LM2673SX-12/NOPB [NSC]
IC 5.4 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, PSSO7, POWER, TO-263, SMT-7, Switching Regulator or Controller;
| 型号： | LM2673SX-12/NOPB |
| 厂家： | 
National Semiconductor |
| 描述： | IC 5.4 A SWITCHING REGULATOR, 280 kHz SWITCHING FREQ-MAX, PSSO7, POWER, TO-263, SMT-7, Switching Regulator or Controller 开关 |
| 文件： | 总26页 (文件大小：378K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
February 29, 2008
LM2673
SIMPLE SWITCHER® 3A Step-Down Voltage Regulator with
Adjustable Current Limit
General Description
Features
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.
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.
Efficiency up to 94%
■
■
Simple and easy to design with (using off-the-shelf
external components)
Resistor programmable peak current limit over a range of
2A to 5A.
■
150 mΩ DMOS output switch
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 in-
ductors for use with the LM2673 are available from several
manufacturers to greatly simplify the design process.
±2%maximum output tolerance over full line and load
conditions
■
Wide input voltage range: 8V to 40V
260 KHz fixed frequency internal oscillator
Softstart capability
■
■
■
■
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 con-
trolled to within a ±11% tolerance.
−40 to +125°C operating junction temperature range
Applications
Simple to design, high efficiency (>90%) step-down
switching regulators
■
Efficient system pre-regulator for linear voltage regulators
■
■
Battery chargers
Typical Application
10091303
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation
© 2008 National Semiconductor Corporation
100913
www.national.com
Connection Diagrams and Ordering Information
TO-263 Package
Top View
TO-220 Package
Top View
10091301
10091302
Order Number
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
LM2673SD-12
Package Marking
S0002SB
Supplied As
250 Units on Tape and Reel
12
12
LM2673SDX-12
LM2673SD-3.3
LM2673SDX-3.3
LM2673SD-5.0
LM2673SDX-5.0
LM2673SD-ADJ
LM2673SDX-ADJ
S0002SB
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
3.3
3.3
5.0
5.0
ADJ
ADJ
S0002TB
S0002TB
S0002UB
S0002UB
S0002VB
S0002VB
www.national.com
2
ESD (Note 2)
Storage Temperature Range
2 kV
−65°C to 150°
C
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Soldering Temperature
Wave
Infrared
4 sec, 260°C
10 sec, 240°C
75 sec, 219°C
Input Supply Voltage
Softstart Pin Voltage
Switch Voltage to Ground (Note 13)
Boost Pin Voltage
45V
−0.1V to 6V
−1V to VIN
Vapor Phase
VSW + 8V
Operating Ratings
Supply Voltage
Feedback Pin Voltage
Power Dissipation
−0.3V to 14V
8V to 40V
Internally
Limited
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
3.234/3.201 3.366/3.399
V
VIN = 8V to 40V, 100mA ≤ IOUT ≤ 3A
VIN = 12V, ILOAD = 3A
86
%
η
LM2673-5.0
Symbol
Parameter
Conditions
Typical
(Note 3)
5.0
Min
Max
Units
(Note 4)
(Note 4)
VOUT
Output Voltage
Efficiency
4.900/4.850 5.100/5.150
V
VIN = 8V to 40V, 100mA ≤ IOUT ≤ 3A
VIN = 12V, ILOAD = 3A
88
%
η
LM2673-12
Symbol
Parameter
Conditions
Typical
(Note 3)
12
Min
Max
Units
(Note 4)
(Note 4)
VOUT
Output Voltage
Efficiency
11.76/11.64 12.24/12.36
V
VIN = 15V to 40V, 100mA ≤ IOUT ≤ 3A
VIN = 24V, ILOAD = 3A
94
%
η
LM2673-ADJ
Symbol
Parameter
Conditions
Typ
Min
Max
Units
(Note 3)
(Note 4)
(Note 4)
VFB
Feedback Voltage
VIN = 8V to 40V, 100mA ≤ IOUT ≤ 3A
1.21
88
1.186/1.174 1.234/1.246
V
VOUT Programmed for 5V
Efficiency
VIN = 12V, ILOAD = 3A
%
η
3
www.national.com
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.
