LM2674 Datasheet by Texas Instruments

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ITEXAS INSTRUMENTS FB W V LM2674-5.0 v 8‘! w W ‘" v 53‘” cIN 9 ON/O_FF GND 5w 500 mA may i ' J.
LM2674
February 15, 2012
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 pro-
vide all the active functions for a step-down (buck) switching
regulator, capable of driving a 500 mA load current with ex-
cellent 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 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 out-
put voltage within specified input voltages and output load
conditions, and ±10% on the oscillator frequency. External
shutdown is included, featuring typically 50 μA stand-by cur-
rent. The output switch includes current limiting, as well as
thermal shutdown for full protection under fault conditions.
To simplify the LM2674 buck regulator design procedure,
there exists computer design software, LM267X Made Sim-
ple (version 6.0).
Features
Efficiency up to 96%
Available in SO-8, 8-pin DIP and LLP packages
Computer Design Software LM267X Made Simple
(version 6.0)
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
0.25Ω 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
Typical Applications
Simple High Efficiency (>90%) Step-Down (Buck)
Regulator
Efficient Pre-Regulator for Linear Regulators
Positive-to-Negative Converter
Typical Application
10004101
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation
Windows® is a registered trademark of Microsoft Corporation.
© 2012 Texas Instruments Incorporated 100041 SNVS007E www.ti.com
LM2674 SIMPLE SWITCHER Power Converter High Efficiency 500 mA Step-Down Voltage
Regulator
‘ No Connecuons "Connectlo Pins 11. 12 an PCB ON/OFF a vsw 7 w 6 mu 5 arm?
Connection Diagrams
16-Lead LLP Surface Mount Package
Top View
10004138
LLP Package
See NSC Package Drawing Number LDA16A
8-Lead Package
Top View
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
3.3 LM2674LD-3.3 S000AB 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
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
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LM2674
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for
availability and specifications.
Supply Voltage 45V
ON/OFF Pin Voltage −0.1V VSH 6V
Switch Voltage to Ground −1V
Boost Pin Voltage VSW + 8V
Feedback Pin Voltage −0.3V VFB 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
LM2674-3.3 Specifications with standard type face are for TJ = 25°C, and those with bold type face apply over full
Operating Temperature Range.
Symbol Parameter Conditions Typical
(Note 4)
Min
(Note 5)
Max
(Note 5)Units
SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)
VOUT Output Voltage VIN = 8V to 40V, ILOAD = 20 mA to 500 mA 3.3 3.251/3.201 3.350/3.399 V
VOUT Output Voltage VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA 3.3 3.251/3.201 3.350/3.399 V
ηEfficiency VIN = 12V, ILOAD = 500 mA 86 %
LM2674-5.0
Symbol Parameter Conditions Typical
(Note 4)
Min
(Note 5)
Max
(Note 5)Units
SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)
VOUT Output Voltage VIN = 8V to 40V, ILOAD = 20 mA to 500 mA 5.0 4.925/4.850 5.075/5.150 V
VOUT Output Voltage VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA 5.0 4.925/4.850 5.075/5.150 V
ηEfficiency VIN = 12V, ILOAD = 500 mA 90 %
LM2674-12
Symbol Parameter Conditions Typical
(Note 4)
Min
(Note 5)
Max
(Note 5)Units
SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)
VOUT Output Voltage VIN = 15V to 40V, ILOAD = 20 mA to 500 mA 12 11.82/11.64 12.18/12.36 V
ηEfficiency VIN = 24V, ILOAD = 500 mA 94 %
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LM2674
LM2674-ADJ
Symbol Parameter Conditions Typ
(Note 4)
Min
(Note 5)
Max
(Note 5)Units
SYSTEM PARAMETERS Test Circuit Figure 3 (Note 3)
VFB Feedback Voltage VIN = 8V to 40V, ILOAD = 20 mA to 500 mA
VOUT Programmed for 5V
(see Circuit of Figure 3)
1.210 1.192/1.174 1.228/1.246 V
VFB Feedback Voltage VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA
VOUT Programmed for 5V
(see Circuit of Figure 3)
1.210 1.192/1.174 1.228/1.246 V
ηEfficiency VIN = 12V, ILOAD = 500 mA 90 %
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, VIN = 12V for the 3.3V, 5V, and Adjustable versions and VIN = 24V for the 12V version, and
ILOAD = 100 mA.
