28-channel SPI GPIO expander for board-level I/O scaling
The Maxim Integrated MAX7301AAX+ is a 28-bit GPIO expander controlled over an SPI interface, clocked up to 26 MHz. It provides 28 push-pull I/O lines in a 36-SSOP package, each capable of sourcing 4.5 mA or sinking 10 mA. The wide supply range of 2.5 V to 5.5 V lets it bridge 3.3 V and 5 V logic domains without a level translator. An interrupt output signals pin-change events, reducing host polling overhead.
26 MHz SPI — bus throughput and polling latency
The 26 MHz SPI clock is the headline rating for this part. At that speed, a full 28-bit read or write transaction completes in just over 1 µs, which means the host MCU can poll all I/O states in a single SPI frame without stalling a real-time control loop. If your design runs a 10 kHz sensor readout or a fast encoder latch, this expander keeps the bus transaction short enough that you don't need a dedicated parallel port.
28 I/O in a 36-SSOP — footprint and routing
The 36-SSOP (7.50 mm body width) gives you 28 I/O in a compact surface-mount footprint. That's enough to replace a handful of 8-bit shift registers or a second MCU port, consolidating BOM lines. The push-pull outputs eliminate external pull-up resistors on outputs, though inputs still need a pull-up if the line floats. The interrupt output (active-low, open-drain) can be wire-ORed with other interrupt sources on the same host line.