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BQ25890H: Boost mode without OTG

Steve Fenwick1
Prodigy 250 points
Part Number: BQ25890H
Other Parts Discussed in Thread: BQ25890, BQ25892, BQ25895, BQ25985

I want to use boost mode without enabling OTG or otherwise placing the boosted voltage on VBUS. I occasionally need a much higher voltage for internal uses than the battery cell voltage, and I'd rather not add a separate boost converter. The load would only be a few milliamps (indicator LED driver).

Is there a way to disable RBFET (Q1) but still run the boost regulator, and take the load from SW or PMID?

Would this be any different if we were using the BQ25890 or BQ25892?

Thanks!

  • 0
    TI__Guru 59141 points

    Hi,

    Please consider pin-compatible BQ25895. For BQ25895, when Boost mode is enabled, RBFET Q1 is off. Only PMID is the boost output.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 250 points

    Can you explain this? I don't see mention of that in the BQ25985 data sheet, but I do see the note:

    During boost mode, the status register VBUS_STAT bits is set to 111, the VBUS output is 5V by default
    (selectable via BOOSTV register bits). The boost output is maintained when BAT is above VOTG_BAT threshold

    Thanks!

  • 0 in reply to Steve Fenwick1
    TI__Guru 59141 points

    Hi,

    For BQ25890/890H, Q1 RBFET is on in boost mode. The boost mode current limit (REG0A[2:0]) is implemented via Q1 RBFET. 

    For BQ25895, since Q1 RBFET is off in boost mode, there's no boost mode current limit and REG0A[2:0] function is removed. So it is important not to overload the boost operation by the system design.

    Thanks,

    Ning.