AD AD628AR High common-mode voltage, programmable gain difference amplifier Datasheet

High Common-Mode Voltage,
Programmable Gain Difference Amplifier
AD628
FEATURES
FUNCTIONAL BLOCK DIAGRAM
REXT2
+VS
–IN
100kΩ
The AD628 is a precision difference amplifier that combines
excellent dc performance with high common-mode rejection
over a wide range of frequencies. When used to scale high
voltages, it allows simple conversion of standard control
voltages or currents for use with single-supply ADCs. A
wideband feedback loop minimizes distortion effects due to
capacitor charging of Σ-Δ ADCs.
A reference pin (VREF) provides a dc offset for converting bipolar
to single-sided signals. The AD628 converts +5 V, +10 V, ±5 V,
±10 V, and 4 to 20 mA input signals to a single-ended output
within the input range of single-supply ADCs.
The AD628 has an input common-mode and differential-mode
operating range of ±120 V. The high common-mode input
impedance makes the device well suited for high voltage
measurements across a shunt resistor. The inverting input of the
buffer amplifier is available for making a remote Kelvin
connection.
10kΩ
–IN
A1
–IN
A2
10kΩ
OUT
+IN
+IN
100kΩ
10kΩ
–VS
VREF
AD628
02992-C-001
+IN
CFILT
Figure 1.
130
120
110
100
CMRR (dB)
GENERAL DESCRIPTION
RG
G = +0.1
APPLICATIONS
High voltage current shunt sensing
Programmable logic controllers
Analog input front end signal conditioning
+5 V, +10 V, ±5 V, ±10 V, and 4 to 20 mA
Isolation
Sensor signal conditioning
Power supply monitoring
Electrohydraulic control
Motor control
REXT1
VS = ±15V
90
80
70
VS = ±2.5V
60
50
40
30
10
100
1k
10k
FREQUENCY (Hz)
100k
02992-C-002
High common-mode input voltage range
±120 V at VS = ±15 V
Gain range 0.1 to 100
Operating temperature range: −40°C to ±85°C
Supply voltage range
Dual supply: ±2.25 V to ±18 V
Single supply: 4.5 V to 36 V
Excellent ac and dc performance
Offset temperature stability RTI: 10 μV/°C maximum
Offset: ±1.5 V mV maximum
CMRR RTI: 75 dB minimum, dc to 500 Hz, G = +1
Figure 2. CMRR vs. Frequency of the AD628
A precision 10 kΩ resistor connected to an external pin is
provided for either a low-pass filter or to attenuate large
differential input signals. A single capacitor implements a lowpass filter. The AD628 operates from single and dual supplies
and is available in an 8-lead SOIC_N or 8-lead MSOP package.
It operates over the standard industrial temperature range of
−40°C to +85°C.
Rev. F
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
©2006 Analog Devices, Inc. All rights reserved.
AD628
TABLE OF CONTENTS
Features .............................................................................................. 1
Theory of Operation ...................................................................... 14
Applications....................................................................................... 1
Applications..................................................................................... 15
General Description ......................................................................... 1
Gain Adjustment ........................................................................ 15
Functional Block Diagram .............................................................. 1
Input Voltage Range................................................................... 15
Revision History ............................................................................... 2
Voltage Level Conversion.......................................................... 16
Specifications..................................................................................... 3
Current Loop Receiver .............................................................. 17
Absolute Maximum Ratings............................................................ 7
Monitoring Battery Voltages..................................................... 17
Thermal Characteristics .............................................................. 7
Filter Capacitor Values............................................................... 18
ESD Caution.................................................................................. 7
Kelvin Connection ..................................................................... 18
Pin Configuration and Function Descriptions............................. 8
Outline Dimensions ....................................................................... 19
Typical Performance Characteristics ............................................. 9
Ordering Guide .......................................................................... 19
Test Circuits..................................................................................... 13
REVISION HISTORY
3/06—Rev. E to Rev. F
Changes to Table 1............................................................................ 3
Changes to Figure 3.......................................................................... 7
Replaced Voltage Level Conversion Section ............................... 16
Changes to Figure 32 and Figure 33............................................. 17
Updated Outline Dimensions ....................................................... 19
