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Original question:

BQ25790: SYS vs. PMID vs. BATT output voltages

BQ25790: PMID pin purpose on BQ25790 series.

Christopher Buckley
Intellectual 330 points
Part Number: BQ25790
Other Parts Discussed in Thread: BQ24179

For the parts based on BQ25790 (in particular BQ24179), After reading through the datasheet and EVM guide, I'm still not exactly sure of the purpose of the PMID pins. Is this only to be used in OTG use-cases? Even with OTG use-cases, why not just use VBUS?

What if I have no use for OTG? Can I leave PMID floating or are the recommended capacitors necessary even if I don't plan to drive anything from PMID?

Also curious if there is a different part that you'd recommend that doesn't include OTG support?

Best regards,
Christopher

  • 0
    TI__Guru*** 143950 points

    Hi Christoper, 

    PMID is the input to the converter for forward/charge mode and output for reverse/OTG mode.  All converters need capacitance at their input/output.  TI does not have a converter that does not require at least some capacitance on PMID.  

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 330 points

    Thanks for your response Jeff.

    So for example, say I never need to use reverse/OTG mode, and have a stable 5V supply at VIN1 and some system load at SYS. Do I need to connect anything at PMID other than the recommended capacitance?

    To secure my understanding, say I wanted to use reverse/OTG mode with the same setup but with VIN1 being a 5V supply from a smartphone or something that can handle OTG. What would change? Would PMID have to be routed back to the phone somehow, or is having it connected at VIN1 sufficient? In other words is the sole purpose of PMID to provide designers a place to connect necessary capacitance for the converter or is there some intention to connect it directly to some load/source?

    Edit 1: To clarify my confusion, I wanted to point out that the EVAL board has what appears to be a current testing circuit between TP13/TP14 and R11 implying some planned source/load at VPMID. What is the intended source/load at VPMID compared to VIN1 or VIN2? In the Typical Applications diagram on the datasheets, nothing other than the capacitance is connected.

    Best regards,
    Christopher

  • 0 in reply to Christopher Buckley
    TI__Mastermind 30015 points

    Dear Christopher,

    Please connect the recommended capacitance to PMID as Jeff described.

    Thanks,

    Mike Emanuel

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