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Integrated package cuts area, losses, in POL regulation

International Rectifier has joined the growing list of suppliers of voltage regulators integrated in small surface-mount packages. Its SupIRBuck series of stepdown point-of-load devices kicks off with a family of nine parts. IR has chosen to reuse the silicon it has already developed for its regulator control IC range, coupled with HEXFET trench MOSFETs similar to the ones it packages in its DirectFET range. Contrasting this approach with various competitors that have opted to build monolithic chips with power devices and control IC on the same silicon die, IR claims several advantages. FETs built on mixedsignal IC silicon technology do not have the same performance in terms of on-resistance or avalanche-rating, for example. IR makes a comparison in which it asserts that its devices maintain higher efficiency across a wider inputvoltage range (and across the range of power loading) than is possible with the compromise devices that other companies build on a monolithic process. It conspicuously omits the same comparison with other competitors that also use a discrete IC-plus- MOSFET construction, with a spokesman generously—if quietly—acknowledging that, “they are pretty good, too.”

IR is aiming this fi rst release, the IR38xx SupIRBuck family, at data-centre applications, with outputs rated at 4, 7 and 12A of output-load current at a 600-kHz switching frequency, uprated by a further 2A in each case if you use a version that switches at 300 kHz. They accept input voltages anywhere from 2.5 to 21V, and output 12V down to 0.6V. Package dissipation will bound available combinations of voltage and current, and you will be able to calculate the operating area in the usual way from data-sheet fi gures: but IR’s Davide Giacomini says that on most PCBs, the 560.9-mm OFN package— which has large heatsinking contact pads—will be able to dissipate around 1W, and with an effi ciency of 90% or better at full load, this indicates that the regulators are in the 10W class, “or a bit more”. You will be able to cut the silicon footprint of a regulator by 70% compared to discrete solutions, and achieve between 8 to 10% higher full-load effi ciency than those competing monolithic ICs, IR adds. All of the nine chips have a common size and pin-out, allowing the designer to upgrade current output without changing board layout. Common features across the family include pre-bias start up, a fi xed 600-kHz switching frequency, hiccup-current limit, thermal shutdown, and precise output-voltage regulation. Optional features—depending on device selection—include tracking, programmable power-good, and a 300-kHz switching frequency. You can mount the package on the reverse side of a motherboard, in space-constrained, highdensity server applications; the main external-component groups that you need to add comprise compensation, the output L/C network, and bootstrap and soft-start capacitors. The devices will work in the 5-to-12V range with no external bias—outside those limits, you will also have to add biasing. Pricing is from $2.25 (10,000), and IR has samples now.

International Rectifier, www.irf.com