3750Vrms isolation in a 6-SOIC 5-lead — what it buys you
The Toshiba TLP109(IGM-TPR,E is a single-channel optocoupler with a DC-coupled input LED and a phototransistor output, rated for 3750Vrms isolation between primary and secondary sides. The 6-SOIC 5-lead package (0.179" body width) saves board area compared to the traditional DIP-8 footprint while still providing a creepage path suitable for 250 Vrms working voltage in pollution degree 2 environments.
450 ns switching — timing margin for isolated signal paths
Turn-on and turn-off times are both 450 ns typical, which means the part can handle data rates up to roughly 1 Mbps with a 50% duty cycle. That is fast enough for isolated RS-232, I2C bus repeaters, or low-speed fieldbus interfaces, but not for high-speed SPI or CAN FD. The symmetric propagation delay is a practical advantage — it avoids pulse-width distortion in the 50–500 kHz range where many isolated gate-drive and feedback circuits operate.
CTR window: 25% to 75% at 10 mA — design the LED drive accordingly
The current transfer ratio is specified as a range: 25% minimum, 75% maximum, both measured at 10 mA forward current. That means with 10 mA into the LED, the output transistor can sink between 2.5 mA and 7.5 mA. The wide spread is typical for phototransistor optocouplers and forces the designer to bias the output pull-up for the minimum CTR case. At 8 mA maximum output per channel, the part is sized for logic-level signaling, not driving relays directly.
Active lifecycle — no last-time-buy risk for new designs
It is ROHS3 compliant.
The 125°C upper limit also covers the junction temperature under self-heating in a 85°C ambient at rated current, leaving margin for derating.