Datasheet AD8205 (Analog Devices) - 9

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Data Sheet AD8205 OUTPUT OFFSET ADJUSTMENT
The output of the AD8205 can be adjusted for unidirectional or
V+ REFERENCED OUTPUT
bidirectional operation. This mode is set when both reference pins are tied to the
UNIDIRECTIONAL OPERATION
positive supply. It is typical y used when the diagnostic scheme Unidirectional operation al ows the AD8205 to measure requires detection of the amplifier and the wiring before power currents through a resistive shunt in one direction. The basic is applied to the load (see Figure 15). modes for unidirectional operation are ground referenced output mode and V+ referenced output mode.
V+
In the case of unidirectional operation, the output could be set
+IN OUT
at the negative rail (near ground) or at the positive rail (near
–IN
V+) when the differential input is 0 V. The output moves to the opposite rail when a correct polarity differential input voltage is
VREF1
applied. In this case, full scale is approximately 100 mV. The
AD8205
required polarity of the differential input depends on the output voltage setting. If the output is set at the positive rail, the input polarity needs to be negative to move the output down. If the
NC VREF2
output is set at ground, the polarity is positive to move the
GND
output up.
NC = NO CONNECT
04315-0-014
GROUND REFERENCED OUTPUT
Figure 15. V+ Referenced Output When using the AD8205 in this mode, both reference inputs are tied to ground, which causes the output to sit at the negative rail when there are zero differential volts at the input (see Figure 14).
Table 5. V+ = 5 V VIN (Referred to −IN) VO
0 V 4.8 V
V+
100 mV 0.05 V
+IN OUT –IN BIDIRECTIONAL OPERATION V
Bidirectional operation al ows the AD8205 to measure currents
REF1 AD8205
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.
NC VREF2 GND
In some cases, however, it is set at a voltage other than half-scale when the bidirectional current is nonsymmetrical.
NC = NO CONNECT
04315-0-013 Figure 14. Ground Referenced Output
Table 6. V+ = 5 V, VO = 2.5 with VIN = 0 V VIN (Referred to −IN) VO Table 4. V+ = 5 V
+40 mV 4.5 V −40 mV 0.5 V
VIN (Referred to −IN) VO
0 V 0.05 V 100 mV 4.8 V Adjusting the output is accomplished by applying voltage(s) to the reference inputs. V REF1 and VREF2 are tied to internal resistors that connect to an internal offset node. There is no operational difference between the pins. Rev. D | Page 9 of 12 Document Outline Features Excellent AC and DC Performance Applications Functional Block Diagram General Description Revision History Specifications Absolute Maximum Ratings ESD Caution Pin Configuration and Function Descriptions Typical Performance Characteristics Theory of Operation Output Offset Adjustment Unidirectional Operation Ground Referenced Output V+ Referenced Output Bidirectional Operation External Reference Output Splitting the Supply Splitting an External Reference Applications Information High-Side Current Sense with a Low-Side Switch High-Side Current Sense with a High-Side Switch Outline Dimensions Ordering Guide Automotive Products