SNVSBN6 April 2020 LM5181-Q1
The flyback diode reverse voltage is given by Equation 19.
Select a 40-V, 3-A Schottky diode for this application to account for inevitable diode voltage overshoot and ringing related to the resonance of transformer leakage inductance and diode parasitic capacitance. Connect an appropriate RC snubber circuit (for example, 100 Ω and 22 pF) across the flyback diode if needed.
In general, choose a flyback diode with current rating greater than the maximum peak secondary winding current of NPS × ISW-PEAK. As mentioned in the Layout section, place adequate copper at the cathode of the diode to improve its thermal performance and prevent overheating during high ambient temperature or overload conditions. Beware of the high leakage current typical of a Schottky diode at elevated operating temperatures.