In essence, the recommended components listed on the data sheet for each IC and their values should be used as reference. Moreover, depending on the DC voltage applied to a capacitor, the effective capacitance of the capacitor is different, and so the characteristic curve provided by the manufacturer indicating the relationship between DC voltage and capacitance should be referenced to select a capacitor for which an effective capacitance equal to that of the recommended component can be ensured. At the same time, recommendations for grade and other parameters should be observed.
From the standpoint of stable operation of a power supply IC, the products and values recommended by the data sheet should first be considered. When it is also necessary to reduce input ripple voltages and spike noise for EMC measures, capacitors should also be studied in accordance with frequency bands to be used and the required impedance characteristics.
That would be correct. However, capacitors with small capacitance changes are larger in size. When space or other issues arise, after considering the capacitance change due to the DC bias characteristic, a capacitor can be selected the actual capacitance of which is equivalent to the recommended value.
In general, the lower the capacitance of a ceramic capacitor, the higher is the self-resonant frequency, so that the device functions as a capacitor up to higher frequencies. There are mainly two types of frequency components in the switching operation of a DC/DC converter: the switching frequency (ranging from hundreds of kHz to several MHz), and the switching rise/fall frequency (from 100 MHz). In order to suppress power supply fluctuations at the latter in particular, 100 MHz and up, a ceramic capacitor with a low capacitance is necessary.
It will probably depend on the design specifications of the set, but a large-value electrolytic capacitor is used for the purpose of delaying attenuation of the input voltage when the set power supply is turned off, whereas a ceramic capacitor has a small ESR and so is used to supply charge when there are sudden current changes, as with switching currents.
Attenuation of the capacitance due to the DC bias characteristic causes the resonance frequency and other impedance characteristics to change accordingly as well. The capacitor manufacturer should be asked for the impedance characteristics for DC biasing, and devices selected on this basis, or else a MLCC should be used with a high rated voltage and a value sufficient to accommodate drops in capacitance at the voltage of use due to the DC bias characteristic.
The bypass capacitor should be closer to the IC. This capacitor must deal with large current changes per unit time, and if it is at a distance from the IC, the parasitic inductance of the wiring is increased, making it less effective.
It is recommended that multiple capacitors be used for different frequencies. As for problems, if multiple capacitors having self-resonant frequencies that are far apart are used, antiresonances may occur between those frequencies, and there are concerns that noise characteristics may be worsened at the antiresonance frequencies. Also, when arranging multiple capacitors, it is preferable that capacitors with higher self-resonant frequencies (mainly small-value capacitors) be placed closer to the IC; if instead capacitors with higher self-resonant frequencies are positioned further away, the line inductance to the capacitors will cause the self-resonant frequency to shift to lower frequencies, and the intended characteristics may not be obtained.