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Original question:

BQ24780S: disable output power

BQ24780S: power path switching gap

Geoffrey Tseng
Prodigy 60 points
Part Number: BQ24780S

Hi, I have a problem on BQ24780s application again.

BQ24780s can do the power path management between battery output and DC input.

When DC input plug in , BQ24780s will auto switch power loop from battery to DC input.

In the meanwhile, there will have a power drop in a sudden.

It inpacts my system's power. Cause the MCU be reset.

How to eliminate or reduce the impulse power drop?

Any help is appreciated.

  • 0
    TI__Expert 5330 points

    Hi Geoffrey,

    When the adapter plugs in, there is a break-before-make behavior in the BATFET and ACFET in order to make sure the adapter is not shorted into the battery.  This is implemented by first turning off the BATFET and then turning on the ACFET.  There is a brief period of time after the BATFET turns off, before the ACFET turns on when the power is supplied to the system from the battery across the body diode of the BATFET.  This causes a forward voltage drop (usually ~0.7V) across the diode until the ACFET turns on.

    Is this what you are seeing?  If your system cannot tolerate the 0.7V drop during the switchover, you could add a Schottky diode in parallel to the body diode of the BATFET.  This will reduce the forward drop to ~0.3V, which will hopefully give you the margin you need.

    Regards,

    Steve