The PCA9545A/45B/45C is a quad bidirectional translating switch controlled via the
I2C-bus. The SCL/SDA upstream pair fans out to four downstream pairs, or channels. Any
individual SCx/SDx channel or combination of channels can be selected, determined by
the contents of the programmable control register. Four interrupt inputs, INT0 to INT3, one
for each of the downstream pairs, are provided. One interrupt output, INT, acts as an AND
of the four interrupt inputs.
An active LOW reset input allows the PCA9545A/45B/45C to recover from a situation
where one of the downstream I2C-buses is stuck in a LOW state. Pulling the RESET pin
LOW resets the I2C-bus state machine and causes all the channels to be deselected as
does the internal power-on reset function.
The pass gates of the switches are constructed such that the VDD pin can be used to limit
the maximum high voltage which is passed by the PCA9545A/45B/45C. This allows the
use of different bus voltages on each pair, so that 1.8 V or 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.
The PCA9545A, PCA9545B and PCA9545C are identical except for the fixed portion of
the target address.