AD8213

Data Sheet

Rev. D | Page 10 of 14

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

can perform the low-pass filtering of the input signal prior to the

amplification stage. By using this resistor, the noise of the input

signal does not amplify but is rejected, resulting in a more precise

output signal that directly interfaces with a converter. A capacitor

from the CF1 pin to GND, results in a low-pass filter with a

corner frequency of



FILTER

dB

C

f

20000

2

1

3







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