AD8213

Rev. 0 | Page 10 of 16

THEORY OF OPERATION

In typical applications, the AD8213 amplifies a small differential

input voltage generated by the load current flowing through a

shunt resistor. The AD8213 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 25 shows a simplified schematic of the AD8213.

The following explanation refers exclusively to Channel 1 of the

AD8213, however, the same explanation applies to Channel 2.

A load current flowing through the external shunt resistor

produces a voltage at the input terminals of the AD8213. The

forces the noninverting input to the same potential. Therefore,

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

Prior to the buffer amplifier, a precision-trimmed 20 kΩ resistor

is available to perform low-pass filtering of the input signal

prior to the amplification stage. This means that the noise of the

input signal is not amplified, but rejected, resulting in a more

precise output signal that will directly interface with a converter.

A capacitor from the CF1 pin to GND, will result in a low-pass

filter with a corner frequency of

()

FILTER

dB

C

f

20000

2

1

3

π

=

−

A2

G = +20

PROPRIETARY

OFFSET

CIRCUITRY

CF2

A1

G = +20

PROPRIETARY

OFFSET

CIRCUITRY

CF1

GND

V+

AD8213

20kΩ

20kΩ

Q2

Q1

Figure 25. Simplified Schematic