Changes to Ordering Guide .......................................................... 19
5/05—Rev. D to Rev. E
Changes to Table 1........................................................................... 3
Changes to Table 2........................................................................... 5
Changes to Figure 33..................................................................... 18
3/05—Rev. C to Rev. D
Updated Format................................................................ Universal
Changes to Table 1........................................................................... 3
Changes to Table 2........................................................................... 5
4/04—Rev. B to Rev. C
Updated Format................................................................ Universal
Changes to Specifications ............................................................... 3
Changes to Absolute Maximum Ratings ...................................... 7
Changes to Figure 3......................................................................... 7
Changes to Figure 26..................................................................... 13
Changes to Figure 27..................................................................... 13
Changes to Theory of Operation................................................. 14
Changes to Figure 29..................................................................... 14
Changes to Table 5......................................................................... 15
Changes to Gain Adjustment Section......................................... 15
Added the Input Voltage Range Section..................................... 15
Added Figure 30 ............................................................................ 15
Added Figure 31 ............................................................................ 15
Changes to Voltage Level Conversion Section .......................... 16
Changes to Figure 32..................................................................... 16
Changes to Table 6......................................................................... 16
Changes to Figure 33 and Figure 34............................................ 17
Changes to Figure 35..................................................................... 18
Changes to Kelvin Connection Section...................................... 18
6/03—Rev. A to Rev. B
Changes to General Description ................................................... 1
Changes to Specifications............................................................... 2
Changes to Ordering Guide ........................................................... 4
Changes to TPCs 4, 5, and 6 .......................................................... 5
Changes to TPC 9............................................................................ 6
Updated Outline Dimensions...................................................... 14
1/03—Rev. 0 to Rev. A
Change to Ordering Guide............................................................. 4
11/02—Rev. 0: Initial Version
Rev. F | Page 2 of 20
AD628
SPECIFICATIONS
TA = 25°C, VS = ±15 V, RL = 2 kΩ, REXT1 = 10 kΩ, REXT2 = ∞, VREF = 0, unless otherwise noted.
Table 1.
Parameter
DIFFERENTIAL AND OUTPUT AMPLIFIER
Gain Equation
Gain Range
Offset Voltage
vs. Temperature
CMRR 3
Conditions
Min
AD628AR
Typ
Max
Min
AD628ARM
Typ
Max
G = +0.1(1+ REXT1/REXT2)
See Figure 29
VCM = 0 V; RTI of input pins 2 ;
output amplifier G = +1
0.1 1
−1.5
100
+1.5
0.11
−1.5
100
+1.5
4
RTI of input pins;
G = +0.1 to +100
500 Hz
Minimum CMRR Over Temperature −40°C to +85°C
vs. Temperature
PSRR (RTI)
VS = ±10 V to ±18 V
Input Voltage Range
Common Mode
Differential
Dynamic Response
Small Signal Bandwidth −3 dB
G = +0.1
Full Power Bandwidth
Settling Time
G = +0.1, to 0.01%, 100 V step
Slew Rate
Noise (RTI)
Spectral Density
1 kHz
0.1 Hz to 10 Hz
DIFFERENTIAL AMPLIFIER
Gain
Error
vs. Temperature
Nonlinearity
vs. Temperature
Offset Voltage
RTI of input pins
vs. Temperature
Input Impedance
Differential
Common Mode
CMRR 4
RTI of input pins;
G = +0.1 to +100
500 Hz
Minimum CMRR Over Temperature −40°C to +85°C
vs. Temperature
Output Resistance
Error
OUTPUT AMPLIFIER
Gain Equation
G = (1 + REXT1/REXT2)
Nonlinearity
G = +1, VOUT = ±10 V
Offset Voltage
RTI of output amp
vs. Temperature
Output Voltage Swing
RL = 10 kΩ
RL = 2 kΩ
8
4
75
75
75
70
75
70
77
1
94
−120
−120
4
77
+120
+120
1
94
−120
−120
600
5
600
5
V
V
300
15
300
15
nV/√Hz
μV p-p
0.1
+0.01
+0.1
5
5
10
+1.5
8
40
−0.1
3
+0.1
5
5
10
+1.5
8
220
55
75
75
70
75
70
1
10
0.1
+0.01
−1.5
75
Rev. F | Page 3 of 20
dB
dB
(μV/V)/°C
dB
0.3
220
55
−14.2
−13.8
μV/°C
dB
0.3
3
−0.15
V/V
V/V
mV
kHz
kHz
μs
V/μs
−1.5
−0.1
4
+120
+120
40
−0.1
8
Unit
4
+0.1
0.5
+0.15
0.6
+14.1
+13.6
1
10
−0.1
−0.15
−14.2
−13.8
V/V
%
ppm/°C
ppm
ppm
mV
μV/°C
kΩ
kΩ
dB
+0.1
dB
dB
(μV/V)/°C
kΩ
%
0.5
+0.15
0.6
+14.1
+13.6
V/V
ppm
mV
μV/°C
V
V
4
AD628
Parameter
Bias Current
Offset Current
CMRR
Open-Loop Gain
POWER SUPPLY
Operating Range
Quiescent Current
TEMPERATURE RANGE
Conditions
Min
VCM = ±13 V
VOUT = ±13 V
130
130
AD628AR
Typ
Max
1.5
3
0.2
0.5
±2.25
−40
1
To use a lower gain, see the Gain Adjustment section.
