What the 1500W rating means on the bench
The 1.5SMC56A-E3/9AT: This Vishay TransZorb TVS clamps a 10/1000µs surge at 19.5A peak pulse current to 77V max. For a 48V nominal rail (47.8V reverse standoff), the 53.2V minimum breakdown means the part starts conducting just above the normal operating voltage, shunting the surge before it reaches downstream caps or ICs. The unidirectional configuration (one channel) is standard for DC rails where the surge polarity is known. On an AC line or bidirectional data pair you would reach for the bidirectional variant in the same 1.5SMC family.
Package and footprint fit
DO-214AB (SMC) is the larger of the common SMC package sizes — the body measures roughly 7.1mm x 6.2mm with a 2.6mm height. The supplier device package is listed as DO-214AB (SMCJ), which is the same footprint. The copper pad area under the cathode tab sets the thermal impedance for repeated surge events; a 25mm² pad on 2oz copper drops RθJA significantly compared to the minimum land pattern. Surface mount with Tape & Reel packaging — the -/9AT suffix indicates the 13-inch reel quantity (typically 3500 pieces per reel for SMC). No power line protection feature, so this is a pure transient suppressor, not a fault-tolerant crowbar device.