Use Equation 18 and Equation 19 to calculate the inductor ripple current (assuming CCM operation) and peak inductor current, respectively.

Equation 18.

Equation 19.

For most applications, choose an inductance such that the inductor ripple current, ΔI_L, is between 30% and 50% of the rated load current at nominal input voltage. Use Equation 20 to calculate the inductance.

Equation 20.

Choosing a 120-μH inductor in this design results in 250-mA peak-to-peak ripple current at a nominal input voltage of 48 V, equivalent to 50% of the 500-mA rated load current.

Check the inductor data sheet to make sure the saturation current of the inductor is well above the current limit setting of the LM5163. Ferrite-core inductors have relatively lower core losses and are preferred at high switching frequencies, but exhibit a hard saturation characteristic – the inductance collapses abruptly when the saturation current is exceeded. This results in an abrupt increase in inductor ripple current, higher output voltage ripple, and reduced efficiency, in turn compromising reliability. Note that inductor saturation current levels generally decrease as the core temperature increases.