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BQ77915: Battery drain issues

Nikhil Ramesh
Prodigy 50 points
Part Number: BQ77915
Other Parts Discussed in Thread: BQ25713, PMP40441,

Hi, we have implemented the BQ77915 battery protection IC along with the BQ25713 charge controller for our product. Our schematic was largely based off of the PMP40441 reference design for a USB-C charging solution for a 4-cell lithium ion battery.

We are seeing an issue where battery assemblies are draining to a much lower voltage than the undervoltage protection voltage threshold given in the BQ77915 (2.9V*4=11.6V). A few of our battery assemblies have shown that they are drained down to ~2.5-4V across the entire assembly (4 series lithium ion cylindrical cells). When we use a power supply + voltage divider to test the under voltage protection, we find that it properly closes the discharge FET and lower current draw to ~600uA.

I've attached a schematic of our charge and protection circuits for review. Please let me know if any additional information is required.

  • 0
    TI__Guru* 80083 points

    Hi Nikhil,

    I think you may need to remove R209 from the board since this will be a constant current drain for the battery. I think this is the reason for the 600uA current draw (11.6V / 20k).

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 50 points

    Hi Matt,

    Thanks for the quick response. I will see if removing R209 eliminates the 600uA current. But even with 600uA being drained constantly (even in undervoltage fault condition), it would take years to drain the battery pack to the voltages we are seeing. Is there anything else in the schematics that jumps out to you as an error that could cause a higher leakage current?

    Thanks,

    Nikhil

  • 0 in reply to Nikhil Ramesh
    TI__Guru* 80083 points

    Hi Nikhil,

    I do not see anything else in the schematic. You may want to measure the voltage across the cell input resistors and other resistors in the system to find where unexpected current may be flowing.

    Regards,

    Matt