NEW POWER MOSFETS ARE PWM OPTIMIZED FOR LINE-POWERED SYNCHRONOUS RECTIFICATION APPLICATIONS
30 May 2001 - Virginia Polytechnic Institute and State University

Two new LITTLE FOOT power MOSFETs for dc-to-dc converter circuits, including the industry's first PWM-optimized n-channel device with a 12-V maximum breakdown voltage rating, were released today by Siliconix incorporated, an 80.4%-owned subsidiary of Vishay Intertechnology, Inc.

Both new devices are intended for synchronous rectifier applications, serving low voltage outputs in dc-to-dc converters for desktop computers, network or routing cards, stand-alone power supplies, and other line-powered systems where a low-voltage microprocessor is needed.

Until now, power MOSFETs optimized for synchronous rectification were available only in voltage ratings of 20 V or greater, sometimes diminishing efficiency and increasing heat generation when used in low-voltage products. The new Vishay Siliconix Si4838DY, with its 12-V VDS, breaks this barrier and offers a 40% overall performance improvement over any comparable device, with a maximum on-resistance of just 3 mΩ and a typical gate charge of 40 nC.

For applications where more headroom is required, Siliconix is offering the new Si4876DY, a 20-V device with 5-mΩ on-resistance and Qg of just 55 nC - specifications which represent a 10% overall improvement compared with any competing device on the market.

In many cases, supply currents require paralleling of synchronous rectification circuits, and many boards are stacked up. This means that the benefits offered by these new LITTLE FOOT devices are multiplied and therefore very significant.

Overall performance for purposes of comparison is defined as the product of on-resistance times gate charge, with a lower score being better.

Supply voltages are getting smaller, and lower-voltage synchronous rectifiers are required to prevent power from being wasted. The low on-resistance/gate charge product of these new devices means that converters can run at higher frequencies or with lower conduction and switching losses. That means more efficient use of power, less heat generated, and smaller space requirements.

Offered in the LITTLE FOOT SO-8 package, samples of the Si4838DY and Si4876DY are available now. Production quantities are available now, with lead times of 8 to 10 weeks for larger orders.

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