Isolation rating and signal transfer
The SFH1690BT: The 3750 Vrms isolation rating defines the reinforced insulation barrier between the input LED and output phototransistor. This is the spec that certifies the part for basic safety isolation in mains-referenced circuits — think AC line monitoring, motor-drive feedback, or any application where the control side must stay galvanically separated from the power stage. Current transfer ratio (CTR) is specified as a range: 100% minimum to 300% maximum, both measured at 5 mA forward current. The 3:1 spread means the receiver-side logic threshold must tolerate the full band; a 100% CTR at 5 mA gives 5 mA output drive, while a 300% unit delivers 15 mA into the same load. Design the pull-up resistor and input current for the minimum case, and the circuit works across the entire distribution. Switching speed is characterised by rise/fall times of 3 µs and 4 µs typical, and turn-on/turn-off times of 5 µs and 3 µs typical. This places the part in the general-purpose optocoupler class — adequate for 10–100 kHz data rates or relay-driving logic, but not for high-speed isolated communication like I²C or SPI without careful derating.
Housed in a 4-SMD gull-wing package with a 4-SOP supplier device package designation, the SFH1690BT uses the standard SOP-4 footprint. The gull-wing leads provide visual solder-joint inspection access and relieve thermal stress between the package body and the board during reflow. The surface-mount form factor suits automated pick-and-place assembly. Operating temperature range of -55 °C to +110 °C covers the full industrial band with margin. The 70 V maximum output voltage and 50 mA continuous output current per channel define the load-driving envelope — suitable for driving a downstream logic gate input, a small relay coil, or a discrete transistor base.