Clamping voltage and standoff — the protection window
The 1.5SMBJ15A-H: With a 15V reverse standoff voltage, this TVS stays transparent on a nominal 12V or 15V supply rail, conducting only leakage current below that threshold. When the transient exceeds 16.7V minimum breakdown, the device avalanches and clamps the surge to 24.4V maximum — that is the voltage the downstream ICs must survive. The unidirectional configuration means the cathode is tied to the protected rail and the anode to ground — it clips only positive transients. For bidirectional protection on AC lines or bipolar supplies, you would stack two devices or select a bidirectional variant from the same 1.5SMBJ family.
Automotive grade and temperature envelope
The -55°C to 150°C junction temperature range covers under-hood and cabin electronics — an ECU on a hot engine block sees 125°C ambient, leaving 25°C margin before the junction limit.
Package and board-fit for the DO-214AA footprint
The 1500W pulse rating demands a low-inductance layout — keep the TVS within 5 mm of the connector or the protected IC to minimise the loop area that adds clamping voltage above the 24.4V spec.