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AN-815
APPLICATION NOTE
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Rev. 0 | Page 1 of 2
AD8210 Bidirectional Operation Using a 3.3 V External Reference
by Henri Sino
INTRODUCTION
One of the key features of the AD8210 bidirectional current
sense amplifier is the ability to offset the output to a voltage
between 0 V (GND) to V
S
(supply voltage). This allows the user
to monitor current flowing in both directions through the input
shunt resistor while still operating with a single 5 V supply.
Typically, bidirectional operation is achieved by tying one V
REF
pin to the supply while the other is tied to GND. In this mode,
the output of the
AD8210 starts at V
S
/2 and goes up or down
depending on the direction of the current at its inputs.
The
AD8210 output can also be offset using an external
reference with a voltage range of 0 V ≤ V
REF
≤ V
S
. The
configuration shown in
Figure 1 makes use of the 3.3 V ADC
supply and offsets the output of the
AD8210 for bidirectional
operation.
3.3V
+IN
+V
S
OUT
–IN
GND
V
REF
2
V
REF
1
NC
AD8210
5V
D1
I
ADC
0.1µF
400pF
1kΩ
SHUNT
05714-001
Figure 1. Bidirectional Operation Using an External Reference
By tying the V
REF
1 pin to the A/D supply and the V
REF
2 pin to
GND (see
Figure 1), the output of the AD8210 is offset to half
of the 3.3 V reference, or 1.65 V. It is important to note that
while the output of the
AD8210 can be referenced to any
voltage within its supply range, the
AD8210 supply voltage must
remain 5 V. This means that regardless of the output offset
voltage, the output range of the
AD8210 must still be 0.05 V to
4.9 V. Calculations should be made so that the
AD8210 output
does not exceed the input range of the converter. Diode D1 is an
optional component that can be used to protect the input of the
converter from excessive overdriving. If D1 is used as shown in
Figure 1, than the maximum voltage at the input of the converter
would be a diode drop of 0.7 V (or 0.4 V if a Schottky diode is
used) above the 3.3 V supply.
Additionally, by using this external 3.3 V supply, the
AD8210
can operate in unidirectional mode. This can be achieved by
connecting both V
REF
pins to the external 3.3 V supply of the
converter. In this case, the output of the
AD8210 starts at 3.3 V.
3.3V
+IN
+V
S
OUT
–IN
GND
V
REF
2
V
REF
1
NC
AD8210
5V
I
ADC
0.1µF
400pF
1kΩ
SHUNT
05714-002
Figure 2. Unidirectional Operation Using an External Reference
When operating in this manner, the current through the input
shunt resistor should flow from the negative input (Pin 1) to the
positive input (Pin 8). As the current across the shunt resistor
increases, the output correspondingly moves from 3.3 V down
to 0.05 V.
