High Common-Mode Voltage,
Programmable Gain Difference Amplifier
AD628
FUNCTIONAL BLOCK DIAGRAM
FEATURES
High common-mode input voltage range
±±12 V at VS = ±±ꢀ V
Gain range 2.± to ±22
R
R
EXT1
EXT2
+V
S
R
G
Operating temperature range: −42°C to ±ꢁꢀ°C
Supply voltage range
Dual supply: ±1.1ꢀ V to ±±ꢁ V
100kΩ
10kΩ
–IN
+IN
G = +0.1
–IN
+IN
OUT
A2
Single supply: 4.ꢀ V to 36 V
–IN
10kΩ
A1
Excellent ac and dc performance
Offset temperature stability RTI: ±2 μV/°C maximum
Offset: ±±.ꢀ V mV maximum
+IN
100kΩ
10kΩ
AD628
CMRR RTI: 7ꢀ dB minimum, dc to ꢀ22 Hz, G = +±
–V
V
S
REF
APPLICATIONS
C
FILT
High voltage current shunt sensing
Programmable logic controllers
Analog input front end signal conditioning
+ꢀ V, +±2 V, ±ꢀ V, ±±2 V, and 4 to 12 mA
Isolation
Sensor signal conditioning
Power supply monitoring
Electrohydraulic control
Figure 1.
130
120
110
100
90
V
= ±15V
S
Motor control
80
GENERAL DESCRIPTION
70
V
= ±2.5V
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.
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_N or 8-lead 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 inverting input of the
buffer amplifier is available for making a remote Kelvin
connection.
Rev. F
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