LM2596

SNVS124C – NOVEMBER 1999 – REVISED APRIL 2013

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LM2596 Series Buck Regulator Design Procedure (Fixed Output)

PROCEDURE (Fixed Output Voltage Version)

EXAMPLE (Fixed Output Voltage Version)

Given:

Given:

1. Inductor Selection (L1)

1. Inductor Selection (L1)

A. Select the correct inductor value selection guide from Figures A. Use the inductor selection guide for the 5V version shown in

Figure 21, Figure 22, or Figure 23. (Output voltages of 3.3V, 5V, or Figure 22.

12V respectively.) For all other voltages, see the Design Procedure B. From the inductor value selection guide shown in Figure 22, the

for the adjustable version.

inductance region intersected by the 12V horizontal line and the 3A

B. From the inductor value selection guide, identify the inductance vertical line is 33

μH, and the inductor code is L40.

region intersected by the Maximum Input Voltage line and the C. The inductance value required is 33 μH. From the table in

Maximum Load Current line. Each region is identified by an Table 3, go to the L40 line and choose an inductor part number from

inductance value and an inductor code (LXX).

any of the four manufacturers shown. (In most instance, both

C. Select an appropriate inductor from the four manufacturer's part through hole and surface mount inductors are available.)

numbers listed in Table 3.

A. In the majority of applications, low ESR (Equivalent Series A. See section on output capacitors in Application Information

Resistance) electrolytic capacitors between 82

μF and 820 μF and section.

low ESR solid tantalum capacitors between 10

μF and 470 μF B. From the quick design component selection table shown in

provide the best results. This capacitor should be located close to Table 1, locate the 5V output voltage section. In the load current

the IC using short capacitor leads and short copper traces. Do not column, choose the load current line that is closest to the current

use capacitors larger than 820

μF .

needed in your application, for this example, use the 3A line. In the

For additional information, see section on output capacitors in maximum input voltage column, select the line that covers the input

Application Information section.

voltage needed in your application, in this example, use the 15V line.

Continuing on this line are recommended inductors and capacitors

B. To simplify the capacitor selection procedure, refer to the quick

that will provide the best overall performance.

design component selection table shown in Table 1. This table

contains different input voltages, output voltages, and load currents, The capacitor list contains both through hole electrolytic and surface

and lists various inductors and output capacitors that will provide the mount

tantalum

capacitors

from

four

different

capacitor

best design solutions.

manufacturers. It is recommended that both the manufacturers and

the manufacturer's series that are listed in the table be used.

C. The capacitor voltage rating for electrolytic capacitors should be

at least 1.5 times greater than the output voltage, and often much In this example aluminum electrolytic capacitors from several

higher voltage ratings

are

needed

to satisfy the low

ESR different manufacturers are available with the range of ESR numbers

requirements for low output ripple voltage.

needed.

D. For computer aided design software, see Switchers Made

330

μF

35V

Panasonic HFQ Series

Simple™ version 4.3 or later.

330

μF

35V

Nichicon PL Series

C. For a 5V output, a capacitor voltage rating at least 7.5V or more

is needed. But even a low ESR, switching grade, 220

μF 10V

aluminum electrolytic capacitor would exhibit approximately 225 m

Ω

of ESR (see the curve in Figure 26 for the ESR vs voltage rating).

This amount of ESR would result in relatively high output ripple

voltage. To reduce the ripple to 1% of the output voltage, or less, a

capacitor with a higher value or with a higher voltage rating (lower

ESR) should be selected. A 16V or 25V capacitor will reduce the

ripple voltage by approximately half.

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