SNVSAE4C July 2015 – October 2018 LM5160-Q1
Select the inductor to limit the inductor ripple current between 20 and 40 percent of the maximum load current. Calculate the minimum value of the inductance required in this application from Equation 13.
Based on Equation 13, determine the minimum value of the inductance as 26 µH for VIN = 65 V (maximum) and inductor ripple current equal to 40 percent of the maximum load current. Allowing some margin for inductance variation with current, select a higher standard value of L1 (L) = 47 µH for this design.
The peak inductor current at maximum load must be smaller than the minimum current limit threshold of the high-side FET, as given inElectrical Characteristics table. Determine the inductor ripple current at any input voltage using Equation 14.
Calculate the peak-to-peak inductor ripple current as 180 mA and 332 mA at the minimum and maximum input voltages, respectively. Determine the maximum peak inductor current in the buck FET using Equation 15.
In this design with an output current of 1.5 A, the maximum peak inductor current is calculated to be approximately 1.67 A, which is less than the high-side FET minimum current limit threshold.
The saturation current of the inductor must also be carefully considered. The peak value of the inductor current is bound by the high-side FET current limit during overload or short circuit conditions. Based on the high-side FET current limit specification in Electrical Characteristics, select an inductor with saturation current rating above 2.875 A.