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BQ76952: Settings:Protection:Body Diode Threshold Set to 6000mA or 600mA, load 6.5A high current discharge, unable to turn on charging FET (CFET).

Part Number: BQ76952

TI experts,

                 1. My MOSFETs are set to series mode.

                 2. Settings:Protection:Body Diode Threshold Set to 6000mA or 600mA, load 6.5A high current discharge, unable to turn on charging FET (CFET).

                 3. I would like the CFET to be automatically enabled on discharge at 6.5A, to prevent thermal damage to the CFET's diode. How should I set the parameters?

                  

                  

                bq76952-6.5A-Discharge-2022-5-25.xlsx

bq76952-0-36-10bei-0.143mR-R00-2022-5-22(CRC).gg.csv

      

  • TI experts,

        I need to add some information.

        DFETOFF and CFETOFF of bq76952 are disabled and enabled by default.

        They are connected to the MCU through a transistor.

        When the MCU sends a high level to the transistor and pulls DFETOFF or CFETOFF to GND,

        the DFET or CFET can be turned on.

        Load 6.5A discharge can not enable CFET, is it caused by my circuit?

        Can't the CFET be automatically enabled when the load is 6.5A using hardware (MCU + triode) control?  

        Do I need to cancel the hardware (transistor + MCU) control?

        Then change to MCU to send commands to control the enable or disable of CFET and DFET?

         

  • Hey Jmyang,

    CFETOFF and DFETOFF are used to bypass any serial communication in order to more quickly turn the FETs off. Your implementation looks a little complicated, and might be contributing to the error you see. The pin can accept up to VSS+6V, so why not connect it directly to your MCU? 

    You can implement control of the FETs using both serial communications and CFETOFF/DFETOFF.

    Try disconnecting the CFETOFF and DFETOFF circuit and see if the issue persists.

    Lastly, make sure this bit is high so that body diode protection is enabled -> Settings:FET:FET Options[SFET] 

    Thanks,
    Caleb

  • Hi Caleb,

         1. Settings:FET:FET Options[SFET] This bit setting is red. As shown in the figure below.

         2. My last version of the circuit diagram did not have this problem.

         The last version of the circuit used the DFETOFF (Both off) function and everything was fine.

         The circuit diagram of this version (that is, the picture I posted above) just adds the CFETOFF function,

         and at the same time, the original DFETOFF function is changed from Both off to only control the DFET.

         It should be noted that the DFETOFF and CFETOFF settings are both 12, that is, the BQ76952 turns off the DFET and CFET by default.

         The MCU only enables (turns on) the DFET and CFET as needed, and the MCU cannot turn off the DFET and CFET.

         I am above, have uploaded the gg file, you can refer to it. 

        

         

  • Hi JM,

    The CFETOFF and DFETOFF pins will disable the FET and body diode protection will not work if the FET is disabled by these pins. In your case is the charge FET disabled by the CFETOFF pin during this test? 

    Regards,

    Matt

  • Hi Matt,

       Yes, the charge FET disabled by the CFETOFF pin during this test.

        As you said, when the charging FET is disabled by the CFETOFF pin,

        then when the load is discharged with a large current, the charging FET can only be enabled through the MCU, right?

       

  • Hi JM,

    That is correct. If they want the body diode protection to work on the CHG FET, they can send the CHG_PCHG_OFF() command and then release the CFETOFF pin - body diode protection will work if the MCU disables the CHG FET with a command.

    Regards,

    Matt