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BQ78350-R1: CHG FET can not turn on when discharge current ≥ Dsg Current Threshold issue

James Liu38
Prodigy 145 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ76200,

Hi TI team,

We use BQ78350-R1+BQ76400+BQ76200 as 14S BMS(DSG and CHG different path) and use scaling by current calibration.

Here we found one issue when battery pack discharge 20A and cell temperature reach OTC(50 degree-C) protection the CHG FET turned off

even under the condition: discharge current ≥ Dsg Current Threshold (shown in the TRM 3.1).

Is there any setting that we have to change or revise?

Thanks and best regards,

James

  • 0
    TI__Mastermind 42060 points

    Hello James,

    The BQ78350-R1 was not made with different CHG/DSG paths in mind, it supports a series FET configuration. Different DSG/CHG paths was not an intended configuration for it.

    Any protection that would disable a FET, can be bypassed if enough current is still flowing through the sense resistor. Which would then enable the disabled FET due to the body-diode protection feature. This is not possible to be disabled. Different path configurations usually have the body-diode protection feature disabled completely.

    OTC should only occur during charging, so I find it odd that it happened during a discharge, are you sure it is not OTD triggering? This would not allow any discharge current to flow through. See Section 3.7 Temperature Protections of the TRM for entry/exit conditions of the temperature protections.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 145 points

    Hello Luis ,


    Thanks a lot for your quick reply.

    After check again, CHG FET didn't turn on due to OTD also is active and stop DSG and CHG. But due to the temperature is still under OTC condition so the CHG FET is still off even there is no charging. It will be no issue for us. Sorry for the condused.

    Thanks again and best regards,

    James