What the clamping voltage means for your downstream circuit
The 1.5SMCJ43: The diode breaks down conductively at 47.8 V minimum, so a 48 V bus that spikes will see the TVS transition from leakage to conduction within that window; the 43 V typ reverse standoff gives you the design margin between nominal operating voltage and the onset of protection.
Rated 1500 W at a 10/1000 µs surge waveform — this is a standard telecom and industrial protection spec, not an automotive 8/20 µs pulse, so the peak current of 19.6 A is tied to that specific double-exponential shape; if your loaddump or inductive kick waveform has a different energy content, derate accordingly using the datasheet curves. The 150°C maximum junction temperature means the PCB pad under the SMC body must be kept cool enough that the device stays below that limit during clamped events — on a poorly thermal-managed board the clamping voltage rises and protection performance degrades.
DO-214AB footprint and unidirectional protection topology
The DO-214AB (SMC) package is the standard 2-pin unidirectional TVS footprint — pin 1 is the cathode (protected line), pin 2 is the anode (ground); the single-channel unidirectional configuration protects the line against positive transients relative to ground but does not clamp negative events the way a bidirectional device does. Classified as general-purpose, not a safety-rated or automotive-qualified device — the absence of a power-line-protection flag means it is not UL-recognized or IEC 62368 tested for equipment-side overvoltage protection in mains-adjacent circuits.