Transient protection for a 15.3 V rail — obsolete last-time-buy reality
The 1.5SMC18AT3G: The 15.3 V reverse standoff voltage means it sits across a 15 V or 12 V rail without conducting, then breaks down at 17.1 V min and clamps at 25.2 V max to shunt the transient to ground. The DO-214AB SMC package is the standard surface-mount footprint for high-power TVS diodes — the same footprint used across the 1.5SMC family.
Obsolete — sourcing through independent channels
Littelfuse has marked the 1.5SMC18AT3G as obsolete. This part is no longer supported for new designs and is not available through standard authorized distribution channels. Procurement for BOM positions using this order code must go through independent surplus and broker channels. No production-status claim is made beyond the manufacturer's own obsolete designation.
Clamping voltage window and rail protection
For a 15 V rail, the 25.2 V clamp provides a 10 V margin above nominal, which is adequate for most 30 V-rated downstream silicon. The single unidirectional channel means this device protects one polarity — it conducts in reverse breakdown only. For AC lines or bidirectional protection, two devices or a bidirectional TVS would be needed.