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BQ76940: BQ76940 how to judge it just connects 14 cells or 14th cell is shorted in 15 cells

Rock Su
Intellectual 2220 points
Part Number: BQ76940

Dear colleague,

BQ76940 how to judge it just connects 14 cells or 14th cell is shorted in 15 cells at the beginning of power on?

  • 0
    TI__Guru 54715 points

    Hi Rock,

    You have to decide how to wire the circuit.  Connect like the table using the top cell for best performance since the capability of the VC14 input is different than VC15.  If you short cell 15 instead cell 15 may still show some voltage which can creep up above the UVMINQUAL level and cause false UV. 

  • 0 in reply to WM5295
    TI__Intellectual 2220 points

    Hi WM5295,

    Thanks! But I think there may be some misunderstanding.

    For example, now customer using a 15 cells pack and 14th cell is shorted, then battery connects to BQ76940. Now BQ76940 how to distinguish 14th cell is shorted or this is a 14 cells configuration?

    And another question is which register could control enable or disable different channel in BQ76940, for example, I want to disable VC14-VC13 voltage sample, how to configure it?

    Thanks a lot!

    Rock Su

  • 0 in reply to Rock Su
    TI__Guru 54715 points

    Hi Rock,

    Sorry, I missed that point.  The BQ76940 auto configures cells by using the UVMINQUAL level.  If the cell voltage is below that threshold it will ignore it for UV status.  If the battery has a dead cell and is connected to the BQ76940 or the BQ76940 is booted, the BQ76940 will not indicate a UV.  The BQ76940 does not turn on FETs by itself however, so the connected host can and should make sure all expected cell voltages are present before enabling the FETs. 

    The BQ76940 always samples all cell voltages.  If the cell is not used it is still sampled, there is no way to turn off the sample.  The host can ignore the regiser value for that cell, but the BQ76940 will still use its value when assembling the pack voltage.