LM2671M-12原理图各脚功能电路原理芯片引脚定义引脚图及功能-中国IC网-芯三七

February 2005

LM2671

SIMPLE SWITCHER^®Power Converter High Efficiency

500mA Step-Down Voltage Regulator with Features

To simplify the LM2671 buck regulator design procedure,

there exists computer design software, LM267X Made

Simple (version 6.0).

General Description

The LM2671 series of regulators are monolithic integrated

circuits built with a LMDMOS process. These regulators

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

switching regulator, capable of driving a 500mA 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.

Features

n Efficiency up to 96%

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

n 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.

n Simple and easy to design with

n Requires only 5 external components

n Uses readily available standard inductors

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

n Adjustable version output voltage range: 1.21V to 37V

The LM2671 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 cop-

per traces on the printed circuit board are the only heat

sinking needed.

n

1.5% max output voltage tolerance over line and load

conditions

>

n Guaranteed 500mA output load current

n 0.25Ω DMOS Output Switch

n Wide input voltage range: 8V to 40V

n 260 kHz fixed frequency internal oscillator

n TTL shutdown capability, low power standby mode

n Soft-start and frequency synchronization

n Thermal shutdown and current limit protection

A family of standard inductors for use with the LM2671 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.

Applications

Other features include a guaranteed 1.5% tolerance on

output voltage within specified input voltages and output

load conditions, and 10% on the oscillator frequency. Ex-

ternal shutdown is included, featuring typically 50 µA

stand-by current. The output switch includes current limiting,

as well as thermal shutdown for full protection under fault

conditions.

>

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

Regulator

n Efficient Pre-Regulator for Linear Regulators

Typical Application (Fixed Output Voltage Versions)

10004201

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

Windows^®is a registered trademark of Microsoft Corporation.

DS100042

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Connection Diagrams

16-Lead LLP Surface Mount Package

8-Lead Package

Top View

10004202

SO-8/DIP Package

See NSC Package Drawing Number MO8A/N08E

10004241

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

LM2671LD-12

S0005B

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

LM2671LDX-12

LM2671LD-3.3

LM2671LDX-3.3

LM2671LD-5.0

LM2671LDX-5.0

LM2671LD-ADJ

LM2671LDX-ADJ

S0005B

S0006B

S0007B

S0008B

3.3

5.0

ADJ

SO-8

12

LM2671M-12

LM2671MX-12

LM2671M-3.3

LM2671MX-3.3

LM2671M-5.0

LM2671MX-5.0

LM2671M-ADJ

LM2671MX-ADJ

2671M-12

2671M-3.3

2671M-5.0

2671M-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

LM2671N-12

LM2671N-3.3

LM2671N-5.0

LM2671N-ADJ

LM2671N-12

LM2671N-3.3

LM2671N-5.0

LM2671N-ADJ

Shipped in Anti-Static Rails

Shipped in Anti-Static Rail

5.0

ADJ

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2

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Supply Voltage

45V

−0.1V ≤ V_SH≤ 6V

−1V

Storage Temperature Range

Lead Temperature

−65˚C to +150˚C

ON/OFF Pin Voltage

Switch Voltage to Ground

Boost Pin Voltage

M Package

V_SW+ 8V

Vapor Phase (60s)

+215˚C

+220˚C

+260˚C

Feedback Pin Voltage

ESD Susceptibility

−0.3V ≤ V_FB≤ 14V

Infrared (15s)

N Package (Soldering, 10s)

LLP Package (See AN-1187)

Maximum Junction Temperature

Human Body Model (Note 2)

Power Dissipation

2 kV

Internally Limited

+150˚C

Operating Ratings

Supply Voltage

6.5V to 40V

Temperature Range

−40˚C ≤ T_J≤ +125˚C

Electrical Characteristics

LM2671-3.3 ^{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 500 mA

V_IN= 6.5V to 40V, I_LOAD= 20 mA to 250 mA

V_IN= 12V, I_LOAD= 500 mA

3.3

86

3.251/3.201

3.350/3.399

V

%

LM2671-5.0

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 500 mA

V_IN= 6.5V to 40V, I_LOAD= 20 mA to 250 mA

V_IN= 12V, I_LOAD= 500 mA

5.0

90

4.925/4.850

5.075/5.150

V

%

LM2671-12

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 500 mA

V_IN= 24V, I_LOAD= 500 mA

12

94

11.82/11.64

12.18/12.36

V

η

%

LM2671-ADJ

Symbol

Parameter

Conditions

Typ

Min

Max

Units

(Note 4)

