The TLP385(GR-TPL,E is a single-channel transistor-output optocoupler from Toshiba, built for galvanic isolation up to 5000 Vrms between a DC input and a phototransistor output. The 4-lead 6-SOIC package (0.173-inch body width, 4.40 mm height) saves board space compared to the traditional DIP-4 footprint while keeping creepage distance adequate for reinforced isolation in mains-referenced circuits.
Current transfer ratio – the BOM-sizing number
The GR rank guarantees a current transfer ratio between 100% and 300% at If=5 mA. This means with 5 mA through the LED, the phototransistor can sink at least 5 mA at the output, and at most 15 mA. The 100% minimum ensures the output saturates with a modest LED drive, keeping the series resistor value low and the input power budget under control. For 3.3V logic interfaces, the 1.25 V typical forward voltage leaves enough headroom to bias the LED through a 330–470 Ω resistor from a 3.3 V rail, and the 2 µs rise / 3 µs fall times are fast enough for 100 kHz switching supplies or general-purpose signal isolation.