National Semiconductor LM2675 Technical data

LM2675
SIMPLE SWITCHER

®

Power Converter High Efficiency

1A Step-Down Voltage Regulator

General Description

The LM2675 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 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.

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) and a fixed frequency oscillator.

The LM2675 series operates at a switching frequency of
260 kHz, thus allowing smaller sized filter components than
what would be needed with lower frequency switching regu­lators. Because of its very high efficiency (
per traces on the printed circuit board are the only heat
sinking needed.

A family of standard inductors for use with the LM2675 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.

Other features include a guaranteed
output voltage within specified input voltages and output
load conditions, and
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.

±

10% on the oscillator frequency. Ex-

>

90%), the cop-

±

1.5% tolerance on

To simplify the LM2675 buck regulator design procedure,
there exists computer design software, LM267X Made
Simple version 6.0.

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)

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

±

n

1.5% max output voltage tolerance over line and load

conditions

n Guaranteed 1A 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 Thermal shutdown and current limit protection

Typical Applications

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

Regulator

n Efficient Pre-Regulator for Linear Regulators
n Positive-to-Negative Converter

LM2675 SIMPLE SWITCHER Power Converter High Efficiency 1A Step-Down Voltage Regulator

June 2005

Typical Application

01280301

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

®

Windows

is a registered trademark of Microsoft Corporation.

© 2005 National Semiconductor Corporation DS012803 www.national.com

Connection Diagrams

LM2675

16-Lead LLP Surface Mount Package

Top View

8-Lead Package

Top View

SO-8/DIP Package

See NSC Package Drawing Number MO8A/N08E

01280338

LLP Package

See NSC Package Drawing Number LDA16A

01280302

Package Marking and Ordering Information

TABLE 1.

Output Voltage Order Information Package Marking Supplied as:

16 Lead LLP

12 LM2675LD-12 S000DB 1000 Units on Tape and Reel

12 LM2675LDX-12 S000DB 4500 Units on Tape and Reel

3.3 LM2675LD-3.3 S000EB 1000 Units on Tape and Reel

3.3 LM2675LDX-3.3 S000EB 4500 Units on Tape and Reel

5.0 LM2675LD-5.0 S000FB 1000 Units on Tape and Reel

5.0 LM2675LDX-5.0 S000FB 4500 Units on Tape and Reel

ADJ LM2675LD-ADJ S000GB 1000 Units on Tape and Reel

ADJ LM2675LDX-ADJ S000GB 4500 Units on Tape and Reel

SO-8

12 LM2675M-12 2675M-12 Shipped in Anti-Static Rails

12 LM2675MX-12 2675M-12 2500 Units on Tape and Reel

3.3 LM2675M-3.3 2675M-3.3 Shipped in Anti-Static Rails

3.3 LM2675MX-3.3 2675M-3.3 2500 Units on Tape and Reel

5.0 LM2675M-5.0 2675M-5.0 Shipped in Anti-Static Rails

5.0 LM2675MX-5.0 2675M-5.0 2500 Units on Tape and Reel

ADJ LM2675M-ADJ 2675M-ADJ Shipped in Anti-Static Rails

ADJ LM2675MX-ADJ 2675M-ADJ 2500 Units on Tape and Reel

DIP

12 LM2675N-12 LM2675N-12 Shipped in Anti-Static Rails

3.3 LM2675N-3.3 LM2675N-3.3 Shipped in Anti-Static Rails

5.0 LM2675N-5.0 LM2675N-5.0 Shipped in Anti-Static Rails

ADJ LM2675N-ADJ LM2675N-ADJ Shipped in Anti-Static Rails

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Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

LM2675

Supply Voltage 45V

ON/OFF Pin Voltage

−0.1V ≤ VSH≤ 6V

Switch Voltage to Ground −1V

Boost Pin Voltage V

Feedback Pin Voltage −0.3V ≤ V

SW

FB

+8V

≤ 14V

ESD Susceptibility

Human Body Model (Note 2) 2 kV

Power Dissipation Internally Limited

Storage Temperature Range −65˚C to +150˚C

Lead Temperature

M Package

Vapor Phase (60s) +215˚C

Infrared (15s) +220˚C

N Package (Soldering, 10s) +260˚C

LLP Package (See AN-1187)

Maximum Junction Temperature +150˚C

Operating Ratings

Supply Voltage 6.5V to 40V Junction Temperature Range −40˚C ≤ TJ≤ +125˚C

Electrical Characteristics LM2675-3.3

Operating Temperature Range.

