What the 5 kV isolation and CTR binning mean for your BOM
The FOD817B3SD is an onsemi optoisolator that provides 5000Vrms galvanic isolation between a DC input and a transistor output — the kind of barrier you need in a mains-referenced power supply, motor drive, or PLC digital input where a fault on the high side must not reach the controller logic. Its current transfer ratio is binned at 130% minimum and 260% maximum at 5 mA forward current, so you get a predictable on-state collector current without overdriving the LED — that matters when you're sizing the input resistor and the pull-up on the output side. The 70 V output rating and 50 mA continuous output current handle 24 V logic rails and low-power relay coils directly, with the 200 mV Vce(sat) keeping dissipation low in the on-state.
Package and temperature range for the board and the environment
Housed in a 4-SMD Gull Wing package (supplier device package 4-SMD), this part is built for reflow soldering — the Gull Wing leads are visible for inspection and rework-friendly if you need to replace one on a populated board.
How the FOD817B3SD compares to its CTR-bin siblings
Within the FOD817 family, the suffix selects a CTR range of 130% to 260% at 5 mA — the same package and isolation as the FOD817BSD (which uses the same CTR bin) and the FOD817ASD (which uses a lower CTR bin). The difference is purely the transfer ratio window, so if your design needs a tighter or higher CTR, you swap the suffix without changing the footprint.