High Common-Mode Voltage
Programmable Gain Difference Amplifier
AD628
FUNCTIONAL BLOCK DIAGRAM
FEATURES
R
R
EXT1
EXT2
High common-mode input voltage range
120 V at VS = 1ꢀ V
Gain range 0.1 to 100
+V
S
R
G
Operating temperature range: −40°C to 8ꢀ°C
Supply voltage range
Dual supply: 2.2ꢀ V to 18 V
Single supply: 4.ꢀ V to 36 V
Excellent ac and dc performance
Offset temperature stability RTI: 10 µV/°C max
Offset: 1.ꢀ V mV max
100kΩ
10kΩ
–IN
+IN
G = +0.1
–IN
+IN
OUT
A2
–IN
10kΩ
A1
+IN
100kΩ
10kΩ
AD628
CMRR RTI: 7ꢀ dB min, dc to ꢀ00 Hz, G = +1
–V
V
S
REF
APPLICATIONS
C
FILT
High voltage current shunt sensing
Programmable logic controllers
Analog input front end signal conditioning
+ꢀ V, +10 V, ꢀ V, 10 V and 4 to 20 mA
Isolation
Figure 1.
130
120
110
100
90
Sensor signal conditioning
Power supply monitoring
Electrohydraulic control
Motor control
V
= ±15V
S
GENERAL DESCRIPTION
80
70
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.
V
= ±2.5V
S
60
50
40
30
10
100
1k
FREQUENCY (Hz)
10k
100k
Figure 2. CMRR vs. Frequency of the AD628
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.
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 low-
pass 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.
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.
Rev. C
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