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LM2596-12

Simple switcher Power Converter 150kHz 3A Step-Down Voltage Regulator

First Components International 

LM2596 Simple switcher Power Converter 150kHz

3A Step-Down Voltage Regulator

LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (FIXED OUTPUT)

PROCEDURE (Fixed Output Voltage Version)

Given:

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

VIN (max) = Maximum DC Input Voltage

ILOAD (max) = Maximum Load Current

EXAMPLE (Fixed Output Voltage Version)

Given:

VOUT =5V

VIN (max) = 12V

ILOAD (max) = 3A

1. Inductor Selection (L1)

1. Inductor Selection (L1)

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

from Figures Figure 4, Figure 5,or Figure 6. (Output in Figure 5.

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

voltages, see the design procedure for the adjustable

version.

B. From the inductor value selection guide, identify the B. From the inductor value selection guide shown in Figure

inductance region intersected by the Maximum Input 5, the inductance region intersected by the 12V horizontal

Voltage line and the Maximum Load Current line. Each line and the 3A vertical line is 33 UH, and the inductor code

region is identified by an inductance value and an

is L40.

inductor code (LXX).

C. Select an appropriate inductor from the four

C. The inductance value required is 33 UH. From the table in

manufacturer’s part numbers listed in Figure 8.

Figure 8, go to the L40 line and choose an inductor part number

from any of the four manufacturers shown. (In most in-stance,

both through hole and surface mount inductors are available.)

2. Output Capacitor Selection (COUT)

2. Output Capacitor Selection (COUT)

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

Series Resistance) electrolytic capacitors between 82 information section.

UF and 820 UF and low ESR solid tantalum capacitors

between 10 UF and 470 UF provide the best results.

This capacitor should be located close to the IC using

short capacitor leads and short copper traces. Do not

use capacitors larger than 820 UF.

B. To simplify the capacitor selection procedure, refer B. From the quick design component selection table shown in

to the quick design component selection table shown Figure 2, locate the 5V output voltage section. In the load current

in Figure 2. This table contains different input voltages, column, choose the load current line that is closest to the current

output voltages, and load currents, and lists various needed in your application, for this example, use the 3A line. In the

inductors and output capacitors that will provide the maximum input voltage column, select the line that covers the input

best design solutions.

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

line. Continuing on this line are recommended inductors and

capacitors that will provide the best overall performance.

The capacitor list contains both through hole electrolytic and

surface mount tantalum capacitors from four different capacitor

manufacturers. It is recommended that both the manufacturers and

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

In this example aluminum electrolytic capacitors from several

different manufacturers are available with the range of ESR

numbers needed.

330 UF 35V Panasonic HFQ Series

330 UF 35V Nichicon PL Series

C. The capacitor voltage rating for electrolytic

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

capacitors should be at least 1.5 times greater than more is needed. B ut even a low ESR, switching grade, 220UF

the output voltage, and often much higher voltage

10V aluminum electrolytic capacitor would exhibit approximately

ratings are needed to satisfy the low ESR requirements 225 mW of ESR (see the curve in Figure 14 for the ESR vs

for low output ripple voltage.

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 volt-age by approximately half.

3. Catch Diode Selection (D1)

A. The catch diode current rating must be at least 1.3

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 LM2596. 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)

3. Catch Diode Selection (D1)

A. Refer to the table shown in Figure 11. In this example, a 5A,

20V, 1N5823 Schottky diode will provide the best performance,

and will not be overstressed even for a shorted output.

8

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