(Note 5)

SYSTEM PARAMETERS Test Circuit Figure 3 (Note 3)

V_FB

Feedback

Voltage

V_IN= 8V to 40V, I_LOAD= 20 mA to 500 mA

1.210

1.192/1.174

1.228/1.246

V

V_OUTProgrammed for 5V

(see Circuit of Figure 3)

3

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LM2671-ADJ (Continued)

Symbol

Parameter

Conditions

Typ

Min

Max

Units

(Note 4)

(Note 5)

V_FB

Feedback

V_IN= 6.5V to 40V, I_LOAD= 20 mA to 250 mA

1.210

1.192/1.174

1.228/1.246

V

Voltage

V_OUTProgrammed for 5V

(see Circuit of Figure 3)

V_IN= 12V, I_LOAD= 500 mA

η

Efficiency

90

%

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

50

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

100/150

1.2/1.25

25

µA

A

0.8 0.62/0.575

I_L

Output Leakage Current

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

V_SWITCH= 0V

1

µA

V_SWITCH= −1V, ON/OFF Pin = 0V

I_SWITCH= 500 mA

6

15

0.40/0.60

275

mA

Ω

R_DS(ON)Switch On-Resistance

0.25

f_O

D

Oscillator Frequency

Maximum Duty Cycle

Minimum Duty Cycle

Feedback Bias

Measured at Switch Pin

260

95

0

225

kHz

%

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

Synchronization Threshold

Voltage

I_S/D

ON/OFF Pin = 0V

20

µA

F_SYNC

V_SYNC

V_SYNC= 3.5V, 50% duty cycle

400

kHz

1.4

V

V_SS

I_SS

Soft-Start Voltage

Soft-Start Current

Thermal Resistance

0.63

4.5

0.53

1.5

0.73

6.9

V

µA

θ_JA

N Package, Junction to Ambient (Note 6)

M Package, Junction to Ambient (Note 6)

95

˚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 LM2671 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

for the LLP (LD) package is specifically dependent on PCB trace area, trace material, and the number of layers and

J−A

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

10004203

10004204

Drain-to-Source

Resistance

Efficiency

10004205

10004206

Operating

Switch Current Limit

Quiescent Current

10004207

10004208

5

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Typical Performance Characteristics (Continued)

Standby

Quiescent Current

ON/OFF Threshold

Voltage

10004209

10004210

10004212

10004214

ON/OFF Pin

Current (Sourcing)

Switching Frequency

10004211

Feedback Pin

Bias Current

Peak Switch Current

10004213

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6

Typical Performance Characteristics (Continued)

Dropout Voltage—3.3V Option

Dropout Voltage—5.0V Option

10004215

10004216

Block Diagram

10004217

* 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= 500 mA

L = 100 µH, C_OUT= 100 µF, C_OUTESR = 0.1Ω

Discontinuous Mode Switching Waveforms

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

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

10004218

10004219

A: V

Pin Voltage, 10 V/div.

A: V

Pin Voltage, 10 V/div.

SW

B: Inductor Current, 0.2 A/div

B: Inductor Current, 0.5 A/div

C: Output Ripple Voltage, 50 mV/div AC-Coupled

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

Load Transient Response for Discontinuous Mode

V_IN= 20V, V_OUT= 5V,

L = 100 µH, C_OUT= 100 µF, C_OUTESR = 0.1Ω

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

10004220

10004221

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

B: Load Current: 100 mA to 500 mA Load Pulse

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

B: Load Current: 100 mA to 400 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

10004222

C

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

IN

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

OUT

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

10004223

C

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

IN

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

OUT

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

= 1.21V

REF

Use a 1% resistor for best stability.

FIGURE 3. Standard Test Circuits and Layout Guides

Adjustable Output Voltage Versions

9

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LM2671 Series Buck Regulator Design Procedure (Fixed Output)

PROCEDURE (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.

EXAMPLE (Fixed Output Voltage Version)

Given:

V_OUT= 5V

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

V

_IN(max) = Maximum DC Input Voltage

_LOAD(max) = Maximum Load Current

1. Inductor Selection (L1)

V_IN(max) = 12V

I

I_LOAD(max) = 500 mA

1. Inductor Selection (L1)

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

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

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

for the adjustable version.

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).

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:

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

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

the inductance region intersected by the 12V horizontal line and

the 500 mA vertical line is 47 µH, and the inductor code is L13.

