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
7
S
R
G
6
Operating temperature range: −40°C to +8ꢀ°C
Supply voltage range
Dual supply: 2.2ꢀ V to 18 V
100kΩ
100kΩ
10kΩ
8
–IN
+IN
G = +0.1
–IN
+IN
OUT
A2
5
–IN
10kΩ
Single supply: 4.ꢀ V to 36 V
A1
+IN
Excellent ac and dc performance
Offset temperature stability RTI: 10 μV/°C maximum
Offset: 1.ꢀ V mV maximum
1
10kΩ
AD628
CMRR RTI: 7ꢀ dB minimum, dc to ꢀ00 Hz, G = +1
2
3
4
–V
V
REF
S
C
FILT
APPLICATIONS
Figure 1.
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
Sensor signal conditioning
Power supply monitoring
Electrohydraulic controls
130
120
110
100
90
V
= ±15V
S
Motor controls
80
70
GENERAL DESCRIPTION
V
= ±2.5V
S
60
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.
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_N or an 8-lead MSOP. 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 inverting input of
the buffer amplifier is available for making a remote Kelvin
connection.
Rev. G
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