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Original question:

BQ77915EVM-014: Cell balancing in BQ77915

BQ77915: Cell balancing not working

sourav kc
Prodigy 70 points
Part Number: BQ77915

Tool/software:

I tested cell balancing for 3cell with cell voltages 3.0V, 3.8V and 2.5V. The charging was stope at 11V. After charging the cell voltages are 3.5V,4.0V, and 3.5V. why it is not charging to Vfc. Is cell balancing is working or not. Also I tested with another 3 cell with cell voltages 3.8V, 2.2V and 2.5V and after charging the cell voltages are 4V, 3.5V and 3.5V. 

  • 0
    TI__Mastermind 34930 points

    Hello Sourav,

    Have you seen our cell balancing video of this part? This video explains how it works in detail:

    Something to keep in mind, is that because cell balancing may only occur while there is a charging current, it may take multiple charge/discharge cycles to fully balance a cell string, depending on how unbalanced the cells are.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 70 points

    Hi Luis,

    The problem is that if any of the three cells charges to 4.1V, the device terminates the charging process by turning the charge FET off. And also I couldn't charge the battery if any of the cell has above 4.0V.

    please check the schematic

  • +1 in reply to sourav kc
    TI__Mastermind 34930 points

    Hello Sourav,

    What is the cell voltage during the charge? What is the voltage between the VCx pins during the charge? 

    I am wondering if possibly during charging the cell voltage is rising above the OVP threshold, causing the protection to trigger. Regardless, as I mentioned, when there is very high discrepancies in voltages, it may take multiple charging/discharge cycles before the cells are balanced.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 70 points

    Hi Luis,

    Thank you for your support. Cell voltages before charging was 3.4v,2.9v and 3.2v. After charging it was 4.1v, 4.0v and 4.08v. I think the cell balancing is worked here. but the led indicators are not responding. On the second charge cycle all cells are balanced. so as per me cell balancing is working, but balancing indications are not.

  • 0 in reply to sourav kc
    TI__Mastermind 34930 points

    Hello Sourav,

    Understood Slight smile.

    Glad to know that it is working! Let me know if there's any more questions.

    Best Regards,

    Luis Hernandez Salomon