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BQ35100: Fuel gauging two cells tied in parallel

Eddie Rossi
Prodigy 30 points
Part Number: BQ35100

I know BQ35100 fuel gauge is meant to work with one battery cell. But can it also monitor two Li-SOCl2 cells tied in parallel in EOS mode, for example? My design must have 2 cells for increased capacity and to allow battery replacement w/o the load supply being interrupted - the cells will be replaced one at the time. Thank you.

  • 0
    Prodigy 30 points

    Here is circuit I plan to use:

  • 0 in reply to Eddie Rossi
    TI__Guru 52115 points

    My colleague who is an expert on this device is on vacation. He will provide the answer when he is back.  

    Andy

  • 0 in reply to Eddie Rossi
    TI__Genius 10370 points

    Eddie,

    The gauge will work with two cells in parallel at the same time. This is why the gauge learns a scale factor. With two cells in parallel the impedance will be about half what it would be with one cell. With this method the gauge treats the pair as the cell. 

    The issue would come in if one of the cells gets replaced. The gauge has no way of knowing if one of the two is about to die. We cannot give an SOH for each cell, only the stack. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 30 points

    Hi Eric,

    Thanks for the quick reply. I understand the issue regarding the stack, but for us it should not be a problem - per operating manual both cells will be replaced when low; just need to make sure they are replaced one at the time (AON circuit must be kept running), then NEW_BATTERY() command must be issued to insure RNEW is refreshed correctly.

    Regards,

    Eddie