1500 W peak pulse — the surge rating that decides the protection margin
The 1.5SMC18AHM6G: That 1500 W rating means it can absorb a 60 A surge pulse and clamp it to 25.5 V maximum — the downstream IC sees only that clamped voltage, not the transient peak. The reverse standoff voltage of 15.3 V sets the maximum DC operating voltage on the protected line without drawing leakage current. For a 12 V automotive rail with a 15.3 V TVS, the diode stays out of the circuit during normal operation and only conducts when a transient exceeds the 17.1 V minimum breakdown threshold.
AEC-Q101 qualification — built for the under-hood temperature band
That is the under-hood automotive band — an ECU, BMS, or headlamp driver that sees 125°C ambient on a hot engine still has margin before the junction hits its 150°C absolute limit. The DO-214AB (SMC) surface-mount package is the standard footprint for 1500 W TVS diodes. The copper pad area under the cathode tab sets the thermal resistance to the board — a solid ground-plane connection pulls heat out of the junction during repetitive surge events.