What this Zener TVS diode does for your 100V rail
Its reverse standoff voltage is 100V typical, so it sits across the supply without conducting during normal operation. When a surge hits, breakdown starts at 111V minimum and the diode clamps the voltage to 179V maximum at the peak pulse current of 2.8A (10/1000µs waveform). The 500W peak pulse power rating tells you it can absorb a decent transient without failing — useful for protecting sensitive downstream circuitry in general-purpose industrial or telecom gear.
Package and mounting — DO-214AC (SMA) surface-mount
This part comes in the DO-214AC (SMA) package, a common surface-mount footprint for TVS diodes. It's supplied on Tape & Reel (TR), which means it's ready for automated pick-and-place and reflow soldering. No power line protection feature — this is a straight transient clamp, not a crowbar or a filter.
Microchip lists the SMAJ100E3/TR13 as Active product status.