AD8210_12 Datasheet, PDF (10/16 Pages) Analog Devices – High Voltage, Bidirectional Current Shunt Monitor

AD8210
THEORY OF OPERATION
In typical applications, the AD8210 amplifies a small differential
input voltage generated by the load current flowing through a
shunt resistor. The AD8210 rejects high common-mode voltages
(up to 65 V) and provides a ground referenced buffered output
that interfaces with an analog-to-digital converter (ADC).
Figure 26 shows a simplified schematic of the AD8210.
The AD8210 is comprised of two main blocks, a differential
amplifier and an instrumentation amplifier. A load current
flowing through the external shunt resistor produces a voltage
at the input terminals of the AD8210. The input terminals are
connected to the differential amplifier (A1) by R1 and R2. A1
nulls the voltage appearing across its own input terminals by
adjusting the current through R1 and R2 with Q1 and Q2.
When the input signal to the AD8210 is 0 V, the currents in R1
and R2 are equal. When the differential signal is nonzero, the
current increases through one of the resistors and decreases in
the other. The current difference is proportional to the size and
polarity of the input signal.
Data Sheet
The differential currents through Q1 and Q2 are converted
into a differential voltage by R3 and R4. A2 is configured as an
instrumentation amplifier. The differential voltage is converted
into a single-ended output voltage by A2. The gain is internally
set with precision-trimmed, thin film resistors to 20 V/V.
The output reference voltage is easily adjusted by the VREF1 pin
and the VREF2 pin. In a typical configuration, VREF1 is connected
to VCC while VREF2 is connected to GND. In this case, the output
is centered at VCC/2 when the input signal is 0 V.
I_SHUNT
R_SHUNT
R1
R2
V_S
AD8210
A1
V_REF1
Q1
Q2
V_OUT = (I_SHUNT × R_SHUNT) × 20
A2
R3
R4
GND
V_REF2
Figure 26. Simplified Schematic
Rev. C | Page 10 of 16