AD AD8657 18 v, precision, micropower cmos rrio operational amplifier Datasheet

18 V, Precision, Micropower
CMOS RRIO Operational Amplifier
AD8657
PIN CONFIGURATION
Micropower at high voltage (18 V): 18 μA typical
Low offset voltage: 350 µV maximum
Single-supply operation: 2.7 V to 18 V
Dual-supply operation: ±1.35 V to ±9 V
Low input bias current: 20 pA
Gain bandwidth: 200 kHz
Unity-gain stable
Excellent electromagnetic interference immunity
OUT A 1
–IN A 2
AD8657
+IN A 3
TOP VIEW
(Not to Scale)
V– 4
8
V+
7
OUT B
6
–IN B
5
+IN B
08804-001
FEATURES
Figure 1. 8-Lead MSOP
APPLICATIONS
Portable operating systems
Current monitors
4 mA to 20 mA loop drivers
Buffer/level shifting
Multipole filters
Remote/wireless sensors
Low power transimpedance amplifiers
GENERAL DESCRIPTION
Table 1. Micropower Op Amps
The AD8657 is a dual, precision, micropower, rail-to-rail
input/output (RRIO) amplifier optimized for low power and
wide operating supply voltage range applications.
Supply Voltage
Single
The AD8657 operates from 2.7 V up to 18 V with a typical
quiescent supply current of 18 μA. It uses the Analog Devices,
Inc., patented DigiTrim® trimming technique, which achieves
low offset voltage. The AD8657 also has high immunity to
electromagnetic interference.
The combination of low supply current, low offset voltage, very
low input bias current, wide supply range, and rail-to-rail input
and output makes the AD8657 ideal for current monitoring and
current loops in process and motor control applications. The
combination of precision specifications makes this device ideal
for dc gain and buffering of sensor front ends or high impedance
input sources in wireless or remote sensors or transmitters.
The AD8657 is specified over the extended industrial temperature range ( −40°C to +125°C) and is available in an 8-lead MSOP
package.
Dual
Quad
5V
AD8500
ADA4505-1
AD8505
AD8541
AD8603
AD8502
ADA4505-2
AD8506
AD8542
AD8607
AD8504
ADA4505-4
AD8508
AD8544
AD8609
12 V to 16 V
AD8663
36 V
AD8667
OP281
OP295
ADA4062-2
AD8669
OP481
OP495
ADA4062-4
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.
www.analog.com
Tel: 781.329.4700
Fax: 781.461.3113
©2011 Analog Devices, Inc. All rights reserved.
AD8657
TABLE OF CONTENTS
Features .............................................................................................. 1
Typical Performance Characteristics ..............................................7
Applications ....................................................................................... 1
Applications Information .............................................................. 17
Pin Configuration ............................................................................. 1
Input Stage ................................................................................... 17
General Description ......................................................................... 1
Output Stage................................................................................ 17
Revision History ............................................................................... 2
Rail to Rail ................................................................................... 18
Specifications..................................................................................... 3
Resistive Load ............................................................................. 18
Electrical Characteristics—2.7 V Operation ............................ 3
Comparator Operation .............................................................. 19
Electrical Characteristics—10 V Operation ............................. 4
EMI Rejection Ratio .................................................................. 20
Electrical Characteristics—18 V Operation ............................. 5
4 mA to 20 mA Process Control Current Loop Transmitter 20
Absolute Maximum Ratings............................................................ 6
Outline Dimensions ....................................................................... 21
Thermal Resistance ...................................................................... 6
Ordering Guide .......................................................................... 21
ESD Caution .................................................................................. 6
REVISION HISTORY
1/11—Revision 0: Initial Version
Rev. 0 | Page 2 of 24
AD8657
SPECIFICATIONS
ELECTRICAL CHARACTERISTICS—2.7 V OPERATION
VSY = 2.7 V, VCM = VSY/2, TA = 25°C, unless otherwise specified.
Table 2.
Parameter
INPUT CHARACTERISTICS
Offset Voltage
Input Bias Current
Symbol
Test Conditions/Comments
VOS
VCM = 0 V to 2.7 V
VCM = 0.3 V to 2.4 V; −40°C ≤ TA ≤ +85°C
VCM = 0 V to 2.7 V; −40°C ≤ TA ≤ +85°C
VCM = 0.3 V to 2.4 V; −40°C ≤ TA ≤ +125°C
VCM = 0 V to 2.7 V; −40°C ≤ TA ≤ +125°C
Min
IB
Typ
1
−40°C ≤ TA ≤ +125°C
Input Offset Current
IOS
−40°C ≤ TA ≤ +125°C
Input Voltage Range
Common-Mode Rejection Ratio
CMRR
Large Signal Voltage Gain
AVO
Offset Voltage Drift
Input Resistance
Input Capacitance, Differential Mode
Input Capacitance, Common Mode
OUTPUT CHARACTERISTICS
Output Voltage High
Output Voltage Low
Short-Circuit Current
Closed-Loop Output Impedance
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current per Amplifier
VCM = 0 V to 2.7 V
VCM = 0.3 V to 2.4 V, −40°C ≤ TA ≤ +85°C
VCM = 0 V to 2.7 V, −40°C ≤ TA ≤ +85°C
VCM = 0.3 V to 2.4 V, −40°C ≤ TA ≤ +125°C
VCM = 0 V to 2.7 V, −40°C ≤ TA ≤ +125°C
RL = 100 kΩ, VO = 0.5 V to 2.2 V
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
0
79
70
64
63
60
94
75
65
ΔVOS/ΔT
RIN
CINDM
CINCM
Unit
350
1
2.2
2.5
4
10
2.6
20
500
2.7
µV
mV
mV
mV
mV
pA
nA
pA
pA
V
dB
dB
dB
dB
dB
dB
dB
dB
μV/°C
GΩ
pF
pF
95
105
2
10
3.5
3.5
VOH
VOL
ISC
ZOUT
RL = 100 kΩ to VCM, −40°C ≤ TA ≤ +125°C
RL = 100 kΩ to VCM, −40°C ≤ TA ≤ +125°C
PSRR
VSY = 2.7 V to 18 V
−40°C ≤ TA ≤ +125°C
IO = 0 mA
−40°C ≤ TA ≤ +125°C
ISY
Max
2.69
10
±4
20
f = 1 kHz, AV = 1
105
70
125
18
22
33
V
mV
mA
Ω
dB
dB
µA
µA
DYNAMIC PERFORMANCE
Slew Rate
Settling Time to 0.1%
Gain Bandwidth Product
Phase Margin
Channel Separation
EMI Rejection Ratio of +IN x
SR
ts
GBP
ΦM
CS
EMIRR
RL = 1 MΩ, CL = 10 pF, AV = 1
VIN = 1 V step, RL = 100 kΩ, CL = 10 pF
RL = 1 MΩ, CL = 10 pF, AV = 1
RL = 1 MΩ, CL = 10 pF, AV = 1
f = 10 kHz, RL = 1 MΩ
VIN = 100 mVPEAK, f = 400 MHz, 900 MHz,
1800 MHz, 2400 MHz
38
14
170
69
105
90
V/ms
µs
kHz
Degrees
dB
dB
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
en p-p
en
f = 0.1 Hz to 10 Hz
f = 1 kHz
f = 10 kHz
f = 1 kHz
6
60
56
0.1
µV p-p
nV/√Hz
nV/√Hz
pA/√Hz
Current Noise Density
in
Rev. 0 | Page 3 of 24
AD8657
ELECTRICAL CHARACTERISTICS—10 V OPERATION
VSY = 10 V, VCM = VSY/2, TA = 25°C, unless otherwise specified.
