Isolation barrier and signal transfer
The CNY17F2SR2M is a single-channel optoisolator from onsemi that passes a 4170Vrms isolation test between input and output — that rating is the safety barrier for breaking ground loops or protecting low-voltage logic from a high-side transient. Current transfer ratio is binned 63% to 125% at If=10 mA. That means at 10 mA LED current the output transistor can sink at least 6.3 mA and up to 12.5 mA. The designer sizes the LED resistor and the output pull-up to work with the 63% floor — the part will never deliver less than that at the test condition.
Switching speed and drive budget
Turn-on time is 2 µs typical, turn-off 3 µs typical, with rise and fall times of 4 µs and 3.5 µs maximum. That puts the useful switching frequency around 50–100 kHz for a clean logic-level transition — fine for isolated serial data at moderate baud rates or for driving a gate driver input. The 400 mV max Vce(sat) at the output keeps the on-state voltage drop low enough to not steal headroom from a 3.3V rail.
The DC input type means the LED is driven by a steady current — no AC line coupling without an external bridge.