Tool/software:
The TCA family of Texas Instruments I2C switches all support voltage translation. It's important to use the correct Vcc for the I2C switch to separate the voltages when channels are enabled. The only requirement is for the Vcc to be low enough to support this, as the Vcc voltage is the gate reference voltage for FETs inside the TCA switch/multiplexer devices.
Consider this scenario: the main SDA/SCL bus is pulled up to 3.3V, Ch1 is enabled with a pull-up of 1.8V, and the VCC of the device is 3.3V. In this scenario, with Ch1 enabled the VCC is too high in relation to the 1.8V pullup voltage, causing the drain-to-source impedance to decrease and turn on the transistor.
This creates a resistor divider between the two pull-up values. If these two resistors are the same, then the voltage on both SCL/SDA lines will likely be the midpoint of these two pull-up values. This midpoint voltage will be the voltage when the lines are idle.
Here's a simulation picture that makes this explanation clearer with both pull-up resistors being 5kΩ.
To avoid this error, designers must make sure to select the appropriate VCC for their device. The correct value can be found by referring to the Vpass diagram in the TCA datasheets. Vpass refers to the lowest pull-up voltage value on device channels, including the main SDA/SCL. For instance, if the lowest pull-up voltage is 1.8V on channel 1, this will be referred to as the passfet voltage, denoted as Vpass.
The maximum allowed Vcc is 3V for proper-level translation in applications where the lowest pull-up voltage is 1.8V. Designers should choose to use either 1.8V or 2.5V for the new Vcc, and the voltage translation of the TCA device will work properly with either option. Furthermore, a schematic demonstrating the voltage translation in action is provided below.
In summary, all the channels and the main SDA/SCL can operate at different voltages, as long as Vcc is within an acceptable range defined by the Vpass graph in the TCA datasheet. Vpass refers to the lowest pullup voltage connected to the TCA switch/multiplexer device.