Table 3.
Parameter
INPUT CHARACTERISTICS
Offset Voltage
Input Bias Current
Symbol
Test Conditions/Comments
VOS
VCM = 0 V to 10 V
VCM = 0 V to 10 V, −40°C ≤ TA ≤ +85°C
VCM = 0 V to 10 V, −40°C ≤ TA ≤ +125°C
Min
IB
Typ
2
−40°C ≤ TA ≤ +125°C
Input Offset Current
IOS
−40°C ≤ TA ≤ +125°C
Input Voltage Range
Common-Mode Rejection Ratio
CMRR
Large Signal Voltage Gain
AVO
Offset Voltage Drift
Input Resistance
Input Capacitance, Differential Mode
Input Capacitance, Common Mode
OUTPUT CHARACTERISTICS
Output Voltage High
Output Voltage Low
Short-Circuit Current
Closed-Loop Output Impedance
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current per Amplifier
VCM = 0 V to 10 V
VCM = 0 V to 10 V, −40°C ≤ TA ≤ +85°C
VCM = 0 V to 10 V, −40°C ≤ TA ≤ +125°C
RL = 100 kΩ, VO = 0.5 V to 9.5 V
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
0
90
72
64
105
95
67
ΔVOS/ΔT
RIN
CINDM
CINCM
Unit
350
2.7
9
15
2.6
30
500
10
µV
mV
mV
pA
nA
pA
pA
V
dB
dB
dB
dB
dB
dB
μV/°C
GΩ
pF
pF
105
120
2
10
3.5
3.5
VOH
VOL
ISC
ZOUT
RL = 100 kΩ to VCM, −40°C ≤ TA ≤ +125°C
RL = 100 kΩ to VCM, −40°C ≤ TA ≤ +125°C
PSRR
VSY = 2.7 V to 18 V
−40°C ≤ TA ≤ +125°C
IO = 0 mA
−40°C ≤ TA ≤ +125°C
ISY
Max
9.98
20
±11
15
f = 1 kHz, AV = 1
105
70
125
18
22
33
V
mV
mA
Ω
dB
dB
µA
µA
DYNAMIC PERFORMANCE
Slew Rate
Settling Time to 0.1%
Gain Bandwidth Product
Phase Margin
Channel Separation
EMI Rejection Ratio of +IN x
SR
ts
GBP
ΦM
CS
EMIRR
RL = 1 MΩ, CL = 10 pF, AV = 1
VIN = 1 V step, RL = 100 kΩ, CL = 10 pF
RL = 1 MΩ, CL = 10 pF, AV = 1
RL = 1 MΩ, CL = 10 pF, AV = 1
f = 10 kHz, RL = 1 MΩ
VIN = 100 mVPEAK, f = 400 MHz, 900 MHz,
1800 MHz, 2400 MHz
60
13
200
60
105
90
V/ms
µs
kHz
Degrees
dB
dB
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
en p-p
en
f = 0.1 Hz to 10 Hz
f = 1 kHz
f = 10 kHz
f = 1 kHz
5
50
45
0.1
µV p-p
nV/√Hz
nV/√Hz
pA/√Hz
Current Noise Density
in
Rev. 0 | Page 4 of 24
AD8657
ELECTRICAL CHARACTERISTICS—18 V OPERATION
VSY = 18 V, VCM = VSY/2, TA = 25°C, unless otherwise specified.
Table 4.