The addition of the difference amplifier and output amplifier offset voltage does not exceed this specification.
(0.1)(VCM )
3
Error due to common mode as seen at the output: VOUT = [
] × [Output Amplifier Gain]
75
2
10 20
4
Error due to common mode as seen at the output of A1: VOUT A1 = [
(0.1)(VCM )
75
10 20
]
Rev. F | Page 4 of 20
Min
AD628ARM
Typ
Max
1.5
3
0.2
0.5
130
130
±18
1.6
+85
±2.25
−40
±18
1.6
+85
Unit
nA
nA
dB
dB
V
mA
°C
AD628
TA = 25°C, VS = 5 V, RL = 2 kΩ, REXT1 = 10 kΩ, REXT2 = ∞, VREF = 2.5, unless otherwise noted.
Table 2.
Parameter
DIFFERENTIAL AND OUTPUT AMPLIFIER
Gain Equation
Gain Range
Offset Voltage
vs. Temperature
CMRR 3
Minimum CMRR Over Temperature
vs. Temperature
PSRR (RTI)
Input Voltage Range
Common Mode 4
Differential
Dynamic Response
Small Signal Bandwidth – 3 dB
Full Power Bandwidth
Settling Time
Slew Rate
Noise (RTI)
Spectral Density
DIFFERENTIAL AMPLIFIER
Gain
Error
Nonlinearity
vs. Temperature
Offset Voltage
vs. Temperature
Input Impedance
Differential
Common Mode
CMRR 5
Minimum CMRR Over Temperature
vs. Temperature
Output Resistance
Error
OUTPUT AMPLIFIER
Gain Equation
Nonlinearity
Output Offset Voltage
vs. Temperature
Output Voltage Swing
Bias Current
Offset Current
CMRR
Open-Loop Gain
Conditions
Min
AD628AR
Typ
Max
Min
AD628ARM
Typ
Max
G = +0.1(1+ REXT1/REXT2)
See Figure 29
VCM = 2.25 V; RTI of input pins 2 ;
output amplifier G = +1
0.1 1
−3.0
100
+3.0
0.11
−3.0
100
+3.0
RTI of input pins; G = +0.1 to +100
500 Hz
−40°C to +85°C
75
75
70
VS = 4.5 V to 10 V
77
6
G = +0.1; to 0.01%, 30 V step
1 kHz
0.1 Hz to 10 Hz
–0.1
1
94
4
77
+17
+15
350
15
nV/√Hz
μV p-p
0.1
+0.01
+0.1
3
10
+2.5
10
–0.1
3
−2.5
130
130
Rev. F | Page 5 of 20
+0.1
3
10
+2.5
10
220
55
4
+0.1
1.5
0.2
VCM = 1 V to 4 V
VOUT = 1 V to 4 V
0.1
+0.01
75
75
70
−0.1
0.9
1
V
V
350
15
1
10
RL = 10 kΩ
RL = 2 kΩ
+17
+15
kHz
kHz
μs
V/μs
75
75
70
−0.15
4
−12
−15
220
55
G = (1 + REXT1/REXT2)
G = +1, VOUT = 1 V to 4 V
RTI of output amplifier
1
94
μV/°C
dB
dB
dB
(μV/V)/°C
dB
440
30
15
0.3
−2.5
RTI of input pins; G = +0.1 to +100
500 Hz
−40°C to +85°C
15
V/V
V/V
mV
440
30
15
0.3
3
RTI of input pins
6
75
75
70
−12
−15
G = +0.1
15
Unit
0.5
0.15
0.6
4.1
4
3
0.5
1
10
−0.1
+0.1
−0.15
0.9
1
1.5
0.2
130
130
4
0.5
0.15
0.6
4.1
4
3
0.5
V/V
%
ppm
ppm
mV
μV/°C
kΩ
kΩ
dB
dB
dB
(μV/V)/°C
kΩ
%
V/V
ppm
mV
μV/°C
V
V
nA
nA
dB
dB
AD628
Parameter
POWER SUPPLY
Operating Range
Quiescent Current
TEMPERATURE RANGE
Conditions
Min
AD628AR
Typ
Max
±2.25
−40
1
To use a lower gain, see the Gain Adjustment section.
The addition of the difference amplifier and output amplifier offset voltage does not exceed this specification.
(0.1)(VCM )
3
Error due to common mode as seen at the output: VOUT = [
] × [Output Amplifier Gain]
75
2
10 20
Greater values of voltage are possible with greater or lesser values of VREF.
