LM2674
SIMPLE SWITCHER®Power Converter High Efficiency
500 mA Step-Down Voltage Regulator
General Description
The LM2674 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 500 mAload 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 LM2674 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.
A family of standard inductors for use with the LM2674 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 ±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.
To simplify the LM2674 buck regulator design procedure,
there exists computer design software,
LM267X Made
Simple
(version 6.0).
Features
nEfficiency up to 96%
nAvailable in SO-8, 8-pin DIP and LLP packages
nComputer Design Software
LM267X Made Simple
(version 6.0)
nSimple and easy to design with
nRequires only 5 external components
nUses readily available standard inductors
n3.3V, 5.0V, 12V, and adjustable output versions
nAdjustable version output voltage range: 1.21V to 37V
n±1.5% max output voltage tolerance over line and load
conditions
nGuaranteed 500mA output load current
n0.25ΩDMOS Output Switch
nWide input voltage range: 8V to 40V
n260 kHz fixed frequency internal oscillator
nTTL shutdown capability, low power standby mode
nThermal shutdown and current limit protection
Typical Applications
nSimple High Efficiency (>90%) Step-Down (Buck)
Regulator
nEfficient Pre-Regulator for Linear Regulators
nPositive-to-Negative Converter
Typical Application
10004101
SIMPLE SWITCHER®is a registered trademark of National Semiconductor Corporation.
Windows®is a registered trademark of Microsoft Corporation.
May 2001
LM2674 SIMPLE SWITCHER Power Converter High Efficiency 500 mA Step-Down Voltage
Regulator
© 2001 National Semiconductor Corporation DS100041 www.national.com
Connection Diagrams
16-Lead LLP Surface Mount Package
Top View 8-Lead Package
Top View
10004138
LLP Package
See NSC Package Drawing Number LDA16A
10004102
SO-8/DIP Package
See NSC Package Drawing Number MO8A/N08E
TABLE 1. Package Marking and Ordering Information
Output Voltage Order Information Package Marking Supplied as:
16 Lead LLP
12 LM2674LD-12 S0009B 1000 Units on Tape and Reel
12 LM2674LDX-12 S0009B 4500 Units on Tape and Reel
3.3 LM2674LD-3.3 S000AB 1000 Units on Tape and Reel
3.3 LM2674LDX-3.3 S000AB 4500 Units on Tape and Reel
5.0 LM2674LD-5.0 S000BB 1000 Units on Tape and Reel
5.0 LM2674LDX-5.0 S000BB 4500 Units on Tape and Reel
ADJ LM2674LD-ADJ S000CB 1000 Units on Tape and Reel
ADJ LM2674LDX-ADJ S000CB 4500 Units on Tape and Reel
SO-8 12 LM2674M-12 2674M-12 Shipped in Anti-Static Rails
12 LM2674MX-12 2674M-12 2500 Units on Tape and Reel
3.3 LM2674M-3.3 2674M-3.3 Shipped in Anti-Static Rails
3.3 LM2674MX-3.3 2674M-3.3 2500 Units on Tape and Reel
5.0 LM2674M-5.0 2674M-5.0 Shipped in Anti-Static Rails
5.0 LM2674MX-5.0 2674M-5.0 2500 Units on Tape and Reel
ADJ LM2674M-ADJ 2674M-ADJ Shipped in Anti-Static Rails
ADJ LM2674MX-ADJ 2674M-ADJ 2500 Units on Tape and Reel
DIP 12 LM2674N-12 LM2674N-12 Shipped in Anti-Static Rails
3.3 LM2674N-3.3 LM2674N-3.3 Shipped in Anti-Static Rails
5.0 LM2674N-5.0 LM2674N-5.0 Shipped in Anti-Static Rails
ADJ LM2674N-ADJ LM2674N-ADJ Shipped in Anti-Static Rails
LM2674
www.national.com 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
ON/OFF Pin Voltage −0.1V ≤V
SH
≤6V
Switch Voltage to Ground −1V
Boost Pin Voltage V
SW
+8V
Feedback Pin Voltage −0.3V ≤V
FB
≤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 ≤T
J
≤+125˚C
Electrical Characteristics
LM2674-3.3 Specifications with standard type face are for T
J
= 25˚C, and those with bold type face apply over full
Operating Temperature Range.
