TIDUEP0 May 2020
In a SEPIC converter, when the power switch Q1 is turned on, the inductor is charging and the output current is supplied by the output capacitor. As a result, the output capacitor sees large ripple currents. Thus the selected output capacitor must be capable of handling the maximum RMS current. The RMS current in the output capacitor is: (14
The ESR, ESL, and the bulk capacitance of the output capacitor directly control the output ripple. Assume half of the ripple is caused by the ESR and the other half is caused by the amount of capacitance. Hence,
The output cap must meet the RMS current, ESR and capacitance requirements. In surface mount applications, tantalum, polymer electrolytic, and polymer tantalum, or multi-layer ceramic capacitors are recommended at the output.