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BQ76930: BQ76930 AFE leakage current

Star Xu
Genius 9645 points
Part Number: BQ76930
Other Parts Discussed in Thread: BQ76940,

Hi

BQ76930 and BQ76940 are used for the two projects of 10 strings and 13 strings respectively.

After mass production, it is found that the battery pack is in stock for a period of time. The 10th string of BQ76930, the 10th, 12th and 13th strings of BQ76940 have leakage current. The analysis found that the adjacent AFE If there is a leakage in the sampling pin of the cell voltage, it can be confirmed that there is no leakage problem in the AFE when the battery pack is stored (If there is leakage in the sampling pin of the AFE when entering the storage, there will be a voltage difference in the 1K sampling filter resistor, which can be detected by the host computer ), after the bad protection board is powered off, let it stand for 1 hour, and then power on again. In most cases, the previous AFE leakage fault will disappear, but after standing for a period of time (maybe 10 minutes or 1 day), The fault will reappear again, the leakage current will gradually increase, the voltage appears on the 1K sampling filter resistance, the sampling voltage will be less than the actual battery voltage, the voltage output by the AFE and the voltage of the AFE sampling pin are the same (AD sampling inside the AFE Still normal). Currently, there is no TVS protection diode added to the voltage sampling port.

I would like to know how to solve it?

8540.Schematic Prints.pdf

Thank you

Star

  • 0
    TI__Guru 54715 points

    Hi Star,

    You can measure the leakage as a voltage across the resistors, and the part can measure it as well.  The challenge now is to find out if the leakage is in:

    • Contamination on the board assembly
    • The IC
    • The capacitor
    • The PC board itself.

    We have seen all of these cases with the BQ769x0.  Similar to removing power, heating the board to desolder parts will often clear the issue also, either temporarily or permanently. You might try to reflow the part and see if it returns, or swap parts between good and bad boards to see if the issue stays with the part or board.

    Creating a table of the voltage across each Rf and Rc filter resistor can be helpful to see where the current is going. If RVC10 has current in and RVC9 has current out, leakage could be in the IC, between the pins, in the board, or in the cap.  If RVC10 has leakage in and RVC5X has current out, it could be the IC or in the board, leakage in a cap is unlikely since none connect directly, and pins are separated. 

    You may be able to lift an IC lead without heating significantly, but often it may be a destructive test cutting IC pins or board traces to see when the leakage stops.