When the TCA4307 first receives power on the VCC pin, either during power-up or during live insertion, it starts in an under voltage lockout (UVLO) state, ignoring any activity on the SDA and SCL pins until V_CC rises above UVLO.

Once the ENABLE pin goes high, the ‘Stop Bit and Bus Idle’ detect circuit is enabled and the device enters the bus idle state.

When V_CC rises above UVLO, the precharge circuitry will activate, which biases the bus pins on both sides to about 1 V through an internal 100 kΩ resistor.