The catch diode current rating must be at least 1.3 times greater than the maximum load current. Also, if the power supply design must withstand a continuous output short, the diode must have a current rating equal to the maximum current limit of the LM2596. The most stressful condition for this diode is an overload or shorted output condition. See Table 9-4. Schottky diodes provide the best performance, and in this example, a 5-A, 40-V, 1N5825 Schottky diode would be a good choice. The 5-A diode rating is more than adequate and will not be overstressed even for a shorted output.
The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage.
This diode must be fast (short reverse recovery time) and must be placed close to the LM2596 using short leads and short-printed circuit traces. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency, and must be the first choice, especially in low output voltage applications. Ultra-fast recovery or high-efficiency rectifiers are also good choices, but some types with an abrupt turnoff characteristic may cause instability or EMl problems. Ultra-fast recovery diodes typically have reverse recovery times of 50 ns or less. Rectifiers such as the 1N4001 series must not be used because they are too slow.