Symbol Parameter Conditions Typical Min Max Units
(Note 4) (Note 5) (Note 5)
SYSTEM PARAMETERS Test Circuit
Figure 2
(Note 3)
V
OUT
Output Voltage V
IN
= 8V to 40V, I
LOAD
= 20 mA to 500 mA 3.3 3.251/3.201 3.350/3.399 V
V
OUT
Output Voltage V
IN
= 6.5V to 40V, I
LOAD
= 20 mA to 250 mA 3.3 3.251/3.201 3.350/3.399 V
ηEfficiency V
IN
= 12V, I
LOAD
= 500 mA 86 %
LM2674-5.0
Symbol Parameter Conditions Typical Min Max Units
(Note 4) (Note 5) (Note 5)
SYSTEM PARAMETERS Test Circuit
Figure 2
(Note 3)
V
OUT
Output Voltage V
IN
= 8V to 40V, I
LOAD
= 20 mA to 500 mA 5.0 4.925/4.850 5.075/5.150 V
V
OUT
Output Voltage V
IN
= 6.5V to 40V, I
LOAD
= 20 mA to 250 mA 5.0 4.925/4.850 5.075/5.150 V
ηEfficiency V
IN
= 12V, I
LOAD
= 500 mA 90 %
LM2674-12
Symbol Parameter Conditions Typical Min Max Units
(Note 4) (Note 5) (Note 5)
SYSTEM PARAMETERS Test Circuit
Figure 2
(Note 3)
V
OUT
Output Voltage V
IN
= 15V to 40V, I
LOAD
= 20 mA to 500 mA 12 11.82/11.64 12.18/12.36 V
ηEfficiency V
IN
= 24V, I
LOAD
= 500 mA 94 %
LM2674-ADJ
Symbol Parameter Conditions Typ Min Max Units
(Note 4) (Note 5) (Note 5)
SYSTEM PARAMETERS Test Circuit
Figure 3
(Note 3)
V
FB
Feedback
Voltage V
IN
= 8V to 40V, I
LOAD
=20mAto500mA
V
OUT
Programmed for 5V
(see Circuit of
Figure 3
)1.210 1.192/1.174 1.228/1.246 V
LM2674
www.national.com3
LM2674-ADJ (Continued)
Symbol Parameter Conditions Typ Min Max Units
(Note 4) (Note 5) (Note 5)
V
FB
Feedback
Voltage V
IN
= 6.5V to 40V, I
LOAD
=20mAto250mA
V
OUT
Programmed for 5V
(see Circuit of
Figure 3
)1.210 1.192/1.174 1.228/1.246 V
ηEfficiency V
IN
= 12V, I
LOAD
= 500 mA 90 %
All Output Voltage Versions
Specifications with standard type face are for T
J
= 25˚C, and those with bold type face apply over full Operating Tempera-
ture Range. Unless otherwise specified, V
IN
= 12V for the 3.3V, 5V, and Adjustable versions and V
IN
= 24V for the 12V ver-
sion, and I
LOAD
= 100 mA.
Symbol Parameters Conditions Typ Min Max Units
DEVICE PARAMETERS
I
Q
Quiescent Current V
FEEDBACK
= 8V 2.5 3.6 mA
For 3.3V, 5.0V, and ADJ Versions
V
FEEDBACK
= 15V 2.5 mA
For 12V Versions
I
STBY
Standby Quiescent
Current ON/OFF Pin = 0V 50 100/150 µA
I
CL
Current Limit 0.8 0.62/0.575 1.2/1.25 A
I
L
Output Leakage Current V
IN
= 40V, ON/OFF Pin = 0V
V
SWITCH
=0V 125µA
V
SWITCH
= −1V, ON/OFF Pin = 0V 615mA
R
DS(ON)
Switch On-Resistance I
SWITCH
= 500 mA 0.25 0.40/0.60 Ω
f
O
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
FEEDBACK
= 1.3V
ADJ Version Only 85 nA
V
S/D
ON/OFF Pin
Voltage Thesholds 1.4 0.8 2.0 V
I
S/D
ON/OFF Pin Current ON/OFF Pin = 0V 20 737µA
θ
JA
Thermal Resistance N Package, Junction to Ambient (Note 6) 95 ˚C/W
M Package, Junction to Ambient (Note 6) 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 kΩresistor 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 LM2674 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
(version 6.0) software. The value θJ−A for 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.
