This is a summary of " Selection of Inductors and Capacitors for DC/DC Converters" in "DC/DC Converters: Design Edition".
As explained in this chapter, inductors and capacitors are important components of step-down DC/DC converters, and their selection has a large influence on performance and characteristics. This selection is explained using the data sheets, application notes, design manuals, and other supplementary materials for the power supply ICs that are used in nearly all cases. We begin by using these explanations and formulae to execute design.
However, even if design is executed according to the manual, the resulting operation is unfortunately not necessarily optimal. In such cases, component values are modified after evaluations; but if changes are made haphazardly, the design process may veer out of control, and even if problems are resolved, it may not be clear why performance improved, so that as a result the designer will not have the confidence to move to mass production.
In order to avoid this kind of situation, it is important that the basic operation of step-down DC/DC converters, and the currents flowing in these devices, be understood. Moreover, it is also necessary to understand in advance what changes and how when there is a change in inductances and capacitances, not only based on equations, but also from experience drawing on actual measurements.
These points are summarized below.
2）Rated ripple current
3）ESR (equivalent series resistance)
2）Rated ripple current and ripple heat generation characteristic
3）In the case of ceramic capacitors, temperature characteristics and DC bias
・In DC/DC converter design, selection of inductors and input/output capacitors is particularly important.
・Circuit operation, current pathways, and the functions of components must be understood.
・Calculations are performed in accordance with the design manual, and optimization is executed based on actual measurements.