Switching Capacitor Voltage Regulator Applicable To VRM

The power consumption of CPU is approximately proportional to the square of its operationvoltage and frequency. As the frequency increases, in order to reduce power consumption, theoperation voltage must be reduced. And in order to get faster speed and ensure the powerrequirements, CPU’s power supply current needs to increase. The trend of next generation computermicroprocessor development is low voltage and high current. The operation voltage is decreasingbelow1V, currents up to130A. Some microprocessors in servers even require as high as170A current.Furthermore, the high clock frequency induces very fast di/dt (the current slew rate) when themicroprocessor operation changes from the sleep mode to the power mode and vice versa. Thisrequires high dynamic characteristic of CPU’s power supply, which is named the voltage regulatormodule (VRM).With rapidly growing computer and telecommunication applications, the point of load (POL)converter has been more and more applied. VRM is one kind of POL converter. The VRM evolutionhas been driven by user’s growing requirements of CPU’s performance. Therefore, the main target ofVRM design is low voltage, high current, high power density and high dynamic performance.The traditional PWM DC-DC converter, such as Buck, Boost, and Buck-Boost converter, theoutput voltage can be regulated by adjusting the duty cycle. But the energy transfer part, inductor,appears in each switch mode. Inductive current doesn’t mutate, which limits the speed of energytransfer, and the magnetic core obstructs power density of the converters. Reducing inductance canimprove dynamic characteristics of converter, but it will also increase inductance current ripple andreduce efficiency.Switching capacitor converters use the capacitors to realize the role played by inductors. Theycan achieve small size, light weight, high power density and high dynamic performance. But theconverters can’t regulate the output voltage for variations in the line voltage and suffer from a relativehigh current ripple during the switching transition.This paper proposes the switching capacitor voltage regulator applicable to VRM. Switchingcapacitor voltage regulator uses capacitors as the energy transfer parts, while the output voltage can beregulated by adjusting the duty cycle. The switching capacitor voltage regulator not only keeps theadvantage of the traditional PWM converter, but also gains good dynamic performance benefits fromthe behaviors of the switching capacitor converter.