7500 Vpk isolation — the headline spec
The 4N26FVM provides 7500 Vpk isolation between input and output. That is a high-voltage rating for a 6-pin SMD package — it suits applications where the logic side must be galvanically separated from a high-voltage DC bus or a mains-referenced circuit, such as in motor-drive feedback or industrial sensor interfaces.
20 % minimum CTR — the gain floor
Minimum current transfer ratio is 20 % at If = 10 mA. This means with 10 mA through the input LED, the output transistor can sink at least 2 mA. For a given load current, you size the input resistor to ensure the LED current stays above the threshold that guarantees the CTR — a common gotcha in marginal designs. Typical turn-on and turn-off times are both 2 µs. That is fast enough for 100 kHz-ish switching in isolated gate drive or logic-level translation, but not for high-speed data links — this is a general-purpose optocoupler, not a digital isolator replacement.
Hand-solderable SMD package
The 6-SMD gull wing package is a through-hole-compatible surface-mount footprint — the leads splay out so it sits flat on the PCB and can be hand-soldered with a fine-tip iron. No hot-air or reflow oven required, which makes it a practical choice for prototyping or low-volume builds where you want the isolation without the assembly hassle.