JAJSFS7B July 2018 – February 2019 LM5180-Q1
ADVANCE INFORMATION for pre-production products; subject to change without notice.
Choose a turns ratio based on an approximate 60% max duty cycle at minimum input voltage using Equation 13, rounding up or down as needed.
Select a magnetizing inductance based on the minimum off-time constraint using Equation 14. Choose a value of 30 µH with a saturation current of 2 A for this application.
Note that a higher magnetizing inductance provides a larger operating range for BCM and FFM, but the leakage inductance may increase based on the increase number of primary turns, NP. The primary and secondary winding RMS currents are given by Equation 15 and Equation 16, respectively.
Find the maximum output power for a given turns ratio using Equation 17, where the typical value for IPRI-PK(max) from Electrical Characteristics is 1.5 A. Iterate by increasing the turns ratio if the output power is too low at minimum input voltage.