Protection window: standoff through clamping
The 1.5SMC91AHM3_A/I: The 77.8V reverse standoff defines the working voltage — the line sits below this without the device conducting. That 125V ceiling is the clamping limit the downstream circuit must survive — it is not a target, it is the hard stop. For a 48V telecom bus, the 77.8V standoff gives adequate headroom above the nominal rail and the 125V clamp sits below the common-mode withstand rating of most PHY interfaces.
AEC-Q101 automotive grade
AEC-Q101 qualification means the die and package passed the automotive stress suite — temperature cycling, high-temperature reverse bias, power temperature cycling, and surge life testing. For telecom hardware that also sees outdoor or transport deployment, this grade raises the confidence floor over a commercial-spec TVS that only passes JEDEC room-condition testing. Junction temperature rating is -65°C to 150°C — the wide cold end matters for outdoor cabinet equipment that sits unpowered in freezing climates before startup. The 150°C ceiling is the die limit; the board-level thermal design still needs to keep the case below the derating curve at the worst-case ambient.
Sourcing posture — active part, quoted to order
Listed Active under Vishay General Semiconductor — Diodes Division. This is not a NRND or EOL item, so no last-time-buy window applies.