Lifecycle reality — obsolete, not NRND
onsemi has marked the FOD817W as Obsolete — this is a full end-of-life status, not a not-recommended-for-new-designs (NRND) flag. Any available stock is date-code-lot-specific; quantities and pricing are confirmed only at the time of an RFQ. The absence of a formal LTB means the remaining supply is whatever the secondary market holds — no guaranteed pipeline.
Isolation and transfer ratio — what the specs mean for fit
The 5000Vrms isolation rating qualifies this optocoupler for reinforced insulation in mains-referenced circuits — think AC-DC power supplies, motor-drive feedback, and industrial PLC I/O where the primary and secondary sides must be galvanically separated. The 4-DIP package provides the creepage distance to sustain that voltage across the moulding. Current transfer ratio spans 50% minimum to 600% maximum at a forward current of 5 mA. That wide CTR window means the same part number can serve both low-duty-cycle logic-level interfaces (where a 50% CTR is enough to saturate the output transistor) and higher-current loads up to 50 mA — but the design must tolerate the full CTR spread without changing bias resistors. Rise and fall times of 4 µs and 3 µs limit the switching frequency to roughly 100 kHz — fine for 50/60 Hz line-sync and low-speed serial, but not for high-speed isolated data links.
Temperature grade and operating envelope
Rated for -55°C to +110°C ambient, the FOD817W covers industrial and some military/aerospace temperature ranges. The 1.2 V typical forward voltage and 50 mA max forward current set the LED drive budget — at 5 mA the CTR is specified, but the LED can be pulsed higher for short-duration signalling if the thermal rise across the DIP moulding stays within limits.