(0.1)(VCM )
5
Error due to common mode as seen at the output of A1: VOUT A1 = [
]
75
4
10 20
Rev. F | Page 6 of 20
+36
1.6
+85
Min
AD628ARM
Typ
Max
±2.25
−40
+36
1.6
+85
Unit
V
mA
°C
AD628
ABSOLUTE MAXIMUM RATINGS
Parameter
Supply Voltage
Internal Power Dissipation
Input Voltage (Common Mode)
Differential Input Voltage
Output Short-Circuit Duration
Storage Temperature
Operating Temperature Range
Lead Temperature (Soldering, 10 sec)
Stresses greater than 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.
THERMAL CHARACTERISTICS
1.6
TJ = 150°C
1.4
When using ±12 V supplies or higher (see the Input Voltage Range section).
POWER DISSIPATION (W)
1
Rating
±18 V
See Figure 3
±120 V 1
±120 V1
Indefinite
−65°C to +125°C
–40°C to +85°C
300°C
1.2
8-LEAD MSOP PACKAGE
1.0
8-LEAD SOIC PACKAGE
0.8
0.6
0.4
MSOP θJA (JEDEC; 4-LAYER BOARD) = 132.54°C/W
SOIC θJA (JEDEC; 4-LAYER BOARD) = 154°C/W
0.2
0
–60
–40
–20
0
20
40
60
80
100
AMBIENT TEMPERATURE (°C)
Figure 3. Maximum Power Dissipation vs. Temperature
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. F | Page 7 of 20
02992-C-003
Table 3.
AD628
+IN 1
–VS 2
AD628
8
–IN
7
+VS
TOP VIEW
VREF 3 (Not to Scale) 6 RG
CFILT 4
5
OUT
02992-C-004
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
Figure 4. Pin Configuration
Table 4. Pin Function Descriptions
Pin No.
1
2
3
4
5
6
7
8
Mnemonic
+IN
−VS
VREF
CFILT
OUT
RG
+VS
−IN
Descriptions
Noninverting Input
Negative Supply Voltage
Reference Voltage Input
Filter Capacitor Connection
Amplifier Output
Output Amplifier Inverting Input
Positive Supply Voltage
Inverting Input
Rev. F | Page 8 of 20
AD628
TYPICAL PERFORMANCE CHARACTERISTICS
140
40
8440 UNITS
G = +0.1
35
120
100
25
PSRR (dB)
20
15
80
–15V
+15V
60
+2.5V
40
10
20
5
–1.2
–0.8
–0.4
0
0.4
0.8
1.2
1.6
2.0
INPUT OFFSET VOLTAGE (mV)
0
0.1
02992-C-005
0
–1.6
1
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 5. Typical Distribution of Input Offset Voltage,
VS = ±15 V, SOIC_N Package
02992-C-008
% OF UNITS
30
Figure 8. PSRR vs. Frequency, Single and Dual Supplies
1000
25
% OF UNITS
20
15
10
0
–74
–78
–82
–86
–90
–94
–98
–102
–106
–110
CMRR (dB)
100
02992-C-006
5
1
10
100
1k
10k
100k
FREQUENCY (Hz)
02992-C-009
VOLTAGE NOISE DENSITY (nV/√Hz)
8440 UNITS
Figure 9. Voltage Noise Spectral Density, RTI, VS = ±15 V
Figure 6. Typical Distribution of Common-Mode Rejection, SOIC_N Package
1000
130
VOLTAGE NOISE DENSITY (nV/√Hz)
120
110
VS = ±15V
90
80
70
VS = ±2.5V
60
50
30
10
100
1k
10k
FREQUENCY (Hz)
100k
100
1
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 10. Voltage Noise Spectral Density, RTI, VS = ±2.5 V
Figure 7. CMRR vs. Frequency
Rev. F | Page 9 of 20
02992-C-010
40
02992-C-007
CMRR (dB)
100
AD628
40
9638 UNITS
1s
35
100
30
% OF DEVICES
NOISE (5μV/DIV)
90
25
20
15
10
10
0
5
0
02992-C-011
0
10
TIME (Sec)
0
1
2
3
4
5
COMMON-MODE VOLTAGE (V)
GAIN (dB)
10
100
G = +100
30
G = +10
10
G = +1
–10
–20
9
UPPER CMV LIMIT
50
0
8
150
60
20
7
Figure 14. Typical Distribution of +1 Gain Error
Figure 11. 0.1 Hz to 10 Hz Voltage Noise, RTI
40
6
GAIN ERROR (ppm)
02992-C-014
5
G = +0.1
–40°C
50
+85°C
0
VREF = 0V
+25°C
–40°C
–50
+85°C
–100
LOWER CMV LIMIT
1k
10k
100k
1M
10M
FREQUENCY (Hz)
–150
02992-C-012
–40
100
0
5
10
15
20
VS (±V)
02992-C-015
–30
Figure 15. Common-Mode Operating Range vs.
