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PCA9544A: Unused Interrupts connected to Vcc

Boris Lysynski1
Prodigy 125 points
Part Number: PCA9544A

The datasheet states "If unused, interrupt input(s) must be connected to VCC", can they be connected directly to Vcc (like A0, A1) or do they need a pull-up?

Thanks for the help.

  • 0
    Guru 316760 points

    CMOS inputs have a high impedance and do not need a resistor.

  • 0 in reply to Clemens Ladisch
    Prodigy 125 points

    Thanks but that's assuming the input is a strict CMOS input, without any other gates/devices.  Perhaps an answer from TI would help.

  • 0 in reply to Boris Lysynski1
    TI__Genius 15345 points

    Hi Boris,

    If you are not using the INT feature at all you can even leave the INTs floating. Connecting the interrupt inputs directly to VCC should not be an issue. However the INT output should not be connected directly to VCC. We recommend using a pull up resistor for that pin.

    Best,

    Chris

  • 0 in reply to Chris Ayoub
    Prodigy 125 points

    Hi Chris,

    Thanks for the reply.

    The datasheet clearly indicates that the INT inputs should not be left floating but doesn't specifically say if they can be directly connected to VCC which is why I'm asking.  I'm aware how CMOS operates an understand that if that's all the input is it shouldn't be a problem but what has me worried is that the datasheet specifically says A0, A1 can be directly connected to VCC but does not indicate it for A2 or any other input... why?

    I hope that explains why I'm hesitant and why I'm asking what appears to be a question with an obvious answer if it were only CMOS.

  • +1 in reply to Boris Lysynski1
    TI__Genius 15345 points

    Hi Boris,

    Let me be more clear. What you are referring to in the datasheet about inputs not being able to float can be read about here. The reason that inputs can't float is because there is a threshold for these CMOS inputs where the NFET and PFET are on at the same time and current will flow from VCC to GND. This surge in current can damage your device. That means for all inputs including all Address ports, they should not be left floating. What you can leave floating is the INT output pin. This is my mistake for not clarifying earlier, hopefully it makes sense now.

    All the interrupt input pins can be shorted to VCC. There is built in protection on the pin to limit the inrush current. This is true as well for all the address pins you can connect them straight to VCC.

    Best,

    Chris