The SMAJ40AQ-13-F: It clamps transients at 64.5V maximum, with a 40V reverse standoff voltage and a 44.4V minimum breakdown point — this defines the protection window for a 40V nominal rail. The DO-214AC SMA package is a standard surface-mount footprint — the same pad layout as many other 400W TVS diodes, making it a drop-in candidate for existing board layouts. The -55°C to 150°C junction temperature range covers the full automotive thermal envelope, including hot-soak conditions near the engine bay.
Clamping voltage and pulse current — what the numbers mean on the bench
At 64.5V maximum clamping, the TVS holds the transient below the absolute maximum rating of most 40V-rated downstream ICs. The 6.2A peak pulse current at the 10/1000µs waveform tells you the surge energy it can absorb — a 40V rail hit with a 300W transient pulse stays within the 400W rating. Power line protection is marked as 'No' — this is a unidirectional Zener TVS, not a bidirectional or steering-diode array. It clamps one polarity (positive transients above breakdown) and conducts like a forward-biased diode on negative swings. For AC-coupled or bipolar lines, you would need a bidirectional part.