The 1.5SMCJ75CA-AQ: The reverse standoff of 75 V sets the maximum working rail this TVS watches without conduction — the circuit runs at nominal voltage below that, and the diode stays invisible until a transient exceeds the breakdown threshold. That 121 V ceiling is the number the downstream protected circuitry must withstand — size your downstream bus accordingly. The 1.5 kW peak pulse rating tells you the energy this part can absorb and survive in the IEC 61000-4-5 surge environment. It is a transient rating, not a continuous rating — the diode dissipates the surge energy in microseconds and then returns to its high-impedance state.
150 °C junction temperature — automotive under-hood margin
The automotive applications designation means the part went through the temperature cycling, humidity, and mechanical stress screening consistent with AEC-Q qualification — the kind of stress a dashboard or under-hood module sees over a vehicle service life.
DO-214AB SMC footprint — drop-in on standard TVS pad geometry
The DO-214AB (SMC) package is the standard two-terminal TVS footprint — the wide metal pad on the cathode side acts as a thermal conductor, and the board designer should tie it to a generous copper plane for surge thermal management.