What this I²C port expander does on the board
It's a common fix when the MCU runs out of pins for pushbuttons, LEDs, or status sensors on an industrial control board or a piece of telecom equipment. The part includes a power-on reset (POR) so the outputs come up in a known state, and an interrupt output that lets the host sleep until an input changes — useful in battery-powered or low-power designs.
The output drive is asymmetric: 1 mA source and 25 mA sink per pin. That sink current is enough to light a standard LED or pull a relay coil low through a transistor, but the weak source means you'll typically wire loads between the pin and VCC (sinking) rather than to ground (sourcing). If you need more than 25 mA total per package, watch the package dissipation — the 20-VQFN exposed pad helps, but stay within the current limit.
The PCF8574ARGYR comes in a 20-VQFN with an exposed thermal pad (3.5 mm x 4.5 mm). That pad needs a good solder joint to the PCB ground plane for both thermal relief and mechanical stability. It's a surface-mount part, so rework with hot air is straightforward — just preheat the board to avoid lifting the pad.
No stock or price figures here, but the RFQ process is straightforward.