LM2673SDX-ADJ [NSC]
SIMPLE SWITCHER 3A Step-Down Voltage Regulator with Adjustable Current Limit; SIMPLE SWITCHER 3A降压型稳压器具有可调电流限制
| 型号： | LM2673SDX-ADJ |
| 厂家： | 
National Semiconductor |
| 描述： | SIMPLE SWITCHER 3A Step-Down Voltage Regulator with Adjustable Current Limit |
| 文件： | 总27页 (文件大小：433K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
October 2003
LM2673
SIMPLE SWITCHER® 3A Step-Down Voltage Regulator
with Adjustable Current Limit
General Description
Features
n Efficiency up to 94%
The LM2673 series of regulators are monolithic integrated
circuits which provide all of the active functions for a step-
down (buck) switching regulator capable of driving up to 3A
loads with excellent line and load regulation characteristics.
n Simple and easy to design with (using off-the-shelf
external components)
n
Resistor programmable peak current limit over a range
of 2A to 5A.
>
High efficiency ( 90%) is obtained through the use of a low
ON-resistance DMOS power switch. The series consists of
fixed output voltages of 3.3V, 5V and 12V and an adjustable
output version.
n 150 mΩ DMOS output switch
n 3.3V, 5V and 12V fixed output and adjustable (1.2V to
37V ) versions
The SIMPLE SWITCHER concept provides for a complete
design using a minimum number of external components. A
high fixed frequency oscillator (260KHz) allows the use of
physically smaller sized components. A family of standard
inductors for use with the LM2673 are available from several
manufacturers to greatly simplify the design process.
n
2%maximum output tolerance over full line and load
conditions
n Wide input voltage range: 8V to 40V
n 260 KHz fixed frequency internal oscillator
n Softstart capability
n −40 to +125˚C operating junction temperature range
Other features include the ability to reduce the input surge
current at power-ON by adding a softstart timing capacitor to
gradually turn on the regulator. The LM2673 series also has
built in thermal shutdown and resistor programmable current
limit of the power MOSFET switch to protect the device and
load circuitry under fault conditions. The output voltage is
guaranteed to a 2% tolerance. The clock frequency is
controlled to within a 11% tolerance.
Applications
>
n Simple to design, high efficiency ( 90%) step-down
switching regulators
n Efficient system pre-regulator for linear voltage
regulators
n Battery chargers
Typical Application
10091303
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation.
© 2003 National Semiconductor Corporation
DS100913
www.national.com
Connection Diagrams and Ordering Information
TO-263 Package
Top View
TO-220 Package
Top View
10091301
Order Number
10091302
Order Number
LM2673S-3.3, LM2673S-5.0,
LM2673S-12 or LM2673S-ADJ
LM2673T-3.3, LM2673T-5.0,
LM2673T-12 or LM2673T-ADJ
See NSC Package Number TS7B
See NSC Package Number TA07B
Top View
10091335
LLP-14
See NS package Number SRC14A
Ordering Information for LLP Package
Output Voltage
Order Information
Package Marking
Supplied As
250 Units on Tape and Reel
2500 Units on Tape and Reel
250 Units on Tape and Reel
2500 Units on Tape and Reel
250 Units on Tape and Reel
2500 Units on Tape and Reel
250 Units on Tape and Reel
2500 Units on Tape and Reel
12
12
LM2673SD-12
S0002SB
LM2673SDX-12
LM2673SD-3.3
LM2673SDX-3.3
LM2673SD-5.0
LM2673SDX-5.0
LM2673SD-ADJ
LM2673SDX-ADJ
S0002SB
3.3
3.3
5.0
5.0
ADJ
ADJ
S0002TB
S0002TB
S0002UB
S0002UB
S0002VB
S0002VB
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2
Absolute Maximum Ratings (Note 1)
Storage Temperature Range
Soldering Temperature
Wave
−65˚C to 150˚C
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
4 sec, 260˚C
10 sec, 240˚C
75 sec, 219˚C
Infrared
Input Supply Voltage
Softstart Pin Voltage
Switch Voltage to Ground
Boost Pin Voltage
45V
−0.1V to 6V
−1V to VIN
Vapor Phase
Operating Ratings
VSW + 8V
Supply Voltage
8V to 40V
Feedback Pin Voltage
Power Dissipation
ESD (Note 2)
−0.3V to 14V
Internally Limited
2 kV
Junction Temperature Range (TJ)
−40˚C to 125˚C
Electrical Characteristics Limits appearing in bold type face apply over the entire junction temperature
range of operation, −40˚C to 125˚C. Specifications appearing in normal type apply for TA = TJ = 25˚C. RADJ = 8.2KΩ
LM2673-3.3
Symbol
Parameter
Conditions
Typical
(Note 3)
3.3
Min
Max
Units
(Note 4)
(Note 4)
VOUT
Output Voltage
Efficiency
VIN = 8V to 40V, 100mA ≤ IOUT ≤ 3A
3.234/3.201
3.366/3.399
V
η
VIN = 12V, ILOAD = 3A
86
%
LM2673-5.0
Symbol
Parameter
Conditions
Typical
(Note 3)
5.0
Min
Max
Units
(Note 4)
(Note 4)
VOUT
Output Voltage
Efficiency
VIN = 8V to 40V, 100mA ≤ IOUT ≤ 3A
4.900/4.850
5.100/5.150
V
η
VIN = 12V, ILOAD = 3A
88
%
LM2673-12
Symbol
Parameter
Conditions
Typical
(Note 3)
12
Min
Max
Units
(Note 4)
(Note 4)
VOUT
Output Voltage
Efficiency
VIN = 15V to 40V, 100mA ≤ IOUT ≤ 3A
11.76/11.64
12.24/12.36
V
η
VIN = 24V, ILOAD = 3A
94
%
LM2673-ADJ
Symbol
Parameter
Conditions
Typ
Min
Max
Units
(Note 3)
(Note 4)
(Note 4)
VFB
Feedback
VIN = 8V to 40V, 100mA ≤ IOUT ≤ 3A
VOUT Programmed for 5V
1.21
88
1.186/1.174
1.234/1.246
V
Voltage
η
Efficiency
VIN = 12V, ILOAD = 3A
%
3
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All Output Voltage Versions
Electrical Characteristics
Limits appearing in bold type face apply over the entire junction temperature range of operation, −40˚C to 125˚C. Specifica-
tions appearing in normal type apply for TA = TJ = 25˚C. Unless otherwise specified, RADJ = 8.2KΩ, VIN=12V for the 3.3V, 5V
and Adjustable versions and VIN=24V for the 12V version.