C. The inductance value required is 47 µH. From the table in

Figure 8, go to the L13 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.)

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

)

2. Output Capacitor Selection (C_OUT)

A. Select an output capacitor from the output capacitor table in A. Use the 5.0V section in the output capacitor table in Figure

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.

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

that contains the inductance value of 47 µH. The capacitance

and voltage rating values corresponding to the 47 µH inductor

are the:

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10

LM2671 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

PROCEDURE (Fixed Output Voltage Version)

The capacitor list contains through-hole electrolytic capacitors

from four different capacitor manufacturers and surface mount

EXAMPLE (Fixed Output Voltage Version)

Surface Mount:

68 µF/10V Sprague 594D Series.

tantalum capacitors from two different capacitor manufacturers. 100 µF/10V AVX TPS Series.

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.

Through Hole:

68 µF/10V Sanyo OS-CON SA Series.

150 µF/35V Sanyo MV-GX Series.

150 µF/35V Nichicon PL Series.

150 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

switch duty cycle, which is approximately the output voltage

divided by the input voltage). The largest value of the catch

diode average 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 LM2671. The most stressful condition for this diode is a

shorted output condition.

circuit must withstand a continuous shorted output, a higher

current Schottky diode is recommended.

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

LM2671 using short leads and short printed circuit traces.

11

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LM2671 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

PROCEDURE (Fixed Output Voltage Version)

EXAMPLE (Fixed Output Voltage Version)

4. Input Capacitor (C_IN

)

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

The important parameters for the input capacitor are the input

voltage rating and the RMS current rating. With a maximum

transients from appearing at the input. This capacitor should be input voltage of 12V, an aluminum electrolytic capacitor with a

located close to the IC using short leads. In addition, the RMS voltage rating greater than 15V (1.25 x V_IN) would be needed.

current rating of the input capacitor should be selected to be at The next higher capacitor voltage rating is 16V.

1

least ⁄

2

the DC load current. The capacitor manufacturer data

The RMS current rating requirement for the input capacitor in a

1

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

buck regulator is approximately

⁄ the DC load current. In this

2

example, with a 500 mA load, a capacitor with a RMS current

rating of at least 250 mA is needed. The curves shown in Figure

14 can be used to select an appropriate input capacitor. From

capacitors may be required to increase the total minimum RMS the curves, locate the 16V line and note which capacitor values

current rating to suit the application requirements. have RMS current ratings greater than 250 mA.

For an aluminum electrolytic capacitor, the voltage rating should For a through hole design, a 100 µF/16V electrolytic capacitor

be at least 1.25 times the maximum input voltage. Caution must (Panasonic HFQ series, Nichicon PL, Sanyo MV-GX series or

be exercised if solid tantalum capacitors are used. The tantalum equivalent) would be adequate. Other types or other

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

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

tested by the manufacturer. The TPS series available from AVX, Components NACZ series could be considered.

and the 593D and 594D series from Sprague are all surge For surface mount designs, solid tantalum capacitors can be

current tested. Another approach to minimize the surge current used, but caution must be exercised with regard to the capacitor

stresses on the input capacitor is to add a small inductor in

series with the input supply line.

surge current rating and voltage rating. In this example,

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

Use caution when using ceramic capacitors for input bypassing, Sprague 594D 15 µF, 25V capacitor is adequate.

because it may cause severe ringing at the V_INpin.

5. Boost Capacitor (C_B)

This capacitor develops the necessary voltage to turn the switch 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 formula for the soft-start capacitor C_SSis:

For this application, selecting a start-up time of 10 ms and using

the formula for C_SSresults in a value of:

where:

I_SS= Soft-Start Current :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.

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12

LM2671 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

PROCEDURE (Fixed Output Voltage Version)

7. Frequency Synchronization (optional)

The LM2671 (oscillator) can be synchronized to run with an

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

LM2671 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.

EXAMPLE (Fixed Output Voltage Version)

7. Frequency Synchronization (optional)

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

for the RC filter.

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.

INDUCTOR VALUE SELECTION GUIDES

(For Continuous Mode Operation)

10004231

10004229

FIGURE 6. LM2671-12

FIGURE 4. LM2671-3.3

10004232

10004230

FIGURE 7. LM2671-ADJ

FIGURE 5. LM2671-5.0

13

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LM2671 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

Schott

Renco

Through

Hole

Pulse Engineering

Coilcraft

Surface

Mount

Ind.

Ref.

Desg.

