LM2672LDX-5.0_技术文档

April 2007

LM2672

SIMPLE SWITCHER^®Power Converter High Efficiency 1A

Step-Down Voltage Regulator with Features

To simplify the LM2672 buck regulator design procedure,

there exists computer design software, LM267X Made Sim-

General Description

The LM2672 series of regulators are monolithic integrated

circuits built with a LMDMOS process. These regulators pro-

vide all the active functions for a step-down (buck) switching

regulator, capable of driving a 1A load current with excellent

line and load regulation. These devices are available in fixed

output voltages of 3.3V, 5.0V, 12V, and an adjustable output

version.

ple version 6.0.

Features

Efficiency up to 96%

■

Available in SO-8, 8-pin DIP and LLP packages

Computer Design Software LM267X Made Simple

version 6.0

Requiring a minimum number of external components, these

regulators are simple to use and include patented internal

frequency compensation (Patent Nos. 5,382,918 and

5,514,947), fixed frequency oscillator, external shutdown,

soft-start, and frequency synchronization.

Simple and easy to design with

■

Requires only 5 external components

Uses readily available standard inductors

3.3V, 5.0V, 12V, and adjustable output versions

The LM2672 series operates at a switching frequency of

260 kHz, thus allowing smaller sized filter components than

what would be needed with lower frequency switching regu-

lators. Because of its very high efficiency (>90%), the copper

traces on the printed circuit board are the only heat sinking

needed.

Adjustable version output voltage range: 1.21V to 37V

±1.5% max output voltage tolerance over line and load

conditions

Guaranteed 1A output load current

■

0.25Ω DMOS Output Switch

Wide input voltage range: 8V to 40V

■

A family of standard inductors for use with the LM2672 are

available from several different manufacturers. This feature

greatly simplifies the design of switch-mode power supplies

using these advanced ICs. Also included in the datasheet are

selector guides for diodes and capacitors designed to work in

switch-mode power supplies.

260 kHz fixed frequency internal oscillator

TTL shutdown capability, low power standby mode

Soft-start and frequency synchronization

Thermal shutdown and current limit protection

Other features include a guaranteed ±1.5% tolerance on out-

put voltage within specified input voltages and output load

conditions, and ±10% on the oscillator frequency. External

shutdown is included, featuring typically 50 μA stand-by cur-

rent. The output switch includes current limiting, as well as

thermal shutdown for full protection under fault conditions.

Typical Applications

Simple High Efficiency (>90%) Step-Down (Buck)

Regulator

■

Efficient Pre-Regulator for Linear Regulators

■

Typical Application

(Fixed Output Voltage Versions)

1293401

SIMPLE SWITCHER^®is a registered trademark of National Semiconductor Corporation

Windows^®is a registered trademark of Microsoft Corporation.

12934

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Connection Diagrams

16-Lead LLP Surface Mount Package

8-Lead Package

Top View

1293402

SO-8/DIP Package

See NSC Package Drawing Number MO8A/N08E

1293441

LLP Package

See NSC Package Drawing Number LDA16A

TABLE 1. Package Marking and Ordering Information

Order Information Package Marking

Output Voltage

16 Lead LLP

Supplied as:

12

LM2672LD-12

S0001B

1000 Units on Tape and Reel

4500 Units on Tape and Reel

1000 Units on Tape and Reel

4500 Units on Tape and Reel

1000 Units on Tape and Reel

4500 Units on Tape and Reel

1000 Units on Tape and Reel

4500 Units on Tape and Reel

LM2672LDX-12

LM2672LD-3.3

LM2672LDX-3.3

LM2672LD-5.0

LM2672LDX-5.0

LM2672LD-ADJ

LM2672LDX-ADJ

S0001B

S0002B

S0003B

S0004B

3.3

5.0

ADJ

SO-8

12

LM2672M-12

LM2672MX-12

LM2672M-3.3

LM2672MX-3.3

LM2672M-5.0

LM2672MX-5.0

LM2672M-ADJ

LM2672MX-ADJ

2672M-12

2672M-3.3

2672M-5.0

2672M-ADJ

Shipped in Anti-Static Rails

2500 Units on Tape and Reel

Shipped in Anti-Static Rails

2500 Units on Tape and Reel

Shipped in Anti-Static Rails

2500 Units on Tape and Reel

Shipped in Anti-Static Rails

2500 Units on Tape and Reel

3.3

5.0

ADJ

DIP

12

3.3

LM2672N-12

LM2672N-3.3

LM2672N-5.0

LM2672N-ADJ

LM2672N-12

LM2672N-3.3

LM2672N-5.0

LM2672N-ADJ

Shipped in Anti-Static Rails

5.0

ADJ

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2

Storage Temperature Range

Lead Temperature

M Package

Vapor Phase (60s)

