Bi-directional opto-coupler hits 15Mbit/s

Bi-directional opto-coupler hits 15Mbit/s

Steve Bush  Wednesday 26 January 2011 14:48

Fairchild's first bi-directional fast opto-coupler

Fairchild has introduced its first full duplex, bi-directional, fast logic gate opto-coupler.

Called FOD8012, it is aimed at industrial field bus communications, programmable logic control, and servo control, as well as inverter, factory automation, process control and test and measurement.

Each channel has a AIGaAs LED, driven by a CMOS buffer IC coupled to a CMOS detector IC.

It uses Fairchild’s proprietary construction, which puts each LED and photodiode pair side-by-side, both facing upwards (see diagram).

FairchildShaped transparent encapsulation puts these components at the two focal points of an ovoid, which refracts light from one to the other.

This, claims the firm, allows internal separation distances to be increased: “Unlike competitive devices which provide less than 0.1mm optical isolation gap, the FOD8012 features a 0.4mm minimum optical isolation.”

“Another advantage of planar rather than on-top construction is lower capacitance and therefore lower capacitive coupling,” Fairchild spokesman Jon Harper told Electronics Weekly.

Common mode rejection is 20kV/µs minimum, which means no false output bits up to this level.

Switching speed is up to 15Mbit/s.

“The width of the output pulse is within +/-15ns of the input pulse width, and skew is 30ns max,” said Harper. Propagation delay is 60ns max.

The temperature range is -40 to +110ºC.

“In the past, the difficulty with opto-couplers was that current transfer ratio dropped with high temperature,” said Harper. “This has temperature compensation in the current amplifier.”

The supply voltage can be 3.3 or 5V, it has a 6x5mm footprint, and isolation voltage is certified by UL1577 and IEC60747-5-2.

Applications requiring the isolation of Profibus, CAN, DeviceNet, RS485, I2C, SPI and USB are expected.



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