400W TVS in an SMA footprint — the automotive-grade clamp for 48V rails
The STMicroelectronics SM4T50AY is a single-channel unidirectional TVS zener diode rated for 400W peak pulse power (10/1000µs waveform), packaged in a DO-214AC (SMA) surface-mount case.
43V standoff, 91V clamp — where the protection window lands
The reverse standoff voltage is 43V, meaning the device does not conduct appreciably below that rail level. Breakdown occurs at a minimum of 47.8V, and the clamping voltage is held to 91V at the rated peak pulse current of 25A (8/20µs waveform). For a 48V nominal bus — common in automotive start-stop and mild-hybrid systems — this clamp window catches transients before they reach downstream silicon without nuisance triggering on normal ripple.
AEC-Q101 and the full temperature envelope
AEC-Q101 qualification covers the device-level stress tests that automotive Tier-1s require: high-temperature reverse bias, temperature cycling, and humidity bias. The -55°C to 150°C operating junction range means this part survives cold-crank at -40°C and under-hood soak at 125°C ambient with margin. No power line protection feature is integrated — this is a pure transient clamp, not a crowbar or overvoltage regulator.