LM2597, LM2597HV

www.ti.com

SNVS119C – MARCH 1998 – REVISED APRIL 2013

PROCEDURE (Fixed Output Voltage Version)

EXAMPLE (Fixed Output Voltage Version)

3. Catch Diode Selection (D1)

3. Catch Diode Selection (D1)

A. The catch diode current rating must be at least 1.3 times greater A. Refer to Table 6. In this example, a 1A, 20V, 1N5817 Schottky

than the maximum load current. Also, if the power supply design diode will provide the best performance, and will not be overstressed

must withstand a continuous output short, the diode should have a even for a shorted output.

current rating equal to the maximum current limit of the LM2597. 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.

C. This diode must be fast (short reverse recovery time) and must be

located close to the LM2597 using short leads and short printed

circuit traces. Because of their fast switching speed and low forward

voltage drop, Schottky diodes provide the best performance and

efficiency, and should be the first choice, especially in low output

voltage applications. Ultra-fast recovery, or High-Efficiency rectifiers

also provide good results. Ultra-fast recovery diodes typically have

reverse recovery times of 50 ns or less. Rectifiers such as the

1N4001 series are much too slow and should not be used.

A low ESR aluminum or tantalum bypass capacitor is needed The important parameters for the Input capacitor are the input

between the input pin and ground to prevent large voltage transients voltage rating and the RMS current rating. With a nominal input

from appearing at the input. In addition, the RMS current rating of voltage of 12V, an aluminum electrolytic capacitor with a voltage

current. The capacitor manufacturers data sheet must be checked to higher capacitor voltage rating is 25V.

assure that this current rating is not exceeded. The curve shown in The RMS current rating requirement for the input capacitor in a buck

Figure 35 shows typical RMS current ratings for several different regulator is approximately ½ the DC load current. In this example,

aluminum electrolytic capacitor values.

with a 400 mA load, a capacitor with a RMS current rating of at least

This capacitor should be located close to the IC using short leads 200 mA is needed. The curves shown in Figure 35 can be used to

and the voltage rating should be approximately 1.5 times the select an appropriate input capacitor. From the curves, locate the

maximum input voltage.

25V line and note which capacitor values have RMS current ratings

greater than 200 mA. Either a 47

μF or 68 μF, 25V capacitor could

If solid tantalum input capacitors are used, it is recommended that

be used.

they be surge current tested by the manufacturer.

For a through hole design, a 68

μF/25V electrolytic capacitor

Use caution when using ceramic capacitors for input bypassing,

(Panasonic HFQ series or Nichicon PL series or equivalent) would

be adequate. Other types or other manufacturers capacitors can be

For additional information, see section on INPUT CAPACITOR in used provided the RMS ripple current ratings are adequate.

Application Information section.

For

surface

mount

designs,

solid

tantalum

capacitors

are

recommended. The TPS series available from AVX, and the 593D

series from Sprague are both surge current tested.

Table 1. LM2597/LM2597HV Fixed Voltage Quick Design Component Selection Table

Conditions

Inductor

Output Capacitor

Through Hole

Surface Mount

Voltage

Current

Voltage

Panasonic

Nichicon

AVX TPS

Sprague

Inductance

Inductor

Output

Load

Max Input

HFQ Series

PL Series

Series

595D Series

(

μH)

(#)

(V)

(A)

(V)

(

μF/V)

(

μF/V)

(

μF/V)

(

μF/V)

5

33

L14

220/16

220/16

100/16

100/6.3

7

47

L13

120/25

120/25

100/16

100/6.3

0.5

10

68

L21

120/25

120/25

100/16

100/6.3

3.3

40

100

L20

120/35

120/35

100/16

100/6.3

6

68

L4

120/25

120/25

100/16

100/6.3

0.2

10

150

L10

120/16

120/16

100/16

100/6.3

40

220

L9

120/16

120/16

100/16

100/6.3

Copyright © 1998–2013, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Links: LM2597 LM2597HV