The PCA9517A is a CMOS integrated circuit that provides level shifting between low  voltage (down to 0.9 V) and higher voltage (2.7 V to 5.5 V) I2C-bus or SMBus applications. While retaining all the operating modes and features of the I2C-bus system during the level shifts, it also permits extension of the I2C-bus by providing bidirectional buffering for both the data (SDA) and the clock (SCL) lines, thus enabling two buses of 400 pF. Using the PCA9517A enables the system designer to isolate two halves of a bus for both voltage and capacitance. The SDA and SCL pins are overvoltage tolerant and are high-impedance when the PCA9517A is unpowered