
High Common-Mode Voltage,
Programmable Gain Difference Amplifier
AD628
Rev. G
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FEATURES
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
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 controls
Motor controls
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 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.
FUNCTIONAL BLOCK DIAGRAM
+IN
–IN
+IN
–IN
–VS
VREF
REXT1
RG
+VS
REXT2
CFILT
A2
A1
+IN
–IN
100k
10k
AD628
OUT
G = +0.1
8
1
2
3
4
5
6
7
0
2992
-001
Figure 1.
30
40
50
60
70
80
90
100
110
120
130
CM
RR
(
d
B)
FREQUENCY (Hz)
100
10
1k
10k
100k
02
99
2-
0
02
VS = ±2.5V
VS = ±15V
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 low-
pass filter. The AD628 operates from single and dual supplies
and is available in an 8-lead SOIC_N or an 8-lead MSOP. It
operates over the standard industrial temperature range of
40°C to +85°C.