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Original question:

BQ76940: bq76940

BQ76940: bq76940

Joao Paulo Teixeira
Intellectual 370 points
Part Number: BQ76940

Hello,

I'd like to know what would happen if the batteries were connected without following the table 8-3. Cell Connections for bq76940.

For example: If 10 cells were conected on the first 10 slots and leave empty the last 5 slots. Would the bq76940 be damaged permanently?

Thanks,

Regards,

João Paulo

  • 0
    TI__Guru 54715 points
    Hi Joao Paulo,
    For several BMS devices fewer cells are configured by shorting the upper inputs. For example a 4 cell device used with 3 cells would be configured by shorting the top cell inputs and using the bottom 3 cells. You have noticed the recommendation in table 8-3 is to use the top cell of each group. For 14 cells, the top cell inputs (VC15 and VC14) are used for the 14th cell and the next cell's inputs (VC14 and VC13) are shorted. This is because the top cell has better common mode rejection to the power supply voltage than the lower cells. If the top cell were shorted it would normally read 0 and the next lower cell would read its voltage, however when the power supply varied the top cell may read a voltage and the lower cell may read incorrectly. This could cause a false UV.
    The cell group must also have a minimum operating voltage, this is why the reduced cell count is distributed over the 3 cell groups. The minimum recommended VBAT supply voltage is 6V which is 3 cells x the minimum recommended cell voltage.
    In the specific case you asked if 10 cells are connected to the bottom 10 inputs of the bq76940, the top group will not have power. The part should be able to be booted but since the top group has no VBAT the part will always show an XREADY fault. Unless the BAT-VC10x abs max of -0.3V is violated the part should not be damaged, when connections are made properly the part should operate.