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INA190: Behavior with floating inputs

TonyMCC
Intellectual 750 points
Part Number: INA190

I have INA190-A1 configured with a single 3V power rail and 1.5V VREF in a current monitoring application.

What type of behavior can I expect if the INA190 inputs are left disconnected (floating) ?  Would the INA190 output tend to drift towards one of the supply rails (0V or 3V) during the time inputs are floating ?

Thanks

  • +1
    Guru 140200 points

    Hi Tony,

    lefting float the inputs is no good idea. You must allow a path for the input bias currents. Otherwise the input and output stages will saturate and tend to drift to one of the supply rails, as you wrote.

    I would mount a dummy resistor at the input pins, just enough low ohmic to allow the input bias currents to flow, but enough high ohmic to cause no big error.

    Kai

  • 0 in reply to kai klaas69
    TI__Mastermind 18780 points

    Tony,

    Kai is correct here. The input bias currents need a path to flow at all times for the part to function correctly. Can you share what condition would occur to isolate the input pins here?

  • 0 in reply to Carolus Andrews
    Intellectual 750 points

    Yes...I have an circuit that measures the potential for a 4-20mA over-current condition using INA190. If the user leaves the 4-20mA terminals disconnected long enough then the INA190 will rail which sends uC an over-current alert.

    If I were to implement Kai's recommendation, do I need a weak (for example 1MEG ohm) pull-up and pull-down on each of the INA190 inputs or will one pull-up (or pull down) be sufficient to satisfy the input bias current path requirement for the INA190, keeping it from railing with floated inputs ?

  • +1 in reply to TonyMCC
    TI__Mastermind 18780 points

    Tony,

    Provided the shunt is still between the two pins, one pull-up or pull-down should be sufficient. I would advise to choose which based on the style of the design to ease common mode transition between switching. If you're measuring on the high side, pull up to the normal VCM used, and if you're on the low side, pull down to GND.