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Original question:

BQ21080: BQ21080 Wont Charge

BQ21080: How to quickly close Q1/Q2 when the input is below VIN_UVLO

Lumina Gui
Genius 3650 points
Part Number: BQ21080

Dear TI Engineer,

We encountered an issue when using BQ21080. When the input VBUS (IN) suddenly surges, the VBUS (IN) will be short circuited to ground by the front-end OVP device, which causing the voltage of the output SYS and VBAT drop to below 2V (Due to the structural limitations of our product, the battery is far from BQ21080, and VBAT cannot be re-powered in time). At this time, the VBAT undervoltage protection of BQ21080 is triggered, which shuts off the VSYS output, causing the system to power off and ultimately leading to system reset.

The conclusion we have analyzed is that VBUS instantly decreased from 5V to below VIN_UVLO, and BQ21080 did not close Q1/Q2 in a timely manner, resulting in VBAT and SYS being pulled down. Therefore, we want to confirm how to achieve quick closure of Q1/Q2 when BQ21080 detects that VBUS is below the input threshold VIN_UVLO.

Thanks,

Kind Regards

  • 0
    TI__Genius 17905 points

    Hi Lumina Gui,

    Can you please provide some waveforms to describe the situation a bit more visually, and to get an idea of the timing?

    Unfortunately there isn't a way to directly force Q1/Q2 to close more quickly but there is a few strategies that we can try to help.

    Lumina Gui said:
    When the input VBUS (IN) suddenly surges, the VBUS (IN) will be short circuited to ground by the front-end OVP device

    To understand better, it looks like there is a device in front of VIN that will pull VBUS to GND (rather than leave it floating) if VIN/VBUS is found to be greater than some OVP threshold.

    A couple things that I can think of are:

    • Using SYS_MODE to select VBAT_ONLY if VIN is falling. This may be difficult to time, but if the house can react to the INT pulse caused by VIN falling below PG, it can set SYS to BAT power before VIN continues to pull it down very quickly.
    • increasing SYS capacitance to make it more resistive to changes in voltage.

    Otherwise we can continue to investigate if there are any other resolutions for this behavior.

    Best Regards,

    Juan Ospina