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LM2596 Datasheet(PDF) 10 Page - Estek Electronics Co. Ltd |
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LM2596 Datasheet(HTML) 10 Page - Estek Electronics Co. Ltd |
10 / 12 page PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version) 1) V V ( R R REF OUT 1 2 − = 2. Inductor Selection (L1) 2. Inductor Selection (L1) A. Calculate the inductor Volt • microsecond constant E •T (V•µs), from the following formula: s) (V kHz 150 1000 V V V V V ) V V (V T E D SAT IN D OUT SAT OUT IN µ • • + − + • − − = • where VSAT = internal switch saturation voltage = 1.16V and VD = diode forward voltage drop = 0.5V A. Calculate the inductor Volt • microsecond constant (E •T), s) (V 150 1000 5 . 0 16 . 1 28 5 . 0 20 ) 16 . 1 20 28 ( T E µ • • + − + • − − = • s) (V . s) (V . . . ) . ( T E µ µ • = • • • = • 2 34 67 6 34 27 5 20 84 6 B. Use the E •T value from the previous formula and match it with the E •T number on the vertical axis of the Inductor Value Selection Guide shown in Figure 7. B. E •T=34.2 (V•µs) C. on the horizontal axis, select the maximum load current. C. ILOAD (max) = 3A D. Identify the inductance region intersected by the E •T value and the Maximum Load Current value. Each region is identified by an inductance value and an inductor code (LXX). D. From the inductor value selection guide shown in Figure 7, the inductance region intersected by the 34 (V •µs) horizontal line and the 3A vertical line is 47 µH, and the inductor code is L39. E. Select an appropriate inductor from the four manufacturer’s part numbers listed in Figure 8. E. From the table in Figure 8, locate line L39, and select an inductor part number from the list of manufacturers part numbers. 3. Output Capacitor Selection (COUT) 3. Output Capacitor SeIection (COUT) A. In the majority of applications, low ESR electrolytic or solid tantalum capacitors between 82 µF and 820 µF provide the best results. This capacitor should be located close to the IC using short capacitor leads and short copper traces. Do not use capacitors larger than 820 µF. B. To simplify the capacitor selection procedure, refer to the quick design table shown in Figure 3. This table contains different output voltages, and lists various output capacitors that will provide the best design solutions. B. From the quick design table shown in Figure 3, locate the output voltage column. From that column, locate the output voltage closest to the output voltage in your application. In this example, select the 24V line. Under the output capacitor section, select a capacitor from the list of through hole electrolytic or surface mount tantalum types from four different capacitor manufacturers. It is recommended that both the manufacturers and the manufacturers series that are listed in the table be used. In this example, through hole aluminum electrolytic capacitors from several different manufacturers are available. 220 µF/35V Panasonic HFQ Series 150 µF/35V Nichicon PL Series C. The capacitor voltage rating should be at least 1.5 times greater than the output voltage, and often much higher voltage ratings are needed to satisfy the low ESR requirements needed for low output ripple voltage. C. For a 20V output, a capacitor rating of at least 30V or more is needed. In this example, either a 35V or 50V capacitor would work. A 35V rating was chosen, although a 50V rating could also be used if a lower output ripple voltage is needed. Other manufacturers or other types of capacitors may also be used, provided the capacitor specifications (especially the 100 kHz ESR) closely match the types listed in the table. Refer to the capacitor manufacturers data sheet for this information. 4. Feedforward Capacitor (CFF ) (See Figure 1) 4. Feedforward Capacitor (CFF ) For output voltages greater than approximately 10V, an additional capacitor is required. The compensation capacitor is typically between 100 pF and 33 nF, and is wired in parallel with the output voltage setting resistor, R2. It provides additional stability for high output voltages, low input-output voltages, and/or very low ESR output capacitors, such as solid tantalum capacitors. 2 FF R 10 31 1 C × × = This capacitor type can be ceramic, plastic, silver mica, etc. (Because of the unstable characteristics of ceramic capacitors made with Z5U material, they are not recommended.) The table shown in Figure 3 contains feed forward capacitor values for various output voltages. In this example, a 560 pF capacitor is needed. 3 10 BEIJING ESTEK ELECTRONICS CO.,LTD LM2596 3AStep-Down VoltageRegulator |
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