Symbol Parameter Conditions Typical Min Max Units

SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)

V

OUT

V

OUT

η Efficiency V

Output Voltage VIN= 8V to 40V, I

Output Voltage VIN= 6.5V to 40V, I

Specifications with standard type face are for TJ= 25˚C, and those with bold type face apply over full

(Note 4) (Note 5) (Note 5)

= 20 mA to 1A 3.3 3.251/3.201 3.350/3.399 V

LOAD

= 20 mA to 500 mA 3.3 3.251/3.201 3.350/3.399 V

LOAD

= 12V, I

IN

=1A 86 %

LOAD

LM2675-5.0

Symbol Parameter Conditions Typical Min Max Units

(Note 4) (Note 5) (Note 5)

SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)

V

OUT

V

OUT

η Efficiency V

Output Voltage VIN= 8V to 40V, I

Output Voltage VIN= 6.5V to 40V, I

= 12V, I

IN

=1A 90 %

LOAD

= 20 mA to 1A 5.0 4.925/4.850 5.075/5.150 V

LOAD

= 20 mA to 500 mA 5.0 4.925/4.850 5.075/5.150 V

LOAD

LM2675-12

Symbol Parameter Conditions Typical Min Max Units

(Note 4) (Note 5) (Note 5)

SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)

V

OUT

η Efficiency V

Output Voltage VIN= 15V to 40V, I

= 24V, I

IN

LOAD

= 20 mA to 1A 12 11.82/11.64 12.18/12.36 V

LOAD

=1A 94 %

LM2675-ADJ

Symbol Parameter Conditions Typ Min Max Units

(Note 4) (Note 5) (Note 5)

SYSTEM PARAMETERS Test Circuit Figure 3 (Note 3)

V

FB

V

FB

Feedback
Voltage

Feedback
Voltage

VIN= 8V to 40V, I

Programmed for 5V

V

OUT

LOAD

(see Circuit of Figure 3)

VIN= 6.5V to 40V, I

Programmed for 5V

V

OUT

LOAD

(see Circuit of Figure 3)

=20mAto1A

1.210 1.192/1.174 1.228/1.246 V

=20mAto500mA

1.210 1.192/1.174 1.228/1.246 V

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LM2675-ADJ (Continued)

LM2675

Symbol Parameter Conditions Typ Min Max Units

(Note 4) (Note 5) (Note 5)

η Efficiency V

= 12V, I

IN

=1A 90 %

LOAD

All Output Voltage Versions

Specifications with standard type face are for TJ= 25˚C, and those with bold type face apply over full Operating Tempera­ture Range. Unless otherwise specified, V

sion, and I

LOAD

= 100 mA.

Symbol Parameters Conditions Typ Min Max Units

DEVICE PARAMETERS

I

Q

I

STBY

Quiescent Current V

Standby Quiescent
Current

I

CL

I

L

R

f

O

DS(ON)

Current Limit 1.55 1.25/1.2 2.1/2.2 A

Output Leakage Current VIN= 40V, ON/OFF Pin = 0V

Switch On-Resistance I

Oscillator Frequency Measured at Switch Pin 260 225 275 kHz

D Maximum Duty Cycle 95 %

Minimum Duty Cycle 0 %

I

BIAS

Feedback Bias
Current

V

S/D

ON/OFF Pin
Voltage Thesholds

I

S/D

θ

JA

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 LM2675 is used as shown in Figures 2, 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 software (version 6.0). The value θ
thermal vias. For improved thermal resistance and power dissipation for the LLP package, refer to Application Note AN-1187.

