Abstract:

Power management for portable low power systems has special needs: generation of multiple supply voltages, miniaturization and high efficiency at low currents. The research activity on this area aims at system with all the components on package and solutions that share the inductor for obtaining multiple supply voltages.
This tutorial deals with the above point and focuses on design methodologies to obtain multiple outputs and to use of very small inductors.
The four possible schemes, buck, boost, and inverting or non-inverting buck-boost, are considered. The key specific problems related to the issue are the inductor current switching scheme, the multiple-loops control, the suitable driving of power switches and, accordingly, the converter power efficiency. All the issues are discussed in details. Moreover, design examples of devices integrated with CMOS technologies and the experimental results are presented.
The miniaturization of dc-dc converter requires using very high switching frequency. This must be achieved while maintaining high efficiency, better than the one of a linear converter. The circuit solution discussed in the tutorial foresee a non conventional loop control that enable operation up to 120-MHz switching frequency with peak power efficiency of 87% for 75% duty cycle and 93% at 60 MHz. The results are confirmed by experimental measurements.