LM2674
www.national.com 4
Typical Performance
Characteristics
Normalized
Output Voltage Line Regulation Efficiency
10004103 10004104 10004105
Drain-to-Source
Resistance Switch Current Limit Operating
Quiescent Current
10004106 10004107 10004108
Standby
Quiescent Current ON/OFF Threshold
Voltage ON/OFF Pin
Current (Sourcing)
10004109 10004110 10004111
LM2674
www.national.com5
Typical Performance Characteristics (Continued)
Switching Frequency Feedback Pin
Bias Current Peak Switch Current
10004112 10004113 10004114
Dropout Voltage—3.3V Option Dropout Voltage—5.0V Option
10004115 10004116
LM2674
www.national.com 6
Block Diagram
10004117
* Active Inductor Patent Number 5,514,947
†Active Capacitor Patent Number 5,382,918
FIGURE 1.
LM2674
www.national.com7
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
OUT
ESR = 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
OUT
ESR=25mΩ
10004118
Horizontal Time Base: 1 µs/div
A: VSW Pin Voltage, 10 V/div.
B: Inductor Current, 0.2 A/div
C: Output Ripple Voltage, 50 mV/div AC-Coupled
10004119
Horizontal Time Base: 1 µs/div
A: VSW Pin Voltage, 10 V/div.
B: Inductor Current, 0.5 A/div
C: Output Ripple Voltage, 20 mV/div AC-Coupled
Load Transient Response for Continuous Mode
V
IN
= 20V, V
OUT
= 5V,
L = 100 µH, C
OUT
= 100 µF, C
OUT
ESR = 0.1Ω
Load Transient Response for Discontinuous Mode
V
IN
= 20V, V
OUT
= 5V,
L = 47 µH, C
OUT
= 68 µF, C
OUT
ESR=50mΩ
10004120
Horizontal Time Base: 50 µs/div
A: Output Voltage, 100 mV/div, AC-Coupled.
B: Load Current: 100 mA to 500 mA Load Pulse
10004121
Horizontal Time Base: 200 µs/div
A: Output Voltage, 100 mV/div, AC-Coupled.
B: Load Current: 100 mA to 400 mA Load Pulse
LM2674
www.national.com 8
Test Circuit and Layout Guidelines
10004122
CIN - 22 µF, 50V Tantalum, Sprague “199D Series”
COUT - 47 µF, 25V Tantalum, Sprague “595D Series”
D1 - 3.3A, 50V Schottky Rectifier, IR 30WQ05F
L1 - 68 µH Sumida #RCR110D-680L
CB- 0.01 µF, 50V Ceramic
FIGURE 2. Standard Test Circuits and Layout Guides
Fixed Output Voltage Versions
10004123
CIN - 22 µF, 50V Tantalum, Sprague “199D Series”
COUT - 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 VREF = 1.21V
Use a 1% resistor for best stability.
FIGURE 3. Standard Test Circuits and Layout Guides
Adjustable Output Voltage Versions
LM2674
www.national.com9
LM2674 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: Given:
V
OUT
= Regulated Output Voltage (3.3V, 5V, or 12V) V
OUT
=5V
V
IN
(max) = Maximum DC Input Voltage V
IN
(max) = 12V
I
LOAD
(max) = Maximum Load Current I
LOAD
(max) = 500 mA
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.
A. Use the inductor selection guide for the 5V version shown in
Figure 5
.
B. From the inductor value selection guide, identify the
inductance region intersected by the Maximum Input Voltage
line and the Maximum Load Current line. Each region is
identified by an inductance value and an inductor code (LXX).