ON/OFF Pin Current ON/OFF Pin = 0V 20 737µA

Thermal Resistance N Package, Junction to Ambient (Note 6) 95 ˚C/W

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

J−A

= 12V for the 3.3V, 5V, and Adjustable versions and VIN= 24V for the 12V ver-

IN

FEEDBACK

= 8V 2.5 3.6 mA

For 3.3V, 5.0V, and ADJ Versions

V

FEEDBACK

= 15V 2.5 mA

For 12V Versions

ON/OFF Pin = 0V

V

V

SWITCH

V

=0V

SWITCH

= −1V, ON/OFF Pin = 0V 615mA

SWITCH

= 1A 0.25 0.30/0.50 Ω

FEEDBACK

= 1.3V

ADJ Version Only

50 100/150 µA

125µA

85 nA

1.4 0.8 2.0 V

M Package, Junction to Ambient (Note 6) 105

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Typical Performance Characteristics

Normalized

Output Voltage Line Regulation

LM2675

Efficiency

Switch Current Limit

01280303

01280305

01280304

Drain-to-Source

Resistance

01280306

Operating

Quiescent Current

01280307

01280308

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Typical Performance Characteristics (Continued)

LM2675

Standby

Quiescent Current

01280309

ON/OFF Threshold

Voltage

ON/OFF Pin

Current (Sourcing) Switching Frequency

01280310

01280311 01280312

Feedback Pin

Bias Current Peak Switch Current

01280313

01280314

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Typical Performance Characteristics (Continued)

Dropout Voltage — 3.3V Option Dropout Voltage —5.0V Option

01280315 01280316

Block Diagram

LM2675

* Active Inductor Patent Number 5,514,947

†

Active Capacitor Patent Number 5,382,918

01280317

FIGURE 1.

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Typical Performance Characteristics (Circuit of Figure 2)

LM2675

Continuous Mode Switching Waveforms

= 20V, V

V

IN

L = 47 µH, C

OUT

= 5V, I

OUT

= 68 µF, C

=1A

LOAD

ESR=50mΩ

OUT

Discontinuous Mode Switching Waveforms

V

= 20V, V

IN

L = 15 µH, C

OUT

= 5V, I

OUT

LOAD

= 68 µF (2x), C

= 300 mA

ESR=25mΩ

OUT

A: VSWPin 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

= 20V, V

V

IN

L = 47 µH, C

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

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

OUT

= 5V, I

OUT

= 68 µF, C

=1A

LOAD

ESR=50mΩ

OUT

Horizontal Time Base: 50 µs/div

01280318

01280320

A: VSWPin 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 Discontinuous Mode

V

= 20V, V

IN

L = 47 µH, C

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

B: Load Current: 100 mA to 400 mA Load Pulse

OUT

= 68 µF, C

OUT

= 5V,

OUT

ESR=50mΩ

Horizontal Time Base: 200 µs/div

01280319

01280321

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Test Circuit and Layout Guidelines

LM2675

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

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

C

OUT

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

#

L1 - 68 µH Sumida

- 0.01 µF, 50V Ceramic

C

B

RCR110D-680L

FIGURE 2. Standard Test Circuits and Layout Guides

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

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

C

OUT

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

#

L1 - 68 µH Sumida

R1 - 1.5 kΩ,1%

- 0.01 µF, 50V Ceramic

C

B

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

RCR110D-680L

01280322

Fixed Output Voltage Versions

01280323

where V

Use a 1% resistor for best stability.

REF

= 1.21V

FIGURE 3. Standard Test Circuits and Layout Guides

Adjustable Output Voltage Version

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LM2675 Series Buck Regulator Design Procedure (Fixed Output)

LM2675

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

Given: Given:

1. Inductor Selection (L1) 1. Inductor Selection (L1)

A. Select the correct inductor value selection guide from Figure

4, 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.

