Datasheet
INA21x-Q1
V+
OUT
GND
IN-
IN+
PRODUCT R and R
3 4
INA213A-Q1
20 kW
C
BYPASS
Shutdown
Control
REF
Reference
Voltage
1 MW
R
3
R
2
R
4
Supply Load
R
SHUNT
Output
INA214-Q1 10 kW
INA212-Q1
1 kW
INA212-Q1, INA213A-Q1
INA214-Q1
SBOS475D –MARCH 2009–REVISED OCTOBER 2013
www.ti.com
SHUTTING DOWN
While the INA21x-Q1 does not have a shutdown pin, its low power consumption allows powering from the output
of a logic gate or transistor switch that can turn on and turn off the INA21x-Q1 power-supply quiescent current.
However, in current shunt monitoring applications. there is also a concern for how much current is drained from
the shunt circuit in shutdown conditions. Evaluating this current drain involves considering the simplified
schematic of the INA21x-Q1 in shutdown mode shown in Figure 25.
NOTE: 1-MW paths from shunt inputs to reference and INA21x outputs.
Figure 25. Basic Circuit for Shutting Down INA21x-Q1 With Grounded Reference
Note that there is typically slightly more than 1-MΩ impedance (from the combination of 1-MΩ feedback and 5-
kΩ input resistors) from each input of the INA21x-Q1 to the OUT pin and to the REF pin. The amount of current
flowing through these pins depends on the respective ultimate connection. For example, if the REF pin is
grounded, the calculation of the effect of the 1-MΩ impedance from the shunt to ground is straightforward.
However, if the reference or op amp is powered while the INA21x-Q1 is shut down, the calculation is direct;
instead of assuming 1 MΩ to ground, however, assume 1 MΩ to the reference voltage. If the reference or op
amp is also shut down, some knowledge of the reference or op amp output impedance under shutdown
conditions is required. For instance, if the reference source behaves as an open circuit when it is unpowered,
little or no current flows through the 1-MΩ path.
Regarding the 1-MΩ path to the output pin, the output stage of a disabled INA21x-Q1 does constitute a good
path to ground; consequently, this current is directly proportional to a shunt common-mode voltage impressed
across a 1-MΩ resistor.
As a final note, when the device is powered up, there is an additional, nearly constant, and well-matched 25 µA
that flows in each of the inputs as long as the shunt common-mode voltage is 3 V or higher. Below 2-V common-
mode, the only current effects are the result of the 1-MΩ resistors.
REF INPUT IMPEDANCE EFFECTS
As with any difference amplifier, the INA21x-Q1 common-mode rejection ratio is affected by any impedance
present at the REF input. This concern is not a problem when the REF pin is connected directly to most
references or power supplies. When using resistive dividers from the power supply or a reference voltage, the
REF pin should be buffered by an op amp.
In systems where the INA21x-Q1 output can be sensed differentially, such as by a differential input analog-to-
digital converter (ADC) or by using two separate ADC inputs, the effects of external impedance on the REF input
can be cancelled. Figure 26 depicts a method of taking the output from the INA21x-Q1 by using the REF pin as a
reference.
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Product Folder Links: INA212-Q1 INA213A-Q1 INA214-Q1