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PWM chip advances digital power

Posted: 20 Jul 2006 ?? ?Print Version ?Bookmark and Share

Keywords:iW1688? PWM IC? iWatt? XX? XX?

Proclaiming a paradigm shift in power supply control techniques with its iW1688 PWM chip, iWatt announced that it is the first to secure significant benefits of digital control as applied to the primary side of low-power AC/DC adapters and chargers. Using what the company says is a unique combination of sampling techniques and an efficient digital engine, the iW1688 is designed to achieve tight regulation and a smaller, less expensive and more efficient implementation for the 2-5W adapters used in cellular and cordless phones, digital music players, and still cameras.

"In an environment of increasing regulatory pressures on AC/DC supplies for low power applications, the iW1688 is a game changing product. It significantly simplifies meeting tighter no-load power requirements while eliminating external components, such as optocouplers, that add both cost and reliability issues," said Doyle Slack, vice president of marketing.

Traditional solutions using analog (DC feedback) methods in the primary loop create problems with regulation, noted George Hill, director of marketing. Indeed, up to this time securing tight supply regulation required secondary feedback loops that add both components and create a concern as to the overall reliability of the optocoupler, Hill said. High regulation with an analog solution and DC feedback becomes more difficult when the feedback signal is too filteredthe feedback loop's cycle-by-cycle response is lost. iWatt's solution, on the other hand, uses AC feedback from the primary side to restore cycle-by-cycle response and high regulationthere are no regulation errors (which become particularly significant during the transition from light-load to full-load conditions) associated with the sampling process. The chip tightly regulates output voltage in the constant-voltage mode to less than 15 percent; and current in the constant-current mode to less than 110 percentbest in-class performance for primary-feedback systems, according to the company.

The iW1688's digital approach, moreover, allows design-in of some valuable functionality, including robust over- and under-voltage shutdown. Its control loop also provides internal compensation, thus doing away with several more external components.

In moving the action to the primary side, the iW1688 does away with the optocoupler and associated components traditionally used for coordinating secondary-side feedback. According to Hill, there are other alternatives to the optocoupler approach. One solution uses an auxiliary winding in a traditional topology to replace the optocoupler. "The drawback to that scheme, is that operating power for the PWM circuitry also goes over the same winding as the feedback information, thus creating an additional regulation issue," said Hill.

The iW1688 is fully qualified and in volume production now. Housed in a RoHS-compliant 5-lead SOT-23 package, it is priced at 31 cents each in 10,000-unit pieces and is available in 3,000-piece reels.

- Vince Biancomano

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