400W Zener TVS for automotive rail protection
It clamps a 20V nominal rail at 42.8V maximum during a 400W peak pulse (10/1000µs waveform), with a peak pulse current rating of 54A (8/20µs). The 22.2V minimum breakdown voltage gives you a clean guard band above the 20V standoff — the rail stays protected without nuisance triggering from normal supply ripple.
AEC-Q101 and the 150°C junction limit
No last-time-buy risk on this line; it remains a current-production part for new vehicle platform designs.
DO-214AC footprint and surface-mount assembly
Housed in a DO-214AC (SMA) package, the SM4T23AY is a surface-mount device with a standard two-pad footprint shared across the SM4TY series. The SMA body is small enough for dense ECU layouts but still dissipates the 400W pulse without requiring an external heatsink — the junction absorbs the transient, then cools through the copper pads and board plane. No power line protection (unidirectional only), so wire it between the protected rail and ground with the cathode to the rail.