400 W peak pulse — the surge rating that matters
The SM4T82CAY is an automotive-grade TVS Zener from STMicroelectronics, rated for 400 W peak pulse power over the standard 10/1000 µs waveform. That 400 W rating is the part's headroom for clamping transients on a 70 V nominal rail — a 24 V truck or 48 V hybrid bus sees repeated load-dump spikes, and this diode shunts them to 146 V max before the silicon gives out.
AEC-Q101 and the -55 to 150 °C window
The operating junction range of -55 to 150 °C covers under-hood and engine-bay thermal cycling — the 150 °C ceiling is the die-attach limit, not the package. In a 125 °C ambient ECU, the junction stays inside the derated power curve.
Bidirectional single-channel clamp
One bidirectional channel — the breakdown starts at 77.8 V min and hard-clamps at 146 V max with a 16 A peak pulse current (8/20 µs waveform). No power-line protection because this is a signal-line TVS, not a mains-side suppressor. The 70 V reverse standoff sits safely below the 77.8 V breakdown knee, so the diode stays off during normal bus operation and only conducts when a transient pushes past the knee.
DO-214AC SMA — footprint and sourcing reality
Housed in a DO-214AC SMA package, the SM4T82CAY is a surface-mount part for standard reflow assembly.