Symbol
Parameter
Conditions
Typ
Min
Max
Units
DEVICE PARAMETERS
IQ
Quiescent
Current
VFEEDBACK = 8V
4.2
6
mA
For 3.3V, 5.0V, and ADJ Versions
VFEEDBACK = 15V
For 12V Versions
VADJ
Current Limit
Adjust Voltage
Current Limit
Output Leakage
Current
1.21
4.5
1.181/1.169
3.8/3.6
1.229/1.246
5.25/5.4
V
A
ICL
IL
RADJ = 8.2KΩ, (Note 5)
VIN = 40V, Softstart Pin = 0V
VSWITCH = 0V
mA
mA
1.0
6
1.5
15
VSWITCH = −1V
RDS(ON) Switch
On-Resistance
ISWITCH = 3A
0.15
0.17/0.29
Ω
fO
Oscillator
Measured at Switch Pin
260
225
280
kHz
Frequency
Duty Cycle
D
Maximum Duty Cycle
Minimum Duty Cycle
VFEEDBACK = 1.3V
ADJ Version Only
91
0
%
%
IBIAS
VSFST
Feedback Bias
Current
85
nA
Softstart
Threshold
Voltage
0.63
0.53
0.74
6.9
V
ISFST
θJA
Softstart Pin
Current
Softstart Pin = 0V
3.7
65
µA
Thermal
T Package, Junction to Ambient
(Note 6)
Resistance
θJA
T Package, Junction to Ambient
(Note 7)
45
θJC
θJA
T Package, Junction to Case
S Package, Junction to Ambient
(Note 8)
2
56
˚C/W
θJA
θJA
S Package, Junction to Ambient
(Note 9)
35
26
S Package, Junction to Ambient
(Note 10)
θJC
θJA
S Package, Junction to Case
SD Package, Junction to Ambient
(Note 11)
2
++
55
˚C/W
θJA
SD Package, Junction to Ambient
(Note 12)
29
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4
All Output Voltage Versions
Electrical Characteristics (Continued)
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings indicate conditions under which of the device is
guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test condition, see the electrical
Characteristics tables.
Note 2: ESD was applied using the human-body model, a 100pF capacitor discharged through a 1.5 kΩ resistor into each pin.
Note 3: Typical values are determined with T = T = 25˚C and represent the most likely norm.
A
J
Note 4: All limits are guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%
tested during production with T = T = 25˚C. All limits at temperature extremes are guaranteed via correlation using standard standard Quality Control (SQC)
A
J
methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
Note 5: The peak switch current limit is determined by the following relationship: I =37,125/ R
.
ADJ
CL
Note 6: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with 1
board with minimum copper area.
⁄
2
inch leads in a socket, or on a PC
inch leads soldered to a PC board
Note 7: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with 1
⁄
2
containing approximately 4 square inches of (1 oz.) copper area surrounding the leads.
Note 8: Junction to ambient thermal resistance for the 7 lead TO-263 mounted horizontally against a PC board area of 0.136 square inches (the same size as the
TO-263 package) of 1 oz. (0.0014 in. thick) copper.
Note 9: Junction to ambient thermal resistance for the 7 lead TO-263 mounted horizontally against a PC board area of 0.4896 square inches (3.6 times the area
of the TO-263 package) of 1 oz. (0.0014 in. thick) copper.
Note 10: Junction to ambient thermal resistance for the 7 lead TO-263 mounted horizontally against a PC board copper area of 1.0064 square inches (7.4 times
the area of the TO-263 package) of 1 oz. (0.0014 in. thick) copper. Additional copper area will reduce thermal resistance further. See the thermal model in Switchers
Made Simple® software.
Note 11: Junction to ambient thermal resistance for the 14-lead LLP mounted on a PC board copper area equal to the die attach paddle.
Note 12: Junction to ambient thermal resistance for the 14-lead LLP mounted on a PC board copper area using 12 vias to a second layer of copper equal to die
attach paddle. Additional copper area will reduce thermal resistance further. For layout recommendations, refer to Application Note AN-1187.
5
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Typical Performance Characteristics
Normalized
Output Voltage
Line Regulation
10091304
10091305
Efficiency vs Input Voltage
Efficiency vs ILOAD
10091306
10091307
Switch Current Limit
Operating Quiescent Current
10091308
10091309
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Typical Performance Characteristics (Continued)
Switching Frequency
Feedback Pin Bias Current
10091312
10091313
Load Transient Response for Continuous Mode
VIN = 20V, VOUT = 5V
Load Transient Response for Discontinuous Mode
VIN = 20V, VOUT = 5V,
L = 33 µH, COUT = 200 µF, COUTESR = 26 mΩ
L = 10 µH, COUT = 400 µF, COUTESR = 13 mΩ
10091317
A: Output Voltage, 100 mV//div, AC-Coupled.
10091318
A: Output Voltage, 100 mV/div, AC-Coupled.
B: Load Current: 500 mA to 3A Load Pulse
B: Load Current: 200 mA to 3A Load Pulse
Horizontal Time Base: 100 µs/div
Horizontal Time Base: 200 µs/div
Continuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 3A
Discontinuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 500 mA
L = 33 µH, COUT = 200 µF, COUTESR = 26 mΩ
L = 10 µH, COUT = 400 µF, COUTESR = 13 mΩ
10091315
A: V
Pin Voltage, 10 V/div.
10091316
SW
A: V
Pin Voltage, 10 V/div.
SW
B: Inductor Current, 1 A/div
B: Inductor Current, 1 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//iv
7
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Block Diagram
10091314
* Active Inductor Patent Number 5,514,947
†
Active Capacitor Patent Number 5,382,918
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8
CURRENT ADJUST
Application Hints
A key feature of the LM2673 is the ability to tailor the peak
switch current limit to a level required by a particular appli-
cation. This alleviates the need to use external components
that must be physically sized to accommodate current levels
(under shorted output conditions for example) that may be
much higher than the normal circuit operating current re-
quirements.
The LM2673 provides all of the active functions required for
a step-down (buck) switching regulator. The internal power
switch is a DMOS power MOSFET to provide power supply
designs with high current capability, up to 3A, and highly
efficient operation.
