Isolators take optocouplers off the I2C bus

Digital isolators provide true bidirectional isolation for the I2C serial computer bus in industrial, networking and power supply applications.

Analog Devices is introducing the industry's first products to provide true bidirectional isolation for the I2C serial computer bus in industrial, networking and power supply applications.

Based on ADI's award-winning iCoupler technology, the ADuM125x family of digital isolators reduces board space by as much as 80% and achieves the lowest cost I2C isolation solution.

This is accomplished by eliminating the optocouplers and support circuitry previously required in isolated I2C interfaces.

The I2C bus is a cost-effective, two wire interface between controllers and peripheral devices such as data convertors, memory products, switches, sensors and power supply ICs.

The bus uses bidirectional lines to transmit and receive signals over the same wire, allowing two-wire signalling of clock and data.

This reduces complexity and cost by eliminating extra wiring and components.

In a variety of applications, controllers or peripherals are isolated from the bus to avoid interference or harmful voltage levels.

Typically, isolation has been achieved with optocouplers, but doing so increases the cost and complexity of the I2C interface because unidirectional optocouplers must be accommodated by separating each of the two bidirectional I2C channels into two unidirectional channels.

The resultant four unidirectional channels are then each isolated with an optocoupler and recombined into two bidirectional channels.

The additional circuitry associated with the bidirectional/unidirectional conversions and the isolation of the four unidirectional channels adds complexity and cost that offset the intended benefits of the I2C bus.

With the ADuM125x isolators, this complexity and cost is avoided as a single component directly provides bidirectional isolation to both of the I2C lines.

This small, complete isolation device ensures the signal integrity of the bidirectional I2C bus while reducing component count, cost, board space, and complexity.

"By delivering the industry's first truly bidirectional isolator for I2C, Analog Devices continues to extend its iCoupler portfolio beyond standard isolators to provide customers with solutions that are tailored to their application needs", said Pat O'Doherty, Product Line Director, Precision Signal Processing.

"The ADuM125x underscores the versatility of the iCoupler technology, which is currently employed in over 50 million channels of isolation".

"With the ADuM125x, we continue to reduce size, cost and time to market for our customers and provide a compelling alternative to optocouplers".

Based on Analog Devices' proprietary iCoupler chip-scale microtransformer technology, the ADuM1250 and ADuM1251 devices provide 2.5kV of isolation across bidirectional I2C lines in a single, narrow-body 8-lead SOIC package.

This eliminates the need for additional circuitry to split I2C signals into separate transmit and receive signals and then use stand-alone optocouplers to isolate the signals.

Both members of the ADuM125x family incorporate a hot-swap interface to prevent data corruption when an unpowered card is inserted onto an active bus.

The ADuM1250 provides two bidirectional channels supporting a complete isolated I2C interface.

The ADuM1251 provides one bidirectional channel and one unidirectional channel for those applications in which a bidirectional clock is not required.

Both devices are capable of operation up to 400Kbit/s and are compatible with SMBus and PMBus protocols.

Isolation devices are used in a wide range of applications to protect people and equipment from unsafe voltage levels and disruptive noise sources.

Analog Devices' iCoupler isolation technology employs chip-scale, microtransformers in contrast to the LEDs and photodiodes used in optocouplers.

compared with optocouplers, iCoupler products consume less power, achieve higher datarates and provide more precise timing, yet still provide isolation ratings of up to 5kV.

Because the microtransformer structures are integrated on semiconductor substrates, iCoupler products can achieve high levels of integration enabling greater functionality, smaller size and lower cost.

The ADuM1250 and ADuM1251 I2C digital isolators are sampling now with full production release scheduled for October 2006.

Each of the devices is available in Pb-free 8-lead SOIC (small outline integrated circuit) packaging with the ADuM1250 priced at $3.38 and the ADuM1251 priced at $3.05 per unit in 1000-piece quantities.

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