AD8210

Rev. 0 | Page 10 of 16

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. 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 Resistor R1 and

Resistor R2. A1 nulls the voltage appearing across its own input

terminals by adjusting the current through R1 and R2 with

Transistor Q1 and Transistor 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.

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.

AD8210

A2

R1

R2

GND

A1

R3

R4

Q1

Q2

Figure 26. Simplified Schematic