The LM2673 is part of the SIMPLE SWITCHER family of
power converters. A complete design uses a minimum num-
ber of external components, which have been pre-
determined from a variety of manufacturers. Using either this
data sheet or a design software program called LM267X
Made Simple (version 2.0) a complete switching power
supply can be designed quickly. The software is provided
free of charge and can be downloaded from National Semi-
conductor’s Internet site located at http://www.national.com.
A resistor connected from pin 5 to ground establishes a
current (I(pin
= 1.2V / RADJ) that sets the peak current
5)
through the power switch. The maximum switch current is
fixed at a level of 37,125 / RADJ
.
FEEDBACK
This is the input to a two-stage high gain amplifier, which
drives the PWM controller. It is necessary to connect pin 6 to
the actual output of the power supply to set the dc output
voltage. For the fixed output devices (3.3V, 5V and 12V
outputs), a direct wire connection to the output is all that is
required as internal gain setting resistors are provided inside
the LM2673. For the adjustable output version two external
resistors are required to set the dc output voltage. For stable
operation of the power supply it is important to prevent
coupling of any inductor flux to the feedback input.
SWITCH OUTPUT
This is the output of a power MOSFET switch connected
directly to the input voltage. The switch provides energy to
an inductor, an output capacitor and the load circuitry under
control of an internal pulse-width-modulator (PWM). The
PWM controller is internally clocked by a fixed 260KHz
oscillator. In a standard step-down application the duty cycle
(Time ON/Time OFF) of the power switch is proportional to
the ratio of the power supply output voltage to the input
voltage. The voltage on pin 1 switches between Vin (switch
ON) and below ground by the voltage drop of the external
Schottky diode (switch OFF).
SOFTSTART
A capacitor connected from pin 7 to ground allows for a slow
turn-on of the switching regulator. The capacitor sets a time
delay to gradually increase the duty cycle of the internal
power switch. This can significantly reduce the amount of
surge current required from the input supply during an abrupt
application of the input voltage. If softstart is not required this
pin should be left open circuited.
INPUT
The input voltage for the power supply is connected to pin 2.
In addition to providing energy to the load the input voltage
also provides bias for the internal circuitry of the LM2673.
For guaranteed performance the input voltage must be in the
range of 8V to 40V. For best performance of the power
supply the input pin should always be bypassed with an input
capacitor located close to pin 2.
DAP (LLP PACKAGE)
The Die Attach Pad (DAP) can and should be connected to
PCB Ground plane/island. For CAD and assembly guide-
lines refer to Application Note AN-1187 at http://
power.national.com.
C BOOST
A capacitor must be connected from pin 3 to the switch
output, pin 1. This capacitor boosts the gate drive to the
internal MOSFET above Vin to fully turn it ON. This mini-
mizes conduction losses in the power switch to maintain high
efficiency. The recommended value for C Boost is 0.01µF.
GROUND
This is the ground reference connection for all components
in the power supply. In fast-switching, high-current applica-
tions such as those implemented with the LM2673, it is
recommended that a broad ground plane be used to mini-
mize signal coupling throughout the circuit
9
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Application Hints (Continued)
DESIGN CONSIDERATIONS
10091323
FIGURE 1. Basic circuit for fixed output voltage applications.
10091324
FIGURE 2. Basic circuit for adjustable output voltage applications
Power supply design using the LM2673 is greatly simplified
by using recommended external components. A wide range
of inductors, capacitors and Schottky diodes from several
manufacturers have been evaluated for use in designs that
cover the full range of capabilities (input voltage, output
voltage and load current) of the LM2673. A simple design
procedure using nomographs and component tables pro-
vided in this data sheet leads to a working design with very
little effort. Alternatively, the design software, LM267X Made
Simple (version 6.0), can also be used to provide instant
component selection, circuit performance calculations for
evaluation, a bill of materials component list and a circuit
schematic.
son of component specifications, equivalent devices from
other manufacturers could be substituted for use in an ap-
plication.
Important considerations for each external component and
an explanation of how the nomographs and selection tables
were developed follows.
INDUCTOR
The inductor is the key component in a switching regulator.
For efficiency the inductor stores energy during the switch
ON time and then transfers energy to the load while the
switch is OFF.
Nomographs are used to select the inductance value re-
quired for a given set of operating conditions. The nomo-
graphs assume that the circuit is operating in continuous
mode (the current flowing through the inductor never falls to
zero). The magnitude of inductance is selected to maintain a
The individual components from the various manufacturers
called out for use are still just a small sample of the vast
array of components available in the industry. While these
components are recommended, they are not exclusively the
only components for use in a design. After a close compari-
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10
greater than this ripple current. The voltage rating of the
output capacitor should be greater than 1.3 times the maxi-
mum output voltage of the power supply. If operation of the
system at elevated temperatures is required, the capacitor
voltage rating may be de-rated to less than the nominal room
temperature rating. Careful inspection of the manufacturer’s
specification for de-rating of working voltage with tempera-
ture is important.
Application Hints (Continued)
maximum ripple current of 30% of the maximum load cur-
rent. If the ripple current exceeds this 30% limit the next
larger value is selected.
The inductors offered have been specifically manufactured
to provide proper operation under all operating conditions of
input and output voltage and load current. Several part types
are offered for a given amount of inductance. Both surface
mount and through-hole devices are available. The inductors
from each of the three manufacturers have unique charac-
teristics.
INPUT CAPACITOR
Fast changing currents in high current switching regulators
place a significant dynamic load on the unregulated power
source. An input capacitor helps to provide additional current
to the power supply as well as smooth out input voltage
variations.
Renco: ferrite stick core inductors; benefits are typically
lowest cost and can withstand ripple and transient peak
currents above the rated value. These inductors have an
external magnetic field, which may generate EMI.
Like the output capacitor, the key specifications for the input
capacitor are RMS current rating and working voltage. The
RMS current flowing through the input capacitor is equal to
one-half of the maximum dc load current so the capacitor
should be rated to handle this. Paralleling multiple capacitors
proportionally increases the current rating of the total capaci-
tance. The voltage rating should also be selected to be 1.3
times the maximum input voltage. Depending on the unregu-
lated input power source, under light load conditions the
maximum input voltage could be significantly higher than
normal operation and should be considered when selecting
an input capacitor.
Pulse Engineering: powdered iron toroid core inductors;
these also can withstand higher than rated currents and,
being toroid inductors, will have low EMI.
Coilcraft: ferrite drum core inductors; these are the smallest
physical size inductors and are available only as surface
mount components. These inductors also generate EMI but
less than stick inductors.