Infrared (15s)

N Package (Soldering, 10s)

LLP Package (see AN-1187)

Maximum Junction Temperature

−65°C to +150°C

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

+215°C

+220°C

+260°C

Supply Voltage

45V

ON/OFF Pin Voltage

−0.1V ≤ V_SH≤ 6V

−1V

Switch Voltage to Ground

Boost Pin Voltage

+150°C

V_SW+ 8V

Feedback Pin Voltage

−0.3V ≤ V_FB≤ 14V

Operating Ratings

ESD Susceptibility

Human Body Model (Note 2)

Power Dissipation

Supply Voltage

6.5V to 40V

2 kV

Internally Limited

Temperature Range

−40°C ≤ T_J≤ +125°C

Electrical Characteristics

LM2672-3.3 Specifications with standard type face are for T_J= 25°C, and those in bold type face apply over full

Operating Temperature Range.

Symbol

Parameter

Conditions

Typical

Min

Max

Units

(Note 4)

(Note 5)

SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)

V_OUT

η

Output Voltage

Efficiency

V_IN= 8V to 40V, I_LOAD= 20 mA to 1A

V_IN= 6.5V to 40V, I_LOAD= 20 mA to 500 mA

V_IN= 12V, I_LOAD= 1A

3.3

86

3.251/3.201 3.350/3.399

V

%

LM2672-5.0

Symbol

Parameter

Conditions

Typical

Min

Max

Units

(Note 4)

(Note 5)

SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)

V_OUT

η

Output Voltage

Efficiency

V_IN= 8V to 40V, I_LOAD= 20 mA to 1A

V_IN= 6.5V to 40V, I_LOAD= 20 mA to 500 mA

V_IN= 12V, I_LOAD= 1A

5.0

90

4.925/4.850 5.075/5.150

V

%

LM2672-12

Symbol

Parameter

Conditions

Typical

Min

Max

Units

(Note 4)

(Note 5)

SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)

V_OUT

Output Voltage

Efficiency

V_IN= 15V to 40V, I_LOAD= 20 mA to 1A

V_IN= 24V, I_LOAD= 1A

12

94

11.82/11.64 12.18/12.36

V

%

η

LM2672-ADJ

Symbol

Parameter

Conditions

Typ

Min

Max

Units

V

(Note 4)

(Note 5)

SYSTEM PARAMETERS Test Circuit Figure 3 (Note 3)

V_FB

η

Feedback Voltage V_IN= 8V to 40V, I_LOAD= 20 mA to 1A

V_OUTProgrammed for 5V

1.210

90

1.192/1.174 1.228/1.246

(see Circuit of Figure 3)

Feedback Voltage V_IN= 6.5V to 40V, I_LOAD= 20 mA to 500 mA

V_OUTProgrammed for 5V

V

(see Circuit of Figure 3)

Efficiency

V_IN= 12V, I_LOAD= 1A

%

3

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All Output Voltage Versions

Specifications with standard type face are for T_J= 25°C, and those in bold type face apply over full Operating Temperature

Range. Unless otherwise specified, V_IN= 12V for the 3.3V, 5V, and Adjustable versions and V_IN= 24V for the 12V version, and

I_LOAD= 100 mA.

