 60 40 20 0 1k
10k
100k FREQUENCY (Hz)
1M
10M
Figure 29. AD8684 CMRR vs. Frequency
Rev. 0 | Page 9 of 16
06278-029
AD8682/AD8684 APPLICATIONS INFORMATION
The AD8682 and AD8684 are dual and quad JFET op amps that are optimized for high speed at low power. This combination makes these amplifiers excellent choices for battery-powered or low power applications that require above average performance. Applications benefiting from this performance combination include telecommunications, geophysical exploration, portable medical equipment, and navigational instrumentation.
PHASE INVERSION
Most JFET input amplifiers invert the phase of the input signal if either input exceeds the input common-mode range. For the AD8682/AD8684, negative signals in excess of approximately 14 V cause phase inversion. This is caused by saturation of the input stage leading to the forward-biasing of a drain-gate diode. A simple fix for this in noninverting applications is to place a resistor in series with the noninverting input. This limits the amount of current through the forward-biased diode and prevents shutting down of the output stage. For the AD8682/AD8684, a value of 200 k has been found to work; however, it adds a significant amount of noise.
15
HIGH-SIDE SIGNAL CONDITIONING
There are many applications requiring the sensing of signals near the positive rail. The AD8682 and the AD8684 were tested and are guaranteed over a common-mode range (-11 V VCM +15 V) that includes the positive supply. The AD8682/AD8684 are commonly used in the sensing of power supply currents and in current sensing applications, such as the partial circuit shown in Figure 32. In this circuit, the voltage drop across a low value resistor, such as the 0.1 shown here, is amplified and compared to 7.5 V. The output can then be used for current limiting.
15V 0.1 500k 100k 100k RL
10
5
VOUT
0
-5
1/2 AD8682
500k
06278-042
-10
-10
-5
0 VIN
5
10
15
Figure 32. High-Side Signal Conditioning
Figure 33. AD8682 Phase Reversal
ACTIVE FILTERS
The wide bandwidth and high slew rates of the AD8682/AD8684 make either one an excellent choice for many filter applications. There are many active filter configurations, but the four most popular configurations are: Butterworth, elliptical, Bessel, and Chebyshev. Each type has a response that is optimized for a given characteristic, as shown in Table 4. Table 4.
Type Butterworth Chebyshev Elliptical Bessel (Thompson) Selectivity Moderate Good Best Poor Overshoot Good Moderate Poor Best Phase Nonlinear Linear Amplitude (Pass Band) Maximum flat Equal ripple Equal ripple Amplitude (Stop Band)
Equal ripple
Rev. 0 | Page 10 of 16
06278-043
-15 -15
AD8682/AD8684
PROGRAMMABLE STATE VARIABLE FILTER
The circuit shown in Figure 34 can be used to accurately program the Q; the cutoff frequency, fC; and the gain of a 2-pole state variable filter. The AD8684 has been used in this design because of its high bandwidth, low power, and low noise. This circuit takes only three packages to build because of the quad configuration of the op amps and DACs. The DACs shown are used in voltage mode; therefore, many values are dependent on the accuracy of the DAC only and not on the absolute values of the DAC resistive ladders. As a result, this makes the circuit unusually accurate for a programmable filter. Adjusting DAC 1 changes the signal amplitude across R1; therefore, the DAC attenuation x R1 determines the amount of signal current that charges the integrating capacitor, C1. This cutoff frequency can be expressed as
fc =
1 D1 2R1C1 256
where D1 is the digital code for the DAC. The gain of this circuit is set by adjusting D3. The gain equation is
Gain = R4 D3 R5 256
DAC 2 is used to set the Q of the circuit. Adjusting this DAC controls the amount of feedback from the band-pass node to the input summing node. Note that the digital value of the DAC is in the numerator; therefore, zero code is not a valid operating point.
Q= R2 256 R3 D2
R7 2k R4 2k
VIN
1/4 DAC8408
1/4 AD8684
R5 2k
C1 1000pF
1/4 AD8684
1/4 DAC8408
HIGH PASS
1/4 AD8684
R1 2k
C1 1000pF
1/4 AD8684
1/4 DAC8408
1/4 AD8684
R1 2k
1/4 AD8684
LOW PASS
R6 2k R3 2k R2 2k
BAND PASS
1/4 AD8684
1/4 AD8684
1/4 DAC8408
06278-044
Figure 34. Programmable State Variable Filter
Rev. 0 | Page 11 of 16
AD8682/AD8684 OUTLINE DIMENSIONS
5.00 (0.1968) 4.80 (0.1890)
4.00 (0.1574) 3.80 (0.1497)
8 1
5 4
6.20 (0.2440) 5.80 (0.2284)
1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) COPLANARITY 0.10 SEATING PLANE
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
0.51 (0.0201) 0.31 (0.0122)
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 35. 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 36. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters
Rev. 0 | Page 12 of 16
060506-A
AD8682/AD8684
8.75 (0.3445) 8.55 (0.3366)
14 1 8 7
4.00 (0.1575) 3.80 (0.1496)
6.20 (0.2441) 5.80 (0.2283)
1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0039) COPLANARITY 0.10 0.51 (0.0201) 0.31 (0.0122)
1.75 (0.0689) 1.35 (0.0531) SEATING PLANE
0.50 (0.0197) 0.25 (0.0098) 8 0 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157)
45
COMPLIANT TO JEDEC STANDARDS MS-012-AB 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 37. 14-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-14) Dimensions shown in millimeters and (inches)
5.10 5.00 4.90
14
8
4.50 4.40 4.30
1 7
6.40 BSC
PIN 1 1.05 1.00 0.80 0.65 BSC 1.20 MAX 0.15 0.05 0.30 0.19
0.20 0.09
SEATING COPLANARITY PLANE 0.10
8 0
0.75 0.60 0.45
COMPLIANT TO JEDEC STANDARDS MO-153-AB-1
Figure 38. 14-Lead Thin Shrink Small Outline Package [TSSOP] (RU-14) Dimensions shown in millimeters
ORDERING GUIDE
Model AD8682ARZ 1 AD8682ARZ-REEL1 AD8682ARZ-REEL71 AD8682ARMZ-R21 AD8682ARMZ-REEL1 AD8684ARZ1 AD8684ARZ-REEL1 AD8684ARZ-REEL71 AD8684ARUZ1 AD8684ARUZ_REEL1
1
Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C
Package Description 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead MSOP 8-Lead MSOP 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead TSSOP 14-Lead TSSOP
Package Option R-8 R-8 R-8 RM-8 RM-8 R-14 R-14 R-14 RU-14 RU-14
060606-A
Branding
A1K A1K
Z= Pb-free part.
Rev. 0 | Page 13 of 16
AD8682/AD8684 NOTES
Rev. 0 | Page 14 of 16
AD8682/AD8684 NOTES
Rev. 0 | Page 15 of 16
AD8682/AD8684 NOTES
(c)2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06278-0-10/06(0)
Rev. 0 | Page 16 of 16

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