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BQ25703A: Can BQ25703A output VSYS when no battery ?

Jeff Yang76
Intellectual 490 points
Part Number: BQ25703A
Other Parts Discussed in Thread: BQSTUDIO

Hi,

If battery not exist, provide VBUS to BQ25703A, can BQ2570A output VSYS provide to system as a buck or boost converter?

Because our battery is not ready, we are thinking about use external power source provide to BQ25703A, then BQ25703A provide power to system.

Thanks!

Jeff

  • 0
    TI__Mastermind 25800 points

    Hey Jeff,

    Yes, the architecture of the BQ25703A is a buck-boost NVDC charger. This means the system voltage, with a valid input source present, can be regulated to any level near, below, or above the input voltage, even with a dead battery.

    This NVDC architecture allows the system voltage to be regulated to a minimum value (programmable via I2C) and will track with the battery as the cell voltage climbs due to charging. This allows for an instant-on system regulation even in the presence of a dead battery.

    You can refer to section 8.6.5.1 System Voltage Regulation of the datasheet for more information on this architecture and the system voltage regulation.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Intellectual 490 points

    Hi Joel,

    I understand NVDC architecture can let system works when battery voltage below minimum system voltage.

    But if battery is totally removal? Is it still work?

    I have tried to provide VBUS 5V and disconnect battery, then set REG0x0D/0C minimum system voltage to 8192mV on BQ25703A EVM,

    But BQ25703A only output about 2.8V.

    Below is my GUI setting on EVM board, could you help me to check there have something wrong?

  • 0 in reply to Jeff Yang76
    TI__Mastermind 25800 points

    Hey Jeff,

    Is this on the BQ25703AEVM or a custom board?

    Does the converter regulate VSYS normally when the input voltage is at 6V?

    Do you have a load present on VSYS at the time you apply the 5V input? 

    Are you using the integrated independent comparator? I noticed you have the FORCE_LATCHOFF bit flipped on in ChargeOption1.

    And last question: Do you have an image of the BQStudio GUI registers when the charger is operating? In other words, does the above image represent the settings you program only, or what you read from BQStudio once the charger is operating and VSYS has fallen to 2.8V?

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Intellectual 490 points

    Hi Joel,

    Sorry, I found my JP6 is turn on, connect to GND, caused BQ25703A into Hi-Z mode.

    After turn off JP6, it is normal work now.

    I will close this case.

    Thanks!

    Jeff