Symbol

Parameters

Conditions

Typ

2.5

Min

Max

Units

DEVICE PARAMETERS

I_Q

Quiescent Current

V_FEEDBACK= 8V

3.6

mA

For 3.3V, 5.0V, and ADJ Versions

V_FEEDBACK= 15V

mA

For 12V Versions

I_STBY

I_CL

Standby Quiescent Current

Current Limit

ON/OFF Pin = 0V

50

1.55

1

100/150

2.1/2.2

25

μA

A

1.25/1.2

I_L

Output Leakage Current

V_IN= 40V, ON/OFF Pin = 0V

V_SWITCH= 0V

μA

V_SWITCH= −1V, ON/OFF Pin = 0V

I_SWITCH= 1A

6

0.25

260

95

15

0.30/0.50

275

mA

R_DS(ON)Switch On-Resistance

Ω

kHz

%

f_O

D

Oscillator Frequency

Maximum Duty Cycle

Minimum Duty Cycle

Feedback Bias

Measured at Switch Pin

225

0

%

I_BIAS

V_S/D

V_FEEDBACK= 1.3V

ADJ Version Only

85

nA

Current

ON/OFF Pin

1.4

0.8

7

2.0

37

V

Voltage Thesholds

ON/OFF Pin Current

Synchronization Frequency

I_S/D

ON/OFF Pin = 0V

20

μA

F_SYNC

V_SYNC

V_SYNC= 3.5V, 50% duty cycle

400

kHz

Synchronization Threshold

Voltage

1.4

V

V_SS

I_SS

Soft-Start Voltage

Soft-Start Current

Thermal Resistance

0.63

4.5

95

0.53

1.5

0.73

6.9

V

μA

N Package, Junction to Ambient (Note 6)

M Package, Junction to Ambient (Note 6)

θ_JA

°C/W

105

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

intended to be functional, but device parameter specifications may not be guaranteed under these conditions. For guaranteed specifications and test conditions,

see the Electrical Characteristics.

Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.

Note 3: External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator

performance. When the LM2672 is used as shown in Figure 2 and Figure 3 test circuits, system performance will be as specified by the system parameters section

of the Electrical Characteristics.

Note 4: Typical numbers are at 25°C and represent the most likely norm.

Note 5: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%

production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used

to calculate Average Outgoing Quality Level (AOQL).

Note 6: Junction to ambient thermal resistance with approximately 1 square inch of printed circuit board copper surrounding the leads. Additional copper area

will lower thermal resistance further. See Application Information section in the application note accompanying this datasheet and the thermal model in LM267X

Made Simple version 6.0 software. The value θ_J−Afor the LLP (LD) package is specifically dependent on PCB trace area, trace material, and the number of layers

and thermal vias. For improved thermal resistance and power dissipation for the LLP package, refer to Application Note AN-1187.

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4

Typical Performance Characteristics

Normalized

Output Voltage

Line Regulation

1293404

1293403

Efficiency

Drain-to-Source

Resistance

1293405

1293406

Switch Current Limit

Operating

Quiescent Current

1293407

1293408

5

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Standby

Quiescent Current

ON/OFF Threshold

Voltage

1293409

1293410

ON/OFF Pin

Current (Sourcing)

Switching Frequency

1293412

1293411

Feedback Pin

Bias Current

ꢀ

Peak Switch Current

1293413

1293414

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6

Dropout Voltage—3.3V Option

Dropout Voltage—5.0V Option

1293415

1293416

Block Diagram

1293417

* Patent Number 5,514,947

† Patent Number 5,382,918

FIGURE 1.

7

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Typical Performance Characteristics (Circuit of Figure 2)

Continuous Mode Switching Waveforms

V_IN= 20V, V_OUT= 5V, I_LOAD= 1A

Discontinuous Mode Switching Waveforms

V_IN= 20V, V_OUT= 5V, I_LOAD= 300 mA

L = 47 μH, C_OUT= 68 μF, C_OUTESR = 50 mΩ

L = 15 μH, C_OUT= 68 μF (2×), C_OUTESR = 25 mΩ

1293418

1293419

A: V_SWPin Voltage, 10 V/div.

B: Inductor Current, 0.5 A/div

C: Output Ripple Voltage, 20 mV/div AC-Coupled

Horizontal Time Base: 1 μs/div

Load Transient Response for Continuous Mode

V_IN= 20V, V_OUT= 5V, I_LOAD= 1A

Load Transient Response for Discontinuous Mode

V_IN= 20V, V_OUT= 5V,

L = 47 μH, C_OUT= 68 μF, C_OUTESR = 50 mΩ

1293420

1293421

A: Output Voltage, 100 mV/div, AC-Coupled

B: Load Current: 200 mA to 1A Load Pulse

A: Output Voltage, 100 mV/div, AC-Coupled

B: Load Current: 100 mA to 300 mA Load Pulse

Horizontal Time Base: 50 μs/div

Horizontal Time Base: 200 μs/div

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8

Test Circuit and Layout Guidelines

1293422

C_IN- 22 μF, 50V Tantalum, Sprague “199D Series”

