MOSFET Chip Set Targets Notebook Buck Converters

Jul 19, 2005 10:35 PM

From International Rectifier, the IRF6621/IRF6612 form a 30-V DirectFET MOSFET synchronous buck converter chip set that is designed for 14 A to 18 A per-phase dc-dc conversion in advanced notebook computer designs using the latest Intel and AMD processors. The chip set consists of the IRF6621 control MOSFET and the IRF6612 synchronous MOSFET, with each device tailored to maximize performance in their role within a synchronous dc-dc buck converter circuit.

Control MOSFETs have reduced switching losses, while synchronous MOSFETs have low conduction losses (low on-resistance), and low reverse-recovery charge. The new chip set achieves above 87% efficiency at 18 A per phase and exceeds 90% efficiency at a mid-current level of 10 A per phase.

“The board space savings alone of two DirectFET MOSFETs vs. three SO-8 devices is almost 50%, and this new chip set is an excellent value for customers seeking very compact and efficient switching in mid-range, 14 to 18 A power converter applications,” said Jeff Sherman, International Rectifier, senior marketing manager, Portable Computing Solutions.

The IRF6621, with its low Q_G and Q_GD of only 11 nC and 3.8 nC, respectively, is best suited as a control FET. The IRF6621 shows a 15% reduction in on resistance-gate charge (108 mΩ-nC) compared to the previous 30VN device (IRF6608, 128 mΩ-nC). The IRF6621 is housed in a small can (SQ) DirectFET package, about 38% smaller than an industry-standard SO-8.

With extremely low typical 4.5V RDS_(ON) of 3.4 mΩ, the IRF6612 is suitable as a synchronous FET in moderate current applications (14 A to 18 A per power channel). The IRF6612 is packaged in a medium can (MX) DirectFET package, enabling an easy design path to other DirectFET family members such as the IRF6611, IRF6678 or IRF6635 in higher current applications or applications where better thermal performance is desired. Pricing is 1.03 each for the IRF6612 and $0.76 each for the IRF6621, both in 10,000-unit quantities.

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