Parameter
INPUT CHARACTERISTICS
Offset Voltage
Input Bias Current
Symbol
Test Conditions/Comments
VOS
VCM = 0 V to 18 V
VCM = 0.3 V to 17.7 V, −40°C ≤ TA ≤ +85°C
VCM = 0 V to 18 V, −40°C ≤ TA ≤ +85°C
VCM = 0.3 V to 17.7 V, −40°C ≤ TA ≤ +125°C
VCM = 0 V to 18 V, −40°C ≤ TA ≤ +125°C
Min
IB
Typ
5
−40°C ≤ TA ≤ +125°C
Input Offset Current
IOS
−40°C ≤ TA ≤ +125°C
Input Voltage Range
Common-Mode Rejection Ratio
CMRR
Large Signal Voltage Gain
AVO
Offset Voltage Drift
Input Resistance
Input Capacitance, Differential Mode
Input Capacitance, Common Mode
OUTPUT CHARACTERISTICS
Output Voltage High
Output Voltage Low
Short-Circuit Current
Closed-Loop Output Impedance
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current per Amplifier
VCM = 0 V to 18 V
VCM = 0.3 V to 17.7 V, −40°C ≤ TA ≤ +85°C
VCM = 0 V to 18 V, −40°C ≤ TA ≤ +85°C
VCM = 0.3 V to 17.7 V, −40°C ≤ TA ≤ +125°C
VCM = 0 V to 18 V, −40°C ≤ TA ≤ +125°C
RL = 100 kΩ, VO = 0.5 V to 17.5 V
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
0
95
83
74
80
67
110
105
73
ΔVOS/ΔT
RIN
CINDM
CINCM
Unit
350
1.2
4
2
11
20
2.9
40
500
18
µV
mV
mV
mV
mV
pA
nA
pA
pA
V
dB
dB
dB
dB
dB
dB
dB
dB
μV/°C
GΩ
pF
pF
110
120
2
10
3.5
10.5
VOH
VOL
ISC
ZOUT
RL = 100 kΩ to VCM, −40°C ≤ TA ≤ +125°C
RL = 100 kΩ to VCM, −40°C ≤ TA ≤ +125°C
PSRR
VSY = 2.7 V to 18 V
−40°C ≤ TA ≤ +125°C
IO = 0 mA
−40°C ≤ TA ≤ +125°C
ISY
Max
17.97
30
±12
15
f = 1 kHz, AV = 1
105
70
125
18
22
33
V
mV
mA
Ω
dB
dB
µA
µA
DYNAMIC PERFORMANCE
Slew Rate
Settling Time to 0.1%
Gain Bandwidth Product
Phase Margin
Channel Separation
EMI Rejection Ratio of +IN x
SR
ts
GBP
ΦM
CS
EMIRR
RL = 1 MΩ, CL = 10 pF, AV = 1
VIN = 1 V step, RL = 100 kΩ, CL = 10 pF
RL = 1 MΩ, CL = 10 pF, AV = 1
RL = 1 MΩ, CL = 10 pF, AV = 1
f = 10 kHz, RL = 1 MΩ
VIN = 100 mVPEAK, f = 400 MHz, 900 MHz,
1800 MHz, 2400 MHz
70
12
200
60
105
90
V/ms
µs
kHz
Degrees
dB
dB
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
en p-p
en
f = 0.1 Hz to 10 Hz
f = 1 kHz
f = 10 kHz
f = 1 kHz
5
50
45
0.1
µV p-p
nV/√Hz
nV/√Hz
pA/√Hz
Current Noise Density
in
Rev. 0 | Page 5 of 24
AD8657
ABSOLUTE MAXIMUM RATINGS
THERMAL RESISTANCE
Table 4.
Parameter
Supply Voltage
Input Voltage
Input Current1
Differential Input Voltage
Output Short-Circuit
Duration to GND
Temperature Range
Storage
Operating
Junction
Lead Temperature
(Soldering, 60 sec)
1
Rating
20.5 V
(V−) − 300 mV to (V+) + 300 mV
±10 mA
±VSY
Indefinite
−65°C to +150°C
−40°C to +125°C
−65°C to +150°C
300°C
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages using a
standard 4-layer board.
Table 5. Thermal Resistance
Package Type
8-Lead MSOP (RM-8)
ESD CAUTION
The input pins have clamp diodes to the power supply pins. Limit the input
current to 10 mA or less whenever input signals exceed the power supply
rail by 0.3 V.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Rev. 0 | Page 6 of 24
θJA
142
θJC
45
Unit
°C/W
AD8657
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
160
160
VSY = 2.7V
VCM = VSY/2
120
NUMBER OF AMPLIFIERS
140
08804-005
120
80
100
60
Figure 5. Input Offset Voltage Distribution
18
20
VSY = 2.7V
–40°C ≤ TA ≤ +125°C
16
VSY = 18V
–40°C ≤ TA ≤ +125°C
18
16
14
NUMBER OF AMPLIFIERS
12
10
8
6
4
14
12
10
8
6
4
2
2
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0
TCVOS (µV/°C)
0
TCVOS (µV/°C)
Figure 3. Input Offset Voltage Drift Distribution
Figure 6. Input Offset Voltage Drift Distribution
300
300
VSY = 2.7V
VSY = 18V
200
100
100
VOS (µV)
200
0
0
–100
–100
–200
–200
0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
VCM (V)
2.7
–300
08804-004
–300
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0
08804-006
0
0
08804-003
0
0
2
4
6
8
10
12
14
16
VCM (V)
Figure 4. Input Offset Voltage vs. Common-Mode Voltage
Figure 7. Input Offset Voltage vs. Common-Mode Voltage
Rev. 0 | Page 7 of 24
18
08804-007
NUMBER OF AMPLIFIERS
40
VOS (µV)
Figure 2. Input Offset Voltage Distribution
VOS (µV)
0
–140
140
VOS (µV)
08804-002
120
80
100
60
40
0
20
–20
–40
–60
–80
0
–100
0
–120
20
–140
20
20
40
–20
40
60
–40
60
80
–60
80
100
–80
100
–100
120
NUMBER OF AMPLIFIERS
VSY = 18V
VCM = VSY/2
140
–120
140
AD8657
4
VSY = 2.7V
–40°C ≤ TA ≤ +85°C
2
0.5
1
VOS (mV)
1.0
0
0
–0.5
–1
–1.0
–2
–1.5
–3
–2.0
0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
VSY = 18V
–40°C ≤ TA ≤ +85°C
