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BQ76940EVM: Cell short-circuit protection, cell connection order

Nikola Felkaroski
Prodigy 40 points
Part Number: BQ76940EVM
Other Parts Discussed in Thread: BQ76940

Dear TI Support,

I am writing to ask you the following two questions.

1) If a cell (e.x. the first cell) unexpectedly shorts itself (e.x. due cell damage), would such an occurrence damage the BQ76940 chip, and if that is the case, is there any recommended protection from such an occurrence?

and

2) When connecting cells for the first time, can the order of connection be reversed (e.x. from highest voltage to lowest), or can all cells be connected at the same time? Or is it absolutely necessary for the order to be bottom up?

Thank you in advance.

  • 0
    TI__Guru 54715 points

    Hi Nikola,

    1. Having a cell short should not damage the BQ76940.  If the cell shorts and the voltage drops slowly so that the voltage is between the UV threshold and the UVMINQUAL threshold for the UVDELAY, the part should set the undervoltage status.  If the voltage drops quickly below UVMINQUAL the part will ignore the low cell voltage and it is up to the system MCU to recognize the missing cell voltage and take action.

    2. GND or battery- should be connected first since voltages are referenced to that potential, VSS of the IC.  After that any voltage could be connected although some have more chance of overstress to the device than others.  Bottom up provides the smallest positive voltage steps to the system.  Top down is also small voltage steps but most connections provide a negative voltage to one or more inputs. See section 10 of the application note https://www.ti.com/lit/pdf/slua749 for various considerations.  Cell 6 or 11 can be a large concern as the second connection due to the different capacitors in the circuit.  A connector may work well, but be aware of tolerances of the pins and the possibility of connecting the wrong potential as the connector is aligned during mating.