Inductance Current

Through

Hole

Surface

Mount

Surface

Mount

Through

Hole

Surface

Mount

(µH)

(A)

L2

L3

150

100

68

0.21

0.26

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

67143920 67144290 RL-5470-4

67143930 67144300 RL-5470-5

RL1500-150 PE-53802 PE-53802-S DO1608-154

RL1500-100 PE-53803 PE-53803-S DO1608-104

L4

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

L5

47

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

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

RL-5471-2

RL-5471-3

RL-5471-4

RL-5471-5

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

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

www.national.com

14

LM2671 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

Output Capacitor

Surface Mount

Sprague

Through Hole

Sanyo OS-CON Sanyo MV-GX Nichicon

Output

Voltage

(V)

Inductance

(µH)

AVX TPS

Series

(µF/V)

100/10

10010

100/10

(2x) 68/20

68/20

Panasonic

HFQ Series

(µF/V)

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

PL Series

(µF/V)

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

FIGURE 10. Output Capacitor Table

Nichicon Corp.

Phone

FAX

(847) 843-7500

(847) 843-2798

(714) 373-7857

(714) 373-7102

(845) 448-9411

(845) 448-1943

(207) 324-4140

(207) 324-7223

(619) 661-6322

(619) 661-1055

Panasonic

Phone

FAX

AVX Corp.

Phone

FAX

Sprague/Vishay

Sanyo Corp.

Phone

FAX

Phone

FAX

FIGURE 11. Capacitor Manufacturers’ Phone Numbers

15

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LM2671 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

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

10004233

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

www.national.com

16

LM2671 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

AVX TPS

Sprague 594D

Recommended

Application Voltage

Voltage

Rating

Recommended

Application Voltage

Voltage

Rating

+85˚C Rating

3.3

5

6.3

2.5

3.3

5

4

10

20

25

35

6.3

10

16

20

25

35

50

10

12

15

8

12

18

24

29

FIGURE 15. Recommended Application Voltage for AVX TPS and

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

LM2671 Series Buck Regulator Design Procedure (Adjustable Output)

PROCEDURE (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 is available on (version 6.0)

Windows 3.1, NT, or 95 operating systems.

EXAMPLE (Adjustable Output Voltage Version)

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) = 500 mA

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

1. Programming Output Voltage (Selecting R₁and R₂, as

shown in Figure 3)

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

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

R₂= 1 kΩ (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.

resistor values minimize noise pickup in the sensitive feedback R₂= 15.4 kΩ.

pin. (For the lowest temperature coefficient and the best stability

with time, use 1% metal film resistors.)

2. Inductor Selection (L1)

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

(V • µs), from the following formula:

2. Inductor Selection (L1)

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

17

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LM2671 Series Buck Regulator Design Procedure (Adjustable Output)

(Continued)

PROCEDURE (Adjustable Output Voltage Version)

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.

EXAMPLE (Adjustable Output Voltage Version)

B. E • T = 21.6 (V • µs)

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

C. I_LOAD(max) = 500 mA

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

and the Maximum Load Current value. Each region is identified the inductance region intersected by the 21.6 (V • µs) horizontal

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

line and the 500 mA vertical line is 100 µH, and the inductor

code is L20.

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

E. From the table in Figure 8, locate line L20, and select an

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

types of inductors, see the inductor selection in the fixed output numbers.

voltage design procedure.

3. Output Capacitor SeIection (C_OUT

A. Select an output capacitor from the capacitor code selection A. Use the appropriate row of the capacitor code selection

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

inductor selection guide, step 1, locate the appropriate capacitor capacitor code corresponding to an inductance of 100 µH is

)

3. Output Capacitor SeIection (C_OUT)

code corresponding to the desired output voltage.

C20.

B. Select an appropriate capacitor value and voltage rating,

using the capacitor code, from the output capacitor selection

B. From the output capacitor selection table in Figure 17,

choose a capacitor value (and voltage rating) that intersects the

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

capacitor manufacturers and four electrolytic (through hole)

The capacitance and voltage rating values corresponding to the

capacitor manufacturers to choose from. It is recommended that capacitor code C20 are the:

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.

Surface Mount:

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

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

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

value of the catch diode average current occurs at the maximum withstand a continuous shorted output, a higher current (at least

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

LM2671. The most stressful condition for this diode is a shorted

output condition.

1.2A) Schottky diode is recommended.

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

1.25 times the maximum input voltage.

www.national.com

18

LM2671 Series Buck Regulator Design Procedure (Adjustable Output)

(Continued)

PROCEDURE (Adjustable Output Voltage Version)

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

LM2671 using short leads and short printed circuit traces.