3
2.7
VCM (V)
–4
08804-108
VOS (mV)
1.5
0
2
4
6
8
10
VCM (V)
12
14
16
18
08804-111
2.0
Figure 11. Input Offset Voltage vs. Common-Mode Voltage
Figure 8. Input Offset Voltage vs. Common-Mode Voltage
6
2.0
VSY = 2.7V
–40°C ≤ TA ≤ +125°C
1.5
VSY = 18V
–40°C ≤ TA ≤ +125°C
4
1.0
2
VOS (mV)
VOS (mV)
0.5
0
–0.5
0
–2
–1.0
–4
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
2.7
VCM (V)
–6
0
8
10
VCM (V)
12
14
16
18
VSY = 18V
VSY = 2.7V
1000
1000
100
IB+
IB–
IB (pA)
IB (pA)
6
10000
10000
10
10
1
1
50
75
100
TEMPERATURE (°C)
125
0.1
25
08804-008
0.1
25
4
Figure 12. Input Offset Voltage vs. Common-Mode Voltage
Figure 9. Input Offset Voltage vs. Common-Mode Voltage
100
2
IB+
IB–
50
75
100
TEMPERATURE (°C)
Figure 10. Input Bias Current vs. Temperature
Figure 13. Input Bias Current vs. Temperature
Rev. 0 | Page 8 of 24
125
08804-011
0
08804-109
–2.0
08804-112
–1.5
AD8657
4
4
VSY = 18V
3
3
2
2
1
1
IB (nA)
0
125°C
85°C
25°C
–1
–2
–2
–3
–3
0.9
1.2
1.5
1.8
2.1
2.4
2.7
VCM (V)
0
2
4
6
8
10
12
14
16
Figure 17. Input Bias Current vs. Common-Mode Voltage
10
10
OUTPUT VOLTAGE (VOH) TO SUPPLY RAIL (V)
Figure 14. Input Bias Current vs. Common-Mode Voltage
VSY = 2.7V
1
–40°C
+25°C
+85°C
+125°C
100m
10m
1m
0.01
0.1
1
LOAD CURRENT (mA)
10
100
VSY = 18V
1
–40°C
+25°C
+85°C
+125°C
100m
10m
1m
0.1m
0.01m
0.001
08804-010
0.1m
0.01m
0.001
18
VCM (V)
Figure 15. Output Voltage (VOH) to Supply Rail vs. Load Current
08804-012
0.6
0.01
0.1
1
LOAD CURRENT (mA)
10
100
08804-013
0.3
08804-009
–4
0
OUTPUT VOLTAGE (VOH) TO SUPPLY RAIL (V)
125°C
85°C
25°C
–1
–4
Figure 18. Output Voltage (VOH) to Supply Rail vs. Load Current
10
OUTPUT VOLTAGE (VOL) TO SUPPLY RAIL (V)
10
VSY = 2.7V
1
100m
10m
–40°C
+25°C
+85°C
+125°C
1m
0.1m
0.01m
0.001
0.01
0.1
1
LOAD CURRENT (mA)
10
100
08804-014
OUTPUT VOLTAGE (VOL) TO SUPPLY RAIL (V)
0
Figure 16. Output Voltage (VOL) to Supply Rail vs. Load Current
VSY = 18V
1
100m
10m
–40°C
+25°C
+85°C
+125°C
1m
0.1m
0.01m
0.001
0.01
0.1
1
LOAD CURRENT (mA)
10
100
Figure 19. Output Voltage (VOL) to Supply Rail vs. Load Current
Rev. 0 | Page 9 of 24
08804-017
IB (nA)
VSY = 2.7V
AD8657
18.000
2.700
RL = 1MΩ
RL = 1MΩ
OUTPUT VOLTAGE, VOH (V)
2.698
2.697
RL = 100kΩ
2.696
17.995
17.990
17.985
17.980
VSY = 2.7V
VSY = 18V
–25
0
25
50
75
100
125
TEMPERATURE (°C)
17.975
–50
08804-015
2.695
–50
–25
0
25
50
75
100
125
TEMPERATURE (°C)
Figure 23. Output Voltage (VOH) vs. Temperature
Figure 20. Output Voltage (VOH) vs. Temperature
12
12
VSY = 2.7V
VSY = 18V
RL = 100kΩ
10
OUTPUT VOLTAGE, VOL (mV)
10
OUTPUT VOLTAGE, VOL (mV)
RL = 100kΩ
08804-018
OUTPUT VOLTAGE, VOH (V)
2.699
8
6
4
RL = 100kΩ
8
6
4
2
2
RL = 1MΩ
–25
0
25
50
75
100
125
TEMPERATURE (°C)
0
–50
08804-016
0
–50
25
50
75
100
125
Figure 24. Output Voltage (VOL) vs. Temperature
35
35
VSY = 18V
VSY = 2.7V
30
25
25
ISY PER AMP (µA)
30
20
15
20
15
10
–40°C
+25°C
+85°C
+125°C
5
0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
–40°C
+25°C
+85°C
+125°C
5
2.7
VCM (V)
0
0
3
6
9
12
15
18
VCM (V)
Figure 25. Supply Current per Amp vs. Common-Mode Voltage
Figure 22. Supply Current per Amp vs. Common-Mode Voltage
Rev. 0 | Page 10 of 24
08804-123
10
08804-120
ISY PER AMP (µA)
0
TEMPERATURE (°C)
Figure 21. Output Voltage (VOL) vs. Temperature
0
–25
08804-019
RL = 1MΩ
AD8657
60
35
30
50
VSY = 2.7V
VSY = 18V
ISY PER AMP (µA)
ISY PER AMP (µA)
25
20
15
40
30
20
10
–40°C
+25°C
5
10
+85°C
9
12
15
18
VSY (V)
0
–50
Figure 26. Supply Current per Amp vs. Supply Voltage
0
–45
–20
CL = 10pF
–90
CL = 100pF
10k
–135
1M
100k
FREQUENCY (Hz)
20
45
0
0
GAIN
–45
–20
CL = 10pF
10k
–135
1M
100k
FREQUENCY (Hz)
Figure 30. Open-Loop Gain and Phase vs. Frequency
60
VSY = 2.7V
AV = 100
40
AV = 10
AV = 1
–20
–40
20
0
VSY = 18V
AV = 100
AV = 10
AV = 1
–20
1k
10k
100k
FREQUENCY (Hz)
1M
–60
100
1k
10k
100k
FREQUENCY (Hz)
Figure 31. Closed-Loop Gain vs. Frequency
Figure 28. Closed-Loop Gain vs. Frequency
Rev. 0 | Page 11 of 24
1M
08804-025
–40
08804-022
–60
100
–90
CL = 100pF
–60
1k
CLOSED-LOOP GAIN (dB)
0
VSY = 18V
RL = 1MΩ
90
60
20
125
40
Figure 27. Open-Loop Gain and Phase vs. Frequency
40
100
135
–40
08804-021
–60
1k
OPEN-LOOP GAIN (dB)
45
PHASE (Degrees)
20
GAIN
75
60
PHASE
90
CLOSED-LOOP GAIN (dB)
OPEN-LOOP GAIN (dB)
PHASE
–40
25
50
TEMPERATURE (°C)
VSY = 2.7V
RL = 1MΩ
40
0
0
