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TCA8418: Can we add series current limiting resistors on ROW / COLUMN lines of TCA8418RTWR ?

Ray Chang
Intellectual 1345 points
Part Number: TCA8418

Hi Team,

The keys on the keypads considered to be arcing contacts when we press them.

So generally its advised to have a series limiting resistors on these lines to theoretically prove that the dome keys are non-arcing contacts.

Have any internal series resistors in TCA8418RTWR ROWs / COLUMNs pins? The datasheet doesn’t explicitly mention it.

Can we add series a current limiting resistors on each ROW / COLUMN lines of TCA8418RTWR ?

Which ohm value is recommended?

Have any side effect in the operation of TCA8418RTWR?


  • 0
    TI__Guru 71790 points

    Hey Ray,

    The Rows of this device are inputs and have a weak (100k) pull up resistor. The Columns switch between Hi-Z and GND. If you put too much resistance between a switch and the column, you could generate a voltage divider, though something low a few 100 ohms won't hurt. one thing you need to keep in mind is that you could affect the RC decay if you put resistor between a switch and a row.

    Can we add series a current limiting resistors on each ROW / COLUMN lines of TCA8418RTWR ?

    Yes but if you want to put a series resistor on the row, you may want to put pull up resistors from the row to Vcc that are stronger than 100k (like 10k or 20k).

    For columns you can choose a series resistor in the 100 ohm range or lower.

    "Have any side effect in the operation of TCA8418RTWR?"

    It may if you put it on the rows without an external pull up resistor.

    Thanks,

    -Bobby