High Common-Mode Voltage
Programmable Gain Difference Amplifier
AD628
FUNCTIONAL BLOCK DIAGRAM
FEATURES
High Common-Mode InputVoltage Range
120V atVS = 1ꢀV
R
R
EXT1
EXT2
Gain Range +0.01 to +100
OperatingTemperature Range
–40ºC to +8ꢀºC
+V
S
R
G
SupplyVoltage Range
Dual Supply: 2.2ꢀV to 18V
Single Supply: +4.ꢀV to +36V
Excellent AC and DC Performance
OffsetTemperature Stability RTI
10 ꢀV/ºC Max
100kꢁ
10kꢁ
–IN
+IN
AD628
G = +0.1
–IN
+IN
OUT
A2
–IN
10kꢁ
A1
+IN
100kꢁ
Offset
10kꢁ
1.ꢀV mV Max
CMRR RTI
7ꢀ dB Min, DC to ꢀ00 Hz, G = 1
–V
V
S
REF
C
FILT
APPLICATIONS
HighVoltage Current Shunt Sensing
Programmable Logic Controllers
Analog Input Front End Signal Conditioning:
+ꢀV, +10V, ꢀV, 10V and 4 to 20 mA
Isolation
Sensor Signal Conditioning
Power Supply Monitoring
Electro-Hydraulic Control
Motor Control
130
120
110
100
V
= ؎15V
S
90
80
70
V
= ؎2.5V
S
60
50
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 A/D converters. A wideband feedback
loop minimizes distortion effects due to capacitor charging of
sigma-delta A/D converters.
40
30
10
100
1k
FREQUENCY – Hz
10k
100k
Figure 1. CMRR vs. Frequency of the AD628
A reference pin (VREF) provides a dc offset for converting bipo-
lar to single-sided signals.The AD628 converts +5 V, +10 V,
5 V, and 10 V and 4 to 20 mA input signals to a single-ended
output within the input range of single-supply A/D converters.
A precision 10 k⍀ resistor connected to an external pin is pro-
vided for either a low-pass filter or to attenuate large differential
input signals. A single capacitor implements a low-pass filter.
The AD628 has an input common-mode and differential mode
operating range of 120V. The high common-mode input
impedance makes the device well suited for high voltage measure-
ments across a shunt resistor.The buffer amplifier inverting input
is available for making a remote Kelvin connection.
The AD628 operates from single- and dual-supplies and is
available in an 8-lead SOIC package. Contact the factory for
availability in MSOP package. It operates over the standard
industrial temperature range of –40ºC to +85ºC.
REV.0
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