For the example shown in figure 2 lets assume a switching
frequency of 250kHz, input voltage range of
12V±10% and a max ripple current of 220mA.
Figure 2
For an input voltage of 13.2V the duty cycle will be:
D = Vo/Vi = 5/13.2 = 0.379 (3)
Where Vo is the output voltage and Vi is the input voltage.
Voltage across the inductance:
V1 = Vi - Vo = 8.2V when the switch is on (4)
V1 = - Vo = -5V when the switch is off (5)
Require inductance:
L = V1.dt/di = (8.2 x 0.379/250 x 103)/0.22 (6)
L = 56.5μH