The buck inductor inductance and power rating must be considered. The inductance is selected so the peak-to-peak ripple current and is between 20% to 40% (K = 0.2 to 0.4) of the device rated current (example 3A for LMR66430-EP). This design uses a ripple factor K, of 0.2, having Equation 7 yield a standard value of 4.7μH.

Ideally, the saturation current rating of the inductor is at least as large as the high-side switch current limit, I_PEAKMAX (see the Electrical Characteristics). This size makes sure that the inductor does not saturate, even during a short circuit on the output. When the inductor core material saturates, the inductance falls to a very low value, causing the inductor current to rise very rapidly. Although the valley current limit, I_VALMAX, is designed to reduce the risk of current runaway, a saturated inductor can cause the current to rise to high values very rapidly. This can lead to component damage. Do not allow the inductor to saturate. Inductors with a ferrite core material have very hard saturation characteristics, but usually have lower core losses than powdered iron cores. Powered iron cores exhibit a soft saturation, allowing some relaxation in the current rating of the inductor. However, there are more core losses at frequencies above about 1MHz.

The maximum inductance is limited by the minimum current ripple for the current mode control to perform correctly. As a general rule, the minimum inductor ripple current must be no less than about 10% of the device maximum rated current under nominal conditions.