FIVE STAR: PRODUCT OF THE MONTH

Low-temp Power MOSFET

Current density doubles for DC-DC converters

Managing heat loads in high-power microprocessor systems is a major challenge when the printed circuit board is the main sink for heat dissipation. Standard SO-8 packages, as well as proprietary derivatives such as the bottomless and leadless SO-8, can only be cooled effec-tively on the side of their case in direct contact with the PCB, owing to their poor top-side thermal resistance.

International Rectifier has introduced a surface-mount power MOSFET packaging technol-ogy, called DirectFET, that allows the SO-8 device to be cooled on both sides to cut MOSFET part count by up to 60%. The device’s silicon die is contained in a copper housing, which forms the drain connection from the other side of the die to the board while providing a heatsink surface that improves junction-to-case thermal resistance to 3ºC/W. This advance reduces board space by as much as 50%, thereby reducing total system cost while doubling current density (A/in²).

DirectFET packaging can help designers reach high current levels without paralleling MOS-FETs, adding an additional phase in multiphase converters, using heat pipes or fans, or adding copper through the entire PCB, all of which reduce current density and add system cost. Where heatsinks and cooling air are feasible, the DirectFET dissipates 50% more heat through the top of its package than a plastic-molded-package SO-8, reducing operating temperatures by up to 50ºC. A dual-side-cooled DirectFET chipset permits the creation of DC-DC converters capable of 30A per phase with a single pair of MOSFETs, at a lower total system cost when compared to single-side-cooled SO-8 designs. Current density would be more than 24A/in², double that of a standard SO-8 package.

Additionally, the DirectFET package has a height of 0.7mm, compared with 1.75mm for an SO-8 package, a further advantage in space-constrained applications, such as notebook computers and 1U servers. The devices are bromide and lead-free, and are compatible with existing high-volume manufacturing equipment and processes.

—RM

For more information:
Circle 155—International Rectifier, or connect directly to their website via the Online Reader Service Program at www.rsleads.com/205df-155