EXAMPLE (Adjustable Output Voltage Version)

5. Input Capacitor (C_IN

)

5. Input Capacitor (C_IN

)

A low ESR aluminum or tantalum bypass capacitor is needed

between the input pin and ground to prevent large voltage

The important parameters for the input capacitor are the input

voltage rating and the RMS current rating. With a maximum

transients from appearing at the input. This capacitor should be input voltage of 28V, an aluminum electrolytic capacitor with a

located close to the IC using short leads. In addition, the RMS voltage rating of at least 35V (1.25 x V_IN) would be needed.

current rating of the input capacitor should be selected to be at The RMS current rating requirement for the input capacitor in a

1

least ⁄

2

the DC load current. The capacitor manufacturer data

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

2

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

example, with a 500 mA load, a capacitor with a RMS current

rating of at least 250 mA is needed. The curves shown in Figure

14 can be used to select an appropriate input capacitor. From

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

capacitors may be required to increase the total minimum RMS have RMS current ratings greater than 250 mA.

current rating to suit the application requirements. For a through hole design, a 68 µF/35V electrolytic capacitor

For an aluminum electrolytic capacitor, the voltage rating should (Panasonic HFQ series, Nichicon PL, Sanyo MV-GX series or

be at least 1.25 times the maximum input voltage. Caution must equivalent) would be adequate. Other types or other

be exercised if solid tantalum capacitors are used. The tantalum manufacturers’ capacitors can be used provided the RMS ripple

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

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.

tested by the manufacturer. The TPS series available from AVX, For surface mount designs, solid tantalum capacitors can be

and the 593D and 594D series from Sprague are all surge used, but caution must be exercised with regard to the capacitor

current tested. Another approach to minimize the surge current surge current rating and voltage rating. In this example,

stresses on the input capacitor is to add a small inductor in

series with the input supply line.

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

Sprague 594D 15 µF, 50V capacitor is adequate.

Use caution when using ceramic capacitors for input bypassing,

because it may cause severe ringing at the V_INpin.

6. Boost Capacitor (C_B)

This capacitor develops the necessary voltage to turn the switch 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.

If the soft-start and frequency synchronization features are

desired, look at steps 6 and 7 in the fixed output design

procedure.

19

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LM2671 Series Buck Regulator Design Procedure (Adjustable Output)

(Continued)

Inductance (µH)

Case

Output

Style (Note 7)

Voltage (V)

22

—

33

—

47

—

68

—

100

C1

150

C2

220

C3

SM and TH

TH

1.21–2.50

2.50–3.75

3.75–5.0

5.0–6.25

6.25–7.5

7.5–10.0

10.0–12.5

12.5–15.0

15.0–20.0

20.0–30.0

30.0–37.0

—

C1

C2

C3

—

C4

C5

C6

—

C4

C7

C6

C8

C4

C7

C6

C9

C10

C11

C16

C19

C22

C24

C11

C12

C17

C20

C22

C24

C12

C17

C20

C22

C25

C13

C17

C20

C22

C25

C13

C17

C20

C22

C25

C13

C17

C20

C22

C25

C14

C15

C18

C21

C23

Note 7: SM - Surface Mount, TH - Through Hole

FIGURE 16. Capacitor Code Selection Guide

www.national.com

20

LM2671 Series Buck Regulator Design Procedure (Adjustable Output)

(Continued)

Output Capacitor

Surface Mount

Through Hole

Sanyo MV-GX

Cap.

Ref.

Desg.

#

Sprague

AVX TPS

Series

(µF/V)

Sanyo OS-CON

SA Series

(µF/V)

Nichicon

PL Series

(µF/V)

Panasonic

HFQ Series

(µF/V)

594D Series

(µF/V)

120/6.3

68/10

Series

(µF/V)

220/35

150/35

120/35

220/35

150/35

120/35

150/35

330/35

220/35

150/35

120/35

220/35

150/35

120/35

220/35

150/35

120/35

150/35

120/35

220/50

150/50

C1

C2

100/10

100/16

68/20

100/10

220/35

150/35

120/35

220/35

150/35

120/35

150/35

330/35

220/35

150/35

120/35

220/35

150/35

120/35

220/35

150/35

120/35

150/35

120/35

100/50

82/50

220/35

150/35

120/35

220/35

150/35

120/35

150/35

330/35

220/35

150/35

120/35

220/35

150/35

120/35

220/35

150/35

120/35

150/35

120/35

120/50

82/50

100/10

C3

100/35

C4

68/10

C5

100/16

68/10

100/10

C6

100/10

C7

68/10

C8

100/16

47/20

100/10

C9

100/16

C10

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C21

C22

C23

C24

C25

68/16

100/16

47/20

68/20

47/20

68/20

47/20

68/25

(2x) 33/25

33/25

47/25 (Note 8)

