LM2597, LM2597HV

SNVS119C – MARCH 1998 – REVISED APRIL 2013

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LM2597/LM2597HV 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 Figure 26, A. Use the inductor selection guide for the 5V version shown in

Figure 27, or Figure 28. (Output voltages of 3.3V, 5V, or 12V Figure 27.

respectively.) For all other voltages, see the design procedure for the B. From the inductor value selection guide shown in Figure 27, the

adjustable version.

inductance region intersected by the 12V horizontal line and the 0.4A

B. From the inductor value selection guide, identify the inductance vertical line is 100

μH, and the inductor code is L20.

region intersected by the Maximum Input Voltage line and the C. The inductance value required is 100 μH. From the table in

Maximum Load Current line. Each region is identified by an Table 3, go to the L20 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 OUTPUT CAPACITOR in Application Information section.

Resistance) electrolytic capacitors between 82

μF and 220 μF and B. From the quick design component selection table shown in

low ESR solid tantalum capacitors between 15

μF and 100 μF Table 1, locate the 5V output voltage section. In the load current

provide the best results. This capacitor should be located close to column, choose the load current line that is closest to the current

the IC using short capacitor leads and short copper traces. Do not needed in your application, for this example, use the 0.5A line. In the

use capacitors larger than 220

μF.

maximum input voltage column, select the line that covers the input

For

additional

information,

see

OUTPUT

CAPACITOR

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

Application Information.

Continuing on this line are recommended inductors and capacitors

that will provide the best overall performance.

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

design component selection table shown in Table 1. This table The capacitor list contains both through hole electrolytic and surface

contains different input voltages, output voltages, and load currents, mount

tantalum

capacitors

from

four

different

capacitor

and lists various inductors and output capacitors that will provide the manufacturers. It is recommended that both the manufacturers and

best design solutions.

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

C. The capacitor voltage rating for electrolytic capacitors should be In this example aluminum electrolytic capacitors from several

at least 1.5 times greater than the output voltage, and often much different manufacturers are available with the range of ESR numbers

higher voltage ratings

are

needed

to satisfy the low

ESR needed.

requirements for low output ripple voltage.

120

μF

25V

Panasonic HFQ Series

D. For computer aided design software, see Switchers Made

120

μF

25V

Nichicon PL Series

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

is needed. But, in this example, even a low ESR, switching grade,

120

μF

10V

aluminum

electrolytic

capacitor

would

exhibit

approximately 400 m

Ω of ESR (see the curve in Figure 36 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 voltage rating (lower ESR)

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

voltage by approximately half.

12

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