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BQ76920EVM: Questions about the Precharge-Circuit

Paul K52
Intellectual 640 points
Part Number: BQ76920EVM
Other Parts Discussed in Thread: BQ76920, BQ78350

Hello,

Im wondering why you are using a PNP-Transistor? Is there are reason why you are not using an NPN-Transistor?

The diode in series with the PNP-Transistor is just to prevent current flow back from the Battery to the REGOUT-Pin of the BQ76920, right?

These quesions are refered to the BQ78350 datasheet on page 15. The circuit with the PNP-Transistor is shown there.

Thanks for helping me.

  • 0
    TI__Expert 4640 points
    Hi Paul,

    For your first answer, the reason we use a PNP is because the bq78350 is active LOW so then when you want to activate the pre-charge feature you drive low and the PNP will draw current from the LDO (REGOUT) of the monitor to drive the charge FET. Usually you would have a deeply discharged battery that the FETs could be OFF so this would allow another way to slowly charge up the battery enough to drive the CHG and DSG FETs.

    You answer to question two is correct.

    Thanks

    Miguel