I have two I2C devices connected together that both have a 3.3V logic level. The issue I am running into though is that one of the devices is powered down via a switch at times. This is causing issues in my circuit because the device has a ESD protection diode and when off these creates a current path from the I2C pullup to GND (Don't adhere to I2C specifications of HiZ when the chip isn't powered).
I am hoping the use the PCA9306 to isolate these two devices so that when one side turns off there is no current path through the SDA/SCL lines. My plan is to place the PCA9306 chip in line and have pullups on both sides (one set to the always on supply and one set to the switched supply).
My question are:
- Can this chip operate correctly if both VREF voltages are 3.3 volts and there is not actually a level shift (I have seen some other similar chips that specify there must be >1V difference between the VREF values)?
- Will this device isolate the two sides if one of the VREF voltages is removed while the other VREF is still present?
- Are there any internal pullup resistors in this chip (I don't see reference to any but again have seen this is other similar chips)?
- Is there a preference to which VREF I connect the switched side?
The following post seems to indicate that the answer to 2 is YES as long as VREF2 and EN are tied together then connected to my supply. Is this still true if both supplies are 3.3V instead of 3.3V and 1.8V?
If this chip is not the best solution, please recommend an alternative.
Thanks in advance!