Datasheet

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
V
REF
1
V
REF
2
RANGE
AD8207
5
V
09160-012
Figure 28. Ground Referenced Output Mode, V+ = 5 V
Table 4. Ground Referenced Output
V
IN
(Referred to −IN) V
O
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
V
REF
1
V
REF
2
AD8207
5
V
09160-013
Figure 29. V+ Referenced Output Mode, V+ = 5 V
Table 5. V+ Referenced Output
V
IN
(Referred to −IN) V
O
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.
Table 6. V
O
= (V+/2) with V
IN
= 0 V
V
IN
(Referred to −IN) V
O
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
to the reference inputs. V
REF
1 and V
REF
2 are tied to internal
resistors that connect to an internal offset node. There is no
operational difference between the pins.