170V rail protection in a DO-214AB footprint
Its 1.5kW peak pulse power rating (10/1000µs waveform) means it can absorb a significant surge before the clamping voltage rises to 275V — the point where downstream silicon must survive or the board layout must handle the let-through energy.
The reverse standoff voltage is 170V (typ) — this is the DC rail voltage the TVS blocks without conducting. Breakdown starts at 189V (min), giving a ~19V guard band before the diode begins to avalanche. The clamping voltage at peak pulse current is 275V (max) at 5.5A — that 86V delta between breakdown and clamp is the voltage the load sees during the event.
Microchip lists the SMCJ170AE3/TR13 as Active.