B. From the inductor value selection guide shown in
Figure 5
,
the inductance region intersected by the 12V horizontal line and
the 500mA vertical line is 47 µH, and the inductor code is L13.
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 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.)
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
) 2. Output Capacitor Selection (C
OUT
)
A. Select an output capacitor from the output capacitor table in
Figure 10
. Using the output voltage and the inductance value
found in the inductor selection guide, step 1, locate the
appropriate capacitor value and voltage rating.
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 47 µH. The capacitance
and voltage rating values corresponding to the 47 µH inductor
are the:
LM2674
www.national.com 10
LM2674 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
.
Surface Mount:
68 µF/10V Sprague 594D Series.
100 µF/10V AVX TPS Series.
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
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 LM2674. The most stressful condition for this diode is a
shorted output condition.
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.
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
LM2674 using short leads and short printed circuit traces.
4. Input Capacitor (C
IN
) 4. Input Capacitor (C
IN
)
LM2674
www.national.com11
LM2674 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
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
least
1
⁄
2
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.
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
IN
pin.
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
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
1
⁄
2
the DC load current. In this
example, with a 500mA load, a capacitor with an 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 16V line and note which capacitor values
have RMS current ratings greater than 250 mA.
For a through hole design, a 100 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.
5. Boost Capacitor (C
B
) 5. Boost Capacitor (C
B
)
This capacitor develops the necessary voltage to turn the switch
gate on fully. All applications should use a 0.01 µF, 50V ceramic
capacitor.
For this application, and all applications, use a 0.01 µF, 50V
ceramic capacitor.
LM2674
www.national.com 12
INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation)
10004126
FIGURE 4. LM2674-3.3
10004127
FIGURE 5. LM2674-5.0
10004128
FIGURE 6. LM2674-12
10004129
FIGURE 7. LM2674-ADJ
LM2674
www.national.com13
INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) (Continued)
Ind.
Ref.
Desg.
Inductance
(µH) Current
(A)
Schott Renco Pulse Engineering Coilcraft
Through Surface Through Surface Through Surface Surface
Hole Mount Hole Mount Hole Mount Mount
L2 150 0.21 67143920 67144290 RL-5470-4 RL1500-150 PE-53802 PE-53802-S DO1608-154
L3 100 0.26 67143930 67144300 RL-5470-5 RL1500-100 PE-53803 PE-53803-S DO1608-104
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
FIGURE 8. Inductor Manufacturers’ Part Numbers
Coilcraft Inc. Phone (800) 322-2645
FAX (708) 639-1469
Coilcraft Inc., Europe Phone +44 1236 730 595
FAX +44 1236 730 627
Pulse Engineering Inc. Phone (619) 674-8100
FAX (619) 674-8262
Pulse Engineering Inc., Phone +353 93 24 107
Europe FAX +353 93 24 459
Renco Electronics Inc. Phone (800) 645-5828
FAX (516) 586-5562
Schott Corp. Phone (612) 475-1173
FAX (612) 475-1786
FIGURE 9. Inductor Manufacturers’ Phone Numbers
LM2674
www.national.com 14
INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) (Continued)
Output
Voltage
(V)
Inductance
(µH)
Output Capacitor
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)
3.3
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
5.0
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
12
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
FIGURE 10. Output Capacitor Table
Nichicon Corp. Phone (847) 843-7500
FAX (847) 843-2798
Panasonic Phone (714) 373-7857
FAX (714) 373-7102
AVX Corp. Phone (845) 448-9411
FAX (845) 448-1943
Sprague/Vishay Phone (207) 324-4140
FAX (207) 324-7223
Sanyo Corp. Phone (619) 661-6322
FAX (619) 661-1055
FIGURE 11. Capacitor Manufacturers’ Phone Numbers
LM2674
www.national.com15
INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) (Continued)
V
R
500mA Diodes 3A Diodes
Surface Through Surface Through
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
Corp. Phone (310) 322-3331
FAX (310) 322-3332
Motorola, Inc. Phone (800) 521-6274
FAX (602) 244-6609
General Instruments
Corp. Phone (516) 847-3000
FAX (516) 847-3236
Diodes, Inc. Phone (805) 446-4800
FAX (805) 446-4850
FIGURE 13. Diode Manufacturers’ Phone Numbers
10004130
FIGURE 14. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical)
LM2674
www.national.com 16
INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) (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
FIGURE 15. Recommended Application Voltage for AVX TPS and
Sprague 594D Tantalum Chip Capacitors Derated for 85˚C.
