MOSFETs yield increased power density with PowerPAK cooling tech

STMicroelectronics (ST) has announced the new STK800 and STK850 power MOSFETs—the company's first power devices to be assembled in the metal-topped Siliconix" target=_blank>PolarPak package, which is touted to provide superior thermal performance and increased power density for components used in high current power supplies.

ST announced in March 2005 a license agreement with Siliconix to use PolarPAK technology. Although it has a leadframe and plastic encapsulation similar to those used in standard power MOSFET packages, PolarPAK dissipates heat more efficiently so it can handle twice the current within the same footprint, said ST.

With PolarPak, the STK800 and STK850 require a board area of 5-by-6mm, the same as the SO-8 package, but with a lower profile of 0.8mm due to both top and bottom heat dissipation paths.

The new devices are manufactured using ST's STripFET technology, which is based on increased cell density and smaller cell features, to achieve low ON-resistance and losses while using less silicon area.

Typical RDS(on) of the 20A STK800 is 6 milliohms and 2.9 milliohms for the 30A STK850 at 10V. The package contributes to the low ON-resistance of both MOSFETs by providing low junction-to-case thermal resistance and lower junction temperatures, ST explained.

With its low capacitance and total gate charge, the STK800 is designed to be a control FET in non-isolated DC/DC step down converters, while the low RDS(on) of STK850 makes it suitable as a synchronous FET.

The product's low operating temperatures contribute to higher efficiency and an increase in lifetime reliability. The new package provides improved die protection and easy handling in manufacture, maintaining compatibility with existing SMD assembly equipment.

Samples of the new devices are available. The STK800 is priced at $1.20 and the STK850 at $1.60, for quantities of 1,000.