The PCA9540BDP is a 2-channel I2C-bus Multiplexer controlled via the I2C-bus. The SCL/SDA upstream pair fans out to two SCx/SDx downstream pairs or channels. Only one SCx/SDx channel is selected at a time, determined by the contents of the programmable control register. A power-on reset function puts the registers in their default state and initializes the I2C-bus state machine with no channels selected. The pass gates of the multiplexer are constructed such that the VDD pin can be used to limit the maximum high voltage that is passed by the multiplexer. This allows the use of different bus voltages on each SCx/SDx pair, so that 1.8/2.5/3.3V parts can communicate with 5V parts without any additional protection. External pull-up resistors can pull the bus up to the desired voltage level for this channel. All I/O pins are 5V tolerant.
