AN1101: Designing a High Efficiency DC-DC Converter with the EL75xx

Since the beginning of the digital revolution, the speed of a microprocessor has been governed by Moore's law postulated in 1968 by Intel's co-founder Gorden Moore. Moore suggested that the speed of a microprocessor would double in every 18 months. However, the principle of conservation of energy, more scientific in nature, will eventually dominate and limit the rate at which the speed of a microprocessor is increasing. The equation P = CV2F, a derivative of the principle of conservation of energy, dictates that the power dissipated in a device is linearly proportional to its clock frequency and distributed capacitance. Microprocessor manufacturers have made great advances in reducing the amount of power dissipation in the device. The popular Pentium microprocessor, for example, employs a combination of heat-sink/fan to extract heat from the package. To further combat the power dissipation problem, a new generation of low voltage CMOS fabrication processes have been developed. The low voltage processes have a smaller transistor geometry that results in lower parasitic capacitance, reducing C in the above equation. Smaller transistor size also allows for a increase in the number of transistors in a given die area, and as a result, the lifetime of Moore's law is extended. However, technical problems are being passed onto the shoulders of power supply designers. Lower microprocessor supply voltages and higher supply currents mean that the linear DC-DC regulator is no longer a viable solution. Power supply designers are forced into using switching regulator techniques. Lower output voltage, higher output current, and smaller output voltage ripple requirements have greatly increased the difficulty of the power supply design. To further burden the problem, power saving “stop-clock” modes have demanded faster and more stable transient response from the DC-DC converter. Table of