AN-815: AD8210 Bidirectional Operation Using a 3.3 V External Reference (Rev. 0) PDF

AN-815
APPLICATION NOTE
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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 VS (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 VREF
pin to the supply while the other is tied to GND. In this mode,
the output of the AD8210 starts at VS/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 ≤ VREF ≤ VS. 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.
By tying the VREF1 pin to the A/D supply and the VREF2 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 VREF pins to the external 3.3 V supply of the
converter. In this case, the output of the AD8210 starts at 3.3 V.
I
SHUNT
–IN
I
+IN
SHUNT
3.3V
VREF 1
VREF 2
5V
1kΩ
+VS
0.1µF
NC
D1
–IN
+IN
ADC
400pF
OUT
3.3V
VREF 1
GND
AD8210
Figure 1. Bidirectional Operation Using an External Reference
VREF 2
1kΩ
5V
ADC
400pF
+VS
0.1µF
NC
OUT
05714-002
AD8210
05714-001
GND
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.
Rev. 0 | Page 1 of 2
AN-815
NOTES
©2006 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
AN05714-0-6/06(0)
T
T
Rev. 0 | Page 2 of 2
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