Specifications 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
1.21
4.5
1.181/1.169 1.229/1.246
V
A
ICL
IL
Current Limit
RADJ = 8.2KΩ, (Note 5)
3.8/3.6
5.25/5.4
Output Leakage
Current
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
D
Duty Cycle
Maximum Duty Cycle
Minimum Duty Cycle
VFEEDBACK = 1.3V
91
0
%
%
IBIAS
VSFST
ISFST
θJA
Feedback Bias
Current
85
nA
ADJ Version Only
Softstart Threshold
Voltage
0.63
0.53
0.74
6.9
V
Softstart Pin
Current
Softstart Pin = 0V
3.7
65
μA
Thermal
Resistance
T Package, Junction to Ambient
(Note 6)
T Package, Junction to Ambient
45
θJA
(Note 7)
T Package, Junction to Case
2
θJC
θJA
S Package, Junction to Ambient
56
°C/W
(Note 8)
S Package, Junction to Ambient
35
26
θJA
θJA
(Note 9)
S Package, Junction to Ambient
(Note 10)
S Package, Junction to Case
2
++
θJC
θJA
SD Package, Junction to Ambient
55
(Note 11)
°C/W
SD Package, Junction to Ambient
(Note 12)
29
θJA
www.national.com
4
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 TA = TJ = 25°C and represent the most likely norm.
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 TA = TJ = 25°C. All limits at temperature extremes are guaranteed via correlation using standard standard Quality Control (SQC)
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: ICL=37,125/ RADJ
.
Note 6: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with ½ inch leads in a socket, or on a
PC board with minimum copper area.
Note 7: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with ½ inch leads soldered to a PC
board 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.
Note 13: The absolute maximum specification of the 'Switch Voltage to Ground' applies to DC voltage. An extended negative voltage limit of -8V applies to a
pulse of up to 20 ns, -6V of 60 ns and -3V of up to 100 ns.
5
www.national.com
Typical Performance Characteristics
Normalized
Output Voltage
Line Regulation
10091305
10091304
Efficiency vs Input Voltage
Efficiency vs ILOAD
10091306
10091307
Switch Current Limit
Operating Quiescent Current
10091308
10091309
www.national.com
6
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
10091318
A: Output Voltage, 100 mV//div, AC-Coupled.
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
7
www.national.com
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
10091316
A: VSW Pin Voltage, 10 V/div.
A: VSW Pin Voltage, 10 V/div.
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
Block Diagram
10091314
* Active Inductor Patent Number 5,514,947
† Active Capacitor Patent Number 5,382,918
www.national.com
8
such as those implemented with the LM2673, it is recom-
mended that a broad ground plane be used to minimize signal
coupling throughout the circuit
Application Hints
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 ef-
ficient operation.
CURRENT ADJUST
A key feature of the LM2673 is the ability to tailor the peak
switch current limit to a level required by a particular applica-
tion. This alleviates the need to use external components that
must be physically sized to accommodate current levels (un-
der shorted output conditions for example) that may be much
higher than the normal circuit operating current requirements.
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 de-
signed quickly. The software is provided free of charge and
can be downloaded from National Semiconductor's Internet
site located at http://www.national.com.
A resistor connected from pin 5 to ground establishes a cur-
rent (I(pin 5) = 1.2V / RADJ) that sets the peak current through
the power switch. The maximum switch current is fixed at a
level of 37,125 / RADJ
.
FEEDBACK
SWITCH OUTPUT
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 volt-
age. 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.
This is the output of a power MOSFET switch connected di-
rectly to the input voltage. The switch provides energy to an
inductor, an output capacitor and the load circuitry under con-
trol 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 volt-
age 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 cur-
rent required from the input supply during an abrupt applica-
tion of the input voltage. If softstart is not required this pin
should be left open circuited. Please see the CSS softstart ca-
pacitor section for further information regarding softstart ca-
pacitor values.
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 ca-
pacitor located close to pin 2.
C BOOST
DAP (LLP PACKAGE)
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 minimizes con-
duction losses in the power switch to maintain high efficiency.
