Lifecycle reality — EOL, not NRND
onsemi classifies the CNY172W as Obsolete. This is not an NRND phase — the manufacturer has discontinued the part with no ongoing last-time-buy window. Any available stock is pre-EOL production, and sourcing goes through independent surplus channels where date-code provenance and lot traceability become the buyer's main diligence point.
Isolation and signal-transfer parametrics
Rated for 5300Vrms isolation, the CNY172W meets the reinforced insulation requirement for mains-separated interfaces in industrial power supplies, motor drives, and PLC digital inputs. Current transfer ratio spans 63% min to 125% max at 10 mA forward current. The 2:1 spread means the downstream circuit must tolerate a gain variation of roughly 2× across the batch — a logic input with a Schmitt trigger or a comparator with hysteresis handles this without false edges; a linear feedback loop may need a tighter CTR bin or a secondary trim. Vce(sat) is 300 mV max, which keeps the output voltage drop low enough to drive a 5 V logic input directly from the 70 V-rated output stage. The 50 mA continuous output current per channel suits isolated relay drivers, solid-state switch interfaces, and isolated I²C or SPI buffers where the load is a few milliamps. Switching speed is modest — 1 µs rise and 2 µs fall typical, with turn-on at 2 µs and turn-off at 3 µs. This limits the part to data rates below roughly 100 kbit/s, which covers status feedback, fault signals, and low-speed isolated serial links but not high-speed fieldbus or gate-drive pulse trains.
Temperature grade and environment
The 100 mA absolute-maximum forward current and 1.35 V typical forward voltage are standard for an LED-driven phototransistor optocoupler in this package class.