The PCA9518 is an expandable five-channel bidirectional buffer for I²C and SMBus applications. The I²C protocol requires a maximum bus capacitance of 400 pF, which is derived from the number of devices on the I²C bus and the bus length. The PCA9518 overcomes this restriction by separating and buffering the I²C data (SDA) and clock (SCL) lines into multiple groups of 400-pF segments. Any segment-to-segment transition sees only one repeater delay. Each PCA9518 can communicate with other PCA9518 hubs through a 4-wire inter-hub expansion bus. Using multiple PCA9518 parts, any width hub (in multiples of five) can be implemented using the expansion pins, with only one repeater delay and no functional degradation of the system performance.

The device is designed for 3-V to 3.6-V V_CC operation, but it has 5-V tolerant I²C and enable (EN) input pins. This feature allows for translation from 3 V to 5 V between a master and slave. The enable pin also can be used to electrically isolate a repeater segment from the I²C bus. This is useful in cases where one segment needs to run at 100 kHz while the rest of the system is at 400 kHz. If the master is running at 400 kHz, the maximum system operating frequency may be less than 400 kHz, because of the delays added by the repeater.