Other Parts Discussed in Thread: INA280, INA281
Hello, I am using the INA281A1-Q1 in a configuration for high-side current sense of a 50V supply. The Vs pin of the current sense amplifier is powered at 3.0 V. When the 50V rail is powered, the current sense resistor is biased as expected and the amplifier correctly amplifies the differential voltage and rejects the common mode offset, producing the expected output on the OUT pin. However, in our particular application there are scenarios where the amplifier is still powered at its Vs pin, but the In- and In+ pins have no voltage bias (they are essentially high impedance other than the current sense resistor) as the 50V rail is disconnected through a power MOSFET before the current sense resistor. In this configuration, we measure between -0.7 and -7V on In- and In+ with respect to ground, depending on the exact loading on this rail. This high negative voltage is causing issues with our power MOSFET's controller/driver IC.
Is is this negative bias voltage normal for the INA281A1-Q1 if the In- and In+ pins are unpowered while Vs is powered? If so, can you provide more information about the input bias circuitry? We would like to keep the input bias voltage between -0.3 and 0V when this 50V rail is off in order to not reverse bias other parts on this rail when it is unpowered.