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TCA9539: Pull-ups/downs on unused inputs

Stefan Lugmair
Prodigy 20 points
Part Number: TCA9539
Other Parts Discussed in Thread: TCA9535,

The DS of the TCA9535 says:

"the TCA9535 does not include the internal I/O pull-up resistor, which requires pull-ups and pulldowns on unused I/O pins when configured as an input and undriven."

I cannot find such information in the TCA9539 DS. Does this mean I can leaf unused input pins floating on the TCA9539?

I have an application where it is neccessary to switch pins to high-Z (by configuring them as inputs) without having a pull-up or pull-down connected.

If I have to pull the inputs to a defined state, what is the max. possible resistor value I can use?

Thank you!

  • 0
    TI__Guru 73991 points
    Hey Stefan,

    The reason why we suggest the use of either pull up or pull down resistors on the inputs is because the inputs stage of the device is connected to CMOS (NFET and PFET) gates. If you have a floating pin on a gate you could partially turn them on and get shoot through current. This is NOT something that would damage the device but it does mean we may see more current consumption then normal.

    If you are not worried about extra current consumption (you may care about this if you are designing a wearable) then you can leave the inputs floating.

    Thanks,
    -Bobby
  • 0 in reply to BOBBY
    Prodigy 20 points

    Hi Bobby,

    thank you for the quick and thorough answer.

    Best,

    Stefan