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TCA9535: Driving I/O pins as high impedance outputs

Amartya Purushottam
Prodigy 10 points
Part Number: TCA9535
Other Parts Discussed in Thread: TCA9555

I am using the I/O expander evm and trying to drive the I/O pins as outputs in a tri-state mode. I am aware that the pins can be driven as high impedance inputs but my use case is specific to these pins be treated as outputs. I was wondering if it was possible to somehow enable this functionality or find a work-around to do the same thing?

Thanks,

- Marty 

  • 0
    TI__Genius 17205 points

    Hello Marty,

    Can you explain why you want this?  This doesn't seem to make any sense to me.  Why do you want an output high-z????  Do you have block diagram or schematic?

    Francis Houde

  • 0 in reply to fhoude
    TI__Expert 7895 points
    Hi Francis,

    Thanks for the reply and offline discussion. We initially thought there was a state where the IOs could be configured as outputs and then disabled (high-Z). But the IO options are input (high-Z but input structure, power-on default), or driven output.

    We tested the case where the TCA9535 is powered on, all IOs configured as inputs and tied together, and swept the voltage across the IOs from GND to VCC in 100 mV increments. As expected, we observed higher ICC between VIL and VIH, peaking ~ 12 mA when VIO = 1.6V.

    This is well below the 160 mA max ICC spec in the datasheet, so we don't anticipate issues with the device in this state. Ideally, we'll either switch to TCA9555 (integrated 100 kohm pull-ups on all IOs) which ensures all IOs are terminated, or if some IOs must be low at power-up, we'll externally pull-down those IOs on TCA9535.

    Thanks,

    Jonathan