Realizing 200 Watt/Cubic Inch in VRM

CPU core converters for personal computers require an ever increasing current demand while placing very stringent requirements on the printed circuit board, PCB, real estate where minimal footprint is required. Semiconductor manufacturers are making a more sophisticated process for producing high performance MOSFETs, which are very widely used as the switching device of choice in all DC/DC converters for this application. Toward that end Fairchild has developed a distributed VRM in the form of several modules, each of which is capable of delivering up to 40 Amps per phase at efficiency over 80%. This VRM would allow designers to deliver 200 Amps with five-phase design. The approach in this module concentrates on the power train optimization to realize the best efficiency possible. The selection of the controller and the output and input capacitors is fairly standard and may be found in the technical literature. For each phase, the section that constitutes all the power components are placed on a small plug-in board of 1.15" times 0.85" that delivers 40 Amps and receives the PWM TTL signal from the controller. This module has a footprint of about 0.85" times 0.25" of the motherboard space and may be placed anywhere on the board as close as possible to the CPU reducing the transmission impedance and losses and giving the motherboard designer the flexibility to optimize the power and PCB space utilization. Each modular board may befitted individually with its own heat sink