The recommended value for C Boost is 0.01μF.
The Die Attach Pad (DAP) can and should be connected to
PCB Ground plane/island. For CAD and assembly guidelines
refer
to
Application
Note
AN-1187
at
http://
power.national.com.
GROUND
This is the ground reference connection for all components in
the power supply. In fast-switching, high-current applications
9
www.national.com
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 volt-
age and load current) of the LM2673. A simple design proce-
dure using nomographs and component tables provided 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.
INDUCTOR
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 compo-
nents are recommended, they are not exclusively the only
components for use in a design. After a close comparison of
component specifications, equivalent devices from other
manufacturers could be substituted for use in an application.
Important considerations for each external component and an
explanation of how the nomographs and selection tables were
developed follows.
current flowing through the inductor never falls to zero). The
magnitude of inductance is selected to maintain a maximum
ripple current of 30% of the maximum load current. If the ripple
current exceeds this 30% limit the next larger value is select-
ed.
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.
The inductors offered have been specifically manufactured to
provide proper operation under all operating conditions of in-
put and output voltage and load current. Several part types
Nomographs are used to select the inductance value required
for a given set of operating conditions. The nomographs as-
sume that the circuit is operating in continuous mode (the
www.national.com
10
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 character-
istics.
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 vari-
ations.
Renco: ferrite stick core inductors; benefits are typically low-
est 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 capac-
itance. 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 nor-
mal 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, be-
ing 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 capaci-
tor, 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 con-
necting 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 de-
signs to add a small valued (0.1μF to 0.47μF) ceramic type
capacitor in parallel with the input capacitor to prevent or min-
imize any ringing.
The output ripple voltage of the power supply is the product
of the capacitor ESR and the inductor ripple current. The ca-
pacitor 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 cur-
rent is through the diode connected between the switch output
and ground. This forward biased diode clamps the switch out-
put 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 recommended. Total effi-
ciency of the entire power supply is significantly 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 ca-
pacitance and the ESR value create a zero. These frequency
response effects together with the internal frequency com-
pensation 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 ca-
pacitor 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 re-
duce 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 capacitance
to reduce the closed loop unity gain bandwidth (to less than
40KHz). When parallel combinations of capacitors are re-
quired 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
greater than this ripple current. The voltage rating of the out-
put capacitor should be greater than 1.3 times the maximum
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 tem-
perature rating. Careful inspection of the manufacturer's
specification for de-rating of working voltage with temperature
is important.
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
(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.
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.
11
www.national.com
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 typi-
cally 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.
subharmonic oscillations, which could cause the inductor
to saturate.
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.
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.
If the output capacitance is sufficiently ‘large’, it may be pos-
sible that as the output tries to recover, the output capacitor
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 output capacitor
varies as the square of the output voltage (½CV2), thus re-
quiring an increased charging current.
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 condi-
tion. In an application with properly selected external compo-
nents, the output will recover smoothly.
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 increas-
es 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.
Practical values of external components that have been ex-
perimentally found to work well under these specific operating
conditions are COUT = 47µF, L = 22µH. It should be noted that
even with these components, for a device’s current limit of
ICLIM, the maximum load current under which the possibility of
the large current limit hysteresis can be minimized 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 confirmed to be at least
3A.
The formula for selecting a softstart capacitor is:
Where:
SIMPLE DESIGN PROCEDURE
ISST = Softstart Current, 3.7μA typical
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 sim-
ple steps.
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 1: Define the power supply operating conditions:
Required output voltage
Maximum DC input voltage
If this feature is not desired, leave the Softstart pin (pin 7)
open circuited
Maximum output load current
Step 2: Set the output voltage by selecting a fixed output
LM2673 (3.3V, 5V or 12V applications) or determine the re-
quired feedback resistors for use with the adjustable LM2673
−ADJ
With certain softstart capacitor values and operating condi-
tions, the LM2673 can exhibit an overshoot on the output
voltage during turn on. Especially when starting up into no
load or low load, the softstart function may not be effective in
preventing a larger voltage overshoot on the output. With
larger loads or lower input voltages during startup this effect
is minimized. In particular, avoid using softstart capacitors
between 0.033µF and 1µF.
