Obsolete — sourcing reality for the BOM
The CNY173FM is marked Obsolete by onsemi.
4170 Vrms isolation and CTR range
Rated for 4170 Vrms isolation between input and output — this is a reinforced-grade isolation level for mains-referenced circuits, suitable for industrial power supplies, motor-drive feedback, and medical equipment where the safety barrier must withstand a 4 kV surge without breakdown. The current transfer ratio (CTR) is specified at 100% minimum to 200% maximum, tested at 10 mA forward current. That range tells you the LED-to-phototransistor gain spread across production lots: a 100% CTR means the output collector current equals the input LED current at the test point; 200% means the output can sink twice the input. For a logic-level interface, the lower bound is the one that governs the pull-up resistor and noise margin — design for 100% CTR and the 200% parts just saturate harder.
Switching speed and output ratings
Turn-on time is 2 µs typical, turn-off 3 µs typical; rise and fall times are 4 µs and 3.5 µs maximum respectively. That puts the useful data rate around 100 kHz — fine for 50/60 Hz zero-crossing detection, relay-driver isolation, or slow digital status feedback, but not for high-speed serial links. The output transistor is rated for 70 V Vce(max) and 50 mA continuous collector current. The 400 mV Vce(sat) at the rated current means the output drops less than half a volt when saturated — the downstream logic sees a clean low state. Forward voltage is 1.35 V typical at 10 mA, with an absolute maximum DC forward current of 60 mA.
Package and temperature grade
Surface-mount 6-SMD Gull Wing package, supplier device package 6-SMD. The Gull Wing leads are solderable with standard reflow profiles and allow visual inspection of the solder joints after assembly. The part ships in Tube packaging.