The 13V reverse standoff voltage means it stays out of the way on a 12V nominal rail, and the 27.2V maximum clamping voltage limits the spike the downstream circuitry sees.
AEC-Q101 and the automotive temperature range
The AEC-Q101 qualification means the part has passed stress tests required for automotive modules. The -55°C to 150°C operating range covers cold-crank and heat soak.
400W peak pulse power — what it buys you
The 400W peak pulse power rating is measured with an 8/20µs current waveform. This part can absorb a single 85A pulse (8/20µs) without failing.
The SM4T15CAY comes in a surface-mount package common for TVS diodes in this power class. The package is small enough for dense PCB layouts.