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BQ40Z50-R1: Overcharge is not protected

Sunrain
Intellectual 615 points
Part Number: BQ40Z50-R1
Other Parts Discussed in Thread: BQ40Z50

Hello,
I have two questions about BQ40Z50 for consultation.
1. There are four groups of PF faults on the customer's side, COV=3650mV SOV=3800mV. When the BMS voltage is 3650, the COV is not triggered, and the charging MOS is not turned off. Until the battery is charged to 3800, the SOV is triggered and the BMS is turned off. What causes this abnormality?
2. After the PF fails, without re-programming the firmware, is there any way to turn on the FET?BQ40Z50.gg.csv

  • 0
    TI__Guru** 105760 points

    Hello Jingming,

    COV will only disable the CHG FET, not the discharge FET, the SOV PF will disable both FETs. Can you share a log that shows COV being triggered and the charge still occurring?

    They would need to send the clear PF command to clear the SOV fault.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 615 points

    Hello,
    1. After I clear the PF status, the charge and discharge test is normal, and the BMS can be protected normally.
    2. The attachment is the data that has not been tested by BMS before clearing the PF Status.
    Please help to check under what circumstances the COV will not act, which will trigger the PF StatusBQ40Z50.log

  • 0 in reply to Sunrain
    TI__Guru** 105760 points

    Hello Jingming,

    I took a look at your logs and settings. The XCHG bit has been set on your gauge since the beginning of the log, so something else is disabling the XCHG and somehow you're still charging. To me this looks like it could be something hardware, since the firmware is saying the FET should be off but there's still charge current flowing. Is there a bypass around this FET or is the FET damaged? Are you testing on an EVM?

    Sincerely,

    Wyatt Keller 

  • 0 in reply to Wyatt Keller
    Intellectual 615 points

    Hello,
    I have already explained it before, but it may not be clear.
    In order to verify whether it is a BMS collection problem, the charger's positive terminal is connected to B+ of the BMS, but not to P+. The negative pole of the charger is connected to the P- of the BMS. So the current can be detected

  • 0 in reply to Sunrain
    TI__Guru** 105760 points

    Hello Jingming.

    If you bypass the protection FETs they will not have any effect even if the COV is triggered. I'm not sure of the intention of the test since if the charger was connected to P+ and P- it would've been disabled. the DSG FET remains active during COV.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 615 points

    Hello,
    1. I have already said this before, it may not be clear. This test just wants to verify whether the voltage collection of the BMS is normal during the charging process. Because the FET has been turned off, it can only be connected to B+ to charge.
    2. There are gg and log files in the attachment. I want to know under what circumstances the COV can't turn off the FET when charging, but the SOV can turn off the FET?

  • +1 in reply to Sunrain
    TI__Guru** 105760 points

    Hello Jingming,

    Sorry for the holiday delays.

    COV only turns off the charge FET, SOV turns off both charge and discharge FETs. The charge FET will remain active during a discharge of the battery even if the COV is active, this is to protect the body diode of the FET since they are in series.

    Besides the FET being enabled during discharge for COV, the COV protection should always disable the charge FET if there is any charge, or current below the dsg current threshold. Otherwise the protection is probably not enabled. The log shared showed the XCHG bit already set in the test so it was not useful to determine if the COV was actually trying to disable the charge FET.

    Sincerely,

    Wyatt Keller