Figure 29. Supply Current per Amp vs. Temperature
135
60
–25
PHASE (Degrees)
6
08804-024
3
08804-020
0
08804-023
+125°C
0
AD8657
1000
1000
AV = 100
AV = 100
AV = 10
AV = 10
100
100
AV = 1
ZOUT (Ω)
ZOUT (Ω)
AV = 1
10
10
1k
10k
FREQUENCY (Hz)
100k
08804-026
100
1
100
Figure 32. Output Impedance vs. Frequency
140
VSY = 2.7V
VCM = 2.4V
120
VSY = 18V
VCM = VSY/2
80
60
80
60
40
40
20
20
1k
10k
100k
1M
FREQUENCY (Hz)
0
100
1k
10k
Figure 33. CMRR vs. Frequency
100
VSY = 2.7V
VSY = 18V
80
60
60
PSRR (dB)
80
PSRR+
PSRR–
40
20
PSRR+
PSRR–
40
1k
10k
100k
FREQUENCY (Hz)
1M
Figure 34. PSRR vs. Frequency
0
100
1k
10k
100k
FREQUENCY (Hz)
Figure 37. PSRR vs. Frequency
Rev. 0 | Page 12 of 24
1M
08804-031
20
08804-028
PSRR (dB)
1M
Figure 36. CMRR vs. Frequency
100
0
100
100k
FREQUENCY (Hz)
08804-030
CMRR (dB)
100
08804-027
CMRR (dB)
100
0
100
100k
Figure 35. Output Impedance vs. Frequency
140
120
1k
10k
FREQUENCY (Hz)
08804-029
VSY = 18V
VSY = 2.7V
1
AD8657
70
70
VSY = 2.7V
VIN = 10mV p-p
RL = 1MΩ
60
OS+
OS–
OS+
OS–
50
40
30
40
30
20
20
10
10
100
1000
CAPACITANCE (pF)
0
10
08804-032
100
1000
CAPACITANCE (pF)
Figure 38. Small Signal Overshoot vs. Load Capacitance
Figure 41. Small Signal Overshoot vs. Load Capacitance
VSY = ±1.35V
AV = 1
RL = 1MΩ
CL = 100pF
TIME (100µs/DIV)
TIME (100µs/DIV)
Figure 39. Large Signal Transient Response
Figure 42. Large Signal Transient Response
VSY = ±9V
AV = 1
RL = 1MΩ
CL = 100pF
VOLTAGE (5mV/DIV)
08804-034
VOLTAGE (5mV/DIV)
VSY = ±1.35V
AV = 1
RL = 1MΩ
CL = 100pF
TIME (100µs/DIV)
08804-036
08804-033
VOLTAGE (5V/DIV)
VOLTAGE (500mV/DIV)
VSY = ±9V
AV = 1
RL = 1MΩ
CL = 100pF
TIME (100µs/DIV)
Figure 40. Small Signal Transient Response
Figure 43. Small Signal Transient Response
Rev. 0 | Page 13 of 24
08804-037
0
10
08804-035
OVERSHOOT (%)
50
OVERSHOOT (%)
VSY = 18V
VIN = 10mV p-p
RL = 1MΩ
60
AD8657
INPUT
2
INPUT VOLTAGE (V)
VSY = ±1.35
AV = –10
RL = 1MΩ
–0.4
OUTPUT VOLTAGE (V)
–1
–2
10
1
5
OUTPUT
OUTPUT
0
TIME (40µs/DIV)
TIME (40µs/DIV)
Figure 44. Positive Overload Recovery
Figure 47. Positive Overload Recovery
VSY = ±9V
AV = –10
RL = 1MΩ
2
0.4
0
OUTPUT
0
–1
–5
–2
–10
08804-038
VSY = ±1.35V
AV = –10
RL = 1MΩ
INPUT
0
TIME (40µs/DIV)
TIME (40µs/DIV)
Figure 45. Negative Overload Recovery
Figure 48. Negative Overload Recovery
INPUT
VOLTAGE (500mV/DIV)
VOLTAGE (500mV/DIV)
INPUT
VSY = 2.7V
RL = 100kΩ
CL = 10pF
+5mV
0
ERROR BAND
08804-041
OUTPUT
INPUT VOLTAGE (V)
0
OUTPUT VOLTAGE (V)
INPUT
VSY = 18V
RL = 100kΩ
CL = 10pF
+5mV
0
ERROR BAND
OUTPUT
OUTPUT
–5mV
–5mV
08804-040
TIME (10µs/DIV)
OUTPUT VOLTAGE (V)
1
0.2
INPUT VOLTAGE (V)
08804-042
08804-039
0
Figure 46. Positive Settling Time to 0.1%
TIME (10µs/DIV)
Figure 49. Positive Settling Time to 0.1%
Rev. 0 | Page 14 of 24
08804-043
INPUT VOLTAGE (V)
INPUT
0
–0.2
VSY = ±9V
AV = –10
RL = 1MΩ
OUTPUT VOLTAGE (V)
0
AD8657
VSY =18V
RL = 100kΩ
CL = 10pF
VOLTAGE (500mV/DIV)
VOLTAGE (500mV/DIV)
VSY = 2.7V
RL = 100kΩ
CL = 10pF
INPUT
+5mV
OUTPUT
0
ERROR BAND
INPUT
+5mV
OUTPUT
–5mV
TIME (10µs/DIV)
Figure 50. Negative Settling Time to 0.1%
Figure 53. Negative Settling Time to 0.1%
1000
1000
VSY = 18V
100
1
100
1k
10k
FREQUENCY (Hz)
100k
1M
1
10
Figure 51. Voltage Noise Density vs. Frequency
100
1k
10k
FREQUENCY (Hz)
100k
1M
Figure 54. Voltage Noise Density vs. Frequency
VSY = 2.7V
TIME (2s/DIV)
08804-046
VOLTAGE (2µV/DIV)
VOLTAGE (2µV/DIV)
VSY = 18V
TIME (2s/DIV)
Figure 52. 0.1 Hz to 10 Hz Noise
Figure 55. 0.1 Hz to 10 Hz Noise
Rev. 0 | Page 15 of 24
08804-049
10
10
08804-045
10
100
08804-048
VOLTAGE NOISE DENSITY (nV/√Hz)
VSY = 2.7V
VOLTAGE NOISE DENSITY (nV/√Hz)
08804-047
08804-044
–5mV
TIME (10µs/DIV)
0
ERROR BAND
AD8657
20
3.0
VSY = 2.7V
VIN = 2.6V
RL = 1MΩ
AV = 1
VSY = 18V
VIN = 17.9V
RL = 1MΩ
AV = 1
18
16
OUTPUT SWING (V)
OUTPUT SWING (V)
2.5
2.0
1.5
1.0
14
12
10
8
6
4
0.5
0
100
1k
10k
100k
1M
FREQUENCY (Hz)
08804-050
0
10
10
10k
100k
1M
Figure 59. Output Swing vs. Frequency
100
100
VSY = 2.7V
VIN = 0.2V rms
RL = 1MΩ
AV = 1
VSY = 18V
VIN = 0.2V rms
RL = 1MΩ
AV = 1
10
THD + N (%)
10
1
0.1
100
1k
10k
100k
FREQUENCY (Hz)
0.01
10
08804-051
0.01
10
100
1k
10k
100k
08804-054
0.1
1
100k
08804-055
THD + N (%)
1k
FREQUENCY (Hz)
Figure 56. Output Swing vs. Frequency
FREQUENCY (Hz)
Figure 57. THD + N vs. Frequency
Figure 60. THD + N vs. Frequency
