ANALOG DEVICES AD628 Service Manual

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High Common-Mode Voltage

Programmable Gain Difference Amplifier

FEATURES

High common-mode input voltage range

±120 V at 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 max
Offset: ±1.5 V mV max
CMRR RTI: 75 dB min, dc to 500 Hz, G = +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

GENERAL DESCRIPTION

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 ∑-∆ ADCs.

A reference pin (V
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 buffer amplifier’s
inverting input is available for making a remote Kelvin
connection.

= ±15 V

S

) provides a dc offset for converting

REF

AD628

FUNCTIONAL BLOCK DIAGRAM

R

+V

S

100kΩ

IN

100kΩ

IN

–V

10kΩ

G = +0.1

–IN

A1

+IN

10kΩ

V

S

REF

10kΩ

C

FILT

Figure 1.

130

120

110

100

90

80

CMRR (dB)

70

60

50

40

30

10010 1k 10k 100k

VS = ±15V

FREQUENCY (Hz)

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 or MSOP package. It operates over
the standard industrial temperature range of −40°C to +85°C.

EXT2

R

VS = ±2.5V

R

EXT1

G

–IN

+IN

AD628

A2

OUT

02992-C-001

02992-C-002

Rev. C

Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] www.analog.com
Fax: [phone] © 2004 Analog Devices, Inc. All rights reserved.

AD628

TABLE OF CONTENTS

Specifications..................................................................................... 3

REVISION HISTORY

Absolute Maximum Ratings............................................................ 7

ESD Caution.................................................................................. 7

Pin Configuration and Function Descriptions............................. 8

Typical Performance Characteristics ............................................. 9

Test Circuits..................................................................................... 13

Theory of Operation ...................................................................... 14

Applications..................................................................................... 15

Gain Adjustment......................................................................... 15

Input Voltage Range ................................................................... 15

Voltage Level Conversion.......................................................... 16

Current Loop Receiver............................................................... 17

Monitoring Battery Voltages..................................................... 17

Filter Capacitor Values............................................................... 18

Kelvin Connection .....................................................................18

Outline Dimensions....................................................................... 19

Ordering Guide........................................................................... 19

4/04—Data Sheet Changed from 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—Data Sheet Changed from 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—Data Sheet Changed from Rev. 0 to Rev. A

Change to Ordering Guide............................................................. 4

11/02—Rev. 0: Initial Version

Rev. C | Page 2 of 20

AD628

SPECIFICATIONS

TA = 25°C, VS = ±15 V, RL = 2 kΩ, R

Table 1.

AD628AR AD628ARM
Parameter Conditions Min Typ Max Min Typ Max Unit

DIFF AMP + OUTPUT AMP

Gain Equation G = +0.1(1+ R

Gain Range See Figure 29. 0.11 100 0.11 100 V/V

Offset Voltage

vs. Temperature 4 8 4 8 µV/°C

CMRR

500 Hz. 75 75 dB

Minimum CMRR Over Temperature −40°C to +85°C. 70 70 dB

vs. Temperature 1 4 1 4 (µV/V)/°C
PSRR (RTI) VS = ±10 V to ±18 V. 77 94 77 94 dB
Input Voltage Range

Common Mode −120 +120 −120 +120 V

Differential −120 +120 −120 +120 V
Dynamic Response

Small Signal BW –3 dB G = +0.1. 600 600 kHz

Full Power Bandwidth 5 5 kHz

Settling Time G = +0.1, to 0.01%, 100 V step. 40 40 µs

Slew Rate 0.3 0.3 V/µs
Noise (RTI)

Spectral Density 1 kHz. 300 300 nV/√Hz

0.1 Hz to 10 Hz. 15 15 µV p-p
DIFF-AMP

Gain 0.1 0.1 V/V

Error −0.1 +0.01 +0.1 −0.1 +0.01 +0.1 %

vs. Temperature 5 5 ppm/°C

Nonlinearity 5 5 ppm

vs. Temperature 3 10 3 10 ppm

Offset Voltage RTI of input pins. −1.5 +1.5 −1.5 +1.5 mV

vs. Temperature 8 8 µV/°C
Input Impedance

Differential 220 220 kΩ

Common Mode 55 55 kΩ
CMRR

500 Hz. 75 75 dB

Minimum CMRR Over Temperature −40°C to +85°C. 70 70 dB

vs. Temperature 1 4 1 4 (µV/V)/°C

Output Resistance 10 10 kΩ

Error −0.1 +0.1 −0.1 +0.1 %

= 10 kΩ, R

EXT1

V

OCM

EXT2

= ∞, V

= 0 unless otherwise noted.

REF

EXT1/REXT2

). V/V

= 0 V. RTI of input pins2.

−1.5 +1.5 −1.5 +1.5 mV

Output amp G = +1.

RTI of input pins.

75 75 dB

G = +0.1 to +100.

RTI of input pins.

75 75 dB

G = +0.1 to +100.

