The onsemi 4N37300W is officially obsolete per the manufacturer's lifecycle status. There is no listed direct successor from onsemi.
Isolation and signal transfer — what the ratings mean
Minimum current transfer ratio of 100% at 10 mA forward current means the output transistor saturates with at least as much collector current as the LED drive current — a 1:1 or better current gain that simplifies the bias design for logic-level interfaces. Typical turn-on and turn-off times of 2 µs each — fast enough for 100 kHz switching or data rates up to about 250 kbps, but not for high-speed digital isolation above 1 Mbps.
Housed in a 6-DIP (0.400-inch, 10.16 mm) through-hole package, supplier device package 6-DIP. The 0.100-inch pin pitch is standard for DIP sockets or direct solder into a PCB. Operating temperature range of -55°C to 100°C covers industrial and some military-grade environments — the lower end suits cold-start conditions in outdoor or unheated enclosures.