An 8 A 100-MHz 4-Phase Buck Converter with Fast Dynamic Response and Enhanced Light-Load Efficiency

A 4-phase buck converter with maximum load of 8 A targeting server applications is presented. The converter switches at 100 MHz to enable fast dynamic response and reduce the required inductance and capacitance to 20 nH (5 nH/phase) and 220 nF. Thus, small foot-print inductors and capacitor can be used and co-packaged with the converter die. To maintain high efficiency across a wide load range, the converter employs PWM control in the 6-8 A load range, and then deactivates phases as the load drops below 6 A while keeping PWM control until only one phase is active when the load is less than 2 A. For loads less than 0.7 A, the converter deactivates the PWM controller and activates a PFM controller to scale switching losses and ensure high efficiency at light loads. The converter is designed and simulated in a 0.13 μm CMOS technology. It operates from 1.5 V input and produces a programmable output in the range of 0.75-1 V. The converter achieves a peak efficiency of 88% at 5 A and 79% at 0.7 A with less than 4 mV output voltage ripple.