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BQ24295: Insufficient current at PMID output

Varun Kirti
Prodigy 40 points
Part Number: BQ24295

Hi,

I have designed an OTG power bank using BQ24295. I am using the default mode of operation. Following is my circuit for reference. But when I try to charge an external device, I get a default charge current of not more than 500 mA at the PMID pin. According to the datasheet, the default current should be 1.5A. I don't seem to understand where does the problem lie.

uHub_project.pdf

  • 0
    TI__Mastermind 25800 points
    hey Varun,

    Is this when there is only a battery present? Or do you have the USB plugged into VBUS (and D+,D-)?


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 40 points
    I tried for the case when USB is plugged into Vbus along with the battery present.
  • 0 in reply to Varun Kirti
    TI__Mastermind 25800 points

    Hey Varun,

    So if you are testing for the case where USB is plugged into P2 (meaning there is a voltage on VBUS), then you cannot be in OTG mode.

    Therefore, any current coming out of PMID into P1 is being pulled from the USB source on VBUS. Basically, your u-USB is powering your USB Type-A connection. 

    Now, in terms of our charger, the default limit for OTG current is 1.5A of output, but only when you are in OTG mode. When the charger is the standard buck mode, we measure current going through Q1 and compare that to the IINDPM limit that is detected using the D+/D- lines. The charger will provide less and less current to the battery the BAT pin if you continue to pull current from through PMID.

    If you want to test OTG mode, you need to remove the source on VBUS (i.e. P2). 

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 40 points
    I tired with and without voltage on P2. On my PC board I also shorted D+ D- on both the USB ports P1 and P2.
    I am using a 2000mAh battery to source the current to charge an iPhone 7 and an One Plus 1.

    I did remove he source on P2 as you said and stil the problem persists.
    So, I notice that when the iPhone had Low Battery it was able to pull upto 800mA of current but it keep on reducing as the battery charges and drops to about 500mA within 30% of charge.
    The current is also dependent on the type of phone, on One Plus One it was about 900mA but the current reduces rather quickly. I thought the IC was able to maintain constant current.
  • 0 in reply to Varun Kirti
    Prodigy 40 points
    Also, is there a way in this IC or another solution offered by TI which is similar but has some sort of led indication for battery capacity of the power bank.
  • 0 in reply to Varun Kirti
    TI__Mastermind 25800 points
    Hey Varun,

    Have you tried to load the charger using an Electronic Load instead of another phone?

    Typically, the current that is pulled by another phone is dictated by the charging system within that phone. If the phone does not draw more current from the power source (i.e. the bq24295 in OTG mode), then the charger will not force more current into it.

    Try a CC load on P1 with no power on P2 such that you only pull current from the OTG output.


    Regards,
    Joel H