C_OUT- 47 μF, 25V Tantalum, Sprague “595D Series”

D1 - 3.3A, 50V Schottky Rectifier, IR 30WQ05F

L1 - 68 μH Sumida #RCR110D-680L

C_B- 0.01 μF, 50V Ceramic

FIGURE 2. Standard Test Circuits and Layout Guides

Fixed Output Voltage Versions

1293423

C_IN- 22 μF, 50V Tantalum, Sprague “199D Series”

C_OUT- 47 μF, 25V Tantalum, Sprague “595D Series”

D1 - 3.3A, 50V Schottky Rectifier, IR 30WQ05F

L1 - 68 μH Sumida #RCR110D-680L

R1 - 1.5 kΩ, 1%

C_B- 0.01 μF, 50V Ceramic

For a 5V output, select R2 to be 4.75 kΩ, 1%

where V_REF= 1.21V

Use a 1% resistor for best stability.

FIGURE 3. Standard Test Circuits and Layout Guides

Adjustable Output Voltage Versions

9

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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= 5V

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

V_IN(max) = Maximum DC Input Voltage

I_LOAD(max) = Maximum Load Current

1. Inductor Selection (L1)

V_IN(max) = 12V

I_LOAD(max) = 1A

1. Inductor Selection (L1)

A. Select the correct inductor value selection guide from Figure 4 A. Use the inductor selection guide for the 5V version shown in

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.

Figure 5.

B. From the inductor value selection guide, identify the inductance B. From the inductor value selection guide shown in Figure 5, the

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).

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 Choose a capacitor value and voltage rating from the line that

)

2. Output Capacitor Selection (C_OUT

)

A. Use the 5.0V section in the output capacitor table in Figure 10.

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

capacitor value and voltage rating.

contains the inductance value of 33 μH. The capacitance and

voltage rating values corresponding to the 33 μH

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10

PROCEDURE (Fixed Output Voltage Version)

EXAMPLE (Fixed Output Voltage Version)

The capacitor list contains through-hole electrolytic capacitors from Surface Mount:

four different capacitor manufacturers and surface mount tantalum

capacitors from two different capacitor manufacturers. It is

recommended that both the manufacturers and the manufacturer's

series that are listed in the table be used. A table listing the

manufacturers' phone numbers is located in Figure 11.

68 μF/10V Sprague 594D Series.

100 μF/10V AVX TPS Series.

Through Hole:

68 μF/10V Sanyo OS-CON SA Series.

220 μF/35V Sanyo MV-GX Series.

220 μF/35V Nichicon PL Series.

220 μF/35V Panasonic HFQ Series.

3. Catch Diode Selection (D1)

A. In normal operation, the average current of the catch diode is A. Refer to the table shown in Figure 12. In this example, a 1A,

the load current times the catch diode duty cycle, 1-D (D is the 20V Schottky diode will provide the best performance. If the circuit

switch duty cycle, which is approximately the output voltage divided must withstand a continuous shorted output, a higher current

by the input voltage). The largest value of the catch diode average Schottky diode is recommended.

current occurs at the maximum load current and maximum input

voltage (minimum D). For normal operation, the catch diode current

rating must be at least 1.3 times greater than its maximum average

current. However, 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 LM2672. The most

stressful condition for this diode is a shorted output condition.

B. The reverse voltage rating of the diode should be at least 1.25

times the maximum input voltage.

C. Because of their fast switching speed and low forward voltage

drop, Schottky diodes provide the best performance and efficiency.

This Schottky diode must be located close to the LM2672 using

short leads and short printed circuit traces.

4. Input Capacitor (C_IN)

A low ESR aluminum or tantalum bypass capacitor is needed

between the input pin and ground to prevent large voltage

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

½ the DC load current. The capacitor manufacturer data sheet must

be checked to assure that this current rating is not exceeded. The

curves shown in Figure 14 show typical RMS current ratings for

several different aluminum electrolytic capacitor values. A parallel

connection of two or more capacitors may be required to increase

the total minimum RMS current rating to suit the application

requirements.

