LM2672N-ADJ [NSC]
SIMPLE SWITCHER Power Converter High Efficiency 1A Step-Down Voltage Regulator with Features; SIMPLE SWITCHER电源转换器高效率1A降压型稳压器与特点型号: | LM2672N-ADJ |
厂家: | National Semiconductor |
描述: | SIMPLE SWITCHER Power Converter High Efficiency 1A Step-Down Voltage Regulator with Features |
文件: | 总25页 (文件大小:890K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
February 2005
LM2672
SIMPLE SWITCHER® Power Converter High Efficiency
1A Step-Down Voltage Regulator with Features
To simplify the LM2672 buck regulator design procedure,
there exists computer design software, LM267X Made
Simple version 1.0.
General Description
The LM2672 series of regulators are monolithic integrated
circuits built with a LMDMOS process. These regulators
provide all the active functions for a step-down (buck)
switching regulator, capable of driving a 1A load current with
excellent line and load regulation. These devices are avail-
able in fixed output voltages of 3.3V, 5.0V, 12V, and an
adjustable output version.
Features
n Efficiency up to 96%
n Available in SO-8 and 8-pin DIP packages
n Computer Design Software LM267X Made Simple
version 1.0
Requiring a minimum number of external components, these
regulators are simple to use and include patented internal
frequency compensation (Patent Nos. 5,382,918 and
5,514,947), fixed frequency oscillator, external shutdown,
soft-start, and frequency synchronization.
n Simple and easy to design with
n Requires only 5 external components
n Uses readily available standard inductors
n 3.3V, 5.0V, 12V, and adjustable output versions
n Adjustable version output voltage range: 1.21V to 37V
The LM2672 series operates at a switching frequency of
260 kHz, thus allowing smaller sized filter components than
what would be needed with lower frequency switching regu-
lators. Because of its very high efficiency ( 90%), the cop-
per traces on the printed circuit board are the only heat
sinking needed.
n
1.5% max output voltage tolerance over line and load
conditions
>
n Guaranteed 1A output load current
n 0.25Ω DMOS Output Switch
n Wide input voltage range: 8V to 40V
n 260 kHz fixed frequency internal oscillator
n TTL shutdown capability, low power standby mode
n Soft-start and frequency synchronization
n Thermal shutdown and current limit protection
A family of standard inductors for use with the LM2672 are
available from several different manufacturers. This feature
greatly simplifies the design of switch-mode power supplies
using these advanced ICs. Also included in the datasheet
are selector guides for diodes and capacitors designed to
work in switch-mode power supplies.
Typical Applications
Other features include a guaranteed 1.5% tolerance on
output voltage within specified input voltages and output
load conditions, and 10% on the oscillator frequency. Ex-
ternal shutdown is included, featuring typically 50 µA
stand-by current. The output switch includes current limiting,
as well as thermal shutdown for full protection under fault
conditions.
>
n Simple High Efficiency ( 90%) Step-Down (Buck)
Regulator
n Efficient Pre-Regulator for Linear Regulators
Typical Application (Fixed Output Voltage
Versions)
01293401
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation.
Windows® is a registered trademark of Microsoft Corporation.
© 2005 National Semiconductor Corporation
DS012934
www.national.com
Absolute Maximum Ratings (Note 1)
Storage Temperature Range
Lead Temperature
−65˚C to +150˚C
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
M Package
Vapor Phase (60s)
+215˚C
+220˚C
+260˚C
+150˚C
Supply Voltage
45V
−0.1V ≤ VSH ≤ 6V
−1V
Infrared (15s)
ON/OFF Pin Voltage
Switch Voltage to Ground
Boost Pin Voltage
N Package (Soldering, 10s)
Maximum Junction Temperature
VSW + 8V
Feedback Pin Voltage
ESD Susceptibility
−0.3V ≤ VFB ≤ 14V
Operating Ratings
Supply Voltage
6.5V to 40V
Human Body Model (Note 2)
Power Dissipation
2 kV
Temperature Range
−40˚C ≤ TJ ≤ +125˚C
Internally Limited
Electrical Characteristics Specifications with standard type face are for TJ = 25˚C, and those in bold type
face apply over full Operating Temperature Range.