LM2674
www.national.com17
LM2674 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:
V
OUT
= Regulated Output Voltage V
OUT
= 20V
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).
F = Switching Frequency
(Fixed at a nominal 260 kHz).
1. Programming Output Voltage (Selecting R
1
and R
2
,as
shown in
Figure 3
)1. Programming Output Voltage (Selecting R
1
and R
2
,as
shown in
Figure 3
)
Use the following formula to select the appropriate resistor
values. Select R
1
to be 1 kΩ, 1%. Solve for R
2
.
where V
REF
= 1.21V
Select a value for R
1
between 240Ωand 1.5 kΩ. The lower
resistor 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.)
R
2
= 1k (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.
R
2
= 15.4 kΩ.
2. Inductor Selection (L1) 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. 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
and the Maximum Load Current value. Each region is identified
by an inductance value and an inductor code (LXX).
D. From the inductor value selection guide shown in
Figure 7
,
the inductance region intersected by the 21.6 (V •µs) horizontal
line and the 500mA vertical line is 100 µH, and the inductor
code is L20.
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
voltage design procedure.
E. From the table in
Figure 8
, locate line L20, and select an
inductor part number from the list of manufacturers part
numbers.
3. Output Capacitor Selection (C
OUT
) 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 selection guide, step 1, locate the appropriate capacitor
code corresponding to the desired output voltage.
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 100 µH is
C20.
LM2674
www.national.com 18
LM2674 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)
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.
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
/V
IN
). 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
LM2674. The most stressful condition for this diode is a shorted
output condition.
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 500mA,
40V Schottky diode would be a good choice. If the circuit must
withstand a continuous shorted output, a higher current (at least
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.
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
LM2674 using short leads and short printed circuit traces.
LM2674
www.national.com19
LM2674 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)
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
least
1
⁄
2
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.
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
IN
pin.
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
IN
) would be needed.
The RMS current rating requirement for the input capacitor in a
buck regulator is approximately
1
⁄
2
the DC load current. In this
example, with a 500mA load, a capacitor with an 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
have RMS current ratings greater than 250 mA.
For a through hole design, a 68 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.
6. Boost Capacitor (C
B
) 6. Boost Capacitor (C
B
)
This capacitor develops the necessary voltage to turn the switch
gate on fully. All applications should use a 0.01 µF, 50V ceramic
capacitor.
For this application, and all applications, use a 0.01 µF, 50V
ceramic capacitor.
Case
Style (Note 7) Output
Voltage (V) Inductance (µH)
22 33 47 68 100 150 220
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
FIGURE 16. Capacitor Code Selection Guide
LM2674
www.national.com 20
LM2674 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
Output Capacitor
Cap.
Ref.
Desg.
#
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)
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.
FIGURE 17. Output Capacitor Selection Table
LM2674
www.national.com21
Application Information
TYPICAL SURFACE MOUNT PC BOARD LAYOUT,
FIXED OUTPUT (4X SIZE)
10004136
CIN - 15 µF, 25V, Solid Tantalum Sprague, “594D series”
COUT - 68 µF, 10V, Solid Tantalum Sprague, “594D series”
D1 - 1A, 40V Schottky Rectifier, Surface Mount
L1 - 47 µH, L13, Coilcraft DO3308
CB- 0.01 µF, 50V, Ceramic
TYPICAL SURFACE MOUNT PC BOARD LAYOUT,
ADJUSTABLE OUTPUT (4X SIZE)
10004137
CIN - 15 µF, 50V, Solid Tantalum Sprague, “594D series”
COUT - 33 µF, 25V, Solid Tantalum Sprague, “594D series”
D1 - 1A, 40V Schottky Rectifier, Surface Mount
L1 - 100 µH, L20, Coilcraft DO3316
CB- 0.01 µF, 50V, Ceramic
R1 - 1k, 1%
R2 - Use formula in Design Procedure
FIGURE 18. PC Board Layout
LM2674
www.national.com 22
Application Information (Continued)
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
OUT
wiring can cause problems.