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

Renco: ferrite stick core inductors; benefits are typically lowest
cost inductors and can withstand E
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
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

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.

PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)

®

3.1, NT, or 95 operating systems.

V

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

OUT

V

(max) = Maximum DC Input Voltage VIN(max) = 12V

IN

I

(max) = Maximum Load Current I

LOAD

OUT

LOAD

=5V

(max) = 1A

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

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. 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.)

T and transient peak

•

T and transient

•

) 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 inductor
are the:

OUT

)

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LM2675 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)

The capacitor list contains through-hole electrolytic capacitors
from 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.

3. Catch Diode Selection (D1)
A. In normal operation, the average current of the catch diode is

the load current times the catch diode duty cycle, 1-D (D is 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 LM2675. 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
LM2675 using short leads and short printed circuit traces.

4. Input Capacitor (C

) 4. Input Capacitor (CIN)

IN

Surface Mount:
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. Refer to the table shown in Figure 12. In this example, a 1A,

20V Schottky diode will provide the best performance. If the
circuit must withstand a continuous shorted output, a higher
current Schottky diode is recommended.

LM2675

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LM2675 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

LM2675

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 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

1

⁄2the DC load current. The capacitor manufacturer data

least
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.
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.
Use caution when using ceramic capacitors for input bypassing,
because it may cause severe ringing at the V

5. Boost Capacitor (C

) 5. Boost Capacitor (CB)

B

pin.

IN

This capacitor develops the necessary voltage to turn the switch
gate on fully. All applications should use a 0.01 µF, 50V ceramic
capacitor.

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 x V

) would be needed.

IN

The next higher capacitor voltage rating is 16V.
The RMS current rating requirement for the input capacitor in a

1

buck regulator is approximately

⁄2the 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 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.

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

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LM2675 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

Inductor Value Selection Guides

(For Continuous Mode Operation)

01280326

01280328

FIGURE 4. LM2675-3.3

FIGURE 6. LM2675-12

LM2675

FIGURE 5. LM2675-5.0

01280327

01280329

FIGURE 7. LM2675-ADJ

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LM2675 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

LM2675

Ind.

Inductance

Ref.

Desg.

