AD8211

Rev. A | Page 10 of 16

THEORY OF OPERATION

In typical applications, the AD8211 amplifies a small differential

input voltage generated by the load current flowing through

a shunt resistor. The AD8211 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 23 shows a simplified schematic of the AD8211.

V+

G = +20

AD8211

A1

PROPRIETARY

OFFSET

CIRCUITRY

GND

R1

Q1

R

Figure 23. Simplified Schematic

A load current flowing through the external shunt resistor

produces a voltage at the input terminals of the AD8211. The

input terminals are connected to Amplifier A1 by Resistor R

and Resistor R1. The inverting terminal, which has very high

input impedance is held to

because negligible current flows through Resistor R. Amplifier

A1 forces the noninverting input to the same potential. Therefore,

the current that flows through Resistor R1, is equal to

output buffer amplifier has a gain of 20 V/V and offers excellent

accuracy as the internal gain setting resistors are precision trimmed

to within 0.01% matching. The resulting output voltage is equal to