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 LM2674 is offered in the 16 lead LLP surface mount
package to allow for increased power dissipation compared
to the SO-8 and DIP. For details on thermal performance as
well as mounting and soldering specifications, refer to Appli-
cation Note AN-1187.
LM2674
www.national.com23
Physical Dimensions inches (millimeters)
unless otherwise noted
8-Lead (0.150" Wide) Molded Small Outline Package, JEDEC
Order Number LM2674M-3.3, LM2674M-5.0,
LM2674M-12 or LM2674M-ADJ
NS Package Number M08A
LM2674
www.national.com 24
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
8-Lead (0.300" Wide) Molded Dual-In-Line Package
Order Number LM2674N-3.3, LM2674N-5.0,
LM2674N-12 or LM2674N-ADJ
NS Package Number N08E
LM2674
www.national.com25
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
16-Lead LLP Surface Mount Package
NS Package Number LDA16A
LIFE SUPPORT POLICY
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.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
National Semiconductor
Europe Fax: +49 (0) 180-530 85 86
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: ap.support@nsc.com
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
www.national.com
LM2674 SIMPLE SWITCHER Power Converter High Efficiency 500 mA Step-Down Voltage
Regulator
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.
National P/N LM2674 - SIMPLE SWITCHER Power Converter High Efficiency 500mA Step-Down Voltage Regulator
See A/D Converters
Products
Products > Analog - Regulators > Simple Switchers > LM2674
LM2674 Product Folder
SIMPLE SWITCHER Power Converter High Efficiency 500mA Step-Down Voltage Regulator
See Also: LM2671 - Has Sync Pin and softstart, frequency synchronization.
Generic P/N 2674
General
Description Features Datasheet Package
& Models Samples
& Pricing Design
Tools Application
Notes
WEBENCH Live Simulation!
LM2674 Webench™ Custom
Design/Analyze/Build It
8.0 <=
V in Lower
V
<=
V in Upper
V
<= 40.0
V out 1.2 <= V<= 40.0
I out A<= 0.50
Ambient Temperature °C <= 100
What is Webench?
Parametric Table
Multiple Output Capability No
On/Off Pin Yes
Error Flag No
Input Voltage, min (Volt) 15, 6.50
Input Voltage, max (Volt) 40
Output Current, max 500 mA
Output Voltage (Volt) 12, 3.30, 5
Adjustable Output Voltage No, Yes
Switching Frequency (Hz) 260000
Adjustable Switching Frequency No
Sync Pin No
Efficiency (%) 94, 86, 90
Flyback No
Step-up No
Step-down Yes
-
Datasheet
Title Size in
Kbytes Date View Online Download Receive via
Email
LM2674 SIMPLE SWITCHER Power Converter High
Efficiency 500 mA Step-Down Voltage Regulator 494
Kbytes
10-
May-
01 View Online Download Receive via
Email
LM2674 SIMPLE SWITCHER Power Converter High
Efficiency 500 mA Step-Down Voltage Regulator
(JAPANESE)271
Kbytes
View Online
Download
Receive via
Email
file:///H|/imaging/BITTING/cpl/20020808_1/08062002_10/NATL/08062002_HTML/LM2674.html (1 of 5) [Aug-09-2002 2:45:35 PM]
11.0
13.0
3.3
0.40
30
Create This Design
National P/N LM2674 - SIMPLE SWITCHER Power Converter High Efficiency 500mA Step-Down Voltage Regulator
If you have trouble printing or viewing PDF file(s), see Printing Problems.
