AD8202

Rev. D | Page 14 of 20

APPLICATIONS

The AD8202 difference amplifier is intended for applications that

require extracting a small differential signal in the presence of

large common-mode voltages. The differential input resistance

is nominally 325 kΩ, and the device can tolerate common-mode

voltages higher than the supply voltage and lower than ground.

The open collector output stage sources current to within

CURRENT SENSING

High Line, High Current Sensing

Basic automotive applications using the large common-mode

range are shown in Figure 2 and Figure 3. The capability of the

device to operate as an amplifier in primary battery supply

circuits is shown in Figure 2; Figure 3 illustrates the ability

of the device to withstand voltages below system ground.

Low Current Sensing

The AD8202 is also used in low current sensing applications,

such as the 4 to 20 mA current loop shown in Figure 42. In such

applications, the relatively large shunt resistor can degrade the

common-mode rejection. Adding a resistor of equal value on the

low impedance side of the input corrects for this error.

5V

OUTPUT

10

Ω

1%

10

Ω

1%

NC = NO CONNECT

+

GND

NC

–IN

+IN

A1

A2

OUT

AD8202

Figure 42. 4 to 20 mA Current Loop Receiver

GAIN ADJUSTMENT

The default gain of the preamplifier and buffer are ×10 and ×2,

respectively, resulting in a composite gain of ×20. With the

addition of external resistor(s) or trimmer(s), the gain can be

lowered, raised, or finely calibrated.

Gains Less than 20

Because the preamplifier has an output resistance of 100 kΩ,

an external resistor connected from Pin 3 and Pin 4 to GND

in Figure 43.

10k

Ω

10k

Ω

100k

Ω

A2

A1

GND

–IN

OUT

NC

+IN

AD8202

OUT

2

GAIN =

GAIN

20 – GAIN

2

NC = NO CONNECT

Figure 43. Adjusting for Gains Less than 20

The overall bandwidth is unaffected by changes in gain by using

this method, although there may be a small offset voltage due

to the imbalance in source resistances at the input to the buffer.

This can often be ignored, but if desired, it can be nulled by

(yielding a composite gain of ×10), the optional offset nulling

resistor is 50 kΩ.

Gains Greater Than 20

Connecting a resistor from the output of the buffer amplifier

to its noninverting input, as shown in Figure 44, increases the

gains as high as 50 are achievable in this way. The accuracy of

the gain becomes critically dependent on the resistor value at

high gains. Also, the effective input offset voltage at Pin 1 and

Pin 8 (about six times the actual offset of A1) limits the part’s

use in high gain, dc-coupled applications.

10k

Ω

10k

Ω

100k

Ω

A2

A1

GND

–IN

OUT

NC

+IN

AD8202

OUT

2

GAIN =

GAIN

GAIN – 20

2

NC = NO CONNECT

Figure 44. Adjusting for Gains > 20