0
0
1MΩ
1MΩ
VSY = 2.7V
RL = 1MΩ
AV = –100
10kΩ
RL
–40
–60
VIN = 0.5V p-p
–80
VIN = 1.5V p-p
VIN = 2.6V p-p
–100
10kΩ
VSY = 18V
RL = 1MΩ
AV = –100
–20
CHANNEL SEPARATION (dB)
–20
RL
–40
VIN = 1V p-p
VIN = 5V p-p
VIN = 10V p-p
VIN = 15V p-p
VIN = 17V p-p
–60
–80
–100
–120
–120
–140
–140
100
1k
10k
FREQUENCY (Hz)
100k
08804-052
CHANNEL SEPARATION (dB)
100
08804-053
2
Figure 58. Channel Separation vs. Frequency
100
1k
10k
FREQUENCY (Hz)
Figure 61. Channel Separation vs. Frequency
Rev. 0 | Page 16 of 24
AD8657
APPLICATIONS INFORMATION
The AD8657 is a low power, rail-to-rail input and output
precision CMOS amplifier that operates over a wide supply
voltage range of 2.7 V to 18 V. This amplifier uses the Analog
Devices DigiTrim technique to achieve a higher degree of
precision than is available from other CMOS amplifiers. The
DigiTrim technique is a method of trimming the offset voltage
of an amplifier after assembly. The advantage of postpackage
trimming is that it corrects any shifts in offset voltage caused by
mechanical stresses of assembly.
The AD8657 also employs unique input and output stages to
achieve a rail-to-rail input and output range with a very low
supply current.
INPUT STAGE
Figure 62 shows the simplified schematic of the AD8657. The
input stage comprises two differential transistor pairs, an NMOS
pair (M1, M2) and a PMOS pair (M3, M4). The input commonmode voltage determines which differential pair turns on and is
more active than the other.
The PMOS differential pair is active when the input voltage
approaches and reaches the lower supply rail. The NMOS pair
is needed for input voltages up to and including the upper supply
rail. This topology allows the amplifier to maintain a wide
dynamic input voltage range and to maximize signal swing to
both supply rails.
For the majority of the input common-mode voltage range, the
PMOS differential pair is active. Differential pairs commonly
exhibit different offset voltages. The handoff from one pair to the
other creates a step-like characteristic that is visible in the VOS vs.
VCM graph (see Figure 4 and Figure 7). This is inherent in all railto-rail amplifiers that use the dual differential pair topology.
Therefore, always choose a common-mode voltage that does not
include the region of handoff from one input differential pair to
the other.
Additional steps in the VOS vs. VCM curves are also visible as the
input common-mode voltage approaches the power supply rails.
These changes are a result of the load transistors (M8, M9, M14,
and M15) running out of headroom. As the load transistors are
forced into the triode region of operation, the mismatch of their
drain impedances contributes to the offset voltage of the amplifier.
This problem is exacerbated at high temperatures due to the
decrease in the threshold voltage of the input transistors (see
Figure 8, Figure 9, Figure 11, and Figure 12 for typical performance data).
Current Source I1 drives the PMOS transistor pair. As the input
common-mode voltage approaches the upper rail, I1 is steered
away from the PMOS differential pair through the M5 transistor.
The bias voltage, VB1, controls the point where this transfer occurs.
M5 diverts the tail current into a current mirror consisting of the
M6 and M7 transistors. The output of the current mirror then
drives the NMOS pair. Note that the activation of this current
mirror causes a slight increase in supply current at high commonmode voltages (see Figure 22 and Figure 25 for more details).
The AD8657 achieves its high performance by using low voltage
MOS devices for its differential inputs. These low voltage MOS
devices offer excellent noise and bandwidth per unit of current.
Each differential input pair is protected by proprietary regulation
circuitry (not shown in the simplified schematic). The regulation circuitry consists of a combination of active devices that
maintain the proper voltages across the input pairs during normal
operation and passive clamping devices that protect the amplifier
during fast transients. However, these passive clamping devices
begin to forward bias as the common-mode voltage approaches
either power supply rail. This causes an increase in the input
bias current (see Figure 14 and Figure 17).