Symbol Parameters Conditions Typ Min Max Units
DEVICE PARAMETERS
IQQuiescent Current VFEEDBACK = 8V 2.5 3.6 mA
For 3.3V, 5.0V, and ADJ Versions
VFEEDBACK = 15V 2.5 mA
For 12V Versions
ISTBY Standby Quiescent Current ON/OFF Pin = 0V 50 100/150 μA
ICL Current Limit 0.8 0.62/0.575 1.2/1.25 A
ILOutput Leakage Current VIN = 40V, ON/OFF Pin = 0V
VSWITCH = 0V 1 25 μA
VSWITCH = −1V, ON/OFF Pin = 0V 6 15 mA
RDS(ON) Switch On-Resistance ISWITCH = 500 mA 0.25 0.40/0.60 Ω
fOOscillator Frequency Measured at Switch Pin 260 225 275 kHz
D Maximum Duty Cycle 95 %
Minimum Duty Cycle 0 %
IBIAS Feedback Bias
Current
VFEEDBACK = 1.3V
ADJ Version Only 85 nA
VS/D ON/OFF Pin
Voltage Theshold Turn-On Threshold, Rising (Note 7) 1.4 0.8 2.0 V
IS/D ON/OFF Pin Current ON/OFF Pin = 0V 20 7 37 μA
θJA 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 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 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.
Note 7: The ON/OFF pin is internally pulled up to 7V and can be left floating for always-on operation.
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LM2674
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Typical Performance Characteristics
Normalized
Output Voltage
10004103
Line Regulation
10004104
Efficiency
10004105
Drain-to-Source
Resistance
10004106
Switch Current Limit
10004107
Operating
Quiescent Current
10004108
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LM2674
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Standby
Quiescent Current
10004109
ON/OFF Threshold
Voltage
10004110
ON/OFF Pin
Current (Sourcing)
10004111
Switching Frequency
10004112
Feedback Pin
Bias Current
10004113
Peak Switch Current
10004114
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LM2674
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Dropout Voltage—3.3V Option
10004115
Dropout Voltage—5.0V Option
10004116
Typical Performance Characteristics (Circuit of Figure 2)
Continuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 500 mA
L = 100 μH, COUT = 100 μF, COUTESR = 0.1Ω
10004118
A: VSW Pin Voltage, 10 V/div.
B: Inductor Current, 0.2 A/div
C: Output Ripple Voltage, 50 mV/div AC-Coupled
Horizontal Time Base: 1 μs/div
Discontinuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 300 mA
L = 15 μH, COUT = 68 μF (2×), COUTESR = 25 mΩ
10004119
A: VSW Pin 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
VIN = 20V, VOUT = 5V,
L = 100 μH, COUT = 100 μF, COUTESR = 0.1Ω
10004120
A: Output Voltage, 100 mV/div, AC-Coupled.
B: Load Current: 100 mA to 500 mA Load Pulse
Horizontal Time Base: 50 μs/div
Load Transient Response for Discontinuous Mode
VIN = 20V, VOUT = 5V,
L = 47 μH, COUT = 68 μF, COUTESR = 50 mΩ
10004121
A: Output Voltage, 100 mV/div, AC-Coupled.
B: Load Current: 100 mA to 400 mA Load Pulse
Horizontal Time Base: 200 μs/div
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LM2674
FEEDBACKE" :st Cam sun — "gm" ‘— Gcnlramr ‘— ‘— 4— UP ON/OFF ’- 7v [name _ _ mm mm 3 2V 05mm» m“. *5st: DW— snnnA caoovsww Swflch \ Drwuv :'_ gl— PWM |_‘ |_‘ eammmu I v [nab‘e SWIYCH ’ Gm] 'r" l Unregnland DC mm , l runam LM237N mm mm DUTPUI Hm, Unes |_. GND m mm a: Keol 5mm And Use Gmund Phne Conschhon For am mm; Keep mama «mg m, From mama: flu ngulahd 0mm
Block Diagram
10004117
* Active Inductor Patent Number 5,514,947
† Active Capacitor Patent Number 5,382,918
FIGURE 1.
