8.2.2.4 Choose output capacitance

When organic semiconductor capacitors (OS-CON) or specialty polymer capacitors (SP-CAP) are used, ESR to achieve required ripple value at stable state or transient load conditions determines the amount of capacitor(s) need, and capacitance is then enough to satisfy stable operation. The peak-to-peak ripple value can be estimated by ESR times the inductor ripple current for stable state, or ESR times the load current step for a fast transient load response. When ceramic capacitor(s) are used, the ESR is usually small enough to meet ripple requirement. In contrast, transient undershoot and overshoot driven by output capacitance becomes the key factor in determining the capacitor(s) required.