LM2576 datasheet(14/23 Pages) ARTSCHIP

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LM2576/LM2576HV

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LM2576 Series Buck Regulator Design Procedure (Continued)

PROCEDURE (Adjustable Output Voltage Versions)

EXAMPLE (Adjustable Output Voltage Versions)

2. Inductor Selection (L1) A. Calculate the inductor Volt

Microsecond constant, E●

T (V●μS), from the following

formula:

B. Use the E●

T value from the previous formula and

match it with E● T number on the vertical axis of the

Inductor Value Selection Guide shown in Figure 7. C. On

the horizontal axis, select the maximum load current. D.

Identify the inductance region intersected by the E● T

value and the maximum load current value, and note the

inductor code for that region. E. Identify the inductor value

from the table shown in Figure 9. Part numbers are listed

for three inductor manufacturers. The inductor chosen

must be rated for operation at the LM2576 switching

frequency (52KHz) 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.

3. 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, the

capacitor must satisfy the following requirement:

The above formula yields capacitor values between 10μF and

2200 μ F that will satisfy the loop requirements for stable

operation. But to achieve an acceptable output ripple voltage,

(approximately 1% of the output voltage) and transient response,

the output capacitor may need to be several times larger than the

above formula yields. B. The capacitor’s voltage rating should be

at last 1.5 times greater than the output voltage. For a 10V

regulator, a rating of at least 15V or more is recommended.

Higher voltage electrolytic capacitors generally have lower ESR

numbers, and for this reason it may be necessary to select a

capacitor rate for a higher voltage than would normally be

needed.

4.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 and overload or shorted

output. See diode selection guide in Figure 8. B. The reverse

voltage rating of the diode should be at least 1.25 times the

maximum input voltage.

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

bypass capacitor located close to the regulator is needed for

stable operation.

2.Inductor Selection (L1) A. Calculate E●

T(V ●μS )

B. E●

T=115 V ●μs C. ILOAD(Max)=3A D. Inductance

Region = H150 E. Inductor Value = 150μ

H Choose from AIE

part #415-0936 Pulse Engineering part #PE-531115, or Renco

part #RL2445.

3.Output Capacitor Selection (COUT)

However, for acceptable output ripple voltage select COUT≥680

F COUT=680μF electrolytic capacitor

4.Catch Diode Selection (D1) A. For this example, a 3.3A

current rating is adequate. B. Use a 30V 31DQ03 Schottky diode,

or any of the suggested fast-recovery diodes in Figure8.

5.Input Capacitor (CIN) A 100 μ F aluminum electrolytic

capacitor located near the input and ground pins provides

sufficient bypassing.

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