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BQ24780S: disable output power

Geoffrey Tseng
Prodigy 60 points
Part Number: BQ24780S

Hi, I need a function that disable BQ24780s power output  by hardware when battery is present .

I tried to short the BQ24780s VCC pin (pin28) to ground , but the output power still there.

It would be appreciated if someone can give me suggestion.

Thanks.

  • 0
    TI__Mastermind 25800 points

    Hey Geoffrey,

    What do you mean disable the output power? You want to isolate the battery or the adapter from your system rail?

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 60 points

    Hi Joel,

    Thanks for your reply.

    BQ24780s manages adapter power and Battery power.

    The situation is:

    My product is composed with 3 PCBs.

    The battery and BQ24780s board are the first order when assembly my product.

    It means, the 2nd order and 3rd order PCB will be assembled with in powered condition if BQ24780s keep power output.

    In this situation, it may cause electrical damaged for these PCBs.

    So I want to find out a way to cut the BQ24780s power output temporary during assembly process (without adapter plug in).

    I found the MOS(high side/low side) will leakage the power from battery.

    Maybe it is the root cause.

    If add a diode to stop leakage, it may add the power consumption.

    Is there any smart way to deal with it?

      

  • 0 in reply to Geoffrey Tseng
    TI__Mastermind 25800 points

    Hey Geoffrey,

    You will always have this issue with any NMOS buck converter where the input to the buck converter is also the input to your system.

    The NMOS body diode will always be able to conduct current.

    Keep in mind that his charger also has an external BATFET that also connects to the system while the adapter is not present.

    You can add a diode to stop the leakage of the HSFET, but you cannot add a diode to the BATFET side. 

    I would suggest adding a load switch to your circuit between your input from PCB1 and your system load on PCB2 and 3.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 60 points

    I see.

    Thanks , Joel.