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TCA8418: Check Iq when device operated in idle key scan mode

Part Number: TCA8418

Hi Team,

Here has a question for TCA8418 supply current Icc,

When we pressed the button(Active key scan mode), the Icc supply current is around 0.1mA, it is normal.

If we don't press any button, the Icc supply current will become 3.6mA. The device should be enter into idle key scan mode, is it correct?

During this mode, the power consumption should be low, why the Icc become 3.6mA?

Should we configure FW to device for idle key scan mode?

  • Hey Ray,

    "When we pressed the button(Active key scan mode), the Icc supply current is around 0.1mA, it is normal.

    If we don't press any button, the Icc supply current will become 3.6mA. The device should be enter into idle key scan mode, is it correct?"

    This sounds odd to me. How long are you waiting before you measure the current at 3.6mA? Do you have a schematic I could take a look at? I am wondering if you have some floating inputs somewhere.

    Thanks,

    -Bobby

  • Hi Bobby,

    We set COL8 and 9 to non-scan key can fix this issue

    By the way, what is the suggestion pull high resistor value for unused col signal?

    And for example, can we set COL8 as an GPIO to output HIGH when the key ROW7 x COL4 is pressed?

    Thanks,

    Kanoe

  • Hey Kanoe,

    "By the way, what is the suggestion pull high resistor value for unused col signal?"

    Any value will work, choosing a lower value gives a stronger pull up but may increase leakage current from Vcc through the resistor. Choosing a weaker pull up would make the line more susceptible to noise but would provide less leakage.

    If it were me, I would probably choose around 4.7k or 10k.

    "And for example, can we set COL8 as an GPIO to output HIGH when the key ROW7 x COL4 is pressed?"

    This works too. This would be the equivalent of a strong pull up using the PMOS of the output stage. The advantage to this is you get to remove the external pull up resistor and save space and cost.

    If the col8 is set as a GPIO you could also just enable the pull up resistor in register 0x2E by setting this register to 0x00h

    Thanks,

    -Bobby