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Smart PWM Controller from STMicroelectronics Increases Efficiency and Reduces Costs for Notebook Power Supplies


Current-mode primary controller IC includes advanced standby function, high-voltage start-up with 700V capability, and dedicated PFC interface

Geneva, December 8, 2005 – STMicroelectronics (NYSE: STM), a world leader in power ICs, has announced an innovative current-mode primary controller IC designed to build sin-gle-ended switching power converters. The L6668’s advanced functions make it one of the most innovative and efficient controllers available for power supplies.

Ideally suited for use in high-end AC/DC adapters and chargers for notebook or laptop PCs, the versatility of the L6668 current-mode PWM controller also makes it suitable for power supplies of set-top boxes, DVD players, low-end LCD TVs and other digital consumer equip-ment. In addition, excellent energy-saving features make the IC a good choice in low-power auxiliary converters used in high-end LCD and plasma-based TVs, desktop PCs and server power supplies.

The IC combines a number of functions able to change the way the device works to optimize power processing under all operating conditions with excellent electrical characteristics. This combination allows development of robust and energy-efficient designs.

One of these innovative functions is the interface with the PFC controller that enables pre-regulator turn off when the load level falls below a threshold, saving typically 0.5 to 1W of no-load power consumption. This interface can be easily connected to the RUN or PFC_OK pins of the ST’s advanced L6563 Power Factor Corrector IC.

In addition, the chip’s high-voltage (HV) technology, when combined with a multi-chip ap-proach, makes it possible to integrate a high-voltage start-up system that is connected directly to the rectified mains voltage. The HV generator is physically located on a separate chip, made with BCD (Bipolar-CMOS-DMOS) off-line technology able to withstand 700V, con-trolled by a low-voltage chip, where all of the control functions reside. This feature, in addi-tion to burst-mode operation and the very low quiescent current, helps it to be compliant with energy saving recommendations with minimum usage of external components. Cost and space saving can be minimized with no compromise on performance.

The L6668 achieves its high level of efficiency by operating in three different modes, de-pending on the load conditions. At heavy load, the IC drives the converter at a programmable fixed frequency to optimize its size and weight. Then, if the load is reduced below a thresh-old, the switching frequency is adapted to minimize conversion losses. Additionally, the im-proved Standby function causes a smooth frequency reduction as the load is progressively re-duced. Eventually, at very light load the device enters a special operating mode (burst-mode with fixed, externally programmed peak current) that brings the switching frequency to ex-tremely low values, hence essentially zeroing all losses related to switching. Optimum size/efficiency trade-off can be achieved and conversion efficiency is maximized under all loading conditions, in addition to the on-board high-voltage start-up. All this means high ef-ficiency benefits with low dissipation on a light load.

The L6668 also includes programmable soft-start, slope compensation for stable operation at duty cycles greater then 50%, a disable function, current sense leading edge blanking to im-prove noise immunity, latched disable for over-voltage or over-temperature shutdown, and protective output current limiting in case the secondary diode fails to short circuit.

The new power supply controller is Blue Angel, Energy Star and EU Code of Conduct com-pliant, and is available now in an SO16 package.

Available in production volumes now, US pricing for the L6668 is $0.40 in quantities of ei-ther 1000 or 2500 for tape-and-reel.

About ST’s Microcontroller, Linear & Discrete Group
STMicroelectronics is a world leader in offering complete system solutions that leverage its rich portfolio of Microcontroller, Linear, and Discrete products, advanced process and design technologies, and applications expertise. This emphasis on solutions allows the Company to minimize time-to-market for all customers worldwide in existing and emerging applications.

About STMicroelectronics
STMicroelectronics is a global leader in developing and delivering semiconductor solutions across the spectrum of microelectronics applications. An unrivalled combination of silicon and system expertise, manufacturing strength, Intellectual Property (IP) portfolio and strate-gic partners positions the Company at the forefront of System-on-Chip (SoC) technology and its products play a key role in enabling today’s convergence markets. The Company’s shares are traded on the New York Stock Exchange, on Euronext Paris and on the Milan Stock Ex-change. In 2004, the Company’s net revenues were $8.76 billion and net earnings were $601 million. Further information on ST can be found at


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