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BQ25892: Boost mode

Tuong PHam
Prodigy 75 points
Part Number: BQ25892

Hi Experts,

We are using bq25892 for Battery charger in our project. Battery is ~8000mAh, (4 cells in parallel) as attached schematic.

We designed with 4A charge current limit.

My question are:

* In case of Adapter is not plug (or power is off), we want use boost mode of bq25892 to supply 5V to system. Will 5V appear at VBUS pin if boost mode is enabled? Is that possible ? And SYS pin still have voltage equal battery voltage?

* Could you review our schematic, please

Thank you very much

Tuong

1464.BMS.pdf

  • 0
    TI__Guru**** 166626 points

    Tuong,

    I do not see any obvious errors on the schematic. 

    The boost operation to provide 5V at VBUS can be enabled if the conditions are valid:

    1. BAT above BATLOWV

    2. VBUS less than BAT+VSLEEP (in sleep mode)

    3. Boost mode operation is enabled (OTG pin HIGH and OTG_CONFIG bit =1)

    4. Voltage at TS (thermistor) pin is within range configured by Boost Mode Temperature Monitor as configured

    by BHOT and BCOLD bits

    5. After 30 ms delay from boost mode

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 75 points

    Hi Jeff,

    Thank you.

    After I posted this post, I read ds again, CE need pull low in case we want it run without a MCU. 

    One more question: Is voltage still available at SYS in Boost mode?

    Tuong

  • 0 in reply to Tuong PHam
    TI__Guru**** 166626 points

    Tuong,

    In boost mode, V(SYS)=V(BAT)-I(BAT)*RdsonQ4.  It is not regulated.  From power balance, efficiency=V(BOOST)*I(BOOST)/(V(BAT)*I(BAT)), you can use datasheet efficiency curves to find I(BAT) and then V(SYS).  I don' recommend loading V(SYS) as there will be less power available for the boosted output at VBUS.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 75 points

    This information very helpful. Thank Jeff.

    Tuong