OUTPUT CAPACITOR
The output capacitor acts to smooth the dc output voltage
and also provides energy storage. Selection of an output
capacitor, with an associated equivalent series resistance
(ESR), impacts both the amount of output ripple voltage and
stability of the control loop.
The input capacitor should be placed very close to the input
pin of the LM2673. Due to relative high current operation
with fast transient changes, the series inductance of input
connecting wires or PCB traces can create ringing signals at
the input terminal which could possibly propagate to the
output or other parts of the circuitry. It may be necessary in
some designs to add a small valued (0.1µF to 0.47µF)
ceramic type capacitor in parallel with the input capacitor to
prevent or minimize any ringing.
The output ripple voltage of the power supply is the product
of the capacitor ESR and the inductor ripple current. The
capacitor types recommended in the tables were selected
for having low ESR ratings.
In addition, both surface mount tantalum capacitors and
through-hole aluminum electrolytic capacitors are offered as
solutions.
CATCH DIODE
When the power switch in the LM2673 turns OFF, the current
through the inductor continues to flow. The path for this
current is through the diode connected between the switch
output and ground. This forward biased diode clamps the
switch output to a voltage less than ground. This negative
voltage must be greater than −1V so a low voltage drop
(particularly at high current levels) Schottky diode is recom-
mended. Total efficiency of the entire power supply is signifi-
cantly impacted by the power lost in the output catch diode.
The average current through the catch diode is dependent
on the switch duty cycle (D) and is equal to the load current
times (1-D). Use of a diode rated for much higher current
than is required by the actual application helps to minimize
the voltage drop and power loss in the diode.
Impacting frequency stability of the overall control loop, the
output capacitance, in conjunction with the inductor, creates
a double pole inside the feedback loop. In addition the
capacitance and the ESR value create a zero. These fre-
quency response effects together with the internal frequency
compensation circuitry of the LM2673 modify the gain and
phase shift of the closed loop system.
As a general rule for stable switching regulator circuits it is
desired to have the unity gain bandwidth of the circuit to be
limited to no more than one-sixth of the controller switching
frequency. With the fixed 260KHz switching frequency of the
LM2673, the output capacitor is selected to provide a unity
gain bandwidth of 40KHz maximum. Each recommended
capacitor value has been chosen to achieve this result.
During the switch ON time the diode will be reversed biased
by the input voltage. The reverse voltage rating of the diode
should be at least 1.3 times greater than the maximum input
voltage.
In some cases multiple capacitors are required either to
reduce the ESR of the output capacitor, to minimize output
ripple (a ripple voltage of 1% of Vout or less is the assumed
performance condition), or to increase the output capaci-
tance to reduce the closed loop unity gain bandwidth (to less
than 40KHz). When parallel combinations of capacitors are
required it has been assumed that each capacitor is the
exact same part type.
BOOST CAPACITOR
The boost capacitor creates a voltage used to overdrive the
gate of the internal power MOSFET. This improves efficiency
by minimizing the on resistance of the switch and associated
power loss. For all applications it is recommended to use a
0.01µF/50V ceramic capacitor.
The RMS current and working voltage (WV) ratings of the
output capacitor are also important considerations. In a typi-
cal step-down switching regulator, the inductor ripple current
(set to be no more than 30% of the maximum load current by
the inductor selection) is the current that flows through the
output capacitor. The capacitor RMS current rating must be
RADJ, ADJUSTABLE CURRENT LIMIT
A key feature of the LM2673 is the ability to control the peak
switch current. Without this feature the peak switch current
would be internally set to 5A or higher to accommodate 3A
load current designs. This requires that both the inductor
11
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2. However, the current limit block is also designed to
momentarily reduce the duty cycle to below 50% to
avoid subharmonic oscillations, which could cause the
inductor to saturate.
Application Hints (Continued)
(which could saturate with excessively high currents) and the
catch diode be able to safely handle up to 5A which would be
conducted under load fault conditions.
3. Thereafter, once the inductor current falls below the
current limit threshold, there is a small relaxation time
during which the duty cycle progressively rises back
above 50% to the value required to achieve regulation.
If an application only requires a load current of 2A or so the
peak switch current can be set to a limit just over the maxi-
mum load current with the addition of a single programming
resistor. This allows the use of less powerful and more cost
effective inductors and diodes.
If the output capacitance is sufficiently ‘large’, it may be
possible that as the output tries to recover, the output ca-
pacitor charging current is large enough to repeatedly re-
trigger the current limit circuit before the output has fully
settled. This condition is exacerbated with higher output
voltage settings because the energy requirement of the out-
put capacitor varies as the square of the output voltage
The peak switch current is equal to a factor of 37,125 divided
by RADJ. A resistance of 8.2KΩ sets the current limit to
typically 4.5A. For predictable control of the current limit it is
recommended to keep the peak switch current greater than
1A. For lower current applications 500mA and 1A switching
regulators, the LM2674 and LM2672, are available.
(1⁄ CV2), thus requiring an increased charging current.
2
When the power switch reaches the current limit threshold it
is immediately turned OFF and the internal switching fre-
quency is reduced. This extends the OFF time of the switch
to prevent a steady state high current condition. As the
switch current falls below the current limit threshold, the
switch will turn back ON. If a load fault continues, the switch
will again exceed the threshold and switch back OFF. This
will result in a low duty cycle pulsing of the power switch to
minimize the overall fault condition power dissipation.
A simple test to determine if this condition might exist for a
suspect application is to apply a short circuit across the
output of the converter, and then remove the shorted output
condition. In an application with properly selected external
components, the output will recover smoothly.
Practical values of external components that have been
experimentally found to work well under these specific oper-
ating conditions are COUT = 47µF, L = 22µH. It should be
noted that even with these components, for a device’s cur-
rent limit of ICLIM, the maximum load current under which the
possibility of the large current limit hysteresis can be mini-
mized is ICLIM/2. For example, if the input is 24V and the set
output voltage is 18V, then for a desired maximum current of
1.5A, the current limit of the chosen switcher must be con-
firmed to be at least 3A.
Css SOFTSTART CAPACITOR
This optional capacitor controls the rate at which the LM2673
starts up at power on. The capacitor is charged linearly by an
internal current source. This voltage ramp gradually in-
creases the duty cycle of the power switch until it reaches
the normal operating duty cycle defined primarily by the ratio
of the output voltage to the input voltage. The softstart
turn-on time is programmable by the selection of Css.
SIMPLE DESIGN PROCEDURE
Using the nomographs and tables in this data sheet (or use
the available design software at http://www.national.com) a
complete step-down regulator can be designed in a few
simple steps.
