Protection ratings and the clamping decision
The SMBJ40A-13: Its 40 V reverse standoff voltage means the protected circuit sees no leakage at normal operating voltage up to 40 V. The 64.5 V clamp ceiling means the protected device needs a breakdown rating above that level — a 60 V-rated IC would be marginal; 75 V or higher is the safer choice.
Housed in the DO-214AA (SMB) surface-mount package, the SMBJ40A-13 occupies a standard footprint shared across the SMBJ series. The part is unidirectional, so polarity matters in layout — the cathode band on the package must face the positive rail.
Active lifecycle and sourcing posture
The base product number SMBJ40 allows cross-referencing within the SMBJ family for alternate voltage variants if the 40 V standoff does not match the rail.