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BQ25890: Conditions to enter VSYS_MIN regulation

Nevin McCallum71
Prodigy 50 points
Part Number: BQ25890
Other Parts Discussed in Thread: BQ25895, ,

I am using an EVM and EV2300 to experiment with the bq25890/bq25890H (also considering the bq25895).

I cannot get the part to enter VSYS_MIN regulation mode. Applying 3.2V from a bench supply to VBAT (no other power), I can enable OTG mode and produce 5V on VBUS. However, VSYS never rises above VBAT.

What conditions am I missing to enable the VSYS_MIN mode?

I need this boost function to provide power to a 3.0V LDO that needs to stay out of drop-out, even when my 1S LiPo battery droops to 3.0V (or below, as seen on my system rail).

Many thanks,

Nevin

  • 0
    TI__Mastermind 25800 points

    Hey Nevin,

    VSYSMIN will only occur when you have a valid power source at VBUS. 

    When you have this, your system rail can be maintained at VSYSMIN while also charging a battery whose voltage has fallen below the setpoint.

    Because you only have the Battery present, and are operating in OTG mode, the Vsys voltage will be relatively equal to Vbat.

    Is Vsys powering another part of your system, separate from the LDO rail?

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 50 points
    Hi Joel,

    Thanks for the quick reply.

    Vsys would power some LDO's and bucks other than this critical one, but those don't need as high an input or are OK to drop out.

    Do you have any other recommendations for generating this rail with a minimum of extra components (I quite like the integration of the charger and boost in the bq2589x)? Using OTG and drawing power from PMID on the bq25895 seems interesting, though 5.0V isn't necessary in our application.

    Thanks,

    Nevin
  • 0 in reply to Nevin McCallum71
    TI__Mastermind 25800 points
    Hey Nevin,

    Just so I make sure I understand your needs; you're looking to power that critical LDO from Vsys rather than Vbus or PMID?

    My recommendation for this scenario is a boost converter in line with the Vsys pin to take care of that low battery voltage case.

    Please note also that the charger integrates the boost converter, but both functions cannot be used at the same time. This is typically used for power bank applications.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 50 points

    Hey Joel,

    No, not strictly necessary to power the LDO from any given rail.

    It's not an issue for my application that the boost is not available simultaneously with charging.

    Thanks,

    Nevin

  • 0 in reply to Nevin McCallum71
    TI__Mastermind 25800 points

    Hey Nevin,

     If you are not providing VBUS, the charger cannot provide a Vsysmin voltage.

    In that scenario, if you need a consistent system voltage, a separate boost converter connected to BAT would be able to provide that voltage.

    Take a look at our integrated switch boost converters here  

    Because you are looking for the minimum number of components, take a look at our power modules here

    If you can get away with very very low load currents. I would also look at our charge pump selections here

    I am less familiar with these parts, so if you have questions about them I can try to find you the right group, or you could power under the specific e2e forum group for that part.

    Hope this helps!

    Regards,

    Joel H