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BQ40Z50: Minimum DISP settling / activation time

Cameron Perl
Expert 5375 points
Part Number: BQ40Z50

Hey team I have a customer who is using an IC to simulate a button press going from HIGH to LOW for 5ms.

What is the minimum time required by the BQ40z50 to activate off of the DISP information? Is this something that is settable via firmware?

I thought that there may be a built in de-bounce time since this is typically handled by a button.

Thanks!

  • 0
    TI__Mastermind 19195 points

    Hi Cameron,

    This pin works with button presses and 5 ms will be ok. There is no configurable parameter this setting. 7.12 of d/s has some more relevant info.

    Best regards,

  • 0 in reply to Nick Brylski
    TI__Expert 5375 points

    For some more context:

    They currently use a solution to determine if a double tap is detected on the device, this IC then outputs a high voltage signal which is inverted to ground to pull the BQ40z50 DISP pin low. The IC detecting this double tap is hard set to a 5ms pulse so they can't really change this value. 

    They're running in to the issue where the BQ40z50 doesn't seem to be responding to that short of a pulse when switching from High to low (5ms) to High. That section of the datasheet does not have anything about timing, just electrical characteristics.

    What are your thoughts on this matter? Do they need some form of buffer to extend the low signal hold time if the BQ40z50 can't respond quick enough?

  • 0 in reply to Cameron Perl
    TI__Mastermind 19195 points

    Hi Cameron,

    Can you provide waveforms of the DISP pin, also can you go into detail what you mean by " doesn't seem to be responding."

    Thanks,

  • 0 in reply to Nick Brylski
    TI__Expert 5375 points

    I sent you a quick email!

  • 0 in reply to Cameron Perl
    TI__Mastermind 19195 points

    Hi Cameron,

    The bq40z50 uses an interrupt to handle the “button” (=display on signal) detection.

    I don’t have profiling info how fast that interrupt is but I do have information what the gauge does after it detected a falling edge:

     

    It will start a (debounce) timer with a timeout of 32 x 488us = 16ms (rounded) and it will reject the display trigger signal if the logic level is not “low” after the timer expired.

     

    So it’s 16ms plus ISR delay. 17ms is probably ok. I would suggest 20ms at a minimum. 5ms will not work.

    Best regards,