What the 1.5SMCJ28A-AQ protects
This is a unidirectional Zener-based TVS (Transient Voltage Suppressor) — it clamps voltage spikes on a single polarity rail by conducting once the transient exceeds the breakdown threshold. That 45.4 V clamping ceiling is what the downstream circuitry never sees. A 1.5 kW TVS in SMC (DO-214AB) is the standard choice for automotive ECU input protection and 24 V industrial rail clamping.
Automotive junction temperature and package
Junction temperature range is -50°C to 150°C — the upper bound puts this in the automotive thermal class, suitable for engine-adjacent modules and ECU protection zones. The SMC (DO-214AB) package is the industry-standard high-current TVS footprint; the cathode bar connects directly to the thermal pad for surge heat dissipation. Surface-mount termination suits reflow assembly on multi-layer boards without any lead-forming step.
Diotec Semiconductor lists this as Active. The part ships in strip packaging — confirm reel or cut-tape orientation before committing to a pick-and-place program.