LM2672-3.3
Symbol
Parameter
Conditions
Typical
Min
Max
Units
(Note 4)
(Note 5)
(Note 5)
SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)
VOUT
VOUT
η
Output Voltage
Output Voltage
Efficiency
VIN = 8V to 40V, ILOAD = 20 mA to 1A
VIN = 6.5V to 40V, ILOAD = 20 mA to 500 mA
VIN = 12V, ILOAD = 1A
3.3
3.3
86
3.251/3.201
3.251/3.201
3.350/3.399
3.350/3.399
V
V
%
LM2672-5.0
Symbol
Parameter
Conditions
Typical
Min
Max
Units
(Note 4)
(Note 5)
(Note 5)
SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)
VOUT
VOUT
η
Output Voltage
Output Voltage
Efficiency
VIN = 8V to 40V, ILOAD = 20 mA to 1A
VIN = 6.5V to 40V, ILOAD = 20 mA to 500 mA
VIN = 12V, ILOAD = 1A
5.0
5.0
90
4.925/4.850
4.925/4.850
5.075/5.150
5.075/5.150
V
V
%
LM2672-12
Symbol
Parameter
Conditions
Typical
Min
Max
Units
(Note 4)
(Note 5)
(Note 5)
SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)
VOUT
Output Voltage
Efficiency
VIN = 15V to 40V, ILOAD = 20 mA to 1A
VIN = 24V, ILOAD = 1A
12
94
11.82/11.64
12.18/12.36
V
η
%
LM2672-ADJ
Symbol
Parameter
Conditions
Typ
Min
Max
Units
(Note 4)
(Note 5)
(Note 5)
SYSTEM PARAMETERS Test Circuit Figure 3 (Note 3)
VFB
Feedback
Voltage
VIN = 8V to 40V, ILOAD = 20 mA to 1A
1.210
1.210
1.192/1.174
1.192/1.174
1.228/1.246
1.228/1.246
V
VOUT Programmed for 5V
(see Circuit of Figure 3)
VFB
Feedback
Voltage
VIN = 6.5V to 40V, ILOAD = 20 mA to 500 mA
V
VOUT Programmed for 5V
(see Circuit of Figure 3)
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2
LM2672-ADJ (Continued)
Symbol
Parameter
Conditions
Typ
(Note 4)
90
Min
Max
Units
(Note 5)
(Note 5)
η
Efficiency
VIN = 12V, ILOAD = 1A
%
All Output Voltage Versions
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those in 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
2.5
2.5
Min
Max
Units
DEVICE PARAMETERS
IQ
Quiescent Current
VFEEDBACK = 8V
3.6
mA
For 3.3V, 5.0V, and ADJ Versions
VFEEDBACK = 15V
mA
For 12V Versions
ISTBY
ICL
Standby Quiescent Current
Current Limit
ON/OFF Pin = 0V
50
1.55
1
100/150
2.1/2.2
25
µA
A
1.25/1.2
IL
Output Leakage Current
VIN = 40V, ON/OFF Pin = 0V
VSWITCH = 0V
µA
VSWITCH = −1V, ON/OFF Pin = 0V
ISWITCH = 1A
6
0.25
260
95
15
0.30/0.50
275
mA
Ω
RDS(ON) Switch On-Resistance
fO
D
Oscillator Frequency
Maximum Duty Cycle
Minimum Duty Cycle
Feedback Bias
Measured at Switch Pin
225
kHz
%
0
%
IBIAS
VS/D
VFEEDBACK = 1.3V
ADJ Version Only
85
nA
Current
ON/OFF Pin
1.4
0.8
7
2.0
37
V
Voltage Thesholds
ON/OFF Pin Current
Synchronization Frequency
Synchronization Threshold
Voltage
IS/D
ON/OFF Pin = 0V
20
µA
FSYNC
VSYNC
VSYNC = 3.5V, 50% duty cycle
400
kHz
1.4
V
VSS
ISS
Soft-Start Voltage
Soft-Start Current
Thermal Resistance
0.63
4.5
0.53
1.5
0.73
6.9
V
µA
θJA
N Package, Junction to Ambient (Note 6)
M Package, Junction to Ambient (Note 6)
95
˚C/W
105
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but device parameter specifications may not be guaranteed under these conditions. For guaranteed specifications and test conditions, see
the Electrical Characteristics.
Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.
Note 3: External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator
performance. When the LM2672 is used as shown in Figure 2 and Figure 3 test circuits, system performance will be as specified by the system parameters section
of the Electrical Characteristics.
Note 4: Typical numbers are at 25˚C and represent the most likely norm.
Note 5: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%
production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used
to calculate Average Outgoing Quality Level (AOQL).
Note 6: Junction to ambient thermal resistance with approximately 1 square inch of printed circuit board copper surrounding the leads. Additional copper area will
lower thermal resistance further. See Application Information section in the application note accompanying this datasheet and the thermal model in LM267X Made
Simple version 1.0 software.
3
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Connection Diagram
8-Lead Package
Top View
01293402
For Surface Mount Package
Order Number
LM2672M-3.3, LM2672M-5.0,
LM2672M-12 or LM2672M-ADJ
See NSC Package Number M08A
For DIP Package
Order Number
LM2672N-3.3, LM2672N-5.0,
LM2672N-12 or LM2672N-ADJ
See NSC Package Number N08E
Typical Performance Characteristics
Normalized
Output Voltage
Line Regulation
01293403
01293404
Drain-to-Source
Resistance
Efficiency
01293405
01293406
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4
Typical Performance Characteristics (Continued)
Operating
Switch Current Limit
Quiescent Current
01293407
01293408
01293410
01293412
Standby
Quiescent Current
ON/OFF Threshold
Voltage
01293409
ON/OFF Pin
Current (Sourcing)
Switching Frequency
01293411
5
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Typical Performance Characteristics (Continued)
Feedback Pin
Bias Current
Peak Switch Current
01293413
01293414
Dropout Voltage—3.3V Option
Dropout Voltage—5.0V Option
01293415
01293416
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6
Block Diagram
01293417
* Patent Number 5,514,947
†
Patent Number 5,382,918
FIGURE 1.
7
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Typical Performance Characteristics
(Circuit of Figure 2)
Continuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 1A
Discontinuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 300 mA
L = 47 µH, COUT = 68 µF, COUTESR = 50 mΩ
L = 15 µH, COUT = 68 µF (2x), COUTESR = 25 mΩ
01293418
01293419
A: V
Pin Voltage, 10 V/div.
A: V
Pin Voltage, 10 V/div.