Package Availability, Models, Samples & Pricing
Part
Number
Package Status Models Samples &
Electronic
Orders
Budgetary
Pricing Std
Pack
Size
Package
Marking
Type Pins MSL SPICE IBIS Qty $US
each
LM2674LD-
12 LLP 16 MSL Full production N/A N/A
Samples
1K+ $1.2400 reel
of
1000
[logo]
¢U¢Z¢2¢T
S0009B
LM2674LD-
3.3 LLP 16 MSL Full production N/A N/A
Samples
1K+ $1.2400 reel
of
1000
[logo]
¢U¢Z¢2¢T
S000AB
LM2674LD-
5.0 LLP 16 MSL Full production N/A N/A
Samples
1K+ $1.2400 reel
of
1000
[logo]
¢U¢Z¢2¢T
S000BB
LM2674LD-
ADJ LLP 16 MSL Full production N/A N/A
Samples
1K+ $1.2400 reel
of
1000
[logo]
¢U¢Z¢2¢T
S000CB
LM2674LDX-
12 LLP 16 MSL Full production N/A N/A 1K+ $1.2400 reel
of
4500
[logo]
¢U¢Z¢2¢T
S0009B
LM2674LDX-
3.3 LLP 16 MSL Full production N/A N/A 1K+ $1.2400 reel
of
4500
[logo]
¢U¢Z¢2¢T
S000AB
LM2674LDX-
5.0 LLP 16 MSL Full production N/A N/A 1K+ $1.2400 reel
of
4500
[logo]
¢U¢Z¢2¢T
S000BB
LM2674LDX-
ADJ LLP 16 MSL Full production N/A N/A 1K+ $1.2400 reel
of
4500
[logo]
¢U¢Z¢2¢T
S000CB
LM2674M-12 SOIC
NARROW 8MSL Full production N/A N/A
24 Hour
Samples
Buy Now
1K+ $1.3900 rail
of
95
[logo]¢2¢T
2674
M-12
LM2674M-3.3 SOIC
NARROW 8MSL Full production N/A N/A
Samples
Buy Now
1K+ $1.3900 rail
of
95
[logo]¢2¢T
2674
M3.3
LM2674M-5.0 SOIC
NARROW 8MSL Full production N/A N/A
24 Hour
Samples
Buy Now
1K+ $1.3900 rail
of
95
[logo]¢2¢T
2674
M5.0
LM2674M-
ADJ SOIC
NARROW 8MSL Full production N/A N/A
24 Hour
Samples
Buy Now
1K+ $1.3900 rail
of
95
[logo]¢2¢T
2674
MADJ
LM2674MX-
12 SOIC
NARROW 8MSL Full production N/A N/A 1K+ $1.3900 reel
of
2500
[logo]¢2¢T
2674
M-12
LM2674MX-
3.3 SOIC
NARROW 8MSL Full production N/A N/A 1K+ $1.3900 reel
of
2500
[logo]¢2¢T
2674
M3.3
file:///H|/imaging/BITTING/cpl/20020808_1/08062002_10/NATL/08062002_HTML/LM2674.html (2 of 5) [Aug-09-2002 2:45:35 PM]
National P/N LM2674 - SIMPLE SWITCHER Power Converter High Efficiency 500mA Step-Down Voltage Regulator
LM2674MX-
5.0 SOIC
NARROW 8MSL Full production N/A N/A
Buy Now
1K+ $1.3900 reel
of
2500
[logo]¢2¢T
2674
M5.0
LM2674MX-
ADJ SOIC
NARROW 8MSL Full production N/A N/A
Buy Now
1K+ $1.3900 reel
of
2500
[logo]¢2¢T
2674
MADJ
LM2674N-12 MDIP 8MSL Full production N/A N/A
24 Hour
Samples
Buy Now
1K+ $1.3900 rail
of
40
[logo]¢U¢Z¢2¢T
LM2674
N-12
LM2674N-3.3 MDIP 8MSL Full production N/A N/A
24 Hour
Samples
Buy Now
1K+ $1.3900 rail
of
40
[logo]¢U¢Z¢2¢T
LM2674
N-3.3
LM2674N-5.0 MDIP 8MSL Full production N/A N/A
24 Hour
Samples
Buy Now
1K+ $1.3900 rail
of
40
[logo]¢U¢Z¢2¢T
LM2674
N-5.0
LM2674N-
ADJ MDIP 8MSL Full production N/A N/A
24 Hour
Samples
Buy Now
1K+ $1.3900 rail
of
40
[logo]¢U¢Z¢2¢T
LM2674
N-ADJ
LM2674-12
MDC Die Full production N/A N/A
Samples
gel
pak
of
N/A
-
LM2674-3.3
MDC Die Full
production N/A N/A
Samples
gel
pak
of
N/A
-
LM2674-5.0
MDC Die Full production N/A N/A
Samples
gel
pak
of
N/A
-
LM2674-ADJ
MDC Die Full production N/A N/A
Samples
gel
pak
of
N/A
-
LM2674-12
MWC Wafer Full production N/A N/A
wafer
jar
of
N/A
-
LM2674-3.3
MWC Wafer Full
production N/A N/A
wafer
jar
of
N/A
-
LM2674-5.0
