PCA9544A: 4-channel I2C-bus multiplexer with interrupt logic

The PCA9544A is a 1-of-4 bidirectional translating multiplexer, controlled via the I²C-bus. The SCL/SDA upstream pair fans out to four 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. Four interrupt inputs, INT0 to INT3, one for each of the SCx/SDx downstream pairs, are provided. One interrupt output, INT, which acts as an AND of the four interrupt inputs, is provided.

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 V_DD pin can be used to limit the maximum high voltage which will be passed by the PCA9544A. This allows the use of different bus voltages on each SCx/SDx pair, so that 1.8 V, 2.5 V or 3.3 V parts can communicate with 5 V parts without any additional protection. External pull-up resistors pull the bus up to the desired voltage level for each channel. All I/O pins are 5 V tolerant.