Power Supply Voltage for Three Temperatures
Figure 12. Small Signal Frequency Response,
VOUT = 200 mV p-p, G = +0.1, +1, +10, and +100
60
500μV
50
100
OUTPUT ERROR (μV)
20
G = +10
10
0
G = +1
–10
–20
RL = 1kΩ
90
RL = 2kΩ
RL = 10kΩ
10
0
G = +0.1
4.0V
–30
–40
10
100
1k
10k
100k
FREQUENCY (Hz)
1M
02992-C-013
GAIN (dB)
30
VS = ±15V
Figure 13. Large Signal Frequency Response,
VOUT = 20 V p-p, G = +0.1, +1, +10, and +100
OUTPUT VOLTAGE (V)
Figure 16. Normalized Gain Error vs. VOUT, VS = ±15 V
Rev. F | Page 10 of 20
02992-C-016
40
G = +100
AD628
VS = ±2.5V
100μV
500mV
RL = 1kΩ
100
100
OUTPUT ERROR (μV)
90
90
RL = 2kΩ
10
0
0
50mV
02992-C-017
500mV
OUTPUT VOLTAGE (V)
4μs
02992-C-020
RL = 10kΩ
10
Figure 20. Small Signal Pulse Response,
RL = 2 kΩ, CL = 0 pF, Top: Input, Bottom: Output
Figure 17. Normalized Gain Error vs. VOUT, VS = ±2.5 V
4
500mV
BIAS CURRENT (nA)
3
100
90
2
1
10
–20
0
20
40
TEMPERATURE (°C)
60
80
100
50mV
02992-C-018
0
–40
4μs
02992-C-021
0
Figure 21. Small Signal Pulse Response,
RL = 2 kΩ, CL = 1000 pF, Top: Input, Bottom: Output
Figure 18. Bias Current vs. Temperature Buffer
15
–40°C
–25°C
500mV
+85°C
100
5
+25°C
90
0
–40°C
–5
–25°C
+85°C
+25°C
10
–10
0
5
10
15
OUTPUT CURRENT (mA)
20
25
50mV
4μs
Figure 22. Large Signal Pulse Response,
RL = 2 kΩ, CL = 1000 pF, Top: Input, Bottom: Output
Figure 19. Output Voltage Operating Range vs. Output Current
Rev. F | Page 11 of 20
02992-C-021
–15
0
02992-C-019
OUTPUT VOLTAGE SWING (V)
10
AD628
100
100
90
90
5V
5V
10mV
10mV
10
10
0
100μs
02992-C-024
100μs
02992-C-023
0
Figure 24. Settling Time to 0.01% 0 V to −10 V Step
Figure 23. Settling Time to 0.01%, 0 V to 10 V Step
Rev. F | Page 12 of 20
AD628
TEST CIRCUITS
HP3589A
SPECTRUM ANALYZER
HP3561A
+VS
SPECTRUM ANALYZER
+VS
10kΩ
–IN
10kΩ
100kΩ
AD829
OUT
–IN
–IN
G = +0.1
+IN
+IN
CFILT
4
7
–
+IN
FET
PROBE
+
–IN
G = +100
8
10kΩ
100kΩ
10kΩ
+IN
OUT
5
100kΩ
AD628
10kΩ
+IN
CFILT
VREF
1
RG
–IN
–IN
G = +0.1
+IN
100kΩ
AD628
10kΩ
VREF
RG
6
10kΩ
02992-C-025
AD707
+
Figure 27. Noise Tests
Figure 25. CMRR vs. Frequency
SCOPE
+VS
1 VAC
+15V
10kΩ
G = +100
G = +100
10kΩ
+IN
100kΩ
+IN
2
–VS
–
–IN
3
OUT
20Ω
–IN
–IN
G = +0.1
+IN
+
AD829
–
100kΩ
AD628
10kΩ
VREF
CFILT
RG
02992-C-026
–VS
Figure 26. PSRR vs. Frequency
Rev. F | Page 13 of 20
10kΩ
02992-C-027
–VS
AD628
THEORY OF OPERATION
The AD628 is a high common-mode voltage difference
amplifier, combined with a user-configurable output amplifier
(see Figure 28 and Figure 29). Differential mode voltages in
excess of 120 V are accurately scaled by a precision 11:1 voltage
divider at the input. A reference voltage input is available to the
user at Pin 3 (VREF). The output common-mode voltage of the
difference amplifier is the same as the voltage applied to the
reference pin. If the uncommitted amplifier is configured for
gain, connect Pin 3 to one end of the external gain resistor to
establish the output common-mode voltage at Pin 5 (OUT).
The uncommitted amplifier is a high open-loop gain, low offset,
low drift op amp, with its noninverting input connected to the
internal 10 kΩ resistor. Both inputs are accessible to the user.