The formula for selecting a softstart capacitor is:
Step 1: Define the power supply operating conditions:
Required output voltage
Where:
Maximum DC input voltage
ISST = Softstart Current, 3.7µA typical
Maximum output load current
tSS = Softstart time, from design requirements
VSST = Softstart Threshold Voltage, 0.63V typical
VOUT = Output Voltage, from design requirements
VSCHOTTKY = Schottky Diode Voltage Drop, typically 0.5V
VIN = Maximum Input Voltage, from design requirements
Step 2: Set the output voltage by selecting a fixed output
LM2673 (3.3V, 5V or 12V applications) or determine the
required feedback resistors for use with the adjustable
LM2673−ADJ
Step 3: Determine the inductor required by using one of the
four nomographs, Figure 3 through Figure 6. Table 1 pro-
vides a specific manufacturer and part number for the induc-
tor.
If this feature is not desired, leave the Softstart pin (pin 7)
open circuited
ADDITIONAL APPLICATION INFORMATION
Step 4: Using Table 3 (fixed output voltage) or Table 6
(adjustable output voltage), determine the output capaci-
tance required for stable operation. Table 2 provides the
specific capacitor type from the manufacturer of choice.
When the output voltage is greater than approximately 6V,
and the duty cycle at minimum input voltage is greater than
approximately 50%, the designer should exercise caution in
selection of the output filter components. When an applica-
tion designed to these specific operating conditions is sub-
jected to a current limit fault condition, it may be possible to
observe a large hysteresis in the current limit. This can affect
the output voltage of the device until the load current is
reduced sufficiently to allow the current limit protection circuit
to reset itself.
Step 5: Determine an input capacitor from Table 4 for fixed
output voltage applications. Use Table 2 to find the specific
capacitor type. For adjustable output circuits select a capaci-
tor from Table 2 with a sufficient working voltage (WV) rating
greater than Vin max, and an rms current rating greater than
one-half the maximum load current (2 or more capacitors in
parallel may be required).
Under current limiting conditions, the LM267x is designed to
respond in the following manner:
Step 6: Select a diode from Table 5. The current rating of the
diode must be greater than I load max and the Reverse
Voltage rating must be greater than Vin max.
1. At the moment when the inductor current reaches the
current limit threshold, the ON-pulse is immediately ter-
minated. This happens for any application condition.
www.national.com
12
t
SS: 50mS
Application Hints (Continued)
Step 7: Include a 0.01µF/50V capacitor for Cboost in the
design and then determine the value of a softstart capacitor
if desired.
VSST: 0.63V
VOUT: 3.3V
VSCHOTTKY: 0.5V
VIN: 16V
Step 8: Define a value for RADJ to set the peak switch
current limit to be at least 20% greater than Iout max to allow
for at least 30% inductor ripple current ( 15% of Iout). For
designs that must operate over the full temperature range
the switch current limit should be set to at least 50% greater
than Iout max (1.5 x Iout max).
Using Vin max ensures that the softstart delay time will be at
least the desired 50mS.
Using the formula for Css a value of 0.148µF is determined
to be required. Use of a standard value 0.22µF capacitor will
produce more than sufficient softstart delay.
FIXED OUTPUT VOLTAGE DESIGN EXAMPLE
Step 8: Determine a value for RADJ to provide a peak switch
current limit of at least 2.5A plus 50% or 3.75A.
A system logic power supply bus of 3.3V is to be generated
from a wall adapter which provides an unregulated DC volt-
age of 13V to 16V. The maximum load current is 2.5A. A
softstart delay time of 50mS is desired. Through-hole com-
ponents are preferred.
Use a value of 10KΩ.
ADJUSTABLE OUTPUT DESIGN EXAMPLE
Step 1: Operating conditions are:
Vout = 3.3V
In this example it is desired to convert the voltage from a two
battery automotive power supply (voltage range of 20V to
28V, typical in large truck applications) to the 14.8VDC alter-
nator supply typically used to power electronic equipment
from single battery 12V vehicle systems. The load current
required is 2A maximum. It is also desired to implement the
power supply with all surface mount components. Softstart is
not required.
Vin max = 16V
Iload max = 2.5A
Step 2: Select an LM2673T-3.3. The output voltage will have
a tolerance of
2% at room temperature and 3% over the full operating
temperature range.
Step 3: Use the nomograph for the 3.3V device ,Figure 3.
The intersection of the 16V horizontal line (Vin max) and the
2.5A vertical line (Iload max) indicates that L33, a 22µH
inductor, is required.
Step 1: Operating conditions are:
Vout = 14.8V
Vin max = 28V
From Table 1, L33 in a through-hole component is available
from Renco with part number RL-1283-22-43 or part number
PE-53933 from Pulse Engineering.
Iload max = 2A
Step 2: Select an LM2673S-ADJ. To set the output voltage
to 14.9V two resistors need to be chosen (R1 and R2 in
Figure 2). For the adjustable device the output voltage is set
by the following relationship:
Step 4: Use Table 3 to determine an output capacitor. With a
3.3V output and a 33µH inductor there are four through-hole
output capacitor solutions with the number of same type
capacitors to be paralleled and an identifying capacitor code
given. Table 2 provides the actual capacitor characteristics.
Any of the following choices will work in the circuit:
1 x 220µF/10V Sanyo OS-CON (code C5)
1 x 1000µF/35V Sanyo MV-GX (code C10)
1 x 2200µF/10V Nichicon PL (code C5)
1 x 1000µF/35V Panasonic HFQ (code C7)
Where VFB is the feedback voltage of typically 1.21V.
A recommended value to use for R1 is 1K. In this example
then R2 is determined to be:
Step 5: Use Table 4 to select an input capacitor. With 3.3V
output and 22µH there are three through-hole solutions.
These capacitors provide a sufficient voltage rating and an
rms current rating greater than 1.25A (1/2 Iload max). Again
using Table 2 for specific component characteristics the
following choices are suitable:
R2 = 11.23KΩ
The closest standard 1% tolerance value to use is 11.3KΩ
This will set the nominal output voltage to 14.88V which is
within 0.5% of the target value.
