AD8206

Rev. 0 | Page 8 of 12

THEORY OF OPERATION

The AD8206 is a single-supply difference amplifier that uses

a unique architecture to accurately amplify small differential

current shunt voltages in the presence of rapidly changing

common-mode voltage. It is offered in both packaged and

die form.

In typical applications, the AD8206 is used to measure current

by amplifying the voltage across a current shunt placed across

the inputs.

The gain of the AD8206 is 20 V/V, with an accuracy of 1.2%.

This accuracy is guaranteed over the operating temperature

range of −40°C to +125°C. The die temperature range is

−40°C to +150°C with a guaranteed gain accuracy of 1.3%.

The input offset is less than 2 mV referred to the input at 25°C,

and 4.5 mV maximum referred to the input over the full

operating temperature range for the packaged part. The die

input offset is less than 6 mV referred to the input over the die

operating temperature range.

The AD8206 operates with a single supply from 4.5 V to

10 V (absolute maximum = 12.5 V). The supply current is

less than 2 mA.

High accuracy trimming of the internal resistors allows the

AD8206 to have a typical common-mode rejection ratio better

than 80 dB from dc to 20 kHz. The minimum common-mode

rejection ratio over the operating temperature is 76 dB for both

the die and packaged part.

The output offset can be adjusted from 0.08 V to 4.7 V

The AD8206 consists of two amplifiers (A1 and A2), a

resistor network, a small voltage reference, and a bias

circuit (not shown), see Figure 16.

voltage range of A1. The two attenuators form a balanced bridge

network. When the bridge is balanced, the differential voltage

created by a common-mode voltage is 0 V at the inputs of A1.

The input attenuation ratio is 1/16.7. The combined series

By attenuating the voltages at Pin 1 and Pin 8, the A1 amplifier

inputs are held within the power supply range, even if Pin 1

and Pin 8 exceed the supply or fall below common (ground). A

reference voltage of 250 mV biases the attenuator above ground.

This allows the amplifier to operate in the presence of negative

common-mode voltages.

The input network also attenuates normal (differential) mode

voltages. A1 amplifies the attenuated signal by 26. The input

and output of this amplifier are differential to maximize the

ac common-mode rejection.

A2 converts the differential voltage from A1 into a single-ended

signal and provides further amplification. The gain of this

second stage is 12.86.

to the positive input of A2, which allows the output offset to be

adjusted anywhere in the output operating range. The gain is

1 V/V from the reference pins to the output when the reference

pins are used in parallel. The gain is 0.5 V/V when they are used

to divide the supply.

high level of precision to allow the common-mode rejection

ratio to exceed 80 dB. This is accomplished by laser trimming

the resistor ratio matching to better than 0.01%.

The total gain of 20 is made up of the input attenuation of

1/16.7 multiplied by the first stage gain of 26 and the second

stage gain of 12.86.

The output stage is a Class A with a PNP pull-up transistor and

a 300 μA current sink pull-down.

AD8206

+IN

–IN

250mV

GND

A1

A2

Figure 16. Simplified Schematic