Darlington gain margin for switching loads
That means the photodarlington can saturate a load drawing 100 mA with only 10 mA on the LED side — useful when the microcontroller or PLC output is already budgeted tight. The Darlington with base output gives you access to the base node for external speed-up or bias tweaks if the 5 µs turn-on / 100 µs turn-off is too slow for your switching edge.
Isolation rating and temperature envelope
Rated at 4170 Vrms isolation, this part supports reinforced insulation between the input and output sides — enough for medical patient-contact barriers or industrial mains isolation where the creepage distance across the 6-SMD Gull Wing package must hold off transients. The 80 V maximum output voltage means the Darlington can switch 24 V or 48 V industrial loads with headroom.