The OLF400 has high current transfer ratio at very low input currents making it ideal for applications such as Metal Oxide Semiconductor (MOS), Complementary MOS (CMOS), and low power logic interfacing or RS232C data transmission systems. Each OLF400 has a light emitting diode and an integrated photodiode Darlington detector IC mounted and coupled in a custom 8-pin hermetic flat pack package providing 1000 Vdc electrical isolation between input and output. The Darlington detector has an integrated base-emitter resistor for superior high temperature performance. The split Darlington design permits lower output saturation voltage and higher switching speed operation than possible with conventional photodarlington design. The internal shield provides excellent common mode immunity performance.