L4 68 0.32 67143940 67144310 RL-1284-68-43 RL1500-68 PE-53804 PE-53804-S DO1608-683

L5 47 0.37 67148310 67148420 RL-1284-47-43 RL1500-47 PE-53805 PE-53805-S DO1608-473

L6 33 0.44 67148320 67148430 RL-1284-33-43 RL1500-33 PE-53806 PE-53806-S DO1608-333

L7 22 0.52 67148330 67148440 RL-1284-22-43 RL1500-22 PE-53807 PE-53807-S DO1608-223

L9 220 0.32 67143960 67144330 RL-5470-3 RL1500-220 PE-53809 PE-53809-S DO3308-224

L10 150 0.39 67143970 67144340 RL-5470-4 RL1500-150 PE-53810 PE-53810-S DO3308-154

L11 100 0.48 67143980 67144350 RL-5470-5 RL1500-100 PE-53811 PE-53811-S DO3308-104

L12 68 0.58 67143990 67144360 RL-5470-6 RL1500-68 PE-53812 PE-53812-S DO3308-683

L13 47 0.70 67144000 67144380 RL-5470-7 RL1500-47 PE-53813 PE-53813-S DO3308-473

L14 33 0.83 67148340 67148450 RL-1284-33-43 RL1500-33 PE-53814 PE-53814-S DO3308-333

L15 22 0.99 67148350 67148460 RL-1284-22-43 RL1500-22 PE-53815 PE-53815-S DO3308-223

L18 220 0.55 67144040 67144420 RL-5471-2 RL1500-220 PE-53818 PE-53818-S DO3316-224

L19 150 0.66 67144050 67144430 RL-5471-3 RL1500-150 PE-53819 PE-53819-S DO3316-154

L20 100 0.82 67144060 67144440 RL-5471-4 RL1500-100 PE-53820 PE-53820-S DO3316-104

L21 68 0.99 67144070 67144450 RL-5471-5 RL1500-68 PE-53821 PE-53821-S DO3316-683

L22 47 1.17 67144080 67144460 RL-5471-6 — PE-53822 PE-53822-S DO3316-473

L23 33 1.40 67144090 67144470 RL-5471-7 — PE-53823 PE-53823-S DO3316-333

L24 22 1.70 67148370 67148480 RL-1283-22-43 — PE-53824 PE-53824-S DO3316-223

L27 220 1.00 67144110 67144490 RL-5471-2 — PE-53827 PE-53827-S DO5022P-224

L28 150 1.20 67144120 67144500 RL-5471-3 — PE-53828 PE-53828-S DO5022P-154

L29 100 1.47 67144130 67144510 RL-5471-4 — PE-53829 PE-53829-S DO5022P-104

L30 68 1.78 67144140 67144520 RL-5471-5 — PE-53830 PE-53830-S DO5022P-683

(µH)

Current

(A)

Schott Renco Pulse Engineering Coilcraft

Through Surface Through Surface Through Surface Surface

Hole Mount Hole Mount Hole Mount Mount

FIGURE 8. Inductor Manufacturers’ Part Numbers

Coilcraft Inc. Phone [phone]

FAX [phone]

Coilcraft Inc., Europe Phone [phone]

FAX [phone]

Pulse Engineering Inc. Phone [phone]

FAX [phone]

Pulse Engineering Inc., Phone [phone]

Europe FAX [phone]

Renco Electronics Inc. Phone [phone]

FAX [phone]

Schott Corp. Phone [phone]

FAX [phone]

FIGURE 9. Inductor Manufacturers’ Phone Numbers

www.national.com 14

LM2675 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

Output Capacitor

Output

Voltage

(V)

3.3

5.0

12

Inductance

(µH)

22 120/6.3 100/10 100/10 330/35 330/35 330/35

33 120/6.3 100/10 68/10 220/35 220/35 220/35

47 68/10 100/10 68/10 150/35 150/35 150/35

68 120/6.3 100/10 100/10 120/35 120/35 120/35

100 120/6.3 100/10 100/10 120/35 120/35 120/35

150 120/6.3 100/10 100/10 120/35 120/35 120/35

22 100/16 100/10 100/10 330/35 330/35 330/35

33 68/10 10010 68/10 220/35 220/35 220/35

47 68/10 100/10 68/10 150/35 150/35 150/35

68 100/16 100/10 100/10 120/35 120/35 120/35

100 100/16 100/10 100/10 120/35 120/35 120/35

150 100/16 100/10 100/10 120/35 120/35 120/35

22 120/20 (2x) 68/20 68/20 330/35 330/35 330/35

33 68/25 68/20 68/20 220/35 220/35 220/35

47 47/20 68/20 47/20 150/35 150/35 150/35

68 47/20 68/20 47/20 120/35 120/35 120/35

100 47/20 68/20 47/20 120/35 120/35 120/35

150 47/20 68/20 47/20 120/35 120/35 120/35

220 47/20 68/20 47/20 120/35 120/35 120/35

Surface Mount Through Hole

Sprague AVX TPS Sanyo OS-CON Sanyo MV-GX Nichicon Panasonic

594D Series Series SA Series Series PL Series HFQ Series

(µF/V) (µF/V) (µF/V) (µF/V) (µF/V) (µF/V)

LM2675

FIGURE 10. Output Capacitor Table

Nichicon Corp. Phone [phone]

FAX [phone]

Panasonic Phone [phone]

FAX [phone]

AVX Corp. Phone [phone]

FAX [phone]

Sprague/Vishay Phone [phone]

FAX [phone]

Sanyo Corp. Phone [phone]

FAX [phone]