Step 3: Determine the inductor required by using one of the
four nomographs, Figure 3 through Figure 6. Table 1 provides
a specific manufacturer and part number for the inductor.
Step 4: Using Table 3 (fixed output voltage) or Table 6 (ad-
justable output voltage), determine the output capacitance
required for stable operation. Table 2 provides the specific
capacitor type from the manufacturer of choice.
ADDITIONAL APPLICATION INFORMATION
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 application
designed to these specific operating conditions is subjected
to a current limit fault condition, it may be possible to observe
a large hysteresis in the current limit. This can affect the out-
put 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 capac-
itor 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).
Step 6: Select a diode from Table 5. The current rating of the
diode must be greater than I load max and the Reverse Volt-
age rating must be greater than Vin max.
Under current limiting conditions, the LM267x is designed to
respond in the following manner:
1. At the moment when the inductor current reaches the
current limit threshold, the ON-pulse is immediately
terminated. This happens for any application condition.
Step 7: Include a 0.01μF/50V capacitor for Cboost in the de-
sign and then determine the value of a softstart capacitor if
desired.
2. However, the current limit block is also designed to
momentarily reduce the duty cycle to below 50% to avoid
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
www.national.com
12
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 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.
Step 8: Determine a value for RADJ to provide a peak switch
current limit of at least 2.5A plus 50% or 3.75A.
FIXED OUTPUT VOLTAGE DESIGN EXAMPLE
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 re-
quired 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 1: Operating conditions are:
Vout = 14.8V
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.
Vin max = 28V
Iload max = 2A
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.
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 ca-
pacitors 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:
Where VFB is the feedback voltage of typically 1.21V.
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)
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 fol-
lowing 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 6: From Table 5 a 3A or more Schottky diode must be
selected. The 20V rated diodes are sufficient for the applica-
tion and for through-hole components two part types are
suitable:
Step 3: To use the nomograph for the adjustable device, Fig-
ure 6, requires a calculation of the inductor 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.
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.
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
tSS: 50mS
VSST: 0.63V
VOUT: 3.3V
VSCHOTTKY: 0.5V
VIN: 16V
For this example E•T is found to be:
Using Vin max ensures that the softstart delay time will be at
least the desired 50mS.
13
www.national.com
Using Figure 6, the intersection of 27V•μS horizontally and
the 2A vertical line (Iload max) indicates that L38 , a 68μH in-
ductor, should be used.
Step 6: From Table 5 a 3A Schottky diode must be selected.
For surface mount diodes with a margin of safety on the volt-
age rating one of five diodes can be used:
From Table 1, L38 in a surface mount component is available
from Pulse Engineering with part number PE-54038S.
SK34
30BQ040
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 solu-
tions. Table 2 provides the actual capacitor characteristics
based on the C Code number. Any of the following choices
can be used:
30WQ04F
MBRS340
MBRD340
Step 7: A 0.01μF capacitor will be used for Cboost.
The softstart pin will be left open circuited.
1 x 33μF/20V AVX TPS (code C6)
1 x 47μF/20V Sprague 594 (code C8)
1 x 47μF/20V Kemet T495 (code C8)
Step 8: Determine a value for RADJ to provide a peak switch
current limit of at least 2A plus 50% or 3A.
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 ei-
ther a 33μH or 47μH inductor and the output capacitors from
Table 6.
Use a value of 12.4KΩ.
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 Ap-
plication Note AN-1187.
