The 1.5SMC540AHM3_A/H: The 459 V reverse standoff voltage places it on 400 VDC bus rails or telecom ring-voltage lines where the normal operating level sits well below the 513 V minimum breakdown threshold.
Clamping voltage and pulse current — the so-what
When the TVS triggers, the clamping voltage holds at 740 V max at the rated 2.03 A peak pulse current. That clamp ceiling tells the downstream silicon what it must survive — a 600 V MOSFET with 800 V Vdss has 60 V of headroom above the clamp, which is tight but workable if the board layout keeps parasitic inductance low. The single unidirectional channel means this diode conducts in avalanche only during a positive overvoltage transient; a negative spike forward-biases the junction and clamps at roughly 1 V, so the protected rail must tolerate that asymmetry or use a bidirectional part instead.