Careful layout design has resulted in exceptional commonmode rejection at higher frequencies. The inputs are connected
to Pin 1 (+IN) and Pin 8 (−IN), which are adjacent to the power
pins, Pin 2 (−VS) and Pin 7 (+VS). Because the power pins are at
ac ground, input impedance balance and, therefore, commonmode rejection are preserved at higher frequencies.
RG
The output of the difference amplifier is internally connected
to a 10 kΩ resistor trimmed to better than ±0.1% absolute
accuracy. The resistor is connected to the noninverting input of
the output amplifier and is accessible at Pin 4 (CFILT). A
capacitor can be connected to implement a low-pass filter, a
resistor can be connected to further reduce the output voltage,
or a clamp circuit can be connected to limit the output swing.
–IN
10kΩ
100kΩ
–IN
G = +0.1
–IN
10kΩ
A1
CFILT
CFILT
+VS
AD628
10kΩ
G = +0.1
10kΩ
A1
+IN
–IN
100kΩ
10kΩ
–VS
VREF
RG
REXT3
REFERENCE
VOLTAGE
REXT2
Figure 29. Circuit Connections
Rev. F | Page 14 of 20
REXT1
02992-C-029
+IN
OUT
A2
+IN
02992-C-028
10kΩ
Figure 28. Simplified Schematic
–IN
+IN
100kΩ
VREF
–IN
OUT
+IN
+IN
100kΩ
A2
AD628
APPLICATIONS
GAIN ADJUSTMENT
INPUT VOLTAGE RANGE
The AD628 system gain is provided by an architecture
consisting of two amplifiers. The gain of the input stage
is fixed at 0.1; the output buffer is user-adjustable as
GA2 = 1 + REXT1/REXT2. The system gain is then
VREF and the supply voltage determine the common-mode
input voltage range. The relation is expressed by
(1)
REXT1
(Ω)
10 k
20 k
25.9 k
49.9 k
100 k
200 k
499 k
1M
REXT2
(Ω)
∞
20 k
18.7 k
12.4 k
11 k
10.5 k
10.2 k
10.2 k
REXT3
(Ω)
0
0
0
0
0
0
0
0
150
100
50
MAXIMUM INPUT COMMON-MODE
VOLTAGE WHEN VREF = GND
0
–50
–100
–150
–200
0
2
4
See Figure 29.
To set the system gain to less than 0.1, create an attenuator by
placing Resistor REXT4 from Pin 4 (CFILT) to the reference voltage.
A divider is formed by the 10 kΩ resistor that is in series with
the positive input of A2 and Resistor REXT4. A2 is configured for
unity gain.
Using a divider and setting A2 to unity gain yields
⎛
REXT4
GW / DIVIDER = 0.1 × ⎜
⎜ 10 kΩ + R
EXT4
⎝
6
8
10
12
14
16
SUPPLY VOLTAGE (±V)
⎞
⎟ ×1
⎟
⎠
Figure 30. Input Common-Mode Voltage vs. Supply Voltage
for Dual Supplies
100
INPUT COMMON-MODE VOLTAGE (V)
1
A2 Gain
(V/V)
1
2
2.5
5
10
20
50
100
200
02992-C-035
Table 5. Nearest Standard 1% Resistor Values for
Various Gains1
where VS+ is the positive supply, VS− is the negative supply,
and 1.2 V is the headroom needed for suitable performance.
Equation 2 provides a general formula for calculating the
common-mode input voltage range. However, keep the AD628
within the maximum limits listed in Table 1 to maintain
optimal performance. This is illustrated in Figure 30 where the
maximum common-mode input voltage is limited to ±120 V.
Figure 31 shows the common-mode input voltage bounds for
single-supply voltages.
80
60
40
20
MAXIMUM INPUT COMMON-MODE
VOLTAGE WHEN VREF = MIDSUPPLY
0
–20
–40
–60
–80
0
2
4
6
8
10
12
14
SINGLE-SUPPLY VOLTAGE (V)
Figure 31. Input Common-Mode Voltage vs.
Supply Voltage for Single Supplies
Rev. F | Page 15 of 20
16
02992-C-034
At a 2 nA maximum, the input bias current of the buffer amplifier
is very low and any offset voltage induced at the buffer amplifier
by its bias current may be neglected (2 nA × 10 kΩ = 20 μV).
However, to absolutely minimize bias current effects, select REXT1
and REXT2 so that their parallel combination is 10 kΩ. If practical
resistor values force the parallel combination of REXT1 and REXT2
below 10 kΩ, add a series resistor (REXT3) to make up for the
difference. Table 5 lists several values of gain and corresponding
resistor values.
