Bus switching is when the bus path is enabled or disabled, but does not translate the bus voltage. External pull-up resistors are not needed for I3C, because the controller enables or disables the pull-up resistor on the SDA line. This presents a unique challenge for FET-based translators, like the TCA39306, because they rely on a pull-up resistor to pull the output side of the switch all the way to supply. For the switching use case, there is no translation, but the enable voltage must be high enough for the switch to stay on for the entire voltage range of the bus (0 V to bus voltage).

R_ON must be low enough for the full push-pull voltage range. The EN voltage must be at least 1 V_t (~0.6 V) above the maximum desired pass-voltage. This comes out to V_EN ≥ V_BUS + 0.6 V. Since the switch enable voltage is being directly controlled, the V_REF1 and V_REF2 pins are not needed, and can be shorted to ground to improve power consumption.

It is possible to control the EN pin with a voltage equal to V_BUS, but external pull-up resistors on the downstream side are a requirement to ensure the bus is pulled entirely to V_BUS.