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BQ76930: over ride error report

Shuang Feng76
Expert 3310 points
Part Number: BQ76930

We are confused about the function about Alert over ride. Such as the details in our datasheet.

Could you please give me some comments about this?

In my opinion, when we use ALERT for output, it only output alert signal. But when the problem is serious, the ALERT pin will be pull high. And only can we manual to set host to clear it up?

Hope for your comments. Have a nice day.

  • 0
    TI__Guru 54715 points
    Hi Shuang,
    The ALERT pin is both an output and an input. When it is outputting a low, it will look for some external signal to pull the pin high to trigger the OVRD_ALERT signal. If the pin remains low, it have not fault.
    When the ALERT pin is output as high, it cannot look for the signal to be high because it is already high, so the input function is disabled.
    When the host clears ALERT, there is a 500 us blanking time for the ALERT signal to transition low before the device starts to check for a high again. This is not a parameter in the data sheet, the internal pull down and the recommended RALERT resistor should pull down a normal trace capacitance allowing the pin to go low. If the capacitance is too high the ALERT may still be above the VIL level when the part starts looking at ALERT as an input again. 250 us may be a good maximum time constant for the signal.
    The host must clear up an issue with ALERT.
    If ALERT goes high from CC_READY, there is no fault and FETs are on, if the host wants to turn off FETs it can not set ALERT since ALERT is already high. The host must clear the CC_READY condition to allow ALERT to go low. While communicating to clear ALERT it might set DSG_ON and CHG_ON low. It could also send ALERT high also, once the CC_READY condition is cleared OVRD_ALERT will set.