L36

L35

MAXIMUM LOAD CURRENT (A)

4

5

6

7

8

9

10

12

1

2

3

4

5

6

7

8

9

10

20

30

40

50

60

70

80

90

100

L01

L02

L03

L04

L05

L06

L07

L08

L09

L10

L11

L12

L13

L14

L15

L16

L17

L18

L19

L20

L21

L22

L23

L24

L34

L33

L32

L25

L26

L27

L28

L29

L30

L31

L48

L47

L46

L45

L44

L37

L38

L39

L40

L41

L42

L43

47 P

H

33 P

H

22 P

H

15 P

H

10 P

H

6.8 P

H

4.7 P

H

3.3 P

H

2.2 P

H

1.5 P

H

1.0 P

H

0.68

PH

0.47

PH

0.33

PH

ET = (Vinmax ± VOUT) x

Vinmax

VOUT

x

fS

1000

(V x Ps)

LM3151, LM3152, LM3153

SNVS562G – SEPTEMBER 2008 – REVISED MARCH 2011

www.ti.com

Design Guide

The design guide provides the equations required to design with the LM3151/2/3 SIMPLE SWITCHER Controller.

WEBENCH design tool can be used with or in place of this section for a more complete and simplified design

process.

1. Define Power Supply Operating Conditions

a. Maximum and Minimum DC Input voltage

b. Maximum Expected Load Current during normal operation

c. Target Switching Frequency

2. Determine which IC Controller to Use

The desired input voltage range will determine which version of the LM3151/2/3 controller will be chosen. The

higher switching frequency options allow for physically smaller inductors but efficiency may decrease.

3. Determine Inductor Required Using Figure 13

To use the nomograph below calculate the inductor volt-microsecond constant ET from the following formula:

where

•

fS is in kHz units

The intersection of the Load Current and the Volt-microseconds lines on the chart below will determine which

inductors are capable for use in the design. The chart shows a sample of parts that can be used. The offline

calculator tools and WEBENCH will fully calculate the requirements for the components needed for the design.

Figure 13. Inductor Nomograph

12

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