Total Gain
(V/V)
0.1
0.2
0.25
0.5
1
2
5
10
(2)
VCM LOWER ≥ 11 (VS − + 1.2 V ) − 10 VREF
⎞
⎛ R
= 0.1 × ⎜⎜1 + EXT1 ⎟⎟
⎝ R EXT2 ⎠
INPUT COMMON-MODE VOLTAGE (V)
GTOTAL
VCMUPPER ≤ 11 (VS + – 1.2 V ) − 10 VREF
AD628
The differential input voltage range is constrained to the linear
operation of the internal amplifiers A1 and A2. The voltage
applied to the inputs of A1 and A2 should be between
VS− + 1.2 V and VS+ − 1.2 V. Similarly, the outputs of A1 and A2
should be kept between VS− + 0.9 V and VS+ − 0.9 V.
•
VOLTAGE LEVEL CONVERSION
•
Industrial signal conditioning and control applications typically
require connections between remote sensors or amplifiers and
centrally located control modules. Signal conditioners provide
output voltages of up to ±10 V full scale. However, ADCs or
microprocessors operating on single 3.3 V to 5 V logic supplies
are now the norm. Thus, the controller voltages require further
reduction in amplitude and reference.
Furthermore, voltage potentials between locations are seldom
compatible, and power line peaks and surges can generate
destructive energy between utility grids. The AD628 offers an
ideal solution to both problems. It attenuates otherwise destructive signal voltage peaks and surges by a factor of 10 and shifts
the differential input signal to the desired output voltage.
Conversion from voltage-driven or current-loop systems is
easily accomplished using the circuit shown in Figure 32. This
shows a circuit for converting inputs of various polarities and
amplitudes to the input of a single-supply ADC.
To adjust common-mode output voltage, connect Pin 3 (VREF)
and the lower end of the 10 kΩ resistor to the desired voltage.
The output common-mode voltage is the same as the reference
voltage.
Designing such an application can be done in a few simple
steps, including the following:
Determine the required gain. For example, if the input
voltage must be transformed from ±10 V to 0 V to +5 V,
the gain is +5/+20 or +0.25.
Determine if the circuit common-mode voltage should be
changed. An AD7940 ADC is illustrated for this example.
When operating from a 5 V supply, the common-mode
voltage of the AD7940 is half the supply, or 2.5 V. If the
AD628 reference pin and the lower terminal of the 10 kΩ
resistor are connected to a 2.5 V voltage source, the output
common-mode voltage is 2.5 V.
Table 6 shows resistor and reference values for commonly used
single-supply converter voltages. REXT3 is included as an option
to balance the source impedance into A2. This is described in
more detail in the Gain Adjustment section.
Table 6. Nearest 1% Resistor Values for Voltage Level
Conversion Applications
Input
Voltage (V)
±10
±5
10
5
±10
±5
10
5
Rev. F | Page 16 of 20
ADC
Supply
Voltage (V)
5
5
5
5
3
3
3
3
Desired
Output
Voltage (V)
2.5
2.5
2.5
2.5
1.25
1.25
1.25
1.25
VREF
(V)
2.5
2.5
0
0
1.25
1.25
0
0
REXT1
(kΩ)
15
39.7
39.7
89.8
2.49
15
15
39.7
REXT2
(kΩ)
10
10
10
10
10
10
10
10
AD628
+12V
–12V
0.1μF
–IN
8
+/–10V
7
10μF
0.1μF
+Vs
–Vs
2
AD628
10kΩ
100kΩ
+IN
1
10μF
SCLK 4
10kΩ
A1
A2
100kΩ
49.9Ω
5
CFILT
3
6
4
AD7940 SDATA 5
VDD
GND
2
33nF
10kΩ
VREF
3 VIN
CS 6
1
RG
VOUT
REXT2
10kΩ
AD628 REFERENCE VOLTAGE
1
10μF
0.1μF
REXT1
15kΩ
15nF
SERIAL DATA
2
AD8606
1/2
7
3
8
5
AD8606
2/2
6
4
0.1μF
10μF
2
6
VIN
+12V
REF195
3
4
02992-030
10kΩ
10kΩ
Figure 32. Level Shifter
CURRENT LOOP RECEIVER
MONITORING BATTERY VOLTAGES
Analog data transmitted on a 4 to 20 mA current loop can be
detected with the receiver shown in Figure 33. The AD628 is an
ideal choice for such a function because the current loop is
driven with a compliance voltage sufficient to stabilize the loop,
and the resultant common-mode voltage often exceeds commonly used supply voltages. Note that with large shunt values, a
resistance of equal value must be inserted in series with the
inverting input to compensate for an error at the noninverting
input.
Figure 34 illustrates how the AD628 is used to monitor a battery
charger. Voltages approximately eight times the power supply
voltage can be applied to the input with no damage. The resistor
divider action is well-suited for the measurement of many
power supply applications, such as those found in battery
chargers or similar equipment.