1 x 1000µF/63V Sanyo MV-GX (code C14)
1 x 820µF/63V Nichicon PL (code C24)
1 x 560µF/50V Panasonic HFQ (code C13)
Step 3: To use the nomograph for the adjustable device,
Figure 6, requires
a
calculation of the inductor
Step 6: From Table 5 a 3A or more Schottky diode must be
selected. The 20V rated diodes are sufficient for the appli-
cation and for through-hole components two part types are
suitable:
Volt•microsecond constant (E•T expressed in V•µS) from
the following formula:
1N5820
SR302
where VSAT is the voltage drop across the internal power
switch which is Rds(ON) times Iload. In this example this would
be typically 0.15Ω x 2A or 0.3V and VD is the voltage drop
across the forward bisased Schottky diode, typically 0.5V.
Step 7: A 0.01µF capacitor will be used for Cboost. For the
50mS softstart delay the following parameters are to be
used:
ISST: 3.7µA
13
www.national.com
Step 5: An input capacitor for this example will require at
least a 35V WV rating with an rms current rating of 1A (1/2
Iout max). From Table 2 it can be seen that C12, a 33µF/35V
capacitor from Sprague, has the required voltage/current
rating of the surface mount components.
Application Hints (Continued)
The switching frequency of 260KHz is the nominal value to
use to estimate the ON time of the switch during which
energy is stored in the inductor.
For this example E•T is found to be:
Step 6: From Table 5 a 3A Schottky diode must be selected.
For surface mount diodes with a margin of safety on the
voltage rating one of five diodes can be used:
SK34
30BQ040
30WQ04F
MBRS340
Using Figure 6, the intersection of 27V•µS horizontally and
the 2A vertical line (Iload max) indicates that L38 , a 68µH
inductor, should be used.
MBRD340
Step 7: A 0.01µF capacitor will be used for Cboost.
The softstart pin will be left open circuited.
From Table 1, L38 in a surface mount component is available
from Pulse Engineering with part number PE-54038S.
Step 8: Determine a value for RADJ to provide a peak switch
current limit of at least 2A plus 50% or 3A.
Step 4: Use Table 6 to determine an output capacitor. With a
14.8V output the 12.5 to 15V row is used and with a 68µH
inductor there are three surface mount output capacitor so-
lutions. Table 2 provides the actual capacitor characteristics
based on the C Code number. Any of the following choices
can be used:
Use a value of 12.4KΩ.
1 x 33µF/20V AVX TPS (code C6)
1 x 47µF/20V Sprague 594 (code C8)
1 x 47µF/20V Kemet T495 (code C8)
LLP PACKAGE DEVICES
The LM2673 is offered in the 14 lead LLP surface mount
package to allow for a significantly decreased footprint with
equivalent power dissipation compared to the TO-263. For
details on mounting and soldering specifications, refer to
Application Note AN-1187.
Important Note: When using the adjustable device in low
voltage applications (less than 3V output), if the nomograph,
Figure 6, selects an inductance of 22µH or less, Table 6 does
not provide an output capacitor solution. With these condi-
tions the number of output capacitors required for stable
operation becomes impractical. It is recommended to use
either a 33µH or 47µH inductor and the output capacitors
from Table 6.
www.national.com
14
Inductor Selection Guides For Continuous Mode Operation
10091319
10091320
FIGURE 3. LM2673-3.3
FIGURE 4. LM2673-5.0
10091322
10091321
FIGURE 6. LM2673-ADJ
FIGURE 5. LM2673-12
15
www.national.com
Inductor Selection Guides For Continuous Mode Operation (Continued)
Table 1. Inductor Manufacturer Part Numbers
Renco
Through Hole
Pulse Engineering
Coilcraft
Inductor
Reference
Number
Inductance Current
Surface
Mount
Through
Hole
Surface
Mount
Surface Mount
(µH)
(A)
L23
L24
L25
L29
L30
L31
L32
L33
L34
L38
L39
L40
L41
L44
L45
33
22
15
100
68
47
33
22
15
68
47
33
22
68
10
1.35
1.65
2.00
1.41
1.71
2.06
2.46
3.02
3.65
2.97
3.57
4.26
5.22
3.45
4.47
RL-5471-7
RL1500-33 PE-53823 PE-53823S DO3316-333
RL-1283-22-43 RL1500-22 PE-53824 PE-53824S DO3316-223
RL-1283-15-43 RL1500-15 PE-53825 PE-53825S DO3316-153
RL-5471-4
RL-5471-5
RL-5471-6
RL-5471-7
RL-6050-100 PE-53829 PE-53829S DO5022P-104
RL6050-68 PE-53830 PE-53830S DO5022P-683
RL6050-47 PE-53831 PE-53831S DO5022P-473
RL6050-33 PE-53932 PE-53932S DO5022P-333
RL-1283-22-43 RL6050-22 PE-53933 PE-53933S DO5022P-223
RL-1283-15-43
RL-5472-2
—
—
—
—
—
—
—
PE-53934 PE-53934S DO5022P-153
PE-54038 PE-54038S
PE-54039 PE-54039S
PE-54040 PE-54040S
PE-54041 P0841
—
RL-5472-3
—
RL-1283-33-43
RL-1283-22-43
RL-5473-3
—
—
—
PE-54044
—
—
RL-1283-10-43
P0845
DO5022P-103HC
Inductor Manufacturer Contact Numbers
Coilcraft
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
Coilcraft, Europe
Pulse Engineering
Pulse Engineering,
Europe
Renco Electronics
www.national.com
16
Capacitor Selection Guides
Table 2. Input and Output Capacitor Codes
Surface Mount
Sprague 594D Series
