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This is the bidirectional operation of the INA199 Current-Shunt Monitor. Can someone please explain me how the output is dependent on Vref? From the datasheet I see that the voltage applied to REF (VREF) sets the output state that corresponds to the zero-input level state.

Does zero-input level state mean that when the sensed current is 0, Vout=Vref?

By how much will the output increase above VREF for positive differential signals (relative to the IN– pin) or decrease below VREF for negative differential signals?

For my application I'm assuming that V+=5V, Vout should not exceed 3.3V, max current sensed in one way is 10A, and -3A in the other direction. Rsense=10mOhm

Why is that voltage divider next to the Reference voltage? Is it there simply as an example on how to get the desired reference voltage?

bidirectional operation of the INA199 Current-Shunt Monitor

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  • \$\begingroup\$ You say up to 10A and a sense resistor of 10 mOhm. That's 100 mV drop across it. Yet the maximum gain error for the device is specified given a max differential (Vsense) of 5 mV. Not 100 mV. Given the input-referred input offset they give, I'm guessing these are bipolar. But have you contacted them about gain error for a Vsense of 100 mV and how this may impact offset voltage? Later in the text I see 10 mV and 60 mV mentioned, but then they suddenly add that it gives 150 uV input-referred offset when the specs suggest 5 uV typical. So all that makes me curious. Calibration may be in your life. \$\endgroup\$
    – jonk
    Nov 17, 2022 at 1:40

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If you want to read a bidirectional current with an ADC that is unipolar you'll need to assign some voltage in the middle (not necessarily the center) to zero current.

Then the voltage can change higher or lower from there over some range without exceeding the power supply rails.

This is explained in the datasheet 9.2.2.2. Since the REF input of the INA99 is not a high-impedance input, you'll need to buffer the voltage if you derive it from a voltage divider, and that is shown. The switch is just for illustrative purposes, you'd normally use one or the other.

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