SW
SW
B: Inductor Current, 0.5 A/div
B: Inductor Current, 0.5 A/div
C: Output Ripple Voltage, 20 mV/div AC-Coupled
C: Output Ripple Voltage, 20 mV/div AC-Coupled
Horizontal Time Base: 1 µs/div
Horizontal Time Base: 1 µs/div
Load Transient Response for Continuous Mode
VIN = 20V, VOUT = 5V, ILOAD = 1A
Load Transient Response for Discontinuous Mode
VIN = 20V, VOUT = 5V,
L = 47 µH, COUT = 68 µF, COUTESR = 50 mΩ
L = 47 µH, COUT = 68 µF, COUTESR = 50 mΩ
01293420
01293421
A: Output Voltage, 100 mV/div, AC-Coupled
A: Output Voltage, 100 mV/div, AC-Coupled
B: Load Current: 200 mA to 1A Load Pulse
B: Load Current: 100 mA to 300 mA Load Pulse
Horizontal Time Base: 50 µs/div
Horizontal Time Base: 200 µs/div
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8
Test Circuit and Layout Guidelines
01293422
C
C
- 22 µF, 50V Tantalum, Sprague “199D Series”
IN
- 47 µF, 25V Tantalum, Sprague “595D Series”
OUT
D1 - 3.3A, 50V Schottky Rectifier, IR 30WQ05F
L1 - 68 µH Sumida #RCR110D-680L
C
- 0.01 µF, 50V Ceramic
B
FIGURE 2. Standard Test Circuits and Layout Guides
Fixed Output Voltage Versions
9
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Test Circuit and Layout Guidelines (Continued)
01293423
C
C
- 22 µF, 50V Tantalum, Sprague “199D Series”
IN
- 47 µF, 25V Tantalum, Sprague “595D Series”
OUT
D1 - 3.3A, 50V Schottky Rectifier, IR 30WQ05F
L1 - 68 µH Sumida #RCR110D-680L
R1 - 1.5 kΩ, 1%
C
B
- 0.01 µF, 50V Ceramic
For a 5V output, select R2 to be 4.75 kΩ, 1%
where VREF = 1.21V
Use a 1% resistor for best stability.
FIGURE 3. Standard Test Circuits and Layout Guides
Adjustable Output Voltage Versions
LM2672 Series Buck Regulator
Design Procedure (Fixed Output)
PROCEDURE (Fixed Output Voltage Version)
To simplify the buck regulator design procedure, National
Semiconductor is making available computer design software to
be used with the SIMPLE SWITCHER line of switching
regulators. LM267X Made Simple version 1.0 is available on
Windows® 3.1, NT, or 95 operating systems.
EXAMPLE (Fixed Output Voltage Version)
Given:
Given:
VOUT = 5V
VOUT = Regulated Output Voltage (3.3V, 5V, or 12V)
V
IN(max) = Maximum DC Input Voltage
VIN(max) = 12V
ILOAD(max) = 1A
I
LOAD(max) = Maximum Load Current
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10
LM2672 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
PROCEDURE (Fixed Output Voltage Version)
1. Inductor Selection (L1)
EXAMPLE (Fixed Output Voltage Version)
1. Inductor Selection (L1)
A. Select the correct inductor value selection guide from Figure A. Use the inductor selection guide for the 5V version shown in
4 and Figure 5 or Figure 6 (output voltages of 3.3V, 5V, or 12V Figure 5.
respectively). For all other voltages, see the design procedure
for the adjustable version.
B. From the inductor value selection guide, identify the
inductance region intersected by the Maximum Input Voltage
line and the Maximum Load Current line. Each region is
identified by an inductance value and an inductor code (LXX).
C. Select an appropriate inductor from the four manufacturer’s
part numbers listed in Figure 8. Each manufacturer makes a
different style of inductor to allow flexibility in meeting various
design requirements. Listed below are some of the
differentiating characteristics of each manufacturer’s inductors:
Schott: ferrite EP core inductors; these have very low leakage
magnetic fields to reduce electro-magnetic interference (EMI)
and are the lowest power loss inductors
B. From the inductor value selection guide shown in Figure 5,
the inductance region intersected by the 12V horizontal line and
the 1A vertical line is 33 µH, and the inductor code is L23.
C. The inductance value required is 33 µH. From the table in
Figure 8, go to the L23 line and choose an inductor part number
from any of the four manufacturers shown. (In most instances,
both through hole and surface mount inductors are available.)
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 A. Use the 5.0V section in the output capacitor table in Figure
Figure 10. Using the output voltage and the inductance value
found in the inductor selection guide, step 1, locate the
appropriate capacitor value and voltage rating.
10. Choose a capacitor value and voltage rating from the line
that contains the inductance value of 33 µH. The capacitance
and voltage rating values corresponding to the 33 µH inductor
are the:
The capacitor list contains through-hole electrolytic capacitors
from four different capacitor manufacturers and surface mount
Surface Mount:
68 µF/10V Sprague 594D Series.
tantalum capacitors from two different capacitor manufacturers. 100 µF/10V AVX TPS Series.
It is recommended that both the manufacturers and the
manufacturer’s series that are listed in the table be used. A
table listing the manufacturers’ phone numbers is located in
Figure 11.
Through Hole:
68 µF/10V Sanyo OS-CON SA Series.
220 µF/35V Sanyo MV-GX Series.
220 µF/35V Nichicon PL Series.
220 µF/35V Panasonic HFQ Series.
