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Original question:

BQ24780S: Design and optimization questions

BQ24780S: Reduce Battery Quiescent Current

user3680879
Intellectual 390 points
Part Number: BQ24780S
Other Parts Discussed in Thread: BQ24800

Hi,Sir,

I am considering the Reduce Battery Quiescent Current when only powered by battery.  Base on our test , the Quiescent Current  reached 28uA when the system is power off. 

There have some word about it on 8.2.2.3 Reduce Battery Quiescent Current of datasheet as below. 

. When the system is totally shutdown, it is not necessary to let the internal BATFET charge pump
work. The host controller can turn off the switches in the battery pack to disconnect the battery from the system.

That means no action taken on our 24780?  How can the host to turn off the switches in the battery pack ,as there usually have not another swich in the battery pack which be controlled. 

Would like to have your advice! 

Best Regards,

James

  • 0
    TI__Mastermind 32745 points

    Hi, James,

    Section 8.2.2.3 discussed the low quiescent current ship mode. BQ24780S discharges SRN by 5mA for 140ms. So SRN stays at zero voltage without waking up the smart battery which is in SHIP mode by host. 

  • 0 in reply to Tiger Zhou
    Intellectual 390 points

    Hi, Tiger ,

    Many Thanks!

    The datasheet said:

    When the system is totally shutdown, it is not necessary to let the internal BATFET charge pump work. 

    But how to turn off the BATFET charge pump?  It is not clear in that section. It is only suggest to disconnect the battery.

    As only the battery power the system and we have not another switch between battery and 24780, it can not disconnect the battery and then discharge the SRN pin.

    In our case, the battery is always connected and our purpose is to Reduce Battery Quiescent Current when the system turn off, to retain the battery energe.

    Best Regards,

    James

  • 0 in reply to Tiger Zhou
    Intellectual 390 points

    Hi,Sir,

    Any update for my topic?

    Best Regards,

    James

  • 0 in reply to user3680879
    TI__Mastermind 32745 points

    There is no register setting to turn off the BATFET charge pump. The only suggestion is to disconnect the battery. If you can't disconnect the battery, the quiescent current is about 25uA. Your test data is right. 

  • 0 in reply to Tiger Zhou
    Intellectual 390 points

    Hi,Tiger ,

    Many thanks!

    Is there any other similar product providing such function to turn off the charge pump  to further reduce the quiescent current? BQ24800? 

    Further more ,for 24780, if the battery is 3S with 12.6V full voltage, what would be the MIN AC voltage to charge it ?

    Best Regards,

    James

  • 0 in reply to user3680879
    TI__Mastermind 32745 points

    BQ24800 has similar battery quiescent current as BQ24780S, however it has other improved feature, such as 300kHz/400kHz switching frequency, which helps with the min AC voltage as close as 12.6V.  

  • 0 in reply to Tiger Zhou
    Intellectual 390 points

    Hi,Tiger ,

    Many thanks again!

    Seems the 247800 is pin to pin comparing to 24780? There is lack of  detail datasheet in your website.

    Further more about the quiescent current . We prepare to use the internal comparator for the battery present detect. But the input resistance is just 140k+100k in the EVM circuit, and the leakage current would be 52.5uA , twice of the quiescent current of the IC itself. How about to disconnect the  battery present detect circuit? Is there any function limitation for not using battery present input?

    Best Regards,

    James