Irms
Capacitor
Reference
Code
AVX TPS Series
Irms
Kemet T495 Series
Irms
C (µF) WV (V) (A)
C (µF) WV (V)
(A)
C (µF) WV (V)
(A)
1.1
C1
C2
330
100
220
47
6.3
10
10
16
16
20
20
25
35
35
1.15
1.1
120
220
68
6.3
6.3
10
10
16
16
16
20
25
25
35
35
50
100
220
330
100
150
220
33
6.3
6.3
6.3
10
10
10
20
20
20
35
35
50
0.82
1.1
1.4
C3
1.15
0.89
1.15
0.77
0.94
0.77
0.63
0.66
1.05
1.35
1
1.1
C4
150
47
1.1
C5
100
33
1.1
C6
100
180
47
1.3
1.1
C7
68
1.95
1.15
1.05
1.6
0.78
0.94
0.94
0.63
0.63
0.66
C8
22
47
C9
10
33
68
C10
C11
C12
C13
22
68
10
15
0.75
1
22
33
4.7
15
0.9
17
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Capacitor Selection Guides (Continued)
Table 2. Input and Output Capacitor Codes (continued)
Through Hole
Sanyo OS-CON SA Series Sanyo MV-GX Series Nichicon PL Series
Capacitor
Reference
Code
Panasonic HFQ Series
Irms
Irms
(A)
Irms
(A)
Irms
(A)
C (µF) WV (V)
C (µF) WV (V)
C (µF) WV (V)
C (µF) WV (V)
(A)
0.4
C1
C2
47
150
330
100
220
33
6.3
6.3
6.3
10
10
16
16
16
20
25
1
1000
270
470
560
820
1000
150
470
680
1000
220
470
680
1000
6.3
16
16
16
16
16
35
35
35
35
63
63
63
63
0.8
680
820
10
10
10
10
10
10
10
10
16
16
16
16
16
16
25
35
35
35
50
50
50
63
63
63
63
0.8
82
120
220
330
560
820
1000
2200
56
35
35
35
35
35
35
35
35
50
50
50
50
50
50
63
63
1.95
2.45
1.87
2.36
0.96
1.92
2.28
2.25
2.09
0.6
0.98
1.06
1.28
1.71
2.18
2.36
2.68
0.41
0.55
0.77
1.02
1.22
1.88
0.63
0.79
1.43
2.68
0.82
1.04
1.3
0.44
0.76
1.01
1.4
C3
0.75
0.95
1.25
1.3
1000
1200
2200
3300
3900
6800
180
C4
C5
C6
1.62
1.73
2.8
C7
100
150
100
47
0.65
1.3
C8
C9
1.4
0.36
0.5
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
1.7
270
100
220
470
560
1200
330
1500
0.76
1.2
470
0.92
1.44
1.68
2.22
1.42
2.51
680
1.5
820
1.75
1800
220
220
560
2200
150
220
330
100
0.75
1.62
2.22
2.51
390
820
1200
Capacitor Manufacturer Contact Numbers
Nichicon
Panasonic
AVX
Phone
FAX
(847) 843-7500
(847) 843-2798
(714) 373-7857
(714) 373-7102
(845) 448-9411
(845) 448-1943
(207) 324-4140
(207) 324-7223
(619) 661-6322
(619) 661-1055
(864) 963-6300
(864) 963-6521
Phone
FAX
Phone
FAX
Sprague/Vishay
Sanyo
Phone
FAX
Phone
FAX
Kemet
Phone
FAX
www.national.com
18
Capacitor Selection Guides (Continued)
Table 3. Output Capacitors for Fixed Output Voltage Application
Surface Mount
Sprague 594D
Series
Output
Voltage (V)
Inductance
(µH)
AVX TPS Series
Kemet T495 Series
No.
4
C Code
C2
No.
3
C Code
No.
4
C Code
C4
10
15
22
33
10
15
22
33
47
10
15
22
33
47
68
100
C1
C1
C7
C6
C6
C7
C7
C3
C7
C6
C7
C6
C7
C6
C5
C5
4
C2
3
4
C4
3.3
5
3
C2
2
3
C4
2
C2
2
2
C4
4
C2
4
4
C4
3
C2
2
3
C4
3
C2
2
3
C4
2
C2
2
2
C4
2
C2
1
2
C4
4
C5
3
5
C9
3
C5
2
4
C8
2
C5
2
3
C8
12
2
C5
1
2
C8
2
C4
1
2
C8
1
C5
1
2
C7
1
C4
1
1
C8
Through Hole
Sanyo MV-GX Series Nichicon PL Series
Output
Voltage (V)
Inductance Sanyo OS-CON SA
Panasonic HFQ
Series
(µH)
Series
C Code
No.
1
No.
1
C Code
C10
C10
C10
C10
C10
C10
C5
No.
1
C Code
C6
No.
2
C Code
C6
10
15
22
33
10
15
22
33
47
10
15
22
33
47
68
100
C3
C3
C5
C2
C4
C5
C5
C4
C4
C7
C8
C7
C7
C7
C7
C7
1
1
1
C6
2
C5
3.3
5
1
1
1
C5
1
C7
1
1
1
C13
C6
1
C5
2
1
1
2
C5
1
1
1
C5
1
C6
1
1
1
C5
1
C5
1
1
C5
1
C13
C13
C18
C17
C13
C11
C10
C10
C9
1
C5
1
1
C4
1
2
C3
2
2
C5
1
2
C5
1
1
C5
1
1
C5
1
1
C5
1
1
C5
12
1
1
C3
1
1
C4
1
1
C3
1
1
C3
1
1
C2
1
1
C3
1
1
C2
1
1
C1
No. represents the number of identical capacitor types to be connected in parallel
C Code indicates the Capacitor Reference number in Table 2 for identifying the specific component from the manufacturer.
19
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Capacitor Selection Guides (Continued)
Table 4. Input Capacitors for Fixed Output Voltage Application
(Assumes worst case maximum input voltage and load current for a given inductance value)
Surface Mount
Output
Voltage (V)
Inductance
(µH)
AVX TPS Series
Sprague 594D
Series
Kemet T495 Series
No.
2
3
*
C Code
No.
1
C Code
No.
2
C Code
C8
10
15
22
33
10
15
22
33
47
10
15
22
33
47
68
100
C5
C9
*
C7
1
C10
C13
C13
C7
3
C10
C12
C12
C8
3.3
5
2
3
*
*
2
2
2
2
3
*
C5
C5
C10
*
1
2
1
C7
2
C8
2
C12
C13
C13
C10
C10
C12
C12
C13
C13
C13
3
C11
C12
C12
C7
2
3
*
*
1
2
2
2
3
3
*
C7
C7
C10
C10
*
2
2
2
2
C7
2
3
C10
C10
C12
C12
C12
12
2
3
2
3
*
*
2
2
*
*
1
2
Through Hole
Sanyo MV-GX Series Nichicon PL Series
Output
Voltage (V)
Inductance Sanyo OS-CON SA
Panasonic HFQ
Series
(µH)
Series
C Code
No.
1
1
*
No.
2
C Code
C4
No.
1
C Code
C5
No.
1
C Code
C6
10
15
22
33
10
15
22
33
47
10
15
22
33
47
68
100
C7
C10
*
1
C10
C14
C12
C4
1
C18
C24
C20
C14
C14
C18
C23
C20
C18
C18
C18
C18
C23
C21
C22
1
C6
3.3
5
1
1
1
C13
C12
C6
*
*
1
1
1
1
1
*
C7
C7
*
2
1
1
2
C4
1
1
C6
1
C10
C14
C12
C10
C10
C10
C10
C13
C12
C11
1
1
C13
C13
C12
C6
*
*
1
1
1
*
*
1
1
1
1
1
1
*
C9
C10
C10
*
1
1
1
1
1
1
C6
1
1
1
C6
12
1
1
1
C6
*
*
1
1
1
C13
C12
C11
*
*
1
1
1
*
*
1
1
1
*
Check voltage rating of capacitors to be greater than application input voltage.