11
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LM2672 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
PROCEDURE (Fixed Output Voltage Version)
3. Catch Diode Selection (D1)
EXAMPLE (Fixed Output Voltage Version)
3. Catch Diode Selection (D1)
A. In normal operation, the average current of the catch diode is A. Refer to the table shown in Figure 12. In this example, a 1A,
the load current times the catch diode duty cycle, 1-D (D is the 20V Schottky diode will provide the best performance. If the
switch duty cycle, which is approximately the output voltage
divided by the input voltage). The largest value of the catch
diode average current occurs at the maximum load current and
maximum input voltage (minimum D). For normal operation, the
catch diode current rating must be at least 1.3 times greater
than its maximum average current. However, if the power supply
design must withstand a continuous output short, the diode
should have a current rating equal to the maximum current limit
of the LM2672. The most stressful condition for this diode is a
shorted output condition.
circuit must withstand a continuous shorted output, a higher
current Schottky diode is recommended.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
C. Because of their fast switching speed and low forward
voltage drop, Schottky diodes provide the best performance and
efficiency. This Schottky diode must be located close to the
LM2672 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
The important parameters for the input capacitor are the input
voltage rating and the RMS current rating. With a maximum
transients from appearing at the input. This capacitor should be input voltage of 12V, an aluminum electrolytic capacitor with a
located close to the IC using short leads. In addition, the RMS voltage rating greater than 15V (1.25 x VIN) would be needed.
current rating of the input capacitor should be selected to be at The next higher capacitor voltage rating is 16V.
1
least ⁄
2
the DC load current. The capacitor manufacturer data
The RMS current rating requirement for the input capacitor in a
1
sheet must be checked to assure that this current rating is not
exceeded. The curves shown in Figure 14 show typical RMS
current ratings for several different aluminum electrolytic
capacitor values. A parallel connection of two or more
buck regulator is approximately
⁄ the DC load current. In this
2
example, with a 1A load, a capacitor with a RMS current rating
of at least 500 mA is needed. The curves shown in Figure 14
can be used to select an appropriate input capacitor. From the
capacitors may be required to increase the total minimum RMS curves, locate the 16V line and note which capacitor values
current rating to suit the application requirements. have RMS current ratings greater than 500 mA.
For an aluminum electrolytic capacitor, the voltage rating should For a through hole design, a 330 µF/16V electrolytic capacitor
be at least 1.25 times the maximum input voltage. Caution must (Panasonic HFQ series, Nichicon PL, Sanyo MV-GX series or
be exercised if solid tantalum capacitors are used. The tantalum equivalent) would be adequate. Other types or other
capacitor voltage rating should be twice the maximum input
voltage. The tables in Figure 15 show the recommended
application voltage for AVX TPS and Sprague 594D tantalum
capacitors. It is also recommended that they be surge current
manufacturers’ capacitors can be used provided the RMS ripple
current ratings are adequate. Additionally, for a complete
surface mount design, electrolytic capacitors such as the Sanyo
CV-C or CV-BS and the Nichicon WF or UR and the NIC
tested by the manufacturer. The TPS series available from AVX, Components NACZ series could be considered.
and the 593D and 594D series from Sprague are all surge For surface mount designs, solid tantalum capacitors can be
current tested. Another approach to minimize the surge current used, but caution must be exercised with regard to the capacitor
stresses on the input capacitor is to add a small inductor in
series with the input supply line.
surge current rating and voltage rating. In this example,
checking Figure 15, and the Sprague 594D series datasheet, a
Use caution when using ceramic capacitors for input bypassing, Sprague 594D 15 µF, 25V capacitor is adequate.
because it may cause severe ringing at the VIN pin.
5. Boost Capacitor (CB)
5. Boost Capacitor (CB)
This capacitor develops the necessary voltage to turn the switch For this application, and all applications, use a 0.01 µF, 50V
gate on fully. All applications should use a 0.01 µF, 50V ceramic ceramic capacitor.
capacitor.
6. Soft-Start Capacitor (CSS - optional)
6. Soft-Start Capacitor (CSS - optional)
This capacitor controls the rate at which the device starts up.
The formula for the soft-start capacitor CSS is:
For this application, selecting a start-up time of 10 ms and using
the formula for CSS results in a value of:
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12
LM2672 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
PROCEDURE (Fixed Output Voltage Version)
EXAMPLE (Fixed Output Voltage Version)
where:
ISS = Soft-Start Current :4.5 µA typical.
tSS = Soft-Start Time :Selected.
VSSTH = Soft-Start Threshold Voltage :0.63V typical.
VOUT = Output Voltage :Selected.
VSCHOTTKY = Schottky Diode Voltage Drop :0.4V typical.
VIN = Input Voltage :Selected.
If this feature is not desired, leave this pin open.
7. Frequency Synchronization (optional)
7. Frequency Synchronization (optional)
For all applications, use a 1 kΩ resistor and a 100 pF capacitor
for the RC filter.
The LM2672 (oscillator) can be synchronized to run with an
external oscillator, using the sync pin (pin 3). By doing so, the
LM2672 can be operated at higher frequencies than the
standard frequency of 260 kHz. This allows for a reduction in
the size of the inductor and output capacitor.
As shown in the drawing below, a signal applied to a RC filter at
the sync pin causes the device to synchronize to the frequency
of that signal. For a signal with a peak-to-peak amplitude of 3V
or greater, a 1 kΩ resistor and a 100 pF capacitor are suitable
values.
INDUCTOR VALUE SELECTION GUIDES (For
Continuous Mode Operation)
01293430
01293429
FIGURE 5. LM2672-5.0
FIGURE 4. LM2672-3.3
13
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LM2672 Series Buck Regulator
Design Procedure (Fixed Output)
(Continued)
01293432
FIGURE 7. LM2672-ADJ
01293431
FIGURE 6. LM2672-12
Schott
Renco
Through
Hole
Pulse Engineering
Coilcraft
Ind.
