The CA9539 is a low-voltage 16-bit remote GPIO expander designed for MCU families using the I²C or SMBus interface. It integrates two 8-bit input port registers, two output port registers, a configuration register and a polarity inversion register, allowing flexible per-pin control of direction and active state. After power-up, all pins default to inputs for safe system initialization.

An open-drain interrupt output notifies the host when any input pin changes state compared to the stored value in the input register. The device includes a built-in power-on reset, a latch function for directly driving LEDs with high current capability, and noise filters on SCL/SDA lines. Operating from 1.65 V to 5.5 V with full 5.5 V-tolerant I/O, the CA9539 is suitable for server and telecom systems. It is available in TSSOP-24 and QFN4×4-24 packages.