What this TVS diode protects — and where the scorch mark lands
The STMicroelectronics SM15T56CAY is a bidirectional TRANSIL™ TVS diode from the automotive SM15TY series, AEC-Q101 qualified. It is a Zener-type transient suppressor, not a regular Zener regulator — its job is clamping fast overvoltage spikes on a 48 V nominal rail, not providing a stable reference. The 100 V clamping voltage tells you the downstream circuitry must survive that peak; if your 48 V bus has a 60 V-rated capacitor bank, this clamp will save it.
48 V standoff, 100 V clamp — the voltage window that decides fit
The reverse standoff voltage is 48 V — that is the DC or peak-AC voltage the diode will not conduct under normal operation. For a 48 V automotive battery line (which can see 60 V during cold-crank or 80 V+ during load dump), this part catches the spike before it reaches the ECU's input capacitors. The 1500 W rating is derated above 25 °C; at 150 °C junction temperature the effective power handling drops, so the thermal path through the SMC package matters.