The PCA9545A is a 4-channel, bidirectional translating I²C switch. The master SCL/SDA signal pair is directed to four channels of slave devices, SC0/SD0-SC3/SD3. Any individual downstream channel can be selected as well as any combination of the four channels. The PCA9545A also supports interrupt signals in order for the master to detect an interrupt on the INT output terminal that can result from any of the slave devices connected to the INT3- INT0 input terminals.

The device offers an active-low RESET input which resets the state machine and allows the PCA9545A 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). Both the RESET function and a POR will cause all 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 terminals), a single 8-bit control register is written to or read from to determine the selected channels and state of the interrupts.

The PCA9545A 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.