Ref.
Desg.
Inductance Current
Through
Hole
Surface
Mount
Surface
Mount
Through
Hole
Surface
Mount
Surface
Mount
(µH)
(A)
L4
68
47
0.32
0.37
0.44
0.52
0.32
0.39
0.48
0.58
0.70
0.83
0.99
0.55
0.66
0.82
0.99
1.17
1.40
1.70
1.00
1.20
1.47
1.78
67143940 67144310 RL-1284-68-43 RL1500-68 PE-53804 PE-53804-S DO1608-683
67148310 67148420 RL-1284-47-43 RL1500-47 PE-53805 PE-53805-S DO1608-473
67148320 67148430 RL-1284-33-43 RL1500-33 PE-53806 PE-53806-S DO1608-333
67148330 67148440 RL-1284-22-43 RL1500-22 PE-53807 PE-53807-S DO1608-223
L5
L6
33
L7
22
L9
220
150
100
68
67143960 67144330
67143970 67144340
67143980 67144350
67143990 67144360
67144000 67144380
RL-5470-3
RL-5470-4
RL-5470-5
RL-5470-6
RL-5470-7
RL1500-220 PE-53809 PE-53809-S DO3308-224
RL1500-150 PE-53810 PE-53810-S DO3308-154
RL1500-100 PE-53811 PE-53811-S DO3308-104
RL1500-68 PE-53812 PE-53812-S DO3308-683
RL1500-47 PE-53813 PE-53813-S DO3308-473
L10
L11
L12
L13
L14
L15
L18
L19
L20
L21
L22
L23
L24
L27
L28
L29
L30
47
33
67148340 67148450 RL-1284-33-43 RL1500-33 PE-53814 PE-53814-S DO3308-333
67148350 67148460 RL-1284-22-43 RL1500-22 PE-53815 PE-53815-S DO3308-223
22
220
150
100
68
67144040 67144420
67144050 67144430
67144060 67144440
67144070 67144450
67144080 67144460
67144090 67144470
RL-5471-2
RL-5471-3
RL-5471-4
RL-5471-5
RL-5471-6
RL-5471-7
RL1500-220 PE-53818 PE-53818-S DO3316-224
RL1500-150 PE-53819 PE-53819-S DO3316-154
RL1500-100 PE-53820 PE-53820-S DO3316-104
RL1500-68 PE-53821 PE-53821-S DO3316-683
47
—
—
—
—
—
—
—
PE-53822 PE-53822-S DO3316-473
PE-53823 PE-53823-S DO3316-333
PE-53824 PE-53824-S DO3316-223
PE-53827 PE-53827-S DO5022P-224
PE-53828 PE-53828-S DO5022P-154
PE-53829 PE-53829-S DO5022P-104
PE-53830 PE-53830-S DO5022P-683
33
22
67148370 67148480 RL-1283-22-43
220
150
100
68
67144110 67144490
67144120 67144500
67144130 67144510
67144140 67144520
RL-5471-2
RL-5471-3
RL-5471-4
RL-5471-5
FIGURE 8. Inductor Manufacturers’ Part Numbers
www.national.com
14
LM2672 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
Coilcraft Inc.
Phone (800) 322-2645
FAX (708) 639-1469
Phone +44 1236 730 595
FAX +44 1236 730 627
Phone (619) 674-8100
FAX (619) 674-8262
Phone +353 93 24 107
FAX +353 93 24 459
Phone (800) 645-5828
FAX (516) 586-5562
Phone (612) 475-1173
FAX (612) 475-1786
Coilcraft Inc., Europe
Pulse Engineering Inc.
Pulse Engineering Inc.,
Europe
Renco Electronics Inc.
Schott Corp.
FIGURE 9. Inductor Manufacturers’ Phone Numbers
Output Capacitor
Surface Mount
Sprague
Through Hole
Sanyo OS-CON Sanyo MV-GX
Output
Voltage
(V)
Inductance
(µH)
AVX TPS
Series
(µF/V)
100/10
100/10
100/10
100/10
100/10
100/10
100/10
10010
100/10
100/10
100/10
100/10
(2x) 68/20
68/20
Nichicon
PL Series
(µF/V)
Panasonic
HFQ Series
(µF/V)
594D Series
(µF/V)
120/6.3
120/6.3
68/10
SA Series
(µF/V)
100/10
68/10
Series
(µF/V)
330/35
220/35
150/35
120/35
120/35
120/35
330/35
220/35
150/35
120/35
120/35
120/35
330/35
220/35
150/35
120/35
120/35
120/35
120/35
22
33
330/35
220/35
150/35
120/35
120/35
120/35
330/35
220/35
150/35
120/35
120/35
120/35
330/35
220/35
150/35
120/35
120/35
120/35
120/35
330/35
220/35
150/35
120/35
120/35
120/35
330/35
220/35
150/35
120/35
120/35
120/35
330/35
220/35
150/35
120/35
120/35
120/35
120/35
47
68/10
3.3
5.0
68
120/6.3
120/6.3
120/6.3
100/16
68/10
100/10
100/10
100/10
100/10
68/10
100
150
22
33
47
68/10
68/10
68
100/16
100/16
100/16
120/20
68/25
100/10
100/10
100/10
68/20
100
150
22
33
68/20
47
47/20
68/20
47/20
12
68
47/20
68/20
47/20
100
150
220
47/20
68/20
47/20
47/20
68/20
47/20
47/20
68/20
47/20
FIGURE 10. Output Capacitor Table
15
www.national.com
LM2672 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
Nichicon Corp.
