Design minimum value of capacitance \( C \) needed for a Buck converter with a frequency \( f = 100 \, \text{kHz} \) so that ripple voltage \( V_r \) is less than 1% of output voltage \( V_o \). Assume the duty ratio \( \delta = 0.6 \) and inductor \( L = 25 \, \mu H \).