The value of the output capacitor together with the inductor defines the dominate pole-pair of the switching regulator loop. For stable operation and an acceptable output ripple voltage, (approximately 1% of the output voltage) TI recommends a value between 100 μF and 470 μF. We choose COUT = 680-μF to 2000-μF standard aluminum electrolytic.
The voltage rating of the capacitor must be at
least 1.5 times greater than the output voltage. For a 5-V regulator, a rating
of at least 8 V is appropriate, and TI recommends a 10-V or 15-V rating.
Capacitor voltage rating = 20 V. Higher voltage electrolytic capacitors
generally have lower ESR numbers, and for this reason it can be necessary to
select a capacitor rated for a higher voltage than can normally be needed.