Power Electronics

Isolation Devices Step Up Battle Against Optocouplers

Seeking to supplant optocouplers in a variety of applications, semiconductor manufacturers continue to develop digital isolation components based on chipscale transformers. This trend, which is evidenced by recent product introductions from Analog Devices, offers designers of power systems and other applications more options for achieving greater functional integration and more stable performance in their designs.

Analog Devices recently expanded its portfolio of digital isolation products with a series of four-channel devices that isolate both data and power. Each device integrates the company’s iCoupler digital isolation technology and its isoPower dc-dc converter within a single, IC-style package. Members of the new ADuM540x family of iCoupler digital isolators are similar to the company’s existing ADuM524x devices, but with improvements in power delivery and channel density. (For background on iCoupler and isoPower technology see “The Benefits of Chipscale Transformers” below.)

The ADuM540x devices increase the power delivered by the dc-dc converter to 0.5 W, which is an order of magnitude greater than the dc-dc converter in the ‘524x. (This dc power is both isolated and regulated.) In making this improvement in power delivery, the company also tripled the dc-dc converter efficiency. Meanwhile, the ADuM540x parts raise the number of data isolation channels from two in the previous generation parts to four channels in the new devices.

To obtain the higher power and greater efficiency, Analog Devices increased the size of the transformer used to transmit power and lowered the switching frequency of the dc-dc converter. The switching frequency in the ADuM540x’s dc-dc converter is 180 MHz, which is down from the 300 MHz used in the ‘524x devices. In addition, the use of feedback for active regulation also improves efficiency. The dc-dc converter operates from either a 3.3-V or 5.0-V input supply and produces a regulated 3.3-V or 5.0-V output.

In addition to the ADuM540x, a version with two channels (ADuM520x) and a version that features only the isoPower power supply (ADuM5000) will be released later this year.

“Delivering 500 mW of isolated power in a small, surface-mount package, the ADuM540x products enable customers to put more channels of isolation into space-constrained designs at reduced cost,” says Ronn Kliger, product line director, Digital Isolation Products, Analog Devices. “For example, industrial control designers can now increase the number of isolated data ports in a single control module without increasing the size of the module, even though each port requires its own isolated power supply.

With alternate solutions, such as optocouplers and separate, isolated dc-dc converters, the control module would need to increase in size and would not be backward compatible with installed industrial control systems.”

In addition to the space savings, the ADuM540x devices provide safety pre-approvals, allowing designers to realize faster design times as compared to discrete-based solutions. The latter may require time-consuming safety approvals that can delay time-to-market.

Available now in 16-lead wide-body SOIC packages, the ADuM540x digital isolators are priced at $5 each in 1000-piece quantities. The ADuM520x and ADuM5000 will be priced at $4.08 and $3.16, respectively, per unit in 1,000-piece quantities. For more information, visit www.analog.com/pr/ADuM540x

In addition to introducing the four-channel family, Analog Devices has also introduced a family of digital isolators designed to operate in the challenging automotive environment. The ADuM120xW, ADuM130xW and ADuM140xW digital isolators were specifically developed for use in hybrid-electric vehicle systems.

Unlike the relatively low-voltage supplies powering most in-car entertainment, safety, and power train systems, hybrid-vehicle batteries can operate at voltages in excess of 600 V. This creates a need to galvanically isolate system-critical electronics. According to Analog Devices, the two-channel ADuM120xW, the three-channel ADuM130xW and the four-channel ADuM140xW digital isolators are the first digital isolators to carry an AEC-Q100 qualified –40°C to +125°C automotive temperature rating.

“Until today, the only isolation available for hybrid car and truck batteries was in the form of optocouplers, which are notorious for being difficult to manage and operate at temperatures over 105°C,” said Robbie McAdam, vice president, Analog Semiconductor Components Division, Analog Devices. “In an application where fuel economy and battery capacity are everything, ADI’s digital isolators not only remove the limitations of optocouplers, they do so at 90% less power consumption.”

The new automotive products operate at data rates up to 25 Mbps. Like the four-channel devices described previously, the automotive-qualified parts also operate with the supply voltage on either side ranging from 3.0 V to 5.5 V. This characteristic provides compatibility with lower-voltage systems as well as enabling voltage translation across the isolation barrier.

Unlike alternative forms of isolation such as optocouplers, which suffer from performance degradation and wear-out at high temperatures, iCoupler isolators are relatively insensitive to temperature and are said to demonstrate excellent long-term reliability. And because iCoupler devices have a digital interface, there is no need for external signal conditioning components.

The ADuM120xW, ADuM130xW and ADuM140xW are available now for sampling and volume production. Offered in 8-lead narrow-body or 16-lead wide-body SOIC packages, the isolators are priced starting at $0.55 per channel in OEM quantities. For more information, visit www.analog.com/pr/ADuM120xW, www.analog.com/pr/ADuM130xW, and www.analog.com/pr/ADuM140xW.

The Benefits of Chipscale Transformers

The iCoupler technology is based on chipscale transformers rather than on the LEDs and photodiodes employed in optocouplers. When compared to LEDs and photodiodes, transformers can support higher data rates, consume less power, and are more stable over their operating life. By fabricating the transformers directly on-chip using wafer-level processing, iCoupler channels can be integrated with each other and other semiconductor functions at low cost.

The iCoupler transformers are planar structures formed from CMOS and gold metal layers. A high-breakdown polyimide layer underneath the gold layer insulates the top transformer coil from the bottom. CMOS circuits connected to the top coil and bottom coil provide the interface between each transformer and its external signals. For more on iCoupler technology, see: www.analog.com/icouplerisolation5-08.

While iCoupler digital isolators condition and drive data across transformers. The isoPower dc-dc converter uses the same chipscale transformer technology. But instead of transmitting data, isoPower employs switches, rectifiers, and regulators to generate power that is isolated to the same degree as the data channels. For more on this topic see www.analog.com/isopoweroverview5-08.

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