The STMicroelectronics SM4T10CAY is a bidirectional Zener TVS diode from the SM4TY TRANSIL™ series, rated for 400W peak pulse power (10/1000µs waveform). It clamps at 19.5V maximum and has an 8.5V reverse standoff voltage, making it a common choice for protecting 12V automotive electronics from load-dump and inductive surge events.
The 400W peak pulse power rating (10/1000µs) translates to a 124A peak pulse current capability at the 8/20µs waveform. For a 12V automotive system, the 8.5V standoff means the diode stays out of conduction during normal battery voltage swings (up to 16V during charge), but clamps hard at 19.5V when a transient hits. That clamping voltage is low enough to protect downstream ECUs and sensors without triggering a crowbar or blowing a fuse.
DO-214AC SMA — rework and assembly notes
For rework, the SMA body is small enough that a hot-air station at 300°C with a fine nozzle lifts the part cleanly without overheating the board.