8-bit I/O expansion over a two-wire bus
The PCA6408APW,118 is an 8-bit I/O expander from NXP that extends a host controller's GPIO count over an I²C or SMBus interface running at up to 400 kHz.
Output drive and interrupt handling
Each I/O pin can sink 25 mA or source 10 mA, enough to directly drive an LED indicator or a small relay coil through a series resistor without a buffer transistor. The push-pull output type eliminates the need for external pull-up resistors on the port pins, simplifying the BOM for output-only applications. A dedicated interrupt output (INT) signals the host when an input changes state, so the controller does not have to poll the expander continuously — useful in battery-powered or latency-sensitive designs. The POR (Power-On Reset) feature ensures all registers initialize to a known state at power-up, preventing spurious outputs during supply ramp.
The part is ROHS3 Compliant, meeting the latest EU restriction-of-hazardous-substances directive for lead-free assembly.