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BQ40Z80: Protection triggered, but charge FET closed and discharge FET open

Dominik Dungl
Prodigy 40 points
Part Number: BQ40Z80

Hi,

I am having troubles understanding why I cannot charge a 2S battery with the BQ40Z80.

Everything seems to work fine in general with the golden image I created.

But if I discharge the two batteries beyond 0% or 6V the following happens:

I can discharge until the built in cell detections triggers, BUT I cannot charge anymore.

It seems the CHG FET is closed but the DSG FET is open?

I assumed some sort of alert or permanent fail was triggered, but when I have a look this does not seem to be the case:

I can only start charging again if I take control by FET_EN and then CHG_FET_TOGGLE.

Why is that the case? What am I missing?

Thanks you,
Dominik

  • 0
    TI__Guru** 105590 points

    Hello Dominik,

    I have assigned someone to take a look at this by the end of business tomorrow.

    Sincerely,

    Wyatt Keller

  • +1 in reply to Wyatt Keller
    TI__Mastermind 37761 points

    Hello Dominik,

    The PCHG bit is enabled in the Operation Status B register which is causing the CHG FET to close.

    One solution for this is changing the PCHG_COMM setting so the CHG FET turns on instead of the PCHG FET.
    To do this go to Data Memory, then go to Settings. Then under Configuration click on FET Options. Then
    set the PCHG_COMM bit to high.

    Also, you could change the charging voltage settings. By default, the gauge will go to precharge if
    the cell voltage is between 2500-2900mV. To change these voltages, go to Data Memory, then go to
    Advanced Charge Algorithm. Then go to Voltage Range. For more details on these settings, go to section 19.5.9 of the TRM.

    Sincerely,
    Nick

  • 0 in reply to Adrian
    Prodigy 40 points

    Hello Nick,

    Thank you, this might be the case. I'll have to investigate further.

    I am confused because we implemented the PCHG FET, but apparently it is not opening correctly.


    I will try to reproduce the issue and then toggle the PCHG_COMM bit and also switch R82 to 100Ohm as shown in the EVM.

    Thank you for pointing me in the right direction,

    Sincerely,
    Dominik

  • 0 in reply to Dominik Dungl
    TI__Mastermind 37761 points

    Hello Dominik,

    Let me know how the test goes.

    Sincerely,

    Nick

  • 0 in reply to Adrian
    Prodigy 40 points

    Hello Nick,

    We have found the issue. We've switched P- and N- FETs for the PCHG.

    Thanks again,
    Dominik