Panasonic
Phone
FAX
(847) 843-7500
(847) 843-2798
(714) 373-7857
(714) 373-7102
(803) 448-9411
(803) 448-1943
(207) 324-4140
(207) 324-7223
(619) 661-6322
(619) 661-1055
Phone
FAX
AVX Corp.
Phone
FAX
Sprague/Vishay
Sanyo Corp.
Phone
FAX
Phone
FAX
FIGURE 11. Capacitor Manufacturers’ Phone Numbers
1A Diodes
3A Diodes
VR
Surface
Through
Hole
Surface
Through
Hole
Mount
SK12
Mount
20V
30V
1N5817
SR102
1N5818
11DQ03
SR103
1N5819
11DQ04
SR104
SK32
1N5820
SR302
1N5821
31DQ03
B120
SK13
SK33
B130
30WQ03F
MBRS130
SK14
40V
SK34
1N5822
MBR340
31DQ04
SR304
B140
30BQ040
30WQ04F
MBRS340
MBRD340
MBRS140
10BQ040
10MQ040
15MQ040
SK15
50V
MBR150
11DQ05
SR105
SK35
MBR350
31DQ05
SR305
B150
30WQ05F
10BQ050
FIGURE 12. Schottky Diode Selection Table
International Rectifier Phone
(310) 322-3331
Corp.
FAX
(310) 322-3332
(800) 521-6274
(602) 244-6609
(516) 847-3000
Motorola, Inc.
Phone
FAX
General Instruments
Corp.
Phone
FAX
(516) 847-3236
(805) 446-4800
(805) 446-4850
Diodes, Inc.
Phone
FAX
FIGURE 13. Diode Manufacturers’ Phone Numbers
www.national.com
16
LM2672 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
01293433
FIGURE 14. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical)
AVX TPS
Recommended
Application Voltage
Voltage
Rating
+85˚C Rating
3.3
5
6.3
10
20
25
35
10
12
15
Sprague 594D
Recommended
Application Voltage
Voltage
Rating
+85˚C Rating
2.5
3.3
5
4
6.3
10
16
20
25
35
50
8
12
18
24
29
FIGURE 15. Recommended Application Voltage for AVX TPS and
Sprague 594D Tantalum Chip Capacitors Derated for 85˚C.
17
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LM2672 Series Buck Regulator
Design Procedure (Adjustable
Output)
PROCEDURE (Adjustable Output Voltage Version)
To simplify the buck regulator design procedure, National
Semiconductor is making available computer design software to
be used with the SIMPLE SWITCHER line of switching
regulators. LM267X Made Simple version 1.0 is available on
Windows 3.1, NT, or 95 operating systems.
Given:
EXAMPLE (Adjustable Output Voltage Version)
Given:
VOUT = 20V
VOUT = Regulated Output Voltage
V
IN(max) = Maximum Input Voltage
VIN(max) = 28V
I
LOAD(max) = Maximum Load Current
ILOAD(max) = 1A
F = Switching Frequency (Fixed at a nominal 260 kHz).
1. Programming Output Voltage (Selecting R1 and R2, as
shown in Figure 3)
F = Switching Frequency (Fixed at a nominal 260 kHz).
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
R2 = 1 kΩ (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.
resistor values minimize noise pickup in the sensitive feedback R2 = 15.4 kΩ.
pin. (For the lowest temperature coefficient and the best stability
with time, use 1% metal film resistors.)
2. Inductor Selection (L1)
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. ILOAD(max) = 1A
C. On the horizontal axis, select the maximum load current.
D. Identify the inductance region intersected by the E • T value D. From the inductor value selection guide shown in Figure 7,
and the Maximum Load Current value. Each region is identified the inductance region intersected by the 21.6 (V • µs) horizontal
by an inductance value and an inductor code (LXX).
line and the 1A vertical line is 68 µH, and the inductor code is
L30.
E. Select an appropriate inductor from the four manufacturer’s
E. From the table in Figure 8, locate line L30, and select an
part numbers listed in Figure 8. For information on the different inductor part number from the list of manufacturers’ part
types of inductors, see the inductor selection in the fixed output numbers.
voltage design procedure.
3. Output Capacitor SeIection (COUT
A. Select an output capacitor from the capacitor code selection A. Use the appropriate row of the capacitor code selection
guide in Figure 16. Using the inductance value found in the guide, in Figure 16. For this example, use the 15–20V row. The
)
3. Output Capacitor SeIection (COUT)
inductor selection guide, step 1, locate the appropriate capacitor capacitor code corresponding to an inductance of 68 µH is C20.
code corresponding to the desired output voltage.
www.national.com
18
LM2672 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
PROCEDURE (Adjustable Output Voltage Version)
B. Select an appropriate capacitor value and voltage rating,
using the capacitor code, from the output capacitor selection
EXAMPLE (Adjustable Output Voltage Version)
B. From the output capacitor selection table in Figure 17,
choose a capacitor value (and voltage rating) that intersects the
table in Figure 17. There are two solid tantalum (surface mount) capacitor code(s) selected in section A, C20.
capacitor manufacturers and four electrolytic (through hole)
The capacitance and voltage rating values corresponding to the
capacitor manufacturers to choose from. It is recommended that capacitor code C20 are the:
both the manufacturers and the manufacturer’s series that are
listed in the table be used. A table listing the manufacturers’
phone numbers is located in Figure 11.
