AD8207

Rev. 0 | Page 12 of 16

OUTPUT OFFSET ADJUSTMENT

The output of the AD8207 can be adjusted for unidirectional or

bidirectional operation.

UNIDIRECTIONAL OPERATION

Unidirectional operation allows the AD8207 to measure

currents through a resistive shunt in one direction. The basic

modes for unidirectional operation are ground referenced

output mode and V+ referenced output mode.

For unidirectional operation, the output can be set at the

negative rail (near ground) or at the positive rail (near V+)

when the differential input is 0 V. The output moves to the

opposite rail when a correct polarity differential input voltage

is applied. In this case, full scale is approximately 250 mV for a

5 V supply or 165 mV for a 3.3 V supply. The required polarity

of the differential input depends on the output voltage setting.

If the output is set at the positive rail, the input polarity must

be negative to move the output down. If the output is set at

ground, the polarity must be positive to move the output up.

Ground Referenced Output Mode

When using the AD8207 in the ground referenced output mode,

both reference inputs are tied to ground, which causes the output to

sit at the negative rail when there are 0 differential volts at the input

(see Figure 28).

REF

ZERO

DRIFT

+IN

–IN

OUT

V+

GND

RANGE

AD8207

5V

Figure 28. Ground Referenced Output Mode, V+ = 5 V

Table 4. Ground Referenced Output

V+ = 5 V

0 V

0.02 V

250 mV

4.95 V

V+ = 3.3 V

0 V

0.02 V

165 mV

3.25 V

V+ Referenced Output Mode

The V+ referenced output mode is set when both reference pins

are tied to the positive supply. This mode is typically used when

the diagnostic scheme requires detection of the amplifier and

the wiring before power is applied to the load (see Figure 29).

RANGE

REF

ZERO

DRIFT

+IN

–IN

OUT

V+

GND

AD8207

5V

Figure 29. V+ Referenced Output Mode, V+ = 5 V

Table 5. V+ Referenced Output

V+ = 5 V

0 V

4.95 V

−250 mV

0.02 V

V+ = 3.3 V

0 V

3.25 V

−165 mV

0.02 V

BIDIRECTIONAL OPERATION

Bidirectional operation allows the AD8207 to measure currents

through a resistive shunt in two directions. In this case, the

output is set anywhere within the output range. Typically, it

is set at half scale for equal range in both directions. In some

cases, however, it is set at a voltage other than half scale when

the bidirectional current is asymmetrical.

V+ = 5 V

+100 mV

4.5 V

−100 mV

0.5 V

V+ = 3.3 V

+67.5 mV

3 V

−67.5 mV

0.3 V

Adjusting the output is accomplished by applying voltages

resistors that connect to an internal offset node. There is no

operational difference between the pins.