The important parameters for the input capacitor are the input

voltage rating and the RMS current rating. With a maximum input

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

rating greater than 15V (1.25 × V_IN) would be needed. The next

higher capacitor voltage rating is 16V.

The RMS current rating requirement for the input capacitor in a

buck regulator is approximately ½ the DC load current. In this

example, with a 1A load, a capacitor with a RMS current rating of

at least 500 mA is needed. The curves shown in Figure 14 can be

used to select an appropriate input capacitor. From the curves,

locate the 16V line and note which capacitor values have RMS

current ratings greater than 500 mA.

For an aluminum electrolytic capacitor, the voltage rating should be

at least 1.25 times the maximum input voltage. Caution must be

exercised if solid tantalum capacitors are used. The tantalum

capacitor voltage rating should be twice the maximum input

voltage. The tables in Figure 15 show the recommended

application voltage for AVX TPS and Sprague 594D tantalum

capacitors. It is also recommended that they be surge current

tested by the manufacturer. The TPS series available from AVX,

and the 593D and 594D series from Sprague are all surge current

tested. Another approach to minimize the surge current stresses

on the input capacitor is to add a small inductor in series with the

input supply line.

For a through hole design, a 330 μF/16V electrolytic capacitor

(Panasonic HFQ series, Nichicon PL, Sanyo MV-GX series or

equivalent) would be adequate. Other types or other

manufacturers' capacitors can be used provided the RMS ripple

current ratings are adequate. Additionally, for a complete surface

mount design, electrolytic capacitors such as the Sanyo CV-C or

CV-BS and the Nichicon WF or UR and the NIC Components NACZ

series could be considered.

For surface mount designs, solid tantalum capacitors can be used,

but caution must be exercised with regard to the capacitor surge

current rating and voltage rating. In this example, checking Figure

15, and the Sprague 594D series datasheet, a Sprague 594D 15

μF, 25V capacitor is adequate.

Use caution when using ceramic capacitors for input bypassing,

because it may cause severe ringing at the V_INpin.

11

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PROCEDURE (Fixed Output Voltage Version)

5. Boost Capacitor (C_B)

This capacitor develops the necessary voltage to turn the switch

EXAMPLE (Fixed Output Voltage Version)

5. Boost Capacitor (C_B)

For this application, and all applications, use a 0.01 μF, 50V

gate on fully. All applications should use a 0.01 μF, 50V ceramic ceramic capacitor.

capacitor.

6. Soft-Start Capacitor (C_SS- optional)

This capacitor controls the rate at which the device starts up. The For this application, selecting a start-up time of 10 ms and using

formula for the soft-start capacitor C_SSis:

the formula for C_SSresults in a value of:

where:

I_SS= Soft-Start Currentꢀ:4.5 μA typical.

t_SS= Soft-Start Time :Selected.

V_SSTH= Soft-Start Threshold Voltage :0.63V typical.

V_OUT= Output Voltage :Selected.

V_SCHOTTKY= Schottky Diode Voltage Drop :0.4V typical.

V_IN= Input Voltage :Selected.

If this feature is not desired, leave this pin open. With certain

softstart capacitor values and operating conditions, the LM2672

can exhibit an overshoot on the output voltage during turn on.

Especially when starting up into no load or low load, the softstart

function may not be effective in preventing a larger voltage

overshoot on the output. With larger loads or lower input voltages

during startup this effect is minimized. In particular, avoid using

softstart capacitors between 0.033µF and 1µF.

7. Frequency Synchronization (optional)

For all applications, use a 1 kΩ resistor and a 100 pF capacitor for

the RC filter.

The LM2672 (oscillator) can be synchronized to run with an

external oscillator, using the sync pin (pin 3). By doing so, the

LM2672 can be operated at higher frequencies than the standard

frequency of 260 kHz. This allows for a reduction in the size of the

inductor and output capacitor.

As shown in the drawing below, a signal applied to a RC filter at the

sync pin causes the device to synchronize to the frequency of that

signal. For a signal with a peak-to-peak amplitude of 3V or greater,

a 1 kΩ resistor and a 100 pF capacitor are suitable values.

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12

Inductor Value Selection Guides

(For Continuous Mode Operation)

1293431

1293429

FIGURE 6. LM2672-12

FIGURE 4. LM2672-3.3

1293430

1293432

FIGURE 5. LM2672-5.0

FIGURE 7. LM2672-ADJ

Pulse Engineering

Schott

Renco

Through

Hole

Coilcraft

Inductanc

Ind.