FIGURE 11. Capacitor Manufacturers’ Phone Numbers

www.national.com15

LM2675 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

LM2675

1A Diodes 3A Diodes

Surface Through Surface Through

V

R

Mount Hole Mount Hole

20V SK12 1N5817 SK32 1N5820

B120 SR102 SR302

30V SK13 1N5818 SK33 1N5821

B130 11DQ03 30WQ03F 31DQ03

MBRS130 SR103

40V SK14 1N5819 SK34 1N5822

B140 11DQ04 30BQ040 MBR340

MBRS140 SR104 30WQ04F 31DQ04

10BQ040 MBRS340 SR304

10MQ040 MBRD340

15MQ040

50V SK15 MBR150 SK35 MBR350

B150 11DQ05 30WQ05F 31DQ05

10BQ050 SR105 SR305

FIGURE 12. Schottky Diode Selection Table

International Rectifier

Phone [phone]

Corp.

FAX [phone]

Motorola, Inc. Phone [phone]

FAX [phone]

General Instruments

Phone [phone]

Corp.

FAX [phone]

Diodes, Inc. Phone [phone]

FAX [phone]

FIGURE 13. Diode Manufacturers’ Phone Numbers

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

www.national.com 16

01280330

LM2675 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

AVX TPS

Recommended Voltage

Application Voltage Rating

+85˚C Rating

3.3 6.3

510

10 20

12 25

15 35

Sprague 594D

Recommended Voltage

Application Voltage Rating

+85˚C Rating

2.5 4

3.3 6.3

510

816

12 20

18 25

24 35

29 50

LM2675

FIGURE 15.

LM2675 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 for
use on Windows 3.1, NT, or 95 operating systems.

Given: Given:

= Regulated Output Voltage V

V

OUT

V

(max) = Maximum Input Voltage VIN(max) = 28V

IN

I

(max) = Maximum Load Current I

LOAD

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

1. Programming Output Voltage (Selecting R
shown in Figure 3)

Use the following formula to select the appropriate resistor

and R2,as

1

1. Programming Output Voltage (Selecting R1and R2,as
shown in Figure 3)

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

values.

where V

Select a value for R1between 240Ω and 1.5 kΩ. The lower
resistor values minimize noise pickup in the sensitive feedback

REF

= 1.21V

R

R
pin. (For the lowest temperature coefficient and the best stability
with time, use 1% metal film resistors.)

= 20V

OUT

(max) = 1A

LOAD

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

2

= 15.4 kΩ.

2

www.national.com17

LM2675 Series Buck Regulator Design Procedure (Adjustable Output)

(Continued)

LM2675

PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)

2. Inductor Selection (L1) 2. Inductor Selection (L1)

A. Calculate the inductor Volt

µs), from the following formula:

microsecond constant E•T(V

•

A. Calculate the inductor Volt

•

microsecond constant (E•T),

•

where V

= internal switch saturation voltage = 0.25V and V

SAT

D

= diode forward voltage drop = 0.5V

B. Use the E
with the E

T value from the previous formula and match it

•

T number on the vertical axis of the Inductor Value

•

B. E

Selection Guide shown in Figure 7.

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

D. Identify the inductance region intersected by the E

and the Maximum Load Current value. Each region is identified
by an inductance value and an inductor code (LXX).

T value

•

D. From the inductor value selection guide shown in Figure 7,
the inductance region intersected by the 21.6 (V
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 numbers listed in Figure 8. For information on the different
types of inductors, see the inductor selection in the fixed output

E. From the table in Figure 8, locate line L30, and select an
inductor part number from the list of manufacturers part
numbers.

voltage design procedure.

3. Output Capacitor Selection (C

A. Select an output capacitor from the capacitor code selection

guide in Figure 16. Using the inductance value found in the
inductor selection guide, step 1, locate the appropriate capacitor

) 3. Output Capacitor SeIection (C

OUT

A. Use the appropriate row of the capacitor code selection

guide, in Figure 16. For this example, use the 15– 20V row. The
capacitor code corresponding to an inductance of 68 µH is C20.

code corresponding to the desired output voltage.

