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Original question:

[FAQ] BQ769142: MOSFET short after short-circuit test - voltage now always ON

BQ769142: SCD frequency

Vladislav Mocluza
Prodigy 80 points
Part Number: BQ769142

Tool/software:

Hello TI team,

In the topic [FAQ] BQ769142: MOSFET short after short-circuit test - voltage now always ON you mentioned that:

"The BQ769x2 devices are designed to switch a modest sized FET or FETs for an infrequent switch for battery protection".

Could you clarify which frequency becomes frequent?

Is 0.5Hz - 2Hz the frequent or infrequent value?

  • +1
    TI__Mastermind 42060 points

    Hello Vladislav,

    The device was designed as load-switch, meaning that it ideally will only switch to power the load or disconnect the power from the load.

    There is no defined frequency where we consider the switching to be frequent. But if switching is too fast I would think it may discharge the charge-pump. There are however limitations to how fast the switching can occur (mostly due to the fact that to power MOSFETs back ON it takes 250-ms before the part powers the MOSFETs). So switching frequency by default may be somewhat slower.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 80 points

    Hello Luis,

    Thank you for clarification.

    Correctly I understand that there is a 250ms gap between moment when BQ chip decides to power MOSFET and moment when MOSFET is powered?

    Where can I find more information about it? 

  • +1 in reply to Vladislav Mocluza
    TI__Mastermind 42060 points

    Hello Vladislav,

    Correct. 

    This is in the TRM:

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 80 points

    Hello Luis,

    Thank you for the screenshoot. Could you clarify, do this 250ms happens only in case of CFETOFF/DFETOFF/command case? 

    If BQ decides to turn off MOSFETs on his own, does this delay happen?

  • +1 in reply to Vladislav Mocluza
    TI__Mastermind 42060 points

    Hello Vladislav,

    The case highlighted is solely for turn-ON, not turn-off. Turn-off will be very fast. In this case it is saying that if you deassert CFETOFF/DFETOFF, it may take up-to 250-ms for the MOSFETs to turn back on.

    Best Regards,

    Luis Hernandez Salomon