No. represents the number of identical capacitor types to be connected in parallel
C Code indicates the Capacitor Reference number in Table 2 for identifying the specific component from the manufacturer.
www.national.com
20
Capacitor Selection Guides (Continued)
Table 5. Schottky Diode Selection Table
Reverse
Voltage
(V)
Surface Mount Through Hole
3A
5A or More
3A
5A or More
20V
SK32
1N5820
SR302
30V
40V
SK33
MBRD835L
1N5821
31DQ03
1N5822
MBR340
31DQ04
SR403
30WQ03F
SK34
MBRB1545CT
6TQ045S
30BQ040
30WQ04F
MBRS340
MBRD340
SK35
MBR745
80SQ045
6TQ045
50V or
More
MBR350
31DQ05
SR305
30WQ05F
Diode Manufacturer Contact Numbers
International Rectifier Phone (310) 322-3331
(310) 322-3332
FAX
Motorola
Phone
FAX
(800) 521-6274
(602) 244-6609
(516) 847-3000
General
Phone
Semiconductor
FAX
(516) 847-3236
(805) 446-4800
(805) 446-4850
Diodes, Inc.
Phone
FAX
21
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Capacitor Selection Guides (Continued)
Table 6. Output Capacitors for Adjustable Output Voltage Applications
Surface Mount
Sprague 594D
Series
Output Voltage Inductance
AVX TPS Series
Kemet T495 Series
(V)
(µH)
No.
7
5
4
3
4
3
2
3
2
2
1
3
2
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
C Code
C1
C1
C1
C1
C1
C1
C1
C2
C2
C2
C2
C2
C2
C3
C2
C5
C5
C5
C4
C5
C5
C5
C5
C6
C6
C6
C6
C8
C8
C8
C8
C9
C10
C9
C9
No.
6
4
3
2
3
2
2
3
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
4
3
2
1
1
1
C Code
No.
7
5
4
3
4
3
2
3
2
2
1
3
2
1
1
2
2
1
1
2
2
1
1
1
1
1
1
2
2
2
1
2
1
1
1
8
5
4
3
2
2
C Code
C3
*
*
*
*
33
47
33
47
C2
C2
1.21 to 2.50
2.5 to 3.75
C3
C2
C3
C2
C3
22
33
47
22
33
47
68
22
33
47
68
33
47
68
100
33
47
68
100
33
47
68
100
33
47
68
100
33
47
68
100
10
15
22
33
47
68
C2
C3
3.75 to 5
5 to 6.25
C2
C3
C2
C3
C3
C4
C3
C4
C3
C4
C3
C4
C4
C4
C3
C4
6.25 to 7.5
7.5 to 10
10 to 12.5
12.5 to 15
15 to 20
C4
C6
C3
C4
C6
C8
C6
C8
C6
C8
C5
C8
C6
C8
C6
C8
C6
C8
C6
C8
C8
C8
C8
C8
C8
C8
C8
C8
C10
C9
C10
C10
C10
C10
C11
C11
C11
C11
C12
C12
C12
C12
C12
C12
C9
C9
C11
C12
C12
C12
C13
C13
C13
C13
C13
C13
20 to 30
No Values Available
30 to 37
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22
Capacitor Selection Guides (Continued)
Table 6. Output Capacitors for Adjustable Output Voltage Applications (continued)
Through Hole
Output Voltage Inductance Sanyo OS-CON SA
Panasonic HFQ
Series
Sanyo MV-GX Series Nichicon PL Series
(V)
(µH)
Series
C Code
No.
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
No.
5
4
3
2
3
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
C Code
C1
No.
5
3
3
2
3
2
1
2
2
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
C Code
C3
No.
3
2
2
1
2
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
C Code
C
*
*
*
*
33
47
33
47
C3
C2
C3
C2
C3
C2
C2
C5
C4
C4
C4
C5
C4
C4
C4
C7
C7
C7
C7
C7
C7
C7
C7
C9
C9
C9
C9
C10
C10
C10
C10
1.21 to 2.50
2.5 to 3.75
C1
C3
C5
C5
C5
C5
C5
C5
C5
C5
C5
C5
C5
C5
C5
C5
C5
C5
C2
C2
C5
C5
C2
C2
C2
C2
C2
C2
C2
C2
C2
C2
C2
C2
C2
C2
C10
C11
C10
C10
C10
C10
C1
C1
C1
C3
22
33
47
22
33
47
68
22
33
47
68
33
47
68
100
33
47
68
100
33
47
68
100
33
47
68
100
33
47
68
100
10
15
22
33
47
68
C1
C1
3.75 to 5
5 to 6.25
C1
C1
C1
C3
C6
C3
C6
C1
C6
C3
C6
C1
C6
C1
C6
C3
6.25 to 7.5
7.5 to 10
10 to 12.5
12.5 to 15
15 to 20
C6
C1
C2
C1
C6
C14
C14
C14
C14
C14
C14
C9
C6
C2
C2
C6
C2
C2
C2
C9
C10
C10
C10
C10
C7
C15
C15
C15
C15
C15
C15
C15
C15
C16
C16
C16
C16
C20
C20
C20
C20
C20
C20
C7
C7
C7
C7
No Values
C7
20 to 30
Available
C7
C7
C12
C11
C11
C11
C11
C11
No Values
Available
30 to 37
* Set to a higher value for a practical design solution. See Applications Hints section
No. represents the number of identical capacitor types to be connected in parallel
C Code indicates the Capacitor Reference number in Table 2 for identifying the specific component from the manufacturer.
23
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Physical Dimensions inches (millimeters)
unless otherwise noted
TO-263 Surface Mount Power Package
Order Number LM2673S-3.3, LM2673S-5.0,
LM2673S-12 or LM2673S-ADJ
NS Package Number TS7B
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24
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
TO-220 Power Package
Order Number LM2673T-3.3, LM2673T-5.0,
LM2673T-12 or LM2673T-ADJ
NS Package Number TA07B
14-Lead LLP Package
NS Package Number SRC14A
25
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Notes
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.
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