Device identity and key isolation parametrics
The 4N28SR2M: Rated for 4170Vrms isolation, this part provides galvanic separation between input and output circuits in a 6-SMD Gull Wing package suited for surface-mount assembly.
The 10% minimum Current Transfer Ratio at 10mA forward current means the output transistor conducts at least 1 mA collector current for every 10 mA LED drive — a low CTR that demands enough LED current to guarantee the output pulls the load rail low. Typical turn-on and turn-off times of 2µs each set the practical switching ceiling around 250 kHz; above that the output pulse width shrinks until the downstream logic misses edges. Maximum Vce saturation of 500mV at the rated collector current keeps the output voltage drop low enough to drive TTL or CMOS inputs without a pull-up resistor eating into the noise margin. The 30V maximum collector-emitter voltage limits the load-side rail to 24V or lower — a 24V PLC input or a 12V relay coil is within range; a 48V industrial bus is not.
Temperature grade and deployment environment
The 60 mA maximum DC forward current on the input side provides headroom for driving the LED at the 10 mA test condition while leaving margin for temperature derating and aging.