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BQ25713: Switcher not starting - SYS_SHORT bit set

Dan Closson
Prodigy 170 points
Part Number: BQ25713
Other Parts Discussed in Thread: EV2400

Hello TI power forum,

I'm testing a design based on the BQ25713 and have noticed that occasionally when cycling the power (VBUS) that the switcher will not start up but VSYS stays just over 1V and the SYS_SHORT bit is set. I've tried but cannot reproduce this behavior on the EVM module. We've stayed very close to the EVM reference design so I'm not too sure what is causing this issue. If I manually clear the SYS_SHORT bit then the switcher will immediately start-up.

Some additional observations. With the EV2400 connected and battery management studio open and monitoring the BQ25713 registers I notice that the SYS_SHORT bit actually gets set on a power down event (only sometimes). If I then turn power on immediately it will be stuck on a SYS_SHORT and power cycling will not help unless I power down long enough for the capacitance to drain and SYS_SHORT bit resets (about 5 seconds).

Any idea as to why this is occurring?? This seems to happen in about every 1 in 10 power downs and will only really manifest itself if I power up right away while the SYS_SHORT bit is set.

Thanks,

Dan C.

  • 0
    TI__Mastermind 25800 points

    Hey Dan,

    Do you have a schematic you can provide?

    Regards,

    Joel H

  • 0 in reply to Dan Closson
    TI__Mastermind 25800 points

    Hey Dan,

    I looked over your schematic but nothing really stood out. The only odd items are diodes D12 adn D13. I am not sure why you have added those, but they are not present on our EVM. You may want to try removing them to see if it makes an impact. 

    When you performed this test, did you have a battery present?

    What input voltage did you test with?

    And did you have any load applied on VSYS when you did this?

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 170 points

    Hi Joel,

    Thanks for having a look. I cannot reproduce this issue with a battery connected, only when no battery is connected. I have been testing with a bench top supply set to 12V. I've tried testing with no load and with a 0.5A load and can produce this fault in both scenarios but only without a battery present.

    I noticed that the EVM does have some additional bulk capacitors (33uF tantalum caps) in addition to the ceramic caps so I tried adding them with no observed difference.

    The schottky diodes across the current sense pins are to protect the differential inputs during high inrush or fault current events.

    Our application should always have a battery connected so I don't anticipate this being an issue but I'd like to understand what is happening.

    Thanks,

    Dan C.

  • 0 in reply to Dan Closson
    TI__Mastermind 25800 points

    Hey Dan,

    It is difficult to say what is different between your custom board and the EVM that would be causing only on your board and not the EVM.

    What I would suggest is comparing two waveforms with the following information:
    EVM vs. Your Board:
    -Rising and Falling edge of your power cycle
    -Capture:
    1) VBUS at the pin of the charger
    2) VSYS at the pin of the charger
    3) SW1 at the pin of the charger
    4) VSRN at the pin of the charger

    Another thing that comes to mind are your register settings as compared the EVM. Is anything programmed into the charger at startup on your board? Do you have a register dump pre-power cycle?

    Regards,
    Joel H