SNVS787I January 2012 – August 2021 LM5018
The minimum inductance is selected to limit the inductor ripple current to 20 to 40 percent of the maximum load current. In addition, the peak inductor current at maximum load must be smaller than the minimum current limit threshold provided in the Section 6.5. The inductor current ripple is given by Equation 13.
The maximum ripple is observed at maximum input voltage. Substituting VIN = 95 V and ΔIL = 40 percent × IOUT(max) results in L1 = 169 μH. The higher standard value of 220 μH is chosen. With this value of inductance, peak-to-peak minimum and maximum inductor current ripple of 27 mA and 92 mA occur at the minimum and maximum input voltages, respectively. The peak inductor and switch current is given by Equation 14.
The peak inductor current of 346 mA is smaller than the minimum current limit threshold of 390 mA. The selected inductor must be able to operate at the maximum current limit of 750 mA during start-up and overload conditions without saturating.