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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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LM2596S-3.3 Fiches technique(PDF) 11 Page - National Semiconductor (TI) |
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LM2596S-3.3 Fiches technique(HTML) 11 Page - National Semiconductor (TI) |
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11 / 31 page  LM2596 Series Buck Regulator Design Procedure (Fixed Output) (Continued) PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version) 3. Catch Diode Selection (D1) A. 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 should 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. B. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. C. This diode must be fast (short reverse recovery time) and must be located 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 should be the first choice, especially in low output voltage applications. Ultra-fast recovery, or High-Efficiency rectifiers also provide good re- sults. Ultra-fast recovery diodes typically have reverse recov- ery times of 50 ns or less. Rectifiers such as the 1N5400 series are much too slow and should not be used. 3. Catch Diode Selection (D1) A. Refer to the table shown in Figure 11. In this example, a 5A, 20V, 1N5823 Schottky diode will provide the best perfor- mance, and will not be overstressed even for a shorted output. 4. Input Capacitor (C IN) A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground pin to prevent large voltage transients from appearing at the input. This capacitor should be located close to the IC using short leads. In addition, the RMS current rating of the input capacitor should be selected to be at least 1⁄2 the DC load current. The capacitor manufactur- ers data sheet must be checked to assure that this current rating is not exceeded. The curve shown in Figure 13 shows typical RMS current ratings for several different aluminum electrolytic capacitor values. For an aluminum electrolytic, the capacitor voltage rating should be approximately 1.5 times the maximum input volt- age. Caution must be exercised if solid tantalum capacitors are used (see Application Information on input capacitor). The tantalum capacitor voltage rating should be 2 times the maxi- mum input voltage and it is recommended that they be surge current tested by the manufacturer. Use caution when using ceramic capacitors for input bypass- ing, because it may cause severe ringing at the V IN pin. For additional information, see section on input capaci- tors in Application Information section. 4. Input Capacitor (C IN) The important parameters for the Input capacitor are the input voltage rating and the RMS current rating. With a nominal input voltage of 12V, an aluminum electrolytic capacitor with a voltage rating greater than 18V (1.5 x V IN) would be needed. The next higher capacitor voltage rating is 25V. The RMS current rating requirement for the input capacitor in a buck regulator is approximately 1⁄2 the DC load current. In this example, with a 3A load, a capacitor with a RMS current rating of at least 1.5A is needed. The curves shown in Figure 13 can be used to select an appropriate input capacitor. From the curves, locate the 35V line and note which capacitor values have RMS current ratings greater than 1.5A. A 680 µF/ 35V capacitor could be used. For a through hole design, a 680 µF/35V electrolytic capacitor (Panasonic HFQ series or Nichicon PL series or equivalent) would be adequate. other types or other manufacturers ca- pacitors can be used provided the RMS ripple current ratings are adequate. For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capaci- tor surge current rating (see Application Information on input capacitors in this data sheet). The TPS series available from AVX, and the 593D series from Sprague are both surge cur- rent tested. www.national.com 11 |
Numéro de pièce similaire - LM2596S-3.3 |
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Description similaire - LM2596S-3.3 |
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