The PCA9548A device has eight bidirectionaltranslating switches that can be controlled through the I2C bus. TheSCL/SDA upstream pair fans out to eight downstream pairs, or channels. Any individual SCx/SDxchannel or combination of channels can be selected, determined by the contents of the programmablecontrol register. These downstream channels can be used to resolve I2Cslave address conflicts. For example, if eight identical digital temperature sensors are needed inthe application, one sensor can be connected at each channel: 0-7.
The system master can reset the PCA9548A in the event of a time-out or other improperoperation by asserting a low in the RESET input. Similarly, the power-onreset deselects all channels and initializes the I2C/SMBus statemachine. Asserting RESET causes the same reset and initialization to occurwithout powering down the part. This allows recovery should once of the downstreamI2C buses get stuck in a low state.
The pass gates of the switches are constructed so that the VCC pincan be used to limit the maximum high voltage, which is passed by the PCA9548A. This allows the useof different bus voltages on each pair, so that 1.8-V, 2.5-V or 3.3-V parts can communicate with5-V parts, without any additional protection. External pull-up resistors pull the bus up to thedesired voltage level for each channel. All I/O pins are 5-V tolerant.