Rev. C | Page 3 of 20

AD628

AD628AR AD628ARM
Parameter Conditions Min Typ Max Min Typ Max Unit

OUTPUT AMPLIFIER

Gain Equation G = (1 + R

Nonlinearity G = +1, V

EXT1/REXT2

OUT

Offset Voltage RTI of output amp. −0.15 +0.15 −0.15 +0.15 mV

vs. Temperature 0.6 0.6 µV/°C
Output Voltage Swing RL = 10 kΩ. −14.2 +14.1 −14.2 +14.1 V
R

= 2 kΩ. −13.8 +13.6 −13.8 +13.6 V

L

Bias Current 1.5 3 1.5 3 nA
Offset Current 0.2 0.5 0.2 0.5 nA
CMRR VCM = ±13 V. 130 130 dB
Open-Loop Gain V

= ±13 V. 130 130 dB

OUT

POWER SUPPLY

Operating Range ±2.25 ±18 ±2.25 ±18 V
Quiescent Current 1.6 1.6 mA

TEMPERATURE RANGE –40 +85 –40 +85 °C

1

To use a lower gain, see the Gain Adjustment section.

2

The addition of the difference amp’s and output amp’s offset voltage does not exceed this specification.

). V/V

= ±10 V. 0.5 0.5 ppm

Rev. C | Page 4 of 20

AD628

TA = 25°C, VS = +5 V, RL = 2 kΩ, R

Table 2.

AD628AR AD628ARM

Parameter Conditions Min Typ Max Min Typ Max Unit

DIFF AMP + OUTPUT AMP

Gain Equation G = +0.1(1+ R
Gain Range See Figure 29. 0.11 100 0.11 100 V/V
Offset Voltage

vs. Temperature 6 15 6 15 µV/°C

CMRR RTI of input pins. G = 0.1 to 100. 75 75 dB

500 Hz. 75 75 dB

Minimum CMRR Over Temperature −40°C to +85°C. 70 70 dB

vs. Temperature 1 4 1 4 (µV/V)/°C
PSRR (RTI) VS = 4.5 V to 10 V. 77 94 77 94 dB
Input Voltage Range

Common Mode3 −12 +17 −12 +17 V

Differential −15 +15 −15 +15 V
Dynamic Response

Small Signal BW –3 dB G = +0.1. 440 440 kHz

Full Power Bandwidth 30 30 kHz

Settling Time G = +0.1, to 0.01%, 30 V step. 15 15 µs

Slew Rate 0.3 0.3 V/µs
Noise (RTI)

Spectral Density 1 kHz. 350 350 nV/√Hz

0.1 Hz to 10 Hz. 15 15 µV p-p
DIFF-AMP

Gain 0.1 0.1 V/V

Error –0.1 +0.01 +0.1 –0.1 +0.01 +0.1 %

Nonlinearity 3 3 ppm

vs. Temperature 3 10 3 10 ppm

Offset Voltage RTI of input pins. −2.5 +2.5 −2.5 +2.5 mV

vs. Temperature 10 10 µV/°C
Input Impedance

Differential 220 220 kΩ

Common Mode 55 55 kΩ
CMRR RTI of input pins. G = +0.1 to +100. 75 75 dB

500 Hz. 75 75 dB

Minimum CMRR Over Temperature −40°C to +85°C. 70 70 dB

vs. Temperature 1 4 1 4 (µV/V)/°C

Output Resistance 10 10 kΩ

Error −0.1 +0.1 −0.1 +0.1 %

OUTPUT AMPLIFIER

Gain Equation G = (1 + R

Nonlinearity G = +1, V
Output Offset Voltage RTI of output amp. −0.15 0.15 −0.15 0.15 mV

vs. Temperature 0.6 0.6 µV/°C
Output Voltage Swing RL = 10 kΩ. 0.9 4.1 0.9 4.1 V
R
Bias Current 1.5 3 1.5 3 nA
Offset Current 0.2 0.5 0.2 0.5 nA
CMRR VCM = 1 V to 4 V. 130 130 dB
Open-Loop Gain V

= 10 kΩ, R

EXT1

= ∞, V

EXT2

= 2.25 V. RTI of input pins2.

V

OCM

= +2.5 unless otherwise noted.

REF

EXT1/REXT2

). V/V

−3.0 +3.0 −3.0 +3.0 mV

Output Amp G = +1.

EXT1/REXT2

OUT

= 2 kΩ. 1 4 1 4 V

L

= 1 V to 4 V. 130 130 dB

OUT

). V/V

= 1 V to 4 V. 0.5 0.5 ppm

Rev. C | Page 5 of 20

AD628

AD628AR AD628ARM
Parameter Conditions Min Typ Max Min Typ Max Unit

POWER SUPPLY

Operating Range ±2.25 +36 ±2.25 +36 V
Quiescent Current 1.6 1.6 mA

TEMPERATURE RANGE −40 +85 −40 +85 °C

1

To use a lower gain, see the Gain Adjustment section.

2

The addition of the difference amp’s and output amp’s offset voltage does not exceed this specification.

3

Greater values of voltage are possible with greater or lesser values of V

.

REF

Rev. C | Page 6 of 20