Surface Mount:
33 µF/25V Sprague 594D Series.
33 µF/25V AVX TPS Series.
Through Hole:
33 µF/25V Sanyo OS-CON SC Series.
120 µF/35V Sanyo MV-GX Series.
120 µF/35V Nichicon PL Series.
120 µF/35V Panasonic HFQ Series.
Other manufacturers or other types of capacitors may also be
used, provided the capacitor specifications (especially the 100
kHz ESR) closely match the characteristics of the capacitors
listed in the output capacitor table. Refer to the capacitor
manufacturers’ data sheet for this information.
4. Catch Diode Selection (D1)
4. Catch Diode Selection (D1)
A. In normal operation, the average current of the catch diode is A. Refer to the table shown in Figure 12. Schottky diodes
the load current times the catch diode duty cycle, 1-D (D is the provide the best performance, and in this example a 1A, 40V
switch duty cycle, which is approximately VOUT/VIN). The largest Schottky diode would be a good choice. If the circuit must
value of the catch diode average current occurs at the maximum withstand a continuous shorted output, a higher current (at least
input voltage (minimum D). For normal operation, the catch
diode current rating must be at least 1.3 times greater than its
maximum average current. However, if the power supply design
must withstand a continuous output short, the diode should have
a current rating greater than the maximum current limit of the
LM2672. The most stressful condition for this diode is a shorted
output condition.
2.2A) 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
LM2672 using short leads and short printed circuit traces.
19
www.national.com
LM2672 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
PROCEDURE (Adjustable Output Voltage Version)
5. Input Capacitor (CIN
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
The important parameters for the input capacitor are the input
voltage rating and the RMS current rating. With a maximum
transients from appearing at the input. This capacitor should be input voltage of 28V, an aluminum electrolytic capacitor with a
located close to the IC using short leads. In addition, the RMS voltage rating of at least 35V (1.25 x VIN) would be needed.
current rating of the input capacitor should be selected to be at The RMS current rating requirement for the input capacitor in a
1
1
least ⁄
2
the DC load current. The capacitor manufacturer data
buck regulator is approximately ⁄ the DC load current. In this
2
sheet must be checked to assure that this current rating is not
exceeded. The curves shown in Figure 14 show typical RMS
current ratings for several different aluminum electrolytic
capacitor values. A parallel connection of two or more
example, with a 1A load, a capacitor with a RMS current rating
of at least 500 mA is needed. The curves shown in Figure 14
can be used to select an appropriate input capacitor. From the
curves, locate the 35V line and note which capacitor values
capacitors may be required to increase the total minimum RMS have RMS current ratings greater than 500 mA.
current rating to suit the application requirements. For a through hole design, a 330 µF/35V electrolytic capacitor
For an aluminum electrolytic capacitor, the voltage rating should (Panasonic HFQ series, Nichicon PL, Sanyo MV-GX series or
be at least 1.25 times the maximum input voltage. Caution must equivalent) would be adequate. Other types or other
be exercised if solid tantalum capacitors are used. The tantalum manufacturers’ capacitors can be used provided the RMS ripple
capacitor voltage rating should be twice the maximum input
voltage. The tables in Figure 15 show the recommended
application voltage for AVX TPS and Sprague 594D tantalum
capacitors. It is also recommended that they be surge current
current ratings are adequate. Additionally, for a complete
surface mount design, electrolytic capacitors such as the Sanyo
CV-C or CV-BS and the Nichicon WF or UR and the NIC
Components NACZ series could be considered.
tested by the manufacturer. The TPS series available from AVX, For surface mount designs, solid tantalum capacitors can be
and the 593D and 594D series from Sprague are all surge used, but caution must be exercised with regard to the capacitor
current tested. Another approach to minimize the surge current surge current rating and voltage rating. In this example,
stresses on the input capacitor is to add a small inductor in
series with the input supply line.
checking Figure 15, and the Sprague 594D series datasheet, a
Sprague 594D 15 µF, 50V capacitor is adequate.
Use caution when using ceramic capacitors for input bypassing,
because it may cause severe ringing at the VIN pin.
6. Boost Capacitor (CB)
6. Boost Capacitor (CB)
This capacitor develops the necessary voltage to turn the switch For this application, and all applications, use a 0.01 µF, 50V
gate on fully. All applications should use a 0.01 µF, 50V ceramic ceramic capacitor.
capacitor.
If the soft-start and frequency synchronization features are
desired, look at steps 6 and 7 in the fixed output design
procedure.
Inductance (µH)
Case
Output
Style (Note 7)
Voltage (V)
22
—
33
—
47
—
68
—
100
C1
150
C2
220
C3
SM and TH
SM and TH
SM and TH
SM and TH
SM and TH
SM and TH
SM and TH
SM and TH
SM and TH
SM and TH
TH
1.21–2.50
2.50–3.75
3.75–5.0
5.0–6.25
6.25–7.5
7.5–10.0
10.0–12.5
12.5–15.0
15.0–20.0
20.0–30.0
30.0–37.0
—
—
—
C1
C2
C3
C3
—
—
C4
C5
C6
C6
C6
—
C4
C7
C6
C6
C6
C6
C8
C4
C7
C6
C6
C6
C6
C9
C10
C11
C16
C19
C22
C24
C11
C12
C17
C20
C22
C24
C12
C12
C17
C20
C22
C25
C13
C13
C17
C20
C22
C25
C13
C13
C17
C20
C22
C25
C13
C13
C17
C20
C22
C25
C14
C15
C18
C21
C23
Note 7: SM - Surface Mount, TH - Through Hole
FIGURE 16. Capacitor Code Selection Guide
www.national.com
20
LM2672 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
Output Capacitor
Surface Mount
Through Hole
Sanyo MV-GX
Cap.
