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BQ769142: Pre-discharge activation scenarios

hamzeh ahangari
Prodigy 111 points
Part Number: BQ769142

Hello,

I wanted to activate pre-discharge on my BMS chip, with only timer based activation. First I thought, even if it does not activate whenever a load is connected (because DSG is already ON in relax mode), it should has no harm to have pre-discharge. it some scenarios it can help, such as automatic recovery from OCDs, where DSG is turn off and on.

However, there is something that concern me. DSG is also used in high-ampere charging. activating PDSG in that case, not only is meaningless, but can also be harmful. When the charge current suddenly rises, if DSG does not turn on quickly, the body diode can be damaged. If first PDSG turns on, still DSG's body diode is active.

Then, shortly, PDSG should only be activated when DSG is going to be turn on for discharging, not charging. it is like that?

thanks

  • 0
    TI__Guru 54715 points

    Hi Hamzeh,

    Body diode protection has priority over the pre-discharge, so if predischarge is running waiting for the timeout to occur and charge current starts to flow the part will recognize the current and turn on DSG before the normal time.  However this may take up to 250 ms.  After DSG is on PDSG will turn off.   You were concerned with the charge FETs burning out in the time to turn on body diode protection during SCD, so it would be good to determine if the DSG can turn on fast enough during charge connection.