Integrated dc/dc regulators improve efficiency in server, embedded-system applications
By Margery Conner, Technical Editor -- EDN, November 29, 2007
Energy efficiency continues to be a major concern for server-farm operators, who can expect to pay three times the cost of the servers in operating costs over the life of the equipment. Further, the Environmental Protection Agency estimates that 1.2% of the total US electricity usage goes into powering server farms. Schemes for improving efficiency often center on power conversion within the server motherboard. Designs for high-density POL (point-of-load) converters fall into one of two camps: One approach uses a power-conversion IC with separate, discrete, power-switching MOSFETs. The advantage of this approach is flexibility; many parts are available to fine-tune a design. The disadvantage is the increase in design time and in parts count, as well as a lack of standardization across the motherboard and product line. The other approach uses a monolithic converter that incorporates the regulation electronics and the power MOSFETs on one die. This approach results in a lower parts count and simplified design but at the expense of flexibility and increased inefficiency at 12V if the part targets use with 5V supplies.
International Rectifier’s SupIRBuck family takes a third approach and incorporates a PWM (pulse-width-modulation) IC with switching MOSFETs into a tiny 5×6-mm module, achieving efficient power conversion and regulation for both 5 and 12V power rails. Providing 4, 7, and 12A of output-load current at a 600-kHz switching frequency, the IR38xx operates from an input-voltage range of 2.5 to 21V and provides output voltage as low as 0.6V. Common features include prebias start-up, fixed 600-kHz switching frequency, hiccup-current limit, thermal shutdown, and precise output-voltage regulation. Optional features include tracking, a programmable power-good signal, and 300-kHz switching frequency to provide 2A more output-current capability. Prices for the SupIRBuck IR38xx devices begin at $2.25 (10,000) each.