Ref.
Desg.
#
Sprague
AVX TPS
Series
(µF/V)
Sanyo OS-CON
SA Series
(µF/V)
Nichicon
PL Series
(µF/V)
Panasonic
HFQ Series
(µF/V)
594D Series
(µF/V)
120/6.3
120/6.3
120/6.3
68/10
Series
(µF/V)
220/35
150/35
120/35
220/35
150/35
120/35
150/35
330/35
330/35
220/35
150/35
120/35
120/35
220/35
220/35
150/35
120/35
220/35
150/35
120/35
150/35
120/35
220/50
150/50
150/50
C1
C2
100/10
100/10
100/10
100/10
100/10
100/10
100/10
100/10
100/16
100/16
100/16
100/16
100/16
100/16
68/20
100/10
220/35
150/35
120/35
220/35
150/35
120/35
150/35
330/35
330/35
220/35
150/35
120/35
120/35
220/35
220/35
150/35
120/35
220/35
150/35
120/35
150/35
120/35
100/50
100/50
82/50
220/35
150/35
120/35
220/35
150/35
120/35
150/35
330/35
330/35
220/35
150/35
120/35
120/35
220/35
220/35
150/35
120/35
220/35
150/35
120/35
150/35
120/35
120/50
120/50
82/50
100/10
C3
100/35
C4
68/10
C5
100/16
100/16
68/10
100/10
C6
100/10
C7
68/10
C8
100/16
100/16
100/16
100/16
100/16
100/16
100/16
47/20
100/10
C9
100/16
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
68/16
68/16
68/16
100/16
100/16
47/20
47/20
68/20
47/20
47/20
68/20
47/20
68/25
(2x) 33/25
33/25
47/25 (Note 8)
33/25 (Note 8)
33/25 (Note 8)
(Note 9)
(Note 9)
(Note 9)
(Note 9)
(Note 9)
33/25
33/25
33/25
33/35
(2x) 22/25
22/35
33/35
(Note 9)
(Note 9)
(Note 9)
(Note 9)
(Note 9)
(Note 9)
Note 8: The SC series of Os-Con capacitors (others are SA series)
Note 9: The voltage ratings of the surface mount tantalum chip and Os-Con capacitors are too low to work at these voltages.
FIGURE 17. Output Capacitor Selection Table
21
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Application Information
TYPICAL SURFACE MOUNT PC BOARD LAYOUT,
FIXED OUTPUT (4X SIZE)
01293439
C
C
- 15 µF, 50V, Solid Tantalum Sprague, “594D series”
IN
- 68 µF, 16V, Solid Tantalum Sprague, “594D series”
OUT
D1 - 1A, 40V Schottky Rectifier, Surface Mount
L1 - 33 µH, L23, Coilcraft DO3316
C
B
- 0.01 µF, 50V, Ceramic
TYPICAL SURFACE MOUNT PC BOARD LAYOUT,
ADJUSTABLE OUTPUT (4X SIZE)
01293440
C
C
- 15 µF, 50V, Solid Tantalum Sprague, “594D series”
IN
- 33 µF, 25V, Solid Tantalum Sprague, “594D series”
OUT
D1 - 1A, 40V Schottky Rectifier, Surface Mount
L1 - 68 µH, L30, Coilcraft DO3316
C
B
- 0.01 µF, 50V, Ceramic
R1 - 1k, 1%
R2 - Use formula in Design Procedure
FIGURE 18. PC Board Layout
Layout is very important in switching regulator designs. Rap-
idly switching currents associated with wiring inductance can
generate voltage transients which can cause problems. For
minimal inductance and ground loops, the wires indicated by
heavy lines (in Figure 2 and Figure 3) should be wide
printed circuit traces and should be kept as short as
possible. For best results, external components should be
located as close to the switcher IC as possible using ground
plane construction or single point grounding.
If open core inductors are used, special care must be
taken as to the location and positioning of this type of induc-
tor. Allowing the inductor flux to intersect sensitive feedback,
IC ground path, and COUT wiring can cause problems.
www.national.com
22
associated wiring. Physically locate both resistors near the
IC, and route the wiring away from the inductor, especially an
open core type of inductor.
Application Information (Continued)
When using the adjustable version, special care must be
taken as to the location of the feedback resistors and the
23
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Physical Dimensions inches (millimeters)
unless otherwise noted
8-Lead (0.150" Wide) Molded Small Outline Package, JEDEC
Order Number LM2672M-3.3, LM2672M-5.0,
LM2672M-12 or LM2672M-ADJ
NS Package Number M08A
www.national.com
24
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
8-Lead (0.300" Wide) Molded Dual-In-Line Package
Order Number LM2672N-3.3, LM2672N-5.0,
LM2672N-12 or LM2672N-ADJ
NS Package Number N08E
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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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.
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Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain
no ‘‘Banned Substances’’ as defined in CSP-9-111S2.
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NSC
LM2673LD-12
IC 5.4 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, PDSO14, LLP-14, Switching Regulator or Controller
NSC
LM2673LD-3.3
IC 5.4 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, PDSO14, LLP-14, Switching Regulator or Controller
NSC
LM2673LDX-3.3
IC 5.4 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, PDSO14, LLP-14, Switching Regulator or Controller
NSC
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