Four isolated channels in a single 16-SOIC
The Toshiba TLP291-4(GB,E) is a 4-channel transistor-output optocoupler in a 16-SOIC surface-mount package. It provides 2500Vrms isolation between a DC input LED and a phototransistor output on each channel, with a current transfer ratio (CTR) guaranteed between 100% and 400% at a forward current of 5mA. The output transistor is rated for up to 80V and 50mA per channel, making it suitable for logic-level interfacing, PLC digital inputs, motor-drive feedback isolation, and general-purpose signal isolation in industrial and telecom equipment.
The CTR is specified as 100% minimum and 400% maximum at If=5mA. At the minimum CTR, the output transistor can sink 5mA with the LED driven at 5mA; at the maximum, it can sink 20mA under the same drive. This wide spread means the design must tolerate the full CTR range — a fixed 5mA LED current guarantees the output will saturate for any unit within spec. If you need tighter gain matching across channels, you may want to sort or select parts, but for most logic-level isolation (5V or 3.3V CMOS), the 100% floor is sufficient to pull the output low with a 10kΩ pull-up.
Rise and fall times are 2µs and 3µs typical; turn-on and turn-off times are both 3µs typical. That puts the usable switching frequency around 100 kHz or lower — fine for 10 kHz PWM or 115.2 kbps serial isolation, but not for high-speed SPI or CAN FD. The 400mV Vce(sat) maximum at the output ensures a clean logic low when driving a 5V CMOS input.
The 2500Vrms isolation is a basic functional isolation rating — sufficient for reinforced insulation in many IEC 60950-1 applications, but check your system's creepage and clearance requirements against the 16-SOIC footprint.