The input devices are also protected from large differential
input voltages by clamp diodes (D1 and D2). These diodes are
buffered from the inputs with two 10 kΩ resistors (R1 and R2).
The differential diodes turn on whenever the differential voltage
exceeds approximately 600 mV; in this condition, the differential
input resistance drops to 20 kΩ.
OUTPUT STAGE
The AD8657 features a complementary output stage consisting
of the M16 and M17 transistors. These transistors are configured
in Class AB topology and are biased by the voltage source, VB2.
This topology allows the output voltage to approach, within
millivolts, the supply rails, achieving a rail-to-rail output swing.
The output voltage is limited by the output impedance of the
transistors, which are low RON MOS devices. The output voltage
swing is a function of the load current and can be estimated using
the output voltage to the supply rail vs. load current plots (see
Figure 15, Figure 16, Figure 18, and Figure 19).
Rev. 0 | Page 17 of 24
AD8657
V+
VB1
I1
M5
+IN x
R1
–IN x
R2
M3
D1
M8
M9
M10
M11
M4
M16
D2
VB2
M1
OUT x
M2
M7
M6
M13
M14
M15
08804-056
M17
M12
V–
Figure 62. Simplified Schematic
RAIL TO RAIL
Inverting Configuration
The AD8657 features rail-to-rail input and output with a supply
voltage from 2.7 V to 18 V. Figure 63 shows the input and output
waveforms of the AD8657 configured as a unity-gain buffer with
a supply voltage of ±9 V and a resistive load of 1 MΩ. With an
input voltage of ±9 V, the AD8657 allows the output to swing
very close to both rails. Additionally, it does not exhibit phase
reversal.
Figure 64 shows AD8657 in an inverting configuration with
a resistive load, RL, at the output. The actual load seen by the
amplifier is the parallel combination of the feedback resistor,
R2, and load, RL. Having a feedback resistor of 1 kΩ and a load
of 1 MΩ results in an equivalent load resistance of 999 Ω at the
output. In this condition, the AD8657 is incapable of driving
such a heavy load; therefore, its performance degrades greatly.
To avoid loading the output, use a larger feedback resistor, but
consider the resistor thermal noise effect on the overall circuit.
VSY = ±9V
RL = 1MΩ
R2
VOLTAGE (5V/DIV)
INPUT
OUTPUT
VIN
+VSY
R1
AD8657
VOUT
1/2
RL
08804-058
–VSY
RL, EFF = RL || R2
Figure 64. Inverting Op Amp
Noninverting Configuration
08804-057
Figure 65 shows the AD8657 in a noninverting configuration
with a resistive load, RL, at the output. The actual load seen by
the amplifier is the parallel combination of R1 + R2 and RL.
Figure 63. Rail-to-Rail Input and Output
RESISTIVE LOAD
The feedback resistor alters the load resistance that an amplifier
sees. It is, therefore, important to be aware of the value of feedback resistors chosen for use with the AD8657. The AD8657 is
capable of driving resistive loads down to 100 kΩ. The following
two examples, inverting and noninverting configurations, show
how the feedback resistor changes the actual load resistance
seen at the output of the amplifier.
R2
+VSY
R1
AD8657
VIN
1/2
VOUT
RL
–VSY
RL, EFF = RL || (R1 + R2)
Figure 65. Noninverting Op Amp
Rev. 0 | Page 18 of 24
08804-059
TIME (200µs/DIV)
AD8657
COMPARATOR OPERATION
Op amps are designed to operate in a closed-loop configuration
with feedback from its output to its inverting input. Figure 66
shows the AD8657 configured as a voltage follower with an input
voltage that is always kept at midpoint of the power supplies.
The same configuration is applied to the unused channel. A1 and
A2 indicate the placement of ammeters to measure supply current.
ISY+ refers to the current flowing from the upper supply rail to
the op amp, and ISY− refers to the current flowing from the op
amp to the lower supply rail. As shown in Figure 67, as expected,
in normal operating condition, the total current flowing into the
op amp is equivalent to the total current flowing out of the op amp,
where, ISY+ = ISY− = 36 μA for the dual AD8657 at VSY = 18 V.
consist of substrate PNP bipolar transistors, and conduct whenever
the differential input voltage exceeds approximately 600 mV; however, these diodes also allow a current path from the input to the
lower supply rail, thus resulting in an increase in the total supply
current of the system. As shown in Figure 70, both configurations
yield the same result. At 18 V of power supply, ISY+ remains at
36 μA per dual amplifier, but ISY− increases to 140 μA in magnitude per dual amplifier.
+VSY
AD8657
+VSY
100kΩ
ISY+
AD8657
ISY–
A2
–VSY
Figure 68. Comparator A
+VSY
ISY–
08804-066
A2
100kΩ
VOUT
1/2
100kΩ
VOUT
1/2
08804-068
A1
ISY+
A1
100kΩ
–VSY
A1
ISY+
100kΩ
Figure 66. Voltage Follower
AD8657
40
VOUT
1/2
100kΩ
A2
ISY–
08804-069
30
25
–VSY
20
Figure 69. Comparator B
15
160
ISY–
ISY+
140
0
0
2
4
6
8
10
VSY (V)
12
14
16
18
08804-067
5
Figure 67. Supply Current vs. Supply Voltage (Voltage Follower)
In contrast to op amps, comparators are designed to work in an
open-loop configuration and to drive logic circuits. Although
op amps are different from comparators, occasionally an unused
section of a dual op amp is used as a comparator to save board
space and cost; however, this is not recommended.
