16 I/O lines on a 400 kHz I²C bus
The PCA9539AHF,128 is a 16-bit general-purpose I/O expander from NXP, controlled over an I²C or SMBus interface at up to 400 kHz. It gives a host microcontroller 16 additional push-pull I/O lines without burning extra GPIO pins — the I²C address is set by three hardware pins, so up to eight of these can share the same bus for 128 total I/O. Each I/O can source 10 mA or sink 25 mA, enough to drive an LED directly or switch a small-signal relay through a transistor.
Supply flexibility and interrupt handling
The part includes a Power-On Reset (POR) circuit — on power-up all I/O default to inputs, preventing uncontrolled output states during rail ramp. An open-drain interrupt output (INT) asserts when any input changes state from the last read. This lets the host sleep between events and wake only on a pin transition — useful for keypad scanning or sensor monitoring where polling the bus would waste power.
Active production, ROHS3 compliant
Supplied in Tape & Reel (TR) or Cut Tape (CT) for pick-and-place assembly. The 24-HWQFN is a standard JEDEC footprint; no special reflow profile beyond the standard lead-free temperature curve is required.