Cherry Semiconductor Corp. (East Greenwich, RI) introduce the CS51313, a switching buck controller designed to power motherboards based on Pentium III microprocessors, which require five different voltages. The CS51313 switching buck controller features a Vref pin and a small external quad op amp. The controller powers Vcore at 2.0V, and the Vref and quad op amp implement four linear regulators at 1.5V, 2.5V, 1.8V and 1.5/3.3V selectable for Vddq. On-chip control and protection features are incorporated to simplify design and the use of multi-function pins minimizes the overall solution size. The external op amp can be placed anywhere on the board, allowing layout flexibility, and the external reference makes it easy to implement additional linear regulators, according to Cherry. The CS51313's two feedback loops are claimed to offer the industry's fastest transient response (200ns) and best overall dc accuracy. The IC requires only one compensation capacitor."Designing for the five voltages required by the Pentium III processor can be a real challenge," stated Cherry Product Marketing Engineer Todd Sherman. "Typical designs are based on a controller in a bulky 24-lead package, which require additional components and complicated compensation schemes for optimal performance. All this takes up valuable board space and adds significantly to the total solution cost."The CS51313 is packaged in a 16-lead SO narrow package, and the external op amp is available in a 14-lead SO narrow package. According to Cherry, the combined footprint of the CS51313 and the op amp is 35 percent smaller than the 24-lead SO wide package.