AP1509 DC-DC Power Supply calculating Inductance?
For a buck operating in CCM (continuous conduction mode), which is what ANP013 is addressing:  

\$V_{\text{out}}\$ = \$D V_{\text{in}}\$  

and  \$T_{\text{on}}\$ = \$\frac{D}{F}\$ while \$T_{\text{off}}\$ = \$\frac{1-D}{F}\$  

The easiest way to calculate the inductance is:  

L = \$\frac{T_{\text{off}} V_{\text{out}}}{2 I_{\text{Load} (\min) }}\$

There is more about choosing buck inductors here.  The equation in the referenced question will give an over estimate of inductance, which will be somewhat higher than you get from the equation shown above.