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BQ24259: BQ24259: Experience larger VBUS variation during USB source plugin

Frank Ip
Prodigy 10 points
Part Number: BQ24259

I would like to understand this product better. 
I experienced a larger variation in VBUS during USB source plug in comparing to no plug in. 
[This is with battery connected]
[This is with VBUS connecting to a load which also will sink current]

Can you help to explain to me why this the case?

For example, if I were to use the same load connecting to VBUS to perform a repeat test, I experience a larger variation during USB source is plugged in comparing to none.

This is my case number:CS0033866


Thanks,
Frank

  • 0
    TI__Guru**** 166876 points

    Hi Frank,

    I apologize but I do not understand your question.  Are you saying that your USB source voltage drooped when you attached to charger VBUS pin?  When charging the battery with input source attached to VBUS, the charger pulls current up to its input current limit setting.  Input current at startup is set by the PSEL pin but clamped with the ILIM pin resistor.  If the charger is pulling too much current from the source, then the source voltage may collapse.   At that time, the charger's VINDPM loop activates and prevents the charge from pulling more current, effectively regulating the charger's input voltage to the VINDPM threshold.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Guru**** 166876 points

    Hi Frank,

    Since I haven't heard from you in over a week, I am closing this thread.

    Regards,

    Jeff