The 6N138SV is officially listed as Obsolete by onsemi.
Isolation and signal transfer
Rated for 2500Vrms isolation between input and output — this is the safety barrier for separating low-voltage logic from a higher-voltage bus or floating signal. The Darlington output with base access gives the designer flexibility to adjust switching threshold or add a pull-up network. Minimum current transfer ratio of 300% at 1.6 mA forward current means the output can sink 60 mA continuously while the input LED draws under 2 mA — a light load on the upstream logic gate. Typical turn-on time is 1.5 µs and turn-off is 7 µs, which sets the practical data rate ceiling around 100 kbit/s in a standard logic interface. The 20 mA absolute-maximum forward current allows a wide drive range without saturating the LED.
Board-fit and environment
The surface-mount footprint matches the industry-standard DIP-8 through-hole pattern on a smaller land area.