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bq769x0 GND position

Fred P
Expert 2015 points
Other Parts Discussed in Thread: BQ76940

On the bq76940 EVM, GND is wired directly to the bottom cell.  Thus, the internal battery circuitry consumption is not monitored through the sense resistor.

Can GND connection be shifted between the sense resistor and discharge FET?

Looking at the bq76940 electrical specifications, I don't see any problem at doing so.  SRP-SRN is a differential sense that measures bipolar current. Shifting from one side to the other should not cause any problem.
That would allow the BMS and extra circuitry consumption to be monitored, given it is not below the ADC resolution of course.

However, there might be some subtilities I am not aware of...

Please advise.

Thanks,


Frederic

  • 0
    TI__Guru 54715 points

    It might be suitable to move the ground in your system.  Generally ground is recommended at the cell side of the sense resistor.  The various pins which connect at "ground" have a larger positive absolute maximum range than negative. SRP has a much smaller recommended operating range than SRN.  If your system has a low short circuit current, it is likely easier to keep the part within its operating limits with the alternate ground.

  • 0 in reply to WM5295
    Expert 2015 points

    I had focused on the absolute and differential ratings only.

    As you are pointing out, the recommended range for SRP is much smaller (±10mV). 

    That means we won't be able to move the GND to SRN in our application.

    Thanks

    Fred

  • 0 in reply to Fred P
    Intellectual 515 points

    I don't know if its relevant, but what we noticed in our design is when you connect GND near to SRP instead of Cell 0 then current measured will be affected because nice will try to move through SRP.

    So better keep it near Cell 0