The continuous-conduction equations

In CCM the duty cycle sets the conversion ratio:

D_{buck} = \frac{V _{o u t}}{V _{in}} D_{boost} = 1 - \frac{V _{in}}{V _{o u t}}

The inductor ripple current and the resulting output ripple voltage are:

Δ I_{L} = \frac{V _{in} D ( 1 - D )}{L f _{s w}} Δ V_{o u t} = \frac{Δ I _{L}}{8 C _{o u t} f _{s w}}

(For boost, $Δ I_{L} = V_{in} D / (L f_{s w})$ and the output ripple is dominated by the load step $I_{o u t} D / (C_{o u t} f_{s w})$ .) Keep $Δ I_{L}$ around 20–40% of the load current: too small wastes a bulky inductor, too large pushes the converter toward discontinuous conduction.

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The continuous-conduction equations