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Original question:

[FAQ] I2C IO Expander Schematic Checklist

TCAL6416: TCAL6416 Floating P Ports

IDK
Intellectual 290 points

Part Number: TCAL6416

Hello, 

The TCAL6416 datasheet has the following note: "Resistors are required for inputs (on P port) that may float. If a driver to an input will never let the input float, then a resistor is not needed. Outputs (in the P port) do not need pullup resistors." 

If we have inputs that may float, can this issue be addressed by enabling the internal pulldowns or pullups on these inputs?

Or is there an issue related to the power up defaults of the device, where those pulldowns & pullups would be disabled, so they would come up as inputs that are floating (because the internal biases have not yet been set)?

What is the actual issue or risk? Would there be excessive current drawing in the case of a floating input? What if we powered up but within 1 second of power up programmed the registers such that the pullups or pulldowns were enabled?

Thanks,

Matthew

  • 0
    TI__Guru 64988 points

    Hi Matthew, 

    IDK said:
    What is the actual issue or risk? Would there be excessive current drawing in the case of a floating input? What if we powered up but within 1 second of power up programmed the registers such that the pullups or pulldowns were enabled?

    This would be a workaround. 

    Floating CMOS input pins can cause increase in ICC current through the supply. Also they can cause indeterminate logic levels, which would affect the input port register and potentially flag a false interrupt if the interrupt is unmasked. 

    Regards,

    Tyler