TCA9555: Not use VCC for I2C bus pull up

3.3 is below V_IH, so this would not work.

There are level-shifting expanders like the TCAL9539, but not for 5 V.

The simplest solution would be an I²C level shifter like the LSF0002. If you want only some I/Os at 5 V, add level shifters like the TXU0104/TXU0204/TXU0304 at the I/Os.

Hi Oscar,

The spec that Clemens is referencing is the VIH spec on the Pxx pins (GPIO side). VIH = 70% of VCC = 0.7 x VCC = 3.5V. 

3.3V is less than the requirement, meaning that when in the HIGH logic state on the IO side, it may or may not be recognized as a HIGH by the IO expander. 

You might need a level translating IO expander, TCA6408A, TCA6416A are two examples of level shifting occurring between the I2C side and the IO side (VCCI and VCCP are separate supplies for the I2C lines and GPIO side respectively). 

If you desire to use TCA9555 with 3.3V inputs, you will need some type of FET for level translation. 

The examples Clemens has suggested are all suitable. 

Regards,

Tyler