Ref.

Desg.

Current

(A)

e

Through

Hole

Surface

Mount

Surface

Mount

Through

Hole

Surface

Mount

Surface

Mount

(μH)

L4

L5

68

47

0.32

0.37

0.44

0.52

0.32

0.39

0.48

0.58

0.70

0.83

0.99

0.55

0.66

0.82

0.99

1.17

1.40

67143940 67144310 RL-1284-68-43 RL1500-68 PE-53804 PE-53804-S DO1608-683

67148310 67148420 RL-1284-47-43 RL1500-47 PE-53805 PE-53805-S DO1608-473

67148320 67148430 RL-1284-33-43 RL1500-33 PE-53806 PE-53806-S DO1608-333

67148330 67148440 RL-1284-22-43 RL1500-22 PE-53807 PE-53807-S DO1608-223

L6

33

L7

22

L9

220

150

100

68

67143960 67144330

67143970 67144340

67143980 67144350

67143990 67144360

67144000 67144380

RL-5470-3

RL-5470-4

RL-5470-5

RL-5470-6

RL-5470-7

RL1500-220 PE-53809 PE-53809-S DO3308-224

RL1500-150 PE-53810 PE-53810-S DO3308-154

RL1500-100 PE-53811 PE-53811-S DO3308-104

RL1500-68 PE-53812 PE-53812-S DO3308-683

RL1500-47 PE-53813 PE-53813-S DO3308-473

L10

L11

L12

L13

L14

L15

L18

L19

L20

L21

L22

L23

47

33

67148340 67148450 RL-1284-33-43 RL1500-33 PE-53814 PE-53814-S DO3308-333

67148350 67148460 RL-1284-22-43 RL1500-22 PE-53815 PE-53815-S DO3308-223

22

220

150

100

68

67144040 67144420

67144050 67144430

67144060 67144440

67144070 67144450

67144080 67144460

67144090 67144470

RL-5471-2

RL-5471-3

RL-5471-4

RL-5471-5

RL-5471-6

RL-5471-7

RL1500-220 PE-53818 PE-53818-S DO3316-224

RL1500-150 PE-53819 PE-53819-S DO3316-154

RL1500-100 PE-53820 PE-53820-S DO3316-104

RL1500-68 PE-53821 PE-53821-S DO3316-683

47

PE-53822 PE-53822-S DO3316-473

PE-53823 PE-53823-S DO3316-333

—

33

13

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Schott

Renco

Through

Hole

Pulse Engineering

Coilcraft

Surface

Mount

Inductanc

Ind.

Ref.

Desg.

Current

(A)

e

Through

Hole

Surface

Mount

Surface

Mount

Through

Hole

Surface

Mount

(μH)

L24

L27

L28

L29

L30

22

220

150

100

68

1.70

1.00

1.20

1.47

1.78

67148370 67148480 RL-1283-22-43

PE-53824 PE-53824-S DO3316-223

PE-53827 PE-53827-S DO5022P-224

PE-53828 PE-53828-S DO5022P-154

PE-53829 PE-53829-S DO5022P-104

PE-53830 PE-53830-S DO5022P-683

—

67144110 67144490

67144120 67144500

67144130 67144510

67144140 67144520

RL-5471-2

RL-5471-3

RL-5471-4

RL-5471-5

FIGURE 8. Inductor Manufacturers' Part Numbers

Coilcraft Inc.

Phone (800) 322-2645

FAX (708) 639-1469

Phone +44 1236 730 595

FAX +44 1236 730 627

Phone (619) 674-8100

FAX (619) 674-8262

Phone +353 93 24 107

FAX +353 93 24 459

Phone (800) 645-5828

FAX (516) 586-5562

Phone (612) 475-1173

FAX (612) 475-1786

Coilcraft Inc., Europe

Pulse Engineering Inc.

Pulse Engineering Inc.,

Europe

Renco Electronics Inc.

Schott Corp.