B. Select an appropriate capacitor value and voltage rating,
using the capacitor code, from the output capacitor selection
table in Figure 17. There are two solid tantalum (surface mount)
capacitor manufacturers and four electrolytic (through hole)
capacitor manufacturers to choose from. 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.

B. From the output capacitor selection table in Figure 17,
choose a capacitor value (and voltage rating) that intersects the
capacitor code(s) selected in section A, C20.
The capacitance and voltage rating values corresponding to the
capacitor code C20 are the:
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.

T = 21.6 (V•µs)

•

(max) = 1A

LOAD

OUT

µs) horizontal

•

)

www.national.com 18

LM2675 Series Buck Regulator Design Procedure (Adjustable Output)

(Continued)

PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)

4. Catch Diode Selection (D1)
A. In normal operation, the average current of the catch diode is

the load current times the catch diode duty cycle, 1-D (D is the
switch duty cycle, which is approximately V

OUT/VIN

). The largest
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
LM2675. 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
LM2675 using short leads and short printed circuit traces.

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
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

1

⁄2the DC load current. The capacitor manufacturer data

least
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.
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.
Use caution when using ceramic capacitors for input bypassing,
because it may cause severe ringing at the V

6. Boost Capacitor (C

) 6. Boost Capacitor (CB)

B

pin.

IN

This capacitor develops the necessary voltage to turn the switch
gate on fully. All applications should use a 0.01 µF, 50V ceramic
capacitor.

4. Catch Diode Selection (D1)
A. Refer to the table shown in Figure 12. Schottky diodes

provide the best performance, and in this example a 1A, 40V
Schottky diode 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.

5. Input Capacitor (C

)

IN

The important parameters for the input capacitor are the input
voltage rating and the RMS current rating. With a maximum
input voltage of 28V, an aluminum electrolytic capacitor with a
voltage rating of at least 35V (1.25 x V

) would be needed.

IN

The RMS current rating requirement for the input capacitor in a

1

buck regulator is approximately

⁄2the 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 35V line and note which capacitor values
have RMS current ratings greater than 500 mA.
For a through hole design, a 330 µF/35V 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, 50V capacitor is adequate.

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

LM2675

www.national.com19

LM2675 Series Buck Regulator Design Procedure (Adjustable Output)

(Continued)

LM2675

Case

Style (Note 7)

SM and TH 1.21–2.50 ————C1C2C3

SM and TH 2.50–3.75 — — — C1 C2 C3 C3

SM and TH 3.75–5.0 — — C4 C5 C6 C6 C6

SM and TH 5.0–6.25 — C4 C7 C6 C6 C6 C6

SM and TH 6.25–7.5 C8 C4 C7 C6 C6 C6 C6

SM and TH 7.5–10.0 C9 C10 C11 C12 C13 C13 C13

SM and TH 10.0–12.5 C14 C11 C12 C12 C13 C13 C13

SM and TH 12.5–15.0 C15 C16 C17 C17 C17 C17 C17

SM and TH 15.0–20.0 C18 C19 C20 C20 C20 C20 C20

SM and TH 20.0–30.0 C21 C22 C22 C22 C22 C22 C22

TH 30.0– 37.0 C23 C24 C24 C25 C25 C25 C25

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

Output

Voltage (V)

22 33 47 68 100 150 220

FIGURE 16. Capacitor Code Selection Guide

Inductance (µH)

www.national.com 20

LM2675 Series Buck Regulator Design Procedure (Adjustable Output)

(Continued)

Output Capacitor

Cap.

Ref.

Desg.

