The PCA9543A is a 2-channel, bidirectional translating I²C switch. The master SCL/SDA signal pair is directed to two channels of slave devices, SC0/SD0-SC1/SD1. Either individual downstream channel can be selected as well as both channels. The PCA9543A also supports interrupt signals in order for the master to detect an interrupt on the INT output pin that can result from any of the slave devices connected to the INT1- INT0 input pins.

The device offers an active-low RESET input which resets the state machine and allows the PCA9543A to recover should one of the downstream I²C buses get stuck in a low state. The state machine of the device can also be reset by cycling the power supply, V_CC, also known as a power-on reset (POR). Either using the RESET function or causing a POR will cause both channels to be deselected.

The connections of the I²C data path are controlled by the same I²C master device that is switched to communicate with multiple I²C slaves. After the successful acknowledgment of the slave address (hardware selectable by A0 and A1 pins), a single 8-bit control register is written to or read from to determine the selected channels and state of the interrupts.

The PCA9543A may also be used for voltage translation, allowing the use of different bus voltages on each SCn/SDn pair such that 1.8-V, 2.5-V, or 3.3-V parts can communicate with 5-V parts. This is achieved by using external pull-up resistors to pull the bus up to the desired voltage for the master and each slave channel.