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BQ24259 OTG short test

Jerry Hsueh
Expert 2730 points
Other Parts Discussed in Thread: BQ24259

Hi

BQ24259 in OTG mode short circuit test (with 0.1Ω resistor connected to VBUS and ground)

1. short test in a short time wiil be no problem as below

2. But after a long time ( Customer's test conditions to maintain OTG short in 1 hour)         

  Hiccup time will be abnormal, turn-on time becomes longer.  Current would be throuth RBFET (Q1) for a short period of time, and cause the battery to discharge below 3.2V.

  Why is this happening? Seems no short circuit protection.

thanks,

Jerry

  • 0
    TI__Genius 13700 points
    Hello Jerry,

    Can you help me understand why the host MCU is not using the INT pin to detect a fault and shut down the OTG instead of leaving it running for so long?

    One thing I am wondering for what might be causing this is that as the battery voltage continues to drop it becomes no longer capable of supplying the pulsed current need to properly trigger the OCP threshold when in OTG operation.

    What does the battery voltage look like when you are in this deeply discharged state? The other option is that when it closes to switches to check to see if the OTG is still shorted the battery voltage droops enough that the bq24259 browns out.

    All of that to say I would strongly recommend that you do not rely on the OTG OCP for anywhere near 1Hr. The part is designed to notify the host controller through the INT pin and REG009:6 that there is and over current on the OTG circuit. I would recommend that if you the host controller uses this information to latch the OTG circuit off or to add a timer loop for periodically checking to see if the short is gone but does so at a much longer interval than 32ms of the integrated Hiccup circuit.