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TCA8418: Question about TCA8418RTWR

Jimmy Huang
Genius 3525 points
Part Number: TCA8418

Hello：

My customer uses TCA8418RTWR.Sometimes it is found that the key fails, and the measurement result is K_ Int is always low，What's the problem? Thanks.

  • 0
    TI__Guru 74252 points

    Jimmy,

    Is it possible to share a schematic?

    Regards,

    Eric Hackett

  • 0 in reply to Eric Hackett
    Genius 3525 points

    Hi Eric：

    When a problem occurs:

    After using for a period of time, the key does not respond  occasionally

    The interrupt pin is always low

    Normal:

    The interrupt pin is high level. When the key is pressed, the interrupt pin has low level for a period of time, and it also has low level when the key is released

    Interim solution is testing stability:

    Use the reset pin to reset when the screen is off

    Question:

    When does this problem happen again? Is there a solution?

  • 0 in reply to Jimmy Huang
    TI__Guru 72901 points

    Hi Jimmy,

    The INT pin is an active low so a key press should assert the INT pin low. If K_INT is the INT trigger then you should read the key event register to see which key was pressed. 

    This sounds like you need to have the software poll the device to read the key event register until the K_INT deasserts the INT pin.

    -Bobby

  • 0 in reply to BOBBY
    Genius 3525 points

    Hi BOBBY：

    We also encounter a new problem. The problem shown in the following will not appear on the BGA encapsulated chip, but the problem shown in the following will be encountered on the new QFN encapsulated chip. The driver is the same.

    [operation steps]

    1. Press "1" and "3" simultaneously in the text input box, or press "1" and "3" quickly

    [expected results]

    Correct input, only "1" and "3"

    [actual results]

    "123" will be entered

  • 0 in reply to Jimmy Huang
    TI__Guru 72901 points

    Hi Jimmy,

    I think the issue has to do with way our device samples keypad presses, in particular the loading on the row is large in your set up so we may need to modify the schematic you currently have a bit. Are you able to short the 1k resistors on the row and then add a ~10k pull up on all the rows to Vcc? This should fix the '123' issue you're seeing because it speeds up the rise time between strobe sampling on the columnns.

    -Bobby