VCM = 15V
+15V –15V
3
7
2
4
AD628
10kΩ
249Ω
1
100kΩ
10kΩ
5
249Ω
8
100kΩ
0V TO 5V
TO ADC
10kΩ
6
210kΩ
+2.5V
100kΩ
9.53kΩ
Figure 33. Level Shifter for 4 to 20 mA Current Loop
Rev. F | Page 17 of 20
02992-C-031
I = 4 TO 20mA
AD628
5V
+VS
nVBAT(V)
100kΩ
10kΩ
10kΩ
+IN
–IN
G = +0.1
–IN
REXT1
10kΩ
A1
+IN
+1.5V
BATTERY
OTHER
BATTERIES IN
CHARGING
CIRCUIT
0V TO 5V
TO ADC
OUT
A2
RG
100kΩ
+IN
AD628
10kΩ
–VS
VREF
02992-C-032
CHARGING
CIRCUIT
–IN
CFILT
Figure 34. Battery Voltage Monitor
FILTER CAPACITOR VALUES
KELVIN CONNECTION
Connect a capacitor to Pin 4 (CFILT) to implement a low-pass
filter. The capacitor value is
In certain applications, it may be desirable to connect the
inverting input of an amplifier to a remote reference point.
This eliminates errors resulting in circuit losses in interconnecting wiring. The AD628 is particularly suited for this type of
connection. In Figure 35, a 10 kΩ resistor added in the feedback
matches the source impedance of A2. This is described in more
detail in the Gain Adjustment section.
where ft is the desired 3 dB filter frequency.
Table 7 shows several frequencies and their closest standard
capacitor values.
5V
Table 7. Capacitor Values for Various Filter Frequencies
Frequency (Hz)
10
50
60
100
400
1k
5k
10 k
Capacitor Value (μF)
1.5
0.33
0.27
0.15
0.039
0.015
0.0033
0.0015
+VS
–IN
100kΩ
10kΩ
–IN
10kΩ
+IN
A2
–IN
G = +0.1
OUT
CIRCUIT
LOSS
RG
10kΩ
A1
+IN
100kΩ
LOAD
+IN
10kΩ
AD628
–VS
VREF
CFILT
VS /2
Figure 35. Kelvin Connection
Rev. F | Page 18 of 20
02992-C-033
C = 15.9/ft (μF)
AD628
OUTLINE DIMENSIONS
3.20
3.00
2.80
8
3.20
3.00
2.80
1
5.00 (0.1968)
4.80 (0.1890)
5
5.15
4.90
4.65
8
4.00 (0.1574)
3.80 (0.1497) 1
4
PIN 1
0.25 (0.0098)
0.10 (0.0040)
1.10 MAX
0.15
0.00
0.38
0.22
COPLANARITY
0.10
0.23
0.08
8°
0°
6.20 (0.2440)
4 5.80 (0.2284)
1.27 (0.0500)
BSC
0.65 BSC
0.95
0.85
0.75
5
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0201)
COPLANARITY
SEATING 0.31 (0.0122)
0.10
PLANE
0.80
0.60
0.40
SEATING
PLANE
0.50 (0.0196)
× 45°
0.25 (0.0099)
8°
0.25 (0.0098) 0° 1.27 (0.0500)
0.40 (0.0157)
0.17 (0.0067)
COMPLIANT TO JEDEC STANDARDS MS-012-AA
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.
COMPLIANT TO JEDEC STANDARDS MO-187-AA
Figure 36. 8-Lead Mini Small Outline Package [MSOP]
(RM-8)
Dimensions shown in millimeters
Figure 37. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body
(R-8)
Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model
AD628AR
AD628AR-REEL
AD628AR-REEL7
AD628ARZ 1
AD628ARZ-RL1
AD628ARZ-R71
AD628ARM
AD628ARM-REEL
AD628ARM-REEL7
AD628ARMZ1
AD628ARMZ-RL1
AD628ARMZ-R71
AD628-EVAL
1
Temperature Range
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
Description
8-Lead SOIC_N
8-Lead SOIC_N 13" Reel
8-Lead SOIC_N 7" Reel
8-Lead SOIC_N
8-Lead SOIC_N 13" Reel
8-Lead SOIC_N 7" Reel
8-Lead MSOP
8-Lead MSOP 13" Reel
8-Lead MSOP 7" Reel
8-Lead MSOP
8-Lead MSOP 13" Reel
8-Lead MSOP 7" Reel
Evaluation Board
Z = Pb-free part.
Rev. F | Page 19 of 20
Package Option
R-8
R-8
R-8
R-8
R-8
R-8
RM-8
RM-8
RM-8
RM-8
RM-8
RM-8
Branding
JGA
JGA
JGA
JGZ
JGZ
JGZ
AD628
NOTES
©2006 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
C02992-0-3/06(F)
T
T
Rev. F | Page 20 of 20