Datasheet

V+
OUT
GND
IN-
IN+
PRODUCT R AND R
3 4
INA199A1, INA199B1
INA199A2, INA199B2
INA199A3, INA199B3
20kW
10kW
5kW
C
BYPASS
Shutdown
Control
REF
Reference
Voltage
1MW
R
3
1MW
R
4
Supply Load
R
SHUNT
Output
INA199A1, INA199B1
INA199A2, INA199B2
INA199A3, INA199B3
SBOS469D –MAY 2009–REVISED NOVEMBER 2012 www.ti.com
SHUTTING DOWN THE INA199 SERIES
While the INA199 series does not have a shutdown pin, the low power consumption allows powering from the
output of a logic gate or transistor switch that can turn on and turn off the INA199 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 INA199 in shutdown mode shown in Figure 22.
NOTE: 1MΩ paths from shunt inputs to reference and INA199 outputs.
Figure 22. Basic Circuit for Shutting Down INA199 with Grounded Reference
Note that there is typically slightly more than 1MΩ impedance (from the combination of 1MΩ feedback and 5kΩ
input resistors) from each input of the INA199 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 1MΩ impedance from the shunt to ground is straightforward. However, if the
reference or op amp is powered while the INA199 is shut down, the calculation is direct; instead of assuming
1MΩ to ground, however, assume 1MΩ 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 1MΩ path.
Regarding the 1MΩ path to the output pin, the output stage of a disabled INA199 does constitute a good path to
ground; consequently, this current is directly proportional to a shunt common-mode voltage impressed across a
1MΩ resistor.
As a final note, when the device is powered up, there is an additional, nearly constant, and well-matched 25μA
that flows in each of the inputs as long as the shunt common-mode voltage is 3V or higher. Below 2V common-
mode, the only current effects are the result of the 1MΩ resistors.
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Product Folder Links: INA199A1 INA199B1 INA199A2 INA199B2 INA199A3 INA199B3