MWC Wafer Full production N/A N/A
wafer
jar
of
N/A
-
LM2674-ADJ
MWC Wafer Full production N/A N/A
wafer
jar
of
N/A
-
General Description
file:///H|/imaging/BITTING/cpl/20020808_1/08062002_10/NATL/08062002_HTML/LM2674.html (3 of 5) [Aug-09-2002 2:45:35 PM]
National P/N LM2674 - SIMPLE SWITCHER Power Converter High Efficiency 500mA Step-Down Voltage Regulator
The LM2674 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
500 mA 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 LM2674 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 (>90%), the copper traces on the printed circuit board are the only heat sinking needed.
A family of standard inductors for use with the LM2674 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 ±1.5% tolerance on output 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 current. The output switch includes current limiting, as well as thermal shutdown for
full protection under fault conditions.
To simplify the LM2674 buck regulator design procedure, there exists computer design software, LM267X
Made Simple (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)
● 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
● Adjustable version output voltage range: 1.21V to 37V
● ±1.5% max output voltage tolerance over line and load conditions
● Guaranteed 500mA output load current
● 0.25 DMOS Output Switch
● Wide input voltage range: 8V to 40V
● 260 kHz fixed frequency internal oscillator
● TTL shutdown capability, low power standby mode
● Thermal shutdown and current limit protection
Applications
● Simple High Efficiency (>90%) Step-Down (Buck) Regulator
● Efficient Pre-Regulator for Linear Regulators
● Positive-to-Negative Converter
Design Tools
file:///H|/imaging/BITTING/cpl/20020808_1/08062002_10/NATL/08062002_HTML/LM2674.html (4 of 5) [Aug-09-2002 2:45:35 PM]
National P/N LM2674 - SIMPLE SWITCHER Power Converter High Efficiency 500mA Step-Down Voltage Regulator
Title Size in Kbytes Date View Online Download Receive via
Email
SimpleSwitcher® DC-DC
Converters Design Software 10 Kbytes 12-Jun-
2002 View
If you have trouble printing or viewing PDF file(s), see Printing Problems.
Application Notes
Title Size in Kbytes Date View Online Download Receive via Email
AN-1157: Application Note 1157
Positive to Negative Buck-Boost
Converter Using LM267X SIMPLE
SWITCHER® Regulators
152 Kbytes 8-Nov-00 View Online Download Receive via Email
AN-1229: Application Note 1229
SIMPLE SWITCHER PCB Layout
Guidelines 229 Kbytes 29-Jul-02 View Online Download Receive via Email
If you have trouble printing or viewing PDF file(s), see Printing Problems.
[Information as of 5-Aug-2002]
Search Design Purchasing Quality Company Home
About Languages . Website Guide . About "Cookies" . National is QS 9000 Certified . Privacy/Security Statement .
Contact Us . Site Terms & Conditions of Use . Copyright 2002 © National Semiconductor Corporation . My Preferences .
Feedback
file:///H|/imaging/BITTING/cpl/20020808_1/08062002_10/NATL/08062002_HTML/LM2674.html (5 of 5) [Aug-09-2002 2:45:35 PM]
