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wirelessZONE Products for the week of March 9, 2009
Fairchild Semiconductor Says…
Optocoupler Offers Excellent Isolation for Industrial Fieldbus Communications
Provides Best-in-Class Noise Immunity
Fairchild Semiconductor brings industrial system designers an optocoupler solution with excellent noise immunity. The FOD8001 answers the need for system engineers’ to design a robust industrial fieldbus network with low transmission error rates, low system failure rates and proven reliability over an extended period of time. Fairchild’s high performance optocouplers offer best-in-class noise immunity resulting from its proprietary coplanar packaging technology, Optoplanar. Its integrated circuits and light emitting diode (LED) are assembled on a coplanar process, rather than a face-to-face or over-under process, helping to reduce package capacitance between input and output and improving noise immunity. It features 25kV/µs@1,500Vcm dynamic Common Mode Transient Immunity (CMTI) rating under high-speed optocoupler switching and 40kV/µs@1,000Vcm static CMTI, making it more resilient to noise.
EN-Genius Says…
This is an optocoupler with a fairly standard architecture, but the bandwidth performance is not. The input side to the optocoupler drives an AlGaAs photodiode (an LED in this case) from a CMOS buffer and, across the isolation gap, a CMOS photodetector’s signal drives a transimpedance amplifier, a voltage comparator and a push-pull output driver.
The part, however, offers a 25 Mbit/s NRZ data rate with only 40 ns propagation delay and a maximum of 6 ns pulse width distortion. The combination of LED and CMOS also makes the part very efficient. The rail voltages on each side of the isolation gap can be between 3.3 V and 5 V.
The logic high output voltage with an output rail of 3.3 V and an input high is a typical 3.3 V with a load of -20 µA and 2.9 V with a load of -4 mA. The logic low output voltage is a typical 0 V with a load of 20 µA and 0.3 V with a load of 4 mA. The absolute maximum output current is 10 mA with an absolute maximum power dissipation for the complete part of 70 mW.
Noise is the killer in data transmission in parts like this but the FOD8001 has a minimum static CMR of 20 kV/µs at Vcm of 1000 V, and a typical dynamic CMR of 25 kV/µs at Vcm of 1500 V and a 20 Mbit/s data rate.
The FOD8001 is rated from -40ºC to +105ºC. Approvals are pending for UL1577 (3750 Vac rms for 1 minute) and IEC60747-5-2.
This part is priced correctly and will be widely used in industrial fieldbus communications such as DeviceNet, CAN, Profibus, Interbus, Modbus, and RS485. It is also ideal for isolation in industrial data acquisition systems.
The FOD8001 is in production in SOP-8 and is priced at $2.79 in 1000-piece lots.
Data Sheet
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