PROCEDURE (Fixed Output Voltage Version)

EXAMPLE (Fixed Output Voltage Version)

A low ESR aluminum or tantalum bypass capacitor is needed between the

input pin and ground pin to prevent large volt-age transients from

appearing at the input. This capacitor should be located close to the IC

using short leads. In addition, the RMS current rating of the input capacitor

should be selected to be at least 1/2 the DC load current. The capacitor

manufacturers data sheet must be checked to assure that this current rating

is not exceeded. The curve shown in Figure 9 shows typical RMS current

ratings for several different aluminum electrolytic capacitor values.

For an aluminum electrolytic, the capacitor voltage rating should be

approximately 1.5 times the maximum input voltage.

The tantalum capacitor voltage rating should be 2 times the maximum

input voltage and it is recommended that they be surge current tested by

the manufacturer.

Use caution when using ceramic capacitors for input bypassing, because it

The important parameters for the Input capacitor are the input voltage rating and the

RMS current rating. With a nominal

input voltage of 12V, an aluminum electrolytic capacitor with a voltage rating

rating is 25V.

The RMS current rating requirement for the input capacitor in

a buck regulator is approximately 1 /2 the DC load current. In this example, with a

3A load, a capacitor with a RMS current rating of at least 1.5A is needed. The

curves shown in Figure 9 can be used to select an appropriate input capacitor.

From the curves, locate the 35V line and note which capacitor values have RMS

current ratings greater than 1.5A. A 680µF/35V capacitor could be used.

For a through hole design, a 680µF/35V electrolytic capacitor (Panasonic HFQ

series or Nichicon PL series or equivalent) would be adequate. other types or other

manufacturers capacitors can be used provided the RMS ripple current ratings are

adequate.

For surface mount designs, solid tantalum capacitors can be used, but caution must

be exercised with regard to the capacitor surge current rating. The TPS series

available from AVX, and the 593D series from Sprague are both surge current

tested.

LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (FIXED OUTPUT) (Continued)

Output Capacitor

Conditions

Inductor

Through Hole Electrolytic

Surface Mount Tantalum

Output

Voltage

(V)

Load

Current

(A)

Max Input

Voltage (V)

Inductance

(

µµµµH)

Inductor

(#)

Panasonic

HFQ Series

(

µµµµF/V)

Nichicon PL

Series (

µµµµF/V)

AVX TPS

Series

(

µµµµF/V)

Sprague 595D Series

(

µµµµF/V)

5

22

L41

470/25

560/16

330/6.3

390/6.3

7

22

L41

560/35

560/35

330/6.3

390/6.3

10

22

L41

680/35

680/35

330/6.3

390/6.3

3

40

33

L40

560/35

470/35

330/6.3

390/6.3

6

22

L33

470/25

470/35

330/6.3

390/6.3

10

33

L32

330/35

330/35

330/6.3

390/6.3

3.3

2

40

47

L39

330/35

270/50

220/10

330/10

8

22

L41

470/25

560/16

220/10

330/10

10

22

L41

560/25

560/25

220/10

330/10

15

33

L40

330/35

330/35

220/10

330/10

3

40

47

L39

330/35

270/35

220/10

330/10

9

22

L33

470/25

560/16

220/10

330/10

20

68

L38

180/35

180/35

100/10

270/10

5

2

40

68

L38

180/35

180/35

100/10

270/10

15

22

L41

470/25

470/25

100/16

180/16

18

33

L40

330/25

330/25

100/16

180/16

30

68

L44

180/25

180/25

100/16

120/20

3

40

68

L44

180/35

180/35

100/16

120/20

15

33

L32

330/25

330/25

100/16

180/16

20

68

L38

180/25

180/25

100/16

120/20

12

2

40

150

L42

82/25

82/25

68/20

68/25

Figure 2. LM2596 Fixed Voltage Quick Design Component Selection Table

LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (ADJUSTABLE OUTPUT)

PROCEDURE (Adjustable Output Voltage Version)

EXAMPLE (Adjustable Output Voltage Version)

Given:

Given:

F=Switching Frequency (Fixed at a nominal 150 kHz).

F=Switching Frequency (Fixed at a nominal 150 kHz).

Figure 1)

Use the following formula to select the appropriate resistor values.

)

R

R

(1

V

V

1

2

REF

OUT

+

=

where

V

1.23

=

values minimize noise pickup in the sensitive feedback pin. (For the

lowest temperature coefficient and the best stability with time, use 1%

metal film resistors.)

in Figure 1)

1)

V

1.23

V

20

k(

1

1)

V

V

(

R

R

REF

OUT

1

2

−

=

−

=

9

BEIJING ESTEK ELECTRONICS CO.,LTD

LM2596

3AStep-Down VoltageRegulator