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INA240: INA240A3 offset

Michael T Schneider
Expert 3780 points
Part Number: INA240

We are experiencing a peculiar offset problem on the INA240A3. The offset seems to be consistently 200mA (measured), 30mV voltage on pin 8.

 We connect the device as shown below. In a “low power mode” the V3P3 voltage is disabled, but there is a battery connected at BUS.

Is there any issue with having a voltage present on pins 3 and 2 while pin 5 is un powered?  The datasheet leads me to think it should be ok, but all the applications show the shunt downstream of a switch. In our case, the shunt is upstream of a switch.

 I am thinking this could potentially be changing the input bias current somehow and causing an offset. We are not seeing this on every part, making it a harder problem to track..  

  • 0
    TI__Mastermind 31870 points

    Hi Michael,

    It is OK to use the device the way you described. The device should not be affected negatively in the absence of V3P3 while BUS is active.

    Under what conditions can the 30mV offset be observed? Is it consistent in the entire current range? If you do a power cycle (turn V3P3 on and off repeatedly) does the offset come to the same value every time? What about the gain, is it correct at around 100?

    If you were to do an A-B-A swap, does the offset follow the problem IC or does it stay with the board?

    As a next step you may also want to examine the output to see if it is oscillating. If not then some tabulated input/output measurement data would help.

    Regards, Guang

  • 0 in reply to Guang Zhou
    TI__Mastermind 27715 points

    Hi Michael,

    It's been some time since your last post, so hopefully your issue has been resolved. I will close the thread for now. If you need further assistance you can reply to re-open the thread.

    Thanks!

    Ian Williams
    Applications Manager
    Current & Magnetic Sensing