15.3 V reverse standoff — the line voltage it guards
The SM6T18CA is a bidirectional TRANSIL™ TVS diode from STMicroelectronics, part of the SM6T series. When the line exceeds the 17.1 V minimum breakdown, the device clamps transients to 32.5 V maximum, shunting up to 123 A of peak pulse current (8/20 µs waveform). The single bidirectional channel protects both polarities from a single device, simplifying BOM for AC signal lines, bipolar supplies, or data pairs.
Rated for 600 W peak pulse power over the standard 10/1000 µs waveform, this part handles the surge energy typical of IEC 61000-4-5 line-to-ground strikes on 12 V or 15 V rails. The 123 A peak current rating at the 8/20 µs shape is the figure to compare against your system's transient immunity target — derate for higher ambient temperature using the datasheet's power derating curve.
Housed in the DO-214AA (SMB) surface-mount package, the SM6T18CA fits standard SMB footprints. The package supports reflow soldering; observe MSL ratings per the reel label for bake requirements before reflow. The surface-mount form factor suits automated assembly for medium-to-high volume production.