Guarding Voltage - Using the "Guarded Inputs" Panel
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SBOU201A – April 2018 – Revised September 2018
Copyright © 2018, Texas Instruments Incorporated
INA190EVM User's Guide
5.3.1
U2x Buffer Not Populated
Jump pins 2 (REF) and 3 (GND) of the J3x header to make REF = GND. The jumper can be removed
from the EVM and the REF test points (TP6x or pin 2 of J3x) can be driven with the external voltage
source. Note this external source needs a common ground with the INA190 power source.
5.3.2
U2x Buffer Populated
Be sure to populate R2x. If R2x equals R1x, then the U2x buffer output will equal VS/2. Jump pins 2
(REF) and 1 (VS/2) of the J3x header to drive the REF pin with the output of U2x.
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Guarding Voltage - Using the "Guarded Inputs" Panel
One panel on the INA190EVM is labeled as "Guarded Inputs" because it includes extra circuitry to help
guard the input traces going into the IN+ and IN– pins of the INA190. When measuring a small current, it
is desirable to minimize the input bias currents of the device, which is in the nanoamps. The input bias
current could increase due to leakage currents sinking into a nearby ground plane and this is simply due
to finite resistance of PCB material and a voltage potential. This voltage potential only grows as common-
mode voltage increases. Guard the input traces with an isolated guarding plane and fence that is at the
same potential and any leakage currents from the input traces will be significantly reduced. This technique
is really more practical when dealing with currents in the picoamps level, but it is included to help evaluate
any extreme cases: low-current or high common-mode voltage or both.
The guarding plane can be driven by an external voltage source using the VG tespoint (TP7) or by
populating R4 with a 0-
Ω
resistor, which will automatically tie common-mode voltage at the inputs to the
guarding plane. If using the VG tespoint, ensure the external source has a common ground with the
INA190.