FIGURE 9. Inductor Manufacturers' Phone Numbers

Output Capacitor

Surface Mount

Sprague

Through Hole

Sanyo OS-CON Sanyo MV-GX

Output

Voltage

(V)

Inductance

AVX TPS

Series

(μF/V)

100/10

10010

100/10

(2×) 68/20

68/20

Nichicon

PL Series

(μF/V)

Panasonic

HFQ Series

(μF/V)

(μH)

594D Series

(μF/V)

120/6.3

68/10

SA Series

(μF/V)

100/10

68/10

Series

(μF/V)

330/35

220/35

150/35

120/35

330/35

220/35

150/35

120/35

330/35

220/35

150/35

120/35

22

33

330/35

220/35

150/35

120/35

330/35

220/35

150/35

120/35

330/35

220/35

150/35

120/35

330/35

220/35

150/35

120/35

330/35

220/35

150/35

120/35

330/35

220/35

150/35

120/35

47

68/10

3.3

5.0

68

120/6.3

100/16

68/10

100/10

68/10

100

150

22

33

47

68/10

68

100/16

120/20

68/25

100/10

68/20

100

150

22

33

68/20

47

47/20

68/20

47/20

12

68

47/20

68/20

47/20

100

150

220

47/20

68/20

47/20

68/20

47/20

68/20

47/20

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14

FIGURE 10. Output Capacitor Table

Nichicon Corp.

Panasonic

Phone

FAX

(847) 843-7500

(847) 843-2798

(714) 373-7857

(714) 373-7102

(803) 448-9411

(803) 448-1943

(207) 324-4140

(207) 324-7223

(619) 661-6322

(619) 661-1055

Phone

FAX

AVX Corp.

Phone

FAX

Sprague/Vishay

Sanyo Corp.

Phone

FAX

Phone

FAX

FIGURE 11. Capacitor Manufacturers' Phone Numbers

1A Diodes

3A Diodes

V_R

Surface

Through

Hole

Surface

Through

Hole

Mount

SK12

Mount

20V

30V

1N5817

SR102

1N5818

11DQ03

SR103

1N5819

11DQ04

SR104

SK32

1N5820

SR302

1N5821

31DQ03

B120

SK13

SK33

B130

30WQ03F

MBRS130

SK14

40V

SK34

1N5822

MBR340

31DQ04

SR304

B140

30BQ040

30WQ04F

MBRS340

MBRD340

MBRS140

10BQ040

10MQ040

15MQ040

SK15

50V

MBR150

11DQ05

SR105

SK35

MBR350

31DQ05

SR305

B150

30WQ05F

10BQ050

FIGURE 12. Schottky Diode Selection Table

International Rectifier Phone

(310) 322-3331

Corp.

FAX

(310) 322-3332

(800) 521-6274

(602) 244-6609

(516) 847-3000

Motorola, Inc.

Phone

FAX

General Instruments

Corp.

Phone

FAX

(516) 847-3236

(805) 446-4800

(805) 446-4850

Diodes, Inc.

Phone

FAX

FIGURE 13. Diode Manufacturers' Phone Numbers

15

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1293433

FIGURE 14. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical)

AVX TPS

Recommended

Application Voltage

Voltage

Rating

+85°C Rating

3.3

5

6.3

10

20

25

35

10

12

15

Sprague 594D

Recommended

Application Voltage

Voltage

Rating

+85°C Rating

2.5

3.3

5

4

6.3

10

16

20

25

35

50

8

12

18

24

29

FIGURE 15. Recommended Application Voltage for AVX TPS and

Sprague 594D Tantalum Chip Capacitors Derated for 85°C.

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16

LM2672 Series Buck Regulator Design Procedure (Adjustable Output)

PROCEDURE (Adjustable Output Voltage Version)

EXAMPLE (Adjustable 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= 20V

V_OUT= Regulated Output Voltage

V_IN(max) = Maximum Input Voltage

V_IN(max) = 28V

I_LOAD(max) = Maximum Load Current

I_LOAD(max) = 1A

F = Switching Frequency (Fixed at a nominal 260 kHz).

1. Programming Output Voltage (Selecting R₁and R₂, as shown 1. Programming Output Voltage (Selecting R₁and R₂, as shown

in Figure 3)

Use the following formula to select the appropriate resistor values.

Select R₁to be 1 kΩ, 1%. Solve for R₂.

where V_REF= 1.21V

Select a value for R₁between 240Ω and 1.5 kΩ. The lower resistor R₂= 1 kΩ (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.

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.)

