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BQ76952: Predischarge corner case in fully autonomous mode

Shyama Agrawal
Intellectual 860 points
Part Number: BQ76952

Hello,

In our BQ stand alone application, we are leaving the DFET ON whenever there is no fault in the system. The creates a problem when suddenly a capacitive load say a motor controller is connected to the output. A large current flows in the output and thus, SCD is getting triggered. When the SCD automatically clears, DFET turns ON again but this time it is preceded by Predischarge which precharges the capacitor of load and now NO SCD fault occurs.

Can we use the load detect or any other feature to decide when to turn ON the DFET in the first place which is generally preceded by Predischarge? Is there a way we could eliminate the first surge current by not leaving the DFET ON by default?

  • 0
    TI__Mastermind 42060 points

    Hello Shyama,

    The image you posted did not upload correctly. It may need to be re-uploaded.

    There are two ways to enable the pre-discharge FET initially. Either through timeout or through a voltage condition set by Settings:FET:Predischarge Stop Delta.

    If using timeout, the PDSG FET will be enabled initially until the timeout time occurs, where the DSG FET gets activated. With a voltage condition the PDSG FET will be enabled initially until the Predischarge Stop Delta condition is met, then it will transition to activating the DSG FET.

    If the DSG FET is already active, the PDSG won't be activated unless the DSG FET is turned off and on again (This could be done through commands).

    See Section 5.2.3.2.2 PREDISCHARGE Mode of the TRM for a description and functioning of the PDSG function.

    Best Regards,

    Luis Hernandez Salomon