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
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LM2674
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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%
CB - 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
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LM2674
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:
VOUT = Regulated Output Voltage (3.3V, 5V, or 12V) VOUT = 5V
VIN(max) = Maximum DC Input Voltage VIN(max) = 12V
ILOAD(max) = Maximum Load Current ILOAD(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 (COUT) 2. Output Capacitor Selection (COUT)
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:
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LM2674
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 (CIN) 4. Input Capacitor (CIN)
A low ESR aluminum or tantalum bypass capacitor is needed
between the input pin and ground to prevent large voltage
transients from appearing at the input. This capacitor should be
located close to the IC using short leads. In addition, the RMS
current rating of the input capacitor should be selected to be at least
½ the DC load current. The capacitor manufacturer data sheet must
be checked to assure that this current rating is not exceeded. The
curves shown in Figure 14 show typical RMS current ratings for
several different aluminum electrolytic capacitor values. A parallel
connection of two or more capacitors may be required to increase
the total minimum RMS current rating to suit the application
requirements.
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 only ceramic capacitors for input
bypassing, because it may cause severe ringing at the VIN 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 × VIN) would be needed. The next
higher capacitor voltage rating is 16V.
The RMS current rating requirement for the input capacitor in a
buck regulator is approximately ½ the DC load current. In this
example, with a 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.
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LM2674
PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)
5. Boost Capacitor (CB) 5. Boost Capacitor (CB)
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.
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LM2674
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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
Ind.
Ref.
Desg.
Inducta
nce
(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
13 www.ti.com
LM2674
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
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 (2×) 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
www.ti.com 14
LM2674
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
VR
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
15 www.ti.com
LM2674
CAPACWOR cumw RAYING @‘Dsnc (PMS MA) men 900 800 700 sea 500 we 300 200 we 0 no ur 220 “F I50 ,‘r mam 62 ,‘r maan w ms»: 10 20 30 40 5:: so CAPkCITO? VOLTAGE RAIING (v) 7a
10004130
FIGURE 14. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical)
AVX TPS
Recommended Voltage
Application Voltage Rating
+85°C Rating
3.3 6.3
5 10
10 20
12 25
15 35
Sprague 594D
Recommended Voltage
Application Voltage Rating
+85°C Rating
2.5 4
3.3 6.3
5 10
8 16
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.
www.ti.com 16
LM2674
R2 Vour ' VREr (1 * E [.T=(za-2o—o.25). E~ T= (7. 75)~ VOUI VREF 2203 255 )=‘kn (32°va ZDHJ‘S 23-02905 ) 1—000 2—60 (V #5) 3.35( (v Ms)= 215 (Vus)
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:
VOUT = Regulated Output Voltage VOUT = 20V
VIN(max) = Maximum Input Voltage VIN(max) = 28V
ILOAD(max) = Maximum Load Current ILOAD(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 R1 and R2, as shown
in Figure 3)
1. Programming Output Voltage (Selecting R1 and R2, as shown
in Figure 3)
Use the following formula to select the appropriate resistor values. Select R1 to be 1 kΩ, 1%. Solve for R2.
where VREF = 1.21V
Select a value for R1 between 240Ω and 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.)
R2 = 1k (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.
R2 = 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 VSAT=internal switch saturation voltage=0.25V and VD =
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. ILOAD(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 (COUT) 3. Output Capacitor SeIection (COUT)
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.
17 www.ti.com
LM2674
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 VOUT/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
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.
www.ti.com 18
LM2674
PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)
5. Input Capacitor (CIN)
A low ESR aluminum or tantalum bypass capacitor is needed
between the input pin and ground to prevent large voltage
transients from appearing at the input. This capacitor should be
located close to the IC using short leads. In addition, the RMS
current rating of the input capacitor should be selected to be at least
½ the DC load current. The capacitor manufacturer data sheet must
be checked to assure that this current rating is not exceeded. The
curves shown in Figure 14 show typical RMS current ratings for
several different aluminum electrolytic capacitor values. A parallel
connection of two or more capacitors may be required to increase
the total minimum RMS current rating to suit the application
requirements.
