Isolation and signal transfer in a 4-pin SOIC
The TLP385(D4-GRH,E is a single-channel DC-input transistor-output optocoupler from Toshiba, delivering 5000Vrms galvanic isolation in a compact 6-SOIC with only 4 leads populated. That isolation rating covers reinforced insulation requirements for industrial drives, PLC digital inputs, and medical patient-interface barriers where a ground break is non-negotiable. Operating from -55°C to 110°C, it spans the full industrial temperature envelope plus a margin into cold-start environments like outdoor base stations or refrigeration controls. The 100% to 300% current transfer ratio at 5mA forward current gives the designer a wide loop-gain window to set the LED drive resistor without overdriving the input.
Switching speed and output drive capability
Rise and fall times are 2µs and 3µs typical, with symmetrical turn-on and turn-off times of 3µs each. This suits 10-100 kHz switching in isolated gate-drive feedback or low-speed serial isolation; for faster edges a logic-output optocoupler would be needed. The output transistor can sink 50mA continuous at up to 80V Vce, with a saturation voltage of 300mV max at rated current. That Vce(sat) floor keeps dissipation low in logic-level translation — a 5V pull-up at 5mA drops only 15mW in the output stage.
The 6-SOIC-4 lead package uses a 0.173-inch body width (4.40mm) — the same footprint as a standard SOIC-8 but with only four pins populated. That means the PCB layout can share a common SOIC-8 land pattern, simplifying BOM consolidation across different channel-count optocouplers.