SPI GPIO expander for industrial and mixed-voltage systems
The Microchip MCP23S18-E/MJ is a 16-bit SPI GPIO expander in a 24-QFN (4x4) package, providing 16 I/O lines with open-drain outputs and a 10 MHz SPI interface. Each I/O can sink or source 25 mA, enough to drive LEDs or small relays directly without external buffers. The open-drain output type allows wired-OR connections and level translation between supply domains on the same bus. An interrupt output pin (INTA) is provided, so the host MCU does not need to poll the expander continuously — the expander asserts the interrupt when an input changes, reducing firmware overhead in event-driven systems.
At 10 MHz SPI clock, each 16-bit read or write completes in 1.6 µs. For a system scanning all 16 inputs sequentially, the total bus occupancy is roughly 3.2 µs per scan cycle. This leaves ample margin for slower MCUs running at 8–16 MHz and for shared SPI buses with multiple peripherals.
The exposed pad is electrically connected to VSS and must be soldered to the ground pour. The small footprint suits space-constrained designs like sensor modules or handheld instruments.
It is RoHS3 compliant, which means no exemptions for lead in solder — compatible with lead-free reflow profiles.