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BQ28Z620EVM-071: BQ28Z620EVM_CELL BALANCING

puppala naresh
Prodigy 140 points
Part Number: BQ28Z620EVM-071
Other Parts Discussed in Thread: BQ28Z620

Tool/software:

Hi Team,

I’m currently working with the BQ28Z620 EVM configured for a 2-series cell pack.

I’ve configured the protection limits for both high and low voltage cutoffs. The issue I’m observing is that as soon as one of the cells reaches the upper voltage threshold, the protection circuit activates and disconnects the charging path—even though the second cell is still within a safe range.

For instance:

  • First cell: 3.8V

  • Second cell: 3.6V

  • Upper limit: 4.0V

When the first cell touches the maximum limit (4.000V), the system shuts off the charging side, even though the second cell hasn’t reached that level (still around 3.8V–3.9V).

I have enabled the balancing feature via the configuration registers, but it doesn’t seem to function as expected during the charging process.

Could you guide me through the correct steps to activate balancing so it works properly while energy is being added to the pack?

I’ve reviewed the documentation, but I’d appreciate a more straightforward explanation.
this is my .gg.csv file
5822.tested_bqfile.gg.csv

  • 0
    TI__Mastermind 37981 points

    Hello,

    Can you send me a log file of when you are trying to charge the battery.

    Regards,

    Adrian

  • 0 in reply to Adrian
    Prodigy 140 points

    Thanks For the Replay Adrian
    I attached log file. kindly look into it

    On my EVM board, the charging and discharging flags and FETs are functioning properly, but cell balancing is not happening correctly. I updated the QMax also. While charging, the CB (Cell Balancing) flag is showing high, but the cells are not balancing.

    If any one cell crosses the COV (Charge Over Voltage) threshold, the FET turns off.
    What I need is for the CHG FET to turn off only when both cells are balanced.



    charging_log_file.log

  • 0 in reply to puppala naresh
    TI__Mastermind 37981 points

    Hello Puppala,

    I have look through the gg file and log file and have ensured that cell balancing is enabled and currently activated. However, the 2 battery cells are severely imbalanced. You can check the CBTime1 and CBTime 2 registers (these gives an estimate of how long cell balancing will take) and CBTime2 is around 65000 seconds which is close to 18 hours to fully balance. You will need to allow the batteries around 18 hours to fully balance. You can also look into an external balancing circuit if you need the batteries to balance faster.

    Regards,

    Adrian