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BQ78350-R1: BQ78350 Won't allow charge or discharge

James Parker
Prodigy 10 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQSTUDIO

We are using a BQ78350-R1 / 76930 with a 7S battery. The customer advises that the batteries stop working after being left for a few weeks, disconnected from anything. We have received these back and it appears both XCHG and XDSG are set and so both FETs are turned off.

We can get it out of this state by RESET on the BQ Studio screen, but the customer cannot access this.

At first we thought it was going into shutdown mode but that doesn't appear to be the case. The Auto_ship mode is not enabled. The cell voltages are low indicating the battery was discharged when it was left, but the CHG FET should still be active. In the current state the battery just appears dead.

Is there any configuration whereby the 78350 can just go "off-grid" after being left? (Config Below)

Many thanks in advance

  • 0
    TI__Guru* 81035 points

    Hi James,

    That is strange. Can you export the data flash settings for this device? (Click Export on the Data Memory screen). I am wondering if there might be any clues in the Lifetime data and I can check if there is anything unusual in the settings. 

    It looks like the [FET_EN] bit is not set in the screen capture. Is the [FET_EN] bit set in the Mfg Init Status data flash? Is it possible they sent the FET_ENABLE() 0x0022 command which would disable the FETs?

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 10 points

    Thanks Matt,

    The customer doesn't use the comms at all. The batteries were working and shipped. They get used but not always recharged after use (which is a different issue) but then when they try to re-charge maybe a couple of weeks later, some are in this state. All have the same settings.

    Here's the datafile.

    Many thanks

    4000 0009.gg.csv

  • 0 in reply to James Parker
    TI__Guru* 81035 points

    Hi James,

    Looking at the Lifetime data, you are correct there are no Shutdown events recorded. The main thing I see is that there are multiple CUV and SCD events recorded. If the battery has been sitting, the CUV events might be of some interest, but this would only open the DSG FET and your BQStudio screen capture does not show this error preset. 

    I am still not sure why the FET_EN bit is set to zero on this device. In the .gg.csv file, is shows the Mfg Status Init register is set to 0x0210 which should set the LED_EN and FET_EN bit. But your BQStudio screenshot shows the LF_EN bit is set and the FET_EN bit is not set. Was this .gg.csv file read directly from the failing device from the screen capture?

    Thanks,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 10 points

    Hi Matt,

    Yes the gg file was exported from the same battery. We program the battery initially but always need to hit the FET_enable and LED_enable to get it into the right state. We never questioned this; thought it was normal, but it shouldn't switch off on its own. Silly question, but would the change to FET_EN off cause the two flags (XCHG and XDSG) to go high? [as well as turning off the FETs].

    Also is there anything else (i.e. a fault condition) that would make FET_EN turn off.

    Many thanks.

  • 0 in reply to James Parker
    TI__Guru* 81035 points

    Hi James,

    Fault conditions can also cause the FETs to open (like ASCD), but the register screen is showing that no faults are present. So it seems this would not explain why XCHG and XDSG are high.

    Matt