The 1.5SMCJ90 is a unidirectional Zener-type TVS in SMC (DO-214AB) package, qualified for general-purpose transient suppression on signal and low-power rails. Reverse standoff of 90 V sets the continuous working voltage the diode ignores; the 160 V clamping maximum at 9.4 A peak pulse (10/1000 µs) is where the device turns on and clamps the spike — 1500 W peak pulse rating confirms it handles the energy without going into secondary breakdown. For a designer protecting a 24 V bus that might see lightning-surge coupling, the 90 V standoff gives comfortable headroom and the 160 V clamp ceiling keeps the downstream IC within its abs-max.
What the ratings don't cover
This part is not a power-line protection device — the listing explicitly marks Power Line Protection as No. For AC line-side applications you need a part with higher standoff and energy capability. The 1.5SMCJ90 is a single unidirectional channel, so it protects one polarity only; a bidirectional clamp requires two series-opposed devices or a bidirectional TVS variant.