594D Series Series SA Series Series PL Series HFQ Series

#

C1 120/6.3 100/10 100/10 220/35 220/35 220/35

C2 120/6.3 100/10 100/10 150/35 150/35 150/35

C3 120/6.3 100/10 100/35 120/35 120/35 120/35

C4 68/10 100/10 68/10 220/35 220/35 220/35

C5 100/16 100/10 100/10 150/35 150/35 150/35

C6 100/16 100/10 100/10 120/35 120/35 120/35

C7 68/10 100/10 68/10 150/35 150/35 150/35

C8 100/16 100/10 100/10 330/35 330/35 330/35

C9 100/16 100/16 100/16 330/35 330/35 330/35

C10 100/16 100/16 68/16 220/35 220/35 220/35

C11 100/16 100/16 68/16 150/35 150/35 150/35

C12 100/16 100/16 68/16 120/35 120/35 120/35

C13 100/16 100/16 100/16 120/35 120/35 120/35

C14 100/16 100/16 100/16 220/35 220/35 220/35

C15 47/20 68/20 47/20 220/35 220/35 220/35

C16 47/20 68/20 47/20 150/35 150/35 150/35

C17 47/20 68/20 47/20 120/35 120/35 120/35

C18 68/25 (2x) 33/25 47/25 (Note 8) 220/35 220/35 220/35

C19 33/25 33/25 33/25 (Note 8) 150/35 150/35 150/35

C20 33/25 33/25 33/25 (Note 8) 120/35 120/35 120/35

C21 33/35 (2x) 22/25 (Note 9) 150/35 150/35 150/35

C22 33/35 22/35 (Note 9) 120/35 120/35 120/35

C23 (Note 9) (Note 9) (Note 9) 220/50 100/50 120/50

C24 (Note 9) (Note 9) (Note 9) 150/50 100/50 120/50

C25 (Note 9) (Note 9) (Note 9) 150/50 82/50 82/50

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.

Surface Mount Through Hole

Sprague AVX TPS Sanyo OS-CON Sanyo MV-GX Nichicon Panasonic

(µF/V) (µF/V) (µF/V) (µF/V) (µF/V) (µF/V)

FIGURE 17. Output Capacitor Selection Table

LM2675

www.national.com21

Application Information

TYPICAL SURFACE MOUNT PC BOARD LAYOUT,

LM2675

FIXED OUTPUT (4X SIZE)

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

- 68 µF, 16V, Solid Tantalum Sprague, “594D series”

C

OUT

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

L1 - 33 µH, L23, Coilcraft DO3316

- 0.01 µF, 50V, Ceramic

C

B

TYPICAL SURFACE MOUNT PC BOARD LAYOUT, ADJUSTABLE OUTPUT (4X SIZE)

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

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

C

OUT

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

L1 - 68 µH, L30, Coilcraft DO3316

- 0.01 µF, 50V, Ceramic

C

B

R1 - 1k, 1%

R2 - Use formula in Design Procedure

01280336

01280337

FIGURE 18. PC Board Layout

Layout is very important in switching regulator designs. Rap­idly 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

www.national.com 22

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 induc­tor. Allowing the inductor flux to intersect sensitive feedback,
IC ground path, and C

wiring can cause problems.

OUT

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 LM2675 is offered in the 16 lead LLP surface mount
package to allow for increased power dissipation compared
to the SO-8 and DIP.

LM2675

The Die Attach Pad (DAP) can and should be connected to
PCB Ground plane/island. For CAD and assembly guide­lines refer to Application Note AN-1187 at http://
power.national.com.

www.national.com23

Physical Dimensions inches (millimeters)

unless otherwise noted

LM2675

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

Order Number LM2675M-3.3, LM2675M-5.0,

LM2675M-12 or LM2675M-ADJ

NS Package Number M08A

www.national.com 24

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

LM2675

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

Order Number LM2675N-3.3, LM2675N-5.0,

LM2675N-12 or LM2675N-ADJ

NS Package Number N08E

www.national.com25

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

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.

provided in the labeling, can be reasonably expected to result
in a significant injury to the user.

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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.

Leadfree products are RoHS compliant.

National Semiconductor
Americas Customer
Support Center

LM2675 SIMPLE SWITCHER Power Converter High Efficiency 1A Step-Down Voltage Regulator

Email: [e-mail]
Tel: [phone]

www.national.com

National Semiconductor
Europe Customer Support Center

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