3.1.1 Input Capacitors

All of the switching converters in this paper (and the vast majority in use) operate as DC/DC converters that chop a DC input voltage at a very high frequency. As the converter switches, it has to draw current pulses from the input source. The source impedance is extremely important, as even a small amount of inductance can cause significant ringing and spiking on the voltage at the input of the converter.

The best practice is to always provide adequate capacitive bypass as near as possible to the switching converter input. For best results, an electrolytic is used with a film capacitor (and possibly a ceramic capacitor) in parallel for optimum high frequency bypassing.