LM2576 datasheet(11/23 Pages) ARTSCHIP

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LM2576/LM2576HV

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LM2576 Series Buck Regulator

Design Procedure

PROCEDURE (Fixed Output Voltage versions)

EXAMPLE (Fixed Output Voltage Versions)

Given: VOUT = Regulated Output Voltage (3.3V, 5V, 12V, or

15V) VIN(Max) = Maximum Input Voltage LLOAD(Max)=Maximum

Load Current

1. Inductor Selection (L1) A. Select the correct Inductor value

selection guide from Figures 3,4,5 or Figure 6.(Output

voltages of 3.3V, 5V, 12V or 15V respectively). For other

output voltages, see the design procedure for the adjustable

version. B. From the inductor value selection guide, identify

the inductance region intersected by VIN(Max) and

LLOAD(Max), and note the inductor code for that region. C.

Identify the inductor value from the inductor code, and select

an appropriate inductor from the table shown in Figure3. Part

numbers are listed for three inductor manufacturers. The

inductor chosen must be rated for operation at the LM2576

switching frequency (52 KHz) and for a current rating of 1.15

X LLOAD. For additional inductor information, see the inductor

section in the Application Hints section of this data sheet.

2. Output Capacitor Selection (COUT) A. The value of the

output capacitor together with the inductor defines the

dominate pole-pair of the switching regulator loop. For stable

operation and an acceptable output ripple voltage,

(approximately 1% of the output voltage) a value between

100μF and 470μF is recommended. B. The capacitor’s

voltage rating should be at least 1.5 times greater than the

output voltage. For a 5V regulator, a rating of at least 8V is

appropriate, and a 10V or 15V rating is recommended.

Higher voltage electrolytic capacitors generally have lower

ESR numbers, and for this reason it may be necessary to

select a capacitor rated for a higher voltage than would

normally be needed.

3. Catch Diode Selection (D1) A. The catch-diode current

rating must be at least 1.2 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 LM2576.

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.

4. Input Capacitor (CIN) An aluminum or tantalum electrolytic

bypass capacitor located close to the regulator is needed for

stable operation.

Given: VOUT =5V VIN(Max) =15V LLOAD(Max)=3A

Inductor Selection (L1) A. Use the selection guide shown

in Figure 4, B. From the selection guide, the inductance

area intersected by the 15V line and 3A line is L100. C.

Inductor value required is 100μH. From the table in Figure

3. Choose AIE 415-0930. Pulse Engineering PE92108, or

Renco RL2444.

Output Capacitor Selection (COUT) A. COUT=680μF to

2000 μ F standard aluminum electrolytic. B. Capacitor

voltage rating=20V.

Catch Diode Selection (D1) A. For this example, a 3A

current rating is adequate. B. Use a 20V 1N5823 or SR302

Schottky diode, or any of the suggested fast-recoverv

diodes shown in Figure8.

Input Capacitor (CIN) A 100 μ F, 25V aluminum

electrolytic capacitor located near the input and ground

pins provides sufficient bypassing.

LM2576 Datasheet(PDF) 11 Page - ARTSCHIP ELECTRONICS CO.,LMITED.

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