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 only ceramic capacitors for input
bypassing, because it may cause severe ringing at the VIN pin.
5. Input Capacitor (CIN)
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 × VIN) would be needed.
The RMS current rating requirement for the input capacitor in a
buck regulator is approximately ½ the DC load current. In this
example, with a 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 (CB) 6. Boost Capacitor (CB)
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 8)
Output
Voltage (V)
Inductance (μH)
22 33 47 68 100 150 220
SM and TH 1.21–2.50 ————C1 C2 C3
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 8: SM - Surface Mount, TH - Through Hole
FIGURE 16. Capacitor Code Selection Guide
19 www.ti.com
LM2674
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 (2×) 33/25 47/25 (Note 9) 220/35 220/35 220/35
C19 33/25 33/25 33/25 (Note 9) 150/35 150/35 150/35
C20 33/25 33/25 33/25 (Note 9) 120/35 120/35 120/35
C21 33/35 (2×) 22/25 (Note 10) 150/35 150/35 150/35
C22 33/35 22/35 (Note 10) 120/35 120/35 120/35
C23 (Note 10) (Note 10) (Note 10) 220/50 100/50 120/50
C24 (Note 10) (Note 10) (Note 10) 150/50 100/50 120/50
C25 (Note 10) (Note 10) (Note 10) 150/50 82/50 82/50
Note 9: The SC series of Os-Con capacitors (others are SA series)
Note 10: 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
www.ti.com 20
LM2674
+ nclnpm VaMage Regu‘aled cuxput VoMage + + DClnput VoHage Regu‘aisd Ou‘pm Vouage +
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
21 www.ti.com
LM2674
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 pos-
sible. For best results, external components should be locat-
ed 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. Al-
lowing the inductor flux to intersect sensitive feedback, IC
ground path, and COUT wiring can cause problems.
When using the adjustable version, special care must be tak-
en as to the location of the feedback resistors and the asso-
ciated 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.
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.ti.com 22
LM2674
4 am x m: om m! "mum mm A, Honuwn ax mu: m: U m m) m) m n IEIHFIH 510 x 2,5: we} uxw sxnzaofi} a w n nan Cr] ‘ M3: ozunl e um nomw®m oourxouwa mum muss w pmnmans >4 k ax n7 2 x m 1F wmgafi uk‘ xmomzunm mm "mm wx n 2' a so .1, ”I" ”H mm um I 0r , mm m z u u \ (m: acm‘ x H[n1.n 5m 5 wummx m INCNIS w wmm om MflsAlRev w
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
23 www.ti.com
LM2674
um man (1.215] a [7| m El nuauaaas [D 513:“ I21! m m (6'25: my mum nnsmfi ~> n «1,112; M'" , x n m nmoiaam "NED «— _ ._ a g I ‘ I _’ (LEI—MIR] ¢ 2“ 1‘—’|/ "I!“ + ¢ \ mutums “minim; thr 1‘ _ uIzs—n m f (“15— 5561 am an 1‘ - M J.I7§ “ ) l" 50') [union-17’ « ‘nu I "F mu +0 mu mm mun nus 0.125 _ n m (qu7 :0 ms) + —+1an ‘_ omnnm (‘ ‘55 41,331) 7—11 swam) unlsgnnli mains.“ ‘7 am 11050 ”.52" “11“] Nani (is. s m 13 e) ' a 2. usx o u]: . ”u 0 25,4 L— l D‘MENSIONS ARE IN M‘LLIMETERS «me v s’ nzcommzwnzn LAND nwzwu 1 , mm wnu m sow” ms 0 a m m u wnEx AREA (0 2. 5:0 I Pm): 32:01 m a 5:11 1 ms. mu m
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
16-Lead LLP Surface Mount Package
NS Package Number LDA16A
www.ti.com 24
LM2674
25 www.ti.com
LM2674
Notes
LM2674 SIMPLE SWITCHER Power Converter High Efficiency 500 mA Step-Down Voltage
Regulator
www.ti.com
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