The LTC4301 supply independent, hot swappable, 2-wire bus buffer allows I/O card insertion into a live backplane without corruption of the data and clock busses. In addition, the LTC4301 allows the VCC, SDAIN and SCLIN pullup voltage and the SDAOUT and SCLOUT pull-up voltage to be independent from each other. Control circuitry prevents the backplane from being connected to the card until a stop bit or a bus idle is present. When the connection is made, the LTC4301 provides bidirectional buffering, keeping the backplane and card capacitances isolated.