5 Output Capacitor Selection C out A C out 680 m F to 2000 m F standard

5 output capacitor selection c out a c out 680 m f to

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5. Output Capacitor Selection (C out ) A. C out = 680 m F to 2000 m F standard aluminium electrolytic. B. Capacitor voltage rating = 20 V. Procedure (Adjustable Output Version: LM2576−ADJ) Procedure Example Given Parameters: V out = Regulated Output Voltage V in(max) = Maximum DC Input Voltage I Load(max) = Maximum Load Current Given Parameters: V out = 8.0 V V in(max) = 25 V I Load(max) = 2.5 A 1. Programming Output Voltage To select the right programming resistor R1 and R2 value (see Figure 2) use the following formula: Resistor R1 can be between 1.0 k and 5.0 k W . (For best temperature coefficient and stability with time, use 1% metal film resistors). V out + V ref ǒ 1.0 ) R2 R1 Ǔ R2 + R1 ǒ V out V ref – 1.0 Ǔ where V ref = 1.23 V 1. Programming Output Voltage (selecting R1 and R2) Select R1 and R2: R2 = 9.91 k W , choose a 9.88 k metal film resistor. R2 + R1 ǒ V out V ref * 1.0 Ǔ + 1.8 k ǒ 8.0 V 1.23 V * 1.0 Ǔ V out + 1.23 ǒ 1.0 ) R2 R1 Ǔ Select R1 = 1.8 k W 2. Input Capacitor Selection (C in ) To prevent large voltage transients from appearing at the input and for stable operation of the converter, an aluminium or tantalum electrolytic bypass capacitor is needed between the input pin +V in and ground pin GND This capacitor should be located close to the IC using short leads. This capacitor should have a low ESR (Equivalent Series Resistance) value . For additional information see input capacitor section in the “Application Hints” section of this data sheet. 2. Input Capacitor Selection (C in ) A 100 m F, 150 V aluminium electrolytic capacitor located near the input and ground pin provides sufficient bypassing. 3. Catch Diode Selection (D1) A. Since the diode maximum peak current exceeds the regulator maximum load current the catch diode current rating must be at least 1.2 times greater than the maximum load current. For a robust design, the diode should have a current rating equal to the maximum current limit of the LM2576 to be able to withstand a continuous output short. B. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. 3. Catch Diode Selection (D1) A. For this example, a 3.0 A current rating is adequate. B. Use a 30 V 1N5821 Schottky diode or any suggested fast recovery diode in the Table 1.
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LM2576 12 Procedure (Adjustable Output Version: LM2576−ADJ) (continued) Procedure Example 4. Inductor Selection (L1) A. Use the following formula to calculate the inductor Volt x microsecond [V x m s] constant: B. Match the calculated E x T value with the corresponding number on the vertical axis of the Inductor Value Selection Guide shown in Figure 22. This E x T constant is a measure of the energy handling capability of an inductor and is dependent upon the type of core, the core area, the number of turns, and the duty cycle. C. Next step is to identify the inductance region intersected by the E x T value and the maximum load current value on the horizontal axis shown in Figure 25.
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  • Spring '19
  • Margaret Earle
  • Switched-mode power supply, Vout

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