The MAX1639 is an ultra-high-performance, step-down DC-DC controller for CPUpower in high-end computer systems. Designed for demanding applications in which output voltage precision and good transient response are critical for proper operation, it delivers over 35A from 1.1V to 4.5V with ±1% total accuracy from a +5V ±10% supply. Excellent dynamic response corrects output transients caused by the latest dynamically clocked CPUs. This controller achieves over 90% efficiency by using synchronous rectification. Flying-capacitor bootstrap circuitry drives inexpensive, external N-channel MOSFETs.

The switching frequency is pin-selectable for 300kHz, 600kHz, or 1MHz. High switching frequencies allow the use of a small surface-mount inductor and decrease output filter capacitor requirements, reducingboard area and system cost.

Output overvoltage protection is enforced by a crowbar circuit that turns on the low-side MOSFET with 100% duty factor when the output is 200mV above the normal regulation point. Other features include internal digital soft-start, a power-good output, and a 3.5V ±1% reference output. The MAX1639 is available in a 16-pin narrow SOIC package.