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BQ76940: BQ76940 failure while short circuit test

Akilan G14
Prodigy 120 points
Part Number: BQ76940

Hi,

We have developed a BMS with BQ76940 and ST microcontroller. The problem is when we are doing short circuit test, the AFE is failing.

Do you have any comment on this ?

  • 0
    TI__Guru 54715 points

    Hi Akilan,

    You do not mention the manner in which the BQ76940 fails.  There are 2 common concerns in the schematic:

    1. The power filter capacitors Cf are too small
    2. The filter resistors Rf and Rc are too small

    Both these lead to discharge of the power filter capacitor during short circuit causing the part to loose power on VC5X before the SCD timer expires. The FETs do not turn off as expected.  See http://www.ti.com/lit/pdf/slua749 section 3 figure 3 and the related text.  Using short SCD delay times also helps maintain operating voltage to the part during SCD.  Compare the recommended values for Cf, Rf, and Rc with the data sheet.  Check VC5X during the short circuit event to see if it remains above VSHUT to see if this may be the issue.

    Another area to look at is the recovery code in the MCU.  Be sure that the MCU is not recovering too quickly for voltages to return to normal and FETs to cool.

    If this does not help resolve the problem please post more description of the observations and the failure.

    still expect to complete the “transient” topic this year