PCA9555: About INT pin's pull-up

Hey Sam,

I always recommend the TCA line up over the PCA as it fixes some bugs, usually has a wider Vcc range, is more cost competitive, and typically pin to pin with the PCA family.

"If the INT pin is floated, can you tell me what is the expected problem?"

-This question depends on if you are using the INT pin.

If you are using the INT pin (connected to an mcu or processor) and there is no pull up resistor then the signal will likely never get pulled high so you will likely just see GND (may float higher). The reason for this is, the INT pin uses open drain architecture which means it will actively pull low when signaled to but when the FET is off, a pull up resistor is expected to pull the signal back high. Without the pull up resistor, there is pull up. So you will not accurately see the INT signal.

If you don't plan on using INT then it can just be left floating as we do not care about the signal integrity of this pin. Mainly because this is an output which does not disturb the internals of the device.

We typically tell people to not let INPUTs float because floating voltages can turn on FETs internally which can cause problems. (INT is an output and not an input so this is not a concern).

""INT should always be pulled up (never left floating) when used. If unused, it can be pulled down to ground, but not left floating.""

-I cannot find this phrase in the datasheet.

Thanks,

-Bobby