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BQ76942: Can not blancing in autonomous mode or manual mode

Hai Phan
Prodigy 120 points
Part Number: BQ76942
Other Parts Discussed in Thread: BQSTUDIO

Tool/software:

Hi

I have a problem in balancing cells pin, I used 9 cells and I customed BQ 76942 by tied VC10 to VC9. I set up in BQ76942_Init() followed by some codes below: 

BQ769x2_SetRegister(BalancingConfiguration, 0x07, 1); // For Relax mode, sleep mode, charging mode

BQ769x2_SetRegister(MinCellTemp, -128, 2); //

BQ769x2_SetRegister(MaxCellTemp, 127, 2);

BQ769x2_SetRegister(MaxInternalTemp, 127, 2);

BQ769x2_SetRegister(CellBalanceInterval, 1, 2); // 1 s interval

BQ769x2_SetRegister(CellBalanceMaxCells, 3, 2); // 3 cells together

BQ769x2_SetRegister(CellBalanceMinCellVCharge, 2500, 2);

BQ769x2_SetRegister(CellBalanceMinDeltaCharge, 30, 2);

BQ769x2_SetRegister(CellBalanceStopDeltaCharge, 20, 2);

BQ769x2_SetRegister(CellBalanceMinCellVRelax, 2500, 2);

BQ769x2_SetRegister(CellBalanceMinDeltaRelax, 30, 2);

BQ769x2_SetRegister(CellBalanceStopDeltaRelax, 20, 2);

BQ769x2_SetRegister(ChgCurrentThreshold, 30000, 2);

BQ769x2_SetRegister(DsgCurrentThreshold, 30000, 2);

I set up this because I used 4,2 battery, and currently the average voltage of cells is 3,85 V

I wonder I missed some command to enable balancing mode in BQ76942, and what I have to check to know blancing are operating or not

Besides, I also used some command
Subcommands(CB_ACTIVE_CELLS, 0x0084, W2); for balancing specified cell with cell 3 and 8

Subcommands(CB_SET_LVL, 0x00, W2); for set minimum voltage that enable balancing

Can anyone help me to find what problem is?

Thank you

This is my screen to see all voltages and temperature

This is my screen for see any alarm or faults

  • 0
    Prodigy 120 points

    This is my schematic, and if any problems happened related to balancing 

  • 0 in reply to Hai Phan
    TI__Genius 17815 points

    Hello Hai,

    When you used 0x0083 CB_ACTIVE_CELLS(), did you read this subcommand as well or only write? When read, it should report a bit mask of which cells are being actively balanced.

    Can you also share the schematic of the cell inputs as well?

    Do you have any voltage/current waveforms you could share at the cell inputs when you send write to the subcommand 0x0083 CB_ACTIVE_CELLS() or any logic analyzer files when you send the command?

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 120 points

    Hell Alexis_H,

    When you used 0x0083 CB_ACTIVE_CELLS(), did you read this subcommand as well or only write? 

    I have both read and write, however, when read, I saw that a bit mask is zero, and can not see any change during watching in my STM32IDE screen.

    Can you also share the schematic of the cell inputs as well?

    Sure, I will share my schematic below my comments

    Do you have any voltage/current waveforms you could share at the cell inputs when you send write to the subcommand 0x0083 CB_ACTIVE_CELLS() or any logic analyzer files when you send the command?

    Sure, I can share all of that. 

    But first of all, I read the Alarmrawbit and I saw that, a third bit indicates cell balancing is turned on if I used code setup above, and if I increased the threshold of delta voltage between maximum cell's voltage and minimum cell's voltage to 50 mV. This third bit turned off. And I didnt know whether my battery is balanced or not. Because I wait about 10 hours with lower threshold such as 30 mV to reach delta V below 30 mV. 

  • 0 in reply to Hai Phan
    TI__Genius 17815 points

    Hello Hai,

    If the Alarm Raw Status Register showed the CB bit HIGH at some point, that should mean cell balancing was active at some point. Were you able to read 0x0083 CB_ACTIVE_CELLS() when this register was set and take waveforms at the pins to see? If you're also using bqStudio, you can take a log to see if the device was cell balancing at any point too after using the command.

    Could you also try reading the subcommands from Table 10-2. Cell Balancing Status Subcommands from the technical reference manual (TRM) to see how long the device may have been balancing for?

    Also, were there any faults that may have triggered? Cell balancing could also be stopped if the Max or Min Cell Temperature limit was violated as well. 

    Something to keep in mind for Cell Balance Stop Delta is explained in this post: Cell Balancing.

    Best Regards,
    Alexis