R₂= 15.4 kΩ.

2. Inductor Selection (L1)

A. Calculate the inductor Volt • microsecond constant E • T

(V • μs), from the following formula:

A. Calculate the inductor Volt • microsecond constant (E • T),

where V_SAT=internal switch saturation voltage=0.25V and

V_D= diode forward voltage drop = 0.5V

B. Use the E • T value from the previous formula and match it with

the E • T number on the vertical axis of the Inductor Value Selection

Guide shown in Figure 7.

B. E • T = 21.6 (V • μs)

C. I_LOAD(max) = 1A

C. On the horizontal axis, select the maximum load current.

D. Identify the inductance region intersected by the E • T value and D. From the inductor value selection guide shown in Figure 7, the

the Maximum Load Current value. Each region is identified by an

inductance value and an inductor code (LXX).

inductance region intersected by the 21.6 (V • μs) horizontal line

and the 1A vertical line is 68 μH, and the inductor code is L30.

E. Select an appropriate inductor from the four manufacturer's part E. From the table in Figure 8, locate line L30, and select an inductor

numbers listed in Figure 8. For information on the different types of part number from the list of manufacturers' part numbers.

inductors, see the inductor selection in the fixed output voltage

design procedure.

3. Output Capacitor SeIection (C_OUT

A. Select an output capacitor from the capacitor code selection

guide in Figure 16. Using the inductance value found in the inductor in Figure 16. For this example, use the 15–20V row. The capacitor

)

3. Output Capacitor SeIection (C_OUT

)

A. Use the appropriate row of the capacitor code selection guide,

selection guide, step 1, locate the appropriate capacitor code

corresponding to the desired output voltage.

code corresponding to an inductance of 68 μH is C20.

17

www.national.com

PROCEDURE (Adjustable Output Voltage Version)

B. Select an appropriate capacitor value and voltage rating, using B. From the output capacitor selection table in Figure 17, choose

the capacitor code, from the output capacitor selection table in a capacitor value (and voltage rating) that intersects the capacitor

Figure 17. There are two solid tantalum (surface mount) capacitor code(s) selected in section A, C20.

EXAMPLE (Adjustable Output Voltage Version)

manufacturers and four electrolytic (through hole) capacitor

manufacturers to choose from. It is recommended that both the

The capacitance and voltage rating values corresponding to the

capacitor code C20 are the:

manufacturers and the manufacturer's series that are listed in the Surface Mount:

table be used. A table listing the manufacturers' phone numbers is

located in Figure 11.

33 μF/25V Sprague 594D Series.

33 μF/25V AVX TPS Series.

Through Hole:

33 μF/25V Sanyo OS-CON SC Series.

120 μF/35V Sanyo MV-GX Series.

120 μF/35V Nichicon PL Series.

120 μF/35V Panasonic HFQ Series.

Other manufacturers or other types of capacitors may also be used,

provided the capacitor specifications (especially the 100 kHz ESR)

closely match the characteristics of the capacitors listed in the

output capacitor table. Refer to the capacitor manufacturers' data

sheet for this information.

4. Catch Diode Selection (D1)

A. In normal operation, the average current of the catch diode is A. Refer to the table shown in Figure 12. Schottky diodes provide

the load current times the catch diode duty cycle, 1-D (D is the the best performance, and in this example a 1A, 40V Schottky diode

switch duty cycle, which is approximately V_OUT/V_IN). The largest would be a good choice. If the circuit must withstand a continuous

shorted output, a higher current (at least 2.2A) Schottky diode is

recommended.

value of the catch diode average current occurs at the maximum

input voltage (minimum D). For normal operation, the catch diode

current rating must be at least 1.3 times greater than its maximum

average current. However, if the power supply design must

withstand a continuous output short, the diode should have a

current rating greater than the maximum current limit of the

LM2672. The most stressful condition for this diode is a shorted

output condition.

B. The reverse voltage rating of the diode should be at least 1.25

times the maximum input voltage.

C. Because of their fast switching speed and low forward voltage

drop, Schottky diodes provide the best performance and efficiency.

The Schottky diode must be located close to the LM2672 using

short leads and short printed circuit traces.

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18

PROCEDURE (Adjustable Output Voltage Version)

EXAMPLE (Adjustable Output Voltage Version)

5. Input Capacitor (C_IN)