TCA39306-Q1: Is it suitable for 1.8V on both side, each 1V8 may power off or power on?

When VCC2 is up, the two sides are connected to each other. You could replace the TCA with two wires.

I would recommend a simple switch like the SN74LVC2G66, but it needs to stay powered, and a control signal.

Hi Shan,

For the TCA39306-Q1 device, in your configuration when Vref1/Vref2 are GND, side 1 and side 2 are HIGH-Z. With how TCA39306 is designed though, if Vref1 is GND and Vref2 side is powered, there will be some leakage current from Vref2 into Vref1 during that case. 

For a switch solution I will reassign the thread to the subject matter expert if you have questions or want a different suggestion (please let us know if Clemen's suggestion works for you or not.)

-Bobby

Thanks for looping me in Bobby!

Hey Shan,

If you're just looking to isolated the I2C bus, Clemens suggestions is a good one here and will work. The SN4LVC2G66 has an automotive version as well (SN74LVC2G66-Q1). It will be able to support the voltage and frequencies for FM+ I2C. As Clemens also mentioned though, you'll need to keep the device powered up. 
If you're also looking for a solution in which the VCC would be powered down occasionally with the 1V8 I2C signals may be present still at the I/O's, your best bet would be 2x TS5A3166-Q1

Thanks,
Rami

Thanks, Rami, Bobby and Clemens.

I think your suggestions are workable. But recently , I found that diode PI4ULS5V202Q can translate I2C between 1.8V on both side and has 2Mbps speed.

I prefer to try PI4ULS5V202Q at first.   

Thank you