Figure 68 and Figure 69 show the AD8657 configured as a comparator, with 100 kΩ resistors in series with the input pins. Any
unused channels are configured as buffers with the input voltage
kept at the midpoint of the power supplies. The AD8657 has input
devices that are protected from large differential input voltages
by Diode D1 and Diode D2 (refer to Figure 62). These diodes
120
100
ISY–
ISY+
80
60
40
20
0
0
2
4
6
8
10
VSY (V)
12
14
16
18
08804-070
10
ISY pER DUAL AMPLIFIER (µA)
ISY PER DUAL AMPLIFIER (µA)
35
Figure 70. Supply Current vs. Supply Voltage (AD8657 as a Comparator)
Note that 100 kΩ resistors are used in series with the input of
the op amp. If smaller resistor values are used, the supply current of
the system increases much more. For more details on op amps as
comparators, refer to the AN-849 Application Note Using Op
Amps as Comparators.
Rev. 0 | Page 19 of 24
AD8657
EMI REJECTION RATIO
Circuit performance is often adversely affected by high frequency
electromagnetic interference (EMI). In the event where signal
strength is low and transmission lines are long, an op amp must
accurately amplify the input signals. However, all op amp pins—
the noninverting input, inverting input, positive supply, negative
supply, and output pins—are susceptible to EMI signals. These
high frequency signals are coupled into an op amp by various
means such as conduction, near field radiation, or far field radiation. For instance, wires and PCB traces can act as antennas and
pick up high frequency EMI signals.
Precision op amps, such as the AD8657, do not amplify EMI or
RF signals because of their relatively low bandwidth. However,
due to the nonlinearities of the input devices, op amps can rectify
these out-of-band signals. When these high frequency signals
are rectified, they appear as a dc offset at the output.
To describe the ability of the AD8657 to perform as intended in
the presence of an electromagnetic energy, the electromagnetic
interference rejection ratio (EMIRR) of the noninverting pin is
specified in Table 2, Table 3, and Table 4 of the Specifications
section. A mathematical method of measuring EMIRR is
defined as follows:
EMIRR = 20 log (VIN_PEAK/ΔVOS)
With a zero-scale input, a current of VREF/RNULL flows through
R´. This creates a current flowing through the sense resistor,
ISENSE, determined by the following equation (see Figure 72 for
details):
ISENSE, MIN = (VREF × R´)/(RNULL × RSENSE)
With a full-scale input voltage, current flowing through R´ is
increased by the full-scale change in VIN/RSPAN. This creates an
increase in the current flowing through the sense resistor.
ISENSE, DELTA = (Full-Scale Change in VIN × R´)/(RSPAN × RSENSE)
Therefore
ISENSE, MAX = ISENSE, MIN + ISENSE, DELTA
When R´ >> RSENSE, the current through the load resistor at the
receiver side is almost equivalent to ISENSE.
Figure 72 is designed for a full-scale input voltage of 5 V. At 0 V
of input, loop current is 3.5 mA, and at a full scale of 5 V, the
loop current is 21 mA. This allows software calibration to fine
tune the current loop to the 4 mA to 20 mA range.
140
120
The AD8657 and ADR125 both consume only 160 μA quiescent
current, making 3.34 mA current available to power additional
signal conditioning circuitry or to power a bridge circuit.
80
ADR125
VREF
VOUT
60
20
10M
VIN = 100mVPEAK
VSY = 2.7V TO 18V
100M
1G
10G
FREQUENCY (Hz)
08804-071
40
RNULL
1MΩ
1%
VIN
0V TO 5V
RSPAN
200kΩ
1%
R1
68kΩ
1%
Figure 71. EMIRR vs. Frequency
4 mA TO 20 mA PROCESS CONTROL CURRENT
LOOP TRANSMITTER
The 2-wire current transmitters are often used in distributed
control systems and process control applications to transmit
analog signals between sensors and process controllers. Figure 72
shows a 4 mA to 20 mA current loop transmitter.
C2
C3
10µF 0.1µF
R2
2kΩ
1%
VIN
GND
C5
C4
0.1µF 10µF
1/2
AD8657
Q1
R4
3.3kΩ
R3
1.2kΩ
VDD
18V
D1
C1
390pF
4mA
TO
20mA
RSENSE
100Ω
1%
NOTES
1. R1 + R2 = R´.
The transmitter powers directly from the control loop power
supply, and the current in the loop carries signal from 4 mA to
20 mA. Thus, 4 mA establishes the baseline current budget within
which the circuit must operate. Using the AD8657 is an excellent
Rev. 0 | Page 20 of 24
Figure 72. 4 mA to 20 mA Current Loop Transmitter
RL
100Ω
08804-060
100
EMIRR (dB)
choice due to its low supply current of 33 μA per amplifier over
temperature and supply voltage. The current transmitter controls
the current flowing in the loop, where a zero-scale input signal
is represented by 4 mA of current and a full-scale input signal
is represented by 20 mA. The transmitter also floats from the
control loop power supply, VDD, while signal ground is in the
receiver. The loop current is measured at the load resistor, RL,
at the receiver side.
AD8657
OUTLINE DIMENSIONS
3.20
3.00
2.80
8
3.20
3.00
2.80
1
5.15
4.90
4.65
5
4
PIN 1
IDENTIFIER
0.65 BSC
0.95
0.85
0.75
15° MAX
1.10 MAX
0.40
0.25
6°
0°
0.23
0.09
0.80
0.55
0.40
COMPLIANT TO JEDEC STANDARDS MO-187-AA
100709-B
0.15
0.05
COPLANARITY
0.10
Figure 73. 8-Lead Mini Small Outline Package [MSOP]
(RM-8)
Dimensions shown in millimeters
ORDERING GUIDE
Model 1
AD8657ARMZ
AD8657ARMZ-R7
AD8657ARMZ-RL
1
Temperature Range
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
Package Description
8-Lead Mini Small Outline Package [MSOP]
8-Lead Mini Small Outline Package [MSOP]
8-Lead Mini Small Outline Package [MSOP]
Z = RoHS Compliant Part.
Rev. 0 | Page 21 of 24
Package Option
RM-8
RM-8
RM-8
Branding
A2N
A2N
A2N
AD8657
NOTES
Rev. 0 | Page 22 of 24
AD8657
NOTES
Rev. 0 | Page 23 of 24
AD8657
NOTES
©2011 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08804-0-1/11(0)
Rev. 0 | Page 24 of 24