33/25 (Note 8)

(Note 9)

33/25

33/35

(2x) 22/25

22/35

33/35

(Note 9)

Note 8: The SC series of Os-Con capacitors (others are SA series)

Note 9: The voltage ratings of the surface mount tantalum chip and Os-Con capacitors are too low to work at these voltages.

FIGURE 17. Output Capacitor Selection Table

21

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Application Information

TYPICAL SURFACE MOUNT PC BOARD LAYOUT,

FIXED OUTPUT (4X SIZE)

10004239

C

- 15 µF, 25V, Solid Tantalum Sprague, “594D series”

IN

- 68 µF, 10V, Solid Tantalum Sprague, “594D series”

OUT

D1 - 1A, 40V Schottky Rectifier, Surface Mount

L1 - 47 µH, L13, Coilcraft DO3308

C

B

- 0.01 µF, 50V, Ceramic

TYPICAL SURFACE MOUNT PC BOARD LAYOUT,

ADJUSTABLE OUTPUT (4X SIZE)

10004240

C

- 15 µF, 50V, Solid Tantalum Sprague, “594D series”

IN

- 33 µF, 25V, Solid Tantalum Sprague, “594D series”

OUT

D1 - 1A, 40V Schottky Rectifier, Surface Mount

L1 - 100 µH, L20, Coilcraft DO3316

C

B

- 0.01 µF, 50V, Ceramic

R1 - 1k, 1%

R2 - Use formula in Design Procedure

FIGURE 18. PC Board Layout

Layout is very important in switching regulator designs. Rap-

idly switching currents associated with wiring inductance can

generate voltage transients which can cause problems. For

minimal inductance and ground loops, the wires indicated by

heavy lines (in Figure 2 and Figure 3) should be wide

printed circuit traces and should be kept as short as

possible. For best results, external components should be

located as close to the switcher IC as possible using ground

plane construction or single point grounding.

If open core inductors are used, special care must be

taken as to the location and positioning of this type of induc-

tor. Allowing the inductor flux to intersect sensitive feedback,

IC ground path, and C_OUTwiring can cause problems.

www.national.com

22

The Die Attach Pad (DAP) can and should be connected to

PCB Ground plane/island. For CAD and assembly guide-

lines refer to Application Note AN-1187 at http://

power.national.com.

Application Information (Continued)

When using the adjustable version, special care must be

taken as to the location of the feedback resistors and the

associated wiring. Physically locate both resistors near the

IC, and route the wiring away from the inductor, especially an

open core type of inductor.

LLP PACKAGE DEVICES

The LM2671 is offered in the 16 lead LLP surface mount

package to allow for increased power dissipation compared

to the SO-8 and DIP.

23

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Physical Dimensions inches (millimeters)

unless otherwise noted

8-Lead (0.150" Wide) Molded Small Outline Package, JEDEC

Order Number LM2671M-3.3, LM2671M-5.0,

LM2671M-12 or LM2671M-ADJ

NS Package Number M08A

www.national.com

24

Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

8-Lead (0.300" Wide) Molded Dual-In-Line Package

Order Number LM2671N-3.3, LM2671N-5.0,

LM2671N-12 or LM2671N-ADJ

NS Package Number N08E

25

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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

16-Lead LLP Surface Mount Package

NS Package Number LDA16A

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves

the right at any time without notice to change said circuitry and specifications.

For the most current product information visit us at www.national.com.

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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS

WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR

CORPORATION. As used herein:

1. Life support devices or systems are devices or systems

which, (a) are intended for surgical implant into the body, or

(b) support or sustain life, and whose failure to perform when

properly used in accordance with instructions for use

provided in the labeling, can be reasonably expected to result

in a significant injury to the user.

2. A critical component is any component of a life support

device or system whose failure to perform can be reasonably

expected to cause the failure of the life support device or

system, or to affect its safety or effectiveness.

BANNED SUBSTANCE COMPLIANCE

National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products

Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain

no ‘‘Banned Substances’’ as defined in CSP-9-111S2.

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Support Center

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