LM2672_01 datasheet(9/25 Pages) NSC

Numer części	LM2672

Szczegółowy opis	SIMPLE SWITCHER짰 Power Converter High Efficiency 1A Step-Down Voltage Regulator with Features

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LM2672 Series Buck Regulator Design Procedure (Fixed Output)

PROCEDURE (Fixed Output Voltage Version)

EXAMPLE (Fixed Output Voltage Version)

To simplify the buck regulator design procedure, National

Semiconductor is making available computer design software to

be used with the SIMPLE SWITCHER line of switching

regulators. LM267X Made Simple version 6.0 is available on

Windows®

3.1, NT, or 95 operating systems.

Given:

V

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

V

OUT =5V

V

IN(max) = Maximum DC Input Voltage

V

IN(max) = 12V

I

LOAD(max) = Maximum Load Current

I

LOAD(max) = 1A

1. Inductor Selection (L1)

A. Select the correct inductor value selection guide from

Figure

4 and Figure 5 or Figure 6 (output voltages of 3.3V, 5V, or 12V

respectively). For all other voltages, see the design procedure

for the adjustable version.

1. Inductor Selection (L1)

A. Use the inductor selection guide for the 5V version shown in

Figure 5.

B. From the inductor value selection guide, identify the

inductance region intersected by the Maximum Input Voltage

line and the Maximum Load Current line. Each region is

identified by an inductance value and an inductor code (LXX).

B. From the inductor value selection guide shown in

Figure 5,

the inductance region intersected by the 12V horizontal line and

the 1A vertical line is 33 µH, and the inductor code is L23.

C. Select an appropriate inductor from the four manufacturer’s

part numbers listed in

Figure 8. Each manufacturer makes a

different style of inductor to allow flexibility in meeting various

design requirements. Listed below are some of the

differentiating characteristics of each manufacturer’s inductors:

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

Figure 8, go to the L23 line and choose an inductor part number

from any of the four manufacturers shown. (In most instances,

both through hole and surface mount inductors are available.)

Schott: ferrite EP core inductors; these have very low leakage

magnetic fields to reduce electro-magnetic interference (EMI)

and are the lowest power loss inductors

Renco: ferrite stick core inductors; benefits are typically lowest

cost inductors and can withstand E

•T and transient peak

currents above rated value. Be aware that these inductors have

an external magnetic field which may generate more EMI than

other types of inductors.

Pulse: powered iron toroid core inductors; these can also be low

cost and can withstand larger than normal E

•T and transient

peak currents. Toroid inductors have low EMI.

Coilcraft: ferrite drum core inductors; these are the smallest

physical size inductors, available only as SMT components. Be

aware that these inductors also generate EMI — but less than

stick inductors.

Complete specifications for these inductors are available from

the respective manufacturers. A table listing the manufacturers’

phone numbers is located in

Figure 9.

2. Output Capacitor Selection (C

OUT)

A. Select an output capacitor from the output capacitor table in

Figure 10. Using the output voltage and the inductance value

found in the inductor selection guide, step 1, locate the

appropriate capacitor value and voltage rating.

2. Output Capacitor Selection (C

OUT)

A. Use the 5.0V section in the output capacitor table in

Figure

10. Choose a capacitor value and voltage rating from the line

that contains the inductance value of 33 µH. The capacitance

and voltage rating values corresponding to the 33 µH

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Podobny numer części - LM2672_01

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