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BQ76940: Short circuit in discharge delay

john xiao
Intellectual 470 points
Part Number: BQ76940

Dear all:

I use BQ76940 design 15S Lithium battery protection board.this is sch1501.pdf

I set the short  discharge delay is 400us,do short  protection test,the BQ76940 enter ship mode.oscilloscope measurement the DSG output drop to zero time about 4ms, please help analyze why the short  discharge delay is not consistent with settings and the short protection test bq76940 enter ship mode?thanks a lot.

  • 0
    TI__Guru 54715 points

    Hi John,
    Your description is consistent with the part losing power during the SCD. Monitor VC5X and see if it is dropping into the VSHUT region.
    Be sure you have implemented the filter for the power pins and used the large value Rc resistors for the input filter.

    Looking at the schematic, the input filter resistors are 1k, this is typical.  The power filter resistors R16, R19 and R22 are 100 ohm, this are probably too small, 1k here is typical also.  The power filter capacitors (C32, C33, C34) size is not shown, from the EVM 10 uF is typical to maintain voltage above VSHUT.