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BQ25628: how to turn off OTG or BYPASS_OTG mode when BQ25628 works?

Ryker She
Prodigy 580 points
Part Number: BQ25628

I try to turn off OTG or BYPASS_OTG mode when BQ25628 works by set EN_OTG=EN_BYPASS_OTG=0, but the output of PMID still exist and less than VBAT 200mV. What cause this phenomenon and how to turn off OTG or BYPASS_OTG mode when BQ25628 works? 

  • 0
    TI__Mastermind 21675 points

    Hello, 

    Are you performing your test on the BQ25628EVM or a custom board? Also do you have any load connected at PMID? 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    TI__Prodigy 580 points

    Hi Garrett,

    I tested on the BQ25628EVM without load connected at PMID, but the output of PMID still exist and less than VBAT 200mV.

    Best Regards,

    Ryker

  • 0 in reply to Ryker She
    TI__Mastermind 21675 points

    Hi Ryker, 

    After OTG mode is disabled PMID voltage should reduce if you have some load attached. You still observe PMID voltage because the PMID capacitor remains charged without any load to discharge it. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    TI__Prodigy 580 points

    Hi Garrett,

    The PMID has output that is less than VBAT 200mV when I just power VBAT without enable OTG mode or BYPASS-OTG mode. So why don't close the Q2 in BQ25628 when disable OTG mode and BYPASS-OTG mode?

    Best Regards,

    Ryker

  • 0 in reply to Ryker She
    TI__Mastermind 21675 points

    Hi Ryker, 

    Apologies for any confusion I caused with my last response please allow me to correct myself. When in battery only mode voltage is expected at PMID because their is a path from BAT to PMID through the body diode of Q2 even when it is off as shown in the functional block diagram in the datasheet. 

    In this scenario Q1 RBFET remains off so there should be no voltage at VBUS while there is voltage < VBAT observed at PMID. 

    Best Regards,

    Garrett  

  • 0 in reply to Garrett Kreger
    TI__Prodigy 580 points

    Hi Garrett,

    Why the forward voltage drop of the body diode only 200mV. Generally, it may should be 600/700mV. And do you consider using a MOSFET without body diode instead of now one for resolving this problem?

  • +1 in reply to Ryker She
    TI__Mastermind 21675 points

    Hi Ryker, 

    The switching FET architecture on the BQ25628 is the same as our other single cell parts with integrated FETs. Voltage observed at PMID when no VBUS is attached due to the path from BAT to PMID through the HS FET body diode is not considered an issue. 

    I cannot comment on the reasoning behind the design decisions made on the part. Please consider this thread closed. 

    Best Regards,

    Garrett