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 ca-
pacitor from Sprague, has the required voltage/current rating
of the surface mount components.
www.national.com
14
Inductor Selection Guides
For Continuous Mode Operation
10091319
10091321
FIGURE 3. LM2673-3.3
FIGURE 5. LM2673-12
10091320
FIGURE 4. LM2673-5.0
10091322
FIGURE 6. LM2673-ADJ
15
www.national.com
Table 1. Inductor Manufacturer Part Numbers
Renco Pulse Engineering
Through Hole
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
Capacitor
Reference
Code
AVX TPS Series
Sprague 594D Series
Kemet T495 Series
C (µF) WV (V) Irms
(A)
C (µF) WV (V) Irms
(A)
C (µF) WV (V) Irms
(A)
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
1.1
1.4
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
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
www.national.com
Input and Output Capacitor Codes (continued)
Through Hole
Capacitor
Reference
Code
Sanyo OS-CON SA Series Sanyo MV-GX Series
Nichicon PL Series
Panasonic HFQ Series
C (µF) WV (V) Irms
(A)
C (µF) WV (V) Irms
(A)
C (µF) WV (V) Irms
(A)
C (µF) WV (V) Irms
(A)
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
0.6
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
0.4
0.44
0.76
1.01
1.4
1.95
2.45
1.87
2.36
0.96
1.92
2.28
2.25
2.09
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
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
Table 3. Output Capacitors for Fixed Output Voltage Application
Surface Mount
Inductance
Output
Voltage (V)
AVX TPS Series
Sprague 594D Series Kemet T495 Series
(µH)
No.
4
C Code
C2
No.
3
C Code
C1
No.
4
C Code
C4
10
15
22
33
10
15
22
33
47
10
15
22
33
47
68
100
4
C2
3
C1
4
C4
3.3
5
3
C2
2
C7
3
C4
2
C2
2
C6
2
C4
4
C2
4
C6
4
C4
3
C2
2
C7
3
C4
3
C2
2
C7
3
C4
2
C2
2
C3
2
C4
2
C2
1
C7
2
C4
4
C5
3
C6
5
C9
3
C5
2
C7
4
C8
2
C5
2
C6
3
C8
12
2
C5
1
C7
2
C8
2
C4
1
C6
2
C8
1
C5
1
C5
2
C7
1
C4
1
C5
1
C8
Through Hole
Sanyo MV-GX Series Nichicon PL Series
Output
Voltage (V)
Inductance Sanyo OS-CON SA
Panasonic HFQ
Series
(µH)
Series
No.
1
C Code
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
www.national.com
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
C7
No.
2
C Code
C8
10
15
22
33
10
15
22
33
47
10
15
22
33
47
68
100
C5
C9
*
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
No.
1
1
*
C Code
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
*
*
C7
C7
*
1
1
1
1
1
*
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
Table 5. Schottky Diode Selection Table
Surface Mount Through Hole
Reverse
Voltage
(V)
3A
5A or More
3A
5A or More
20V
30V
40V
SK32
1N5820
SR302
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
www.national.com
Table 6. Output Capacitors for Adjustable Output Voltage Applications
Surface Mount
Output Voltage Inductance
AVX TPS Series
Sprague 594D 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
C2
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*
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
1.21 to 2.50
2.5 to 3.75
C2
C3
C2
C3
C2
C3
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
www.national.com
22
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
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
C Code
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*
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
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
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
www.national.com
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
www.national.com
24
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
www.national.com
Notes
For more National Semiconductor product information and proven design tools, visit the following Web sites at:
Products
www.national.com/amplifiers
Design Support
Amplifiers
WEBENCH
www.national.com/webench
www.national.com/AU
Audio
www.national.com/audio
www.national.com/timing
www.national.com/adc
Analog University
App Notes
Clock Conditioners
Data Converters
Displays
www.national.com/appnotes
www.national.com/contacts
www.national.com/quality/green
www.national.com/packaging
Distributors
www.national.com/displays
www.national.com/ethernet
www.national.com/interface
www.national.com/lvds
Green Compliance
Packaging
Ethernet
Interface
Quality and Reliability www.national.com/quality
LVDS
Reference Designs
Feedback
www.national.com/refdesigns
www.national.com/feedback
Power Management
Switching Regulators
LDOs
www.national.com/power
www.national.com/switchers
www.national.com/ldo
LED Lighting
PowerWise
www.national.com/led
www.national.com/powerwise
Serial Digital Interface (SDI) www.national.com/sdi
Temperature Sensors
Wireless (PLL/VCO)
www.national.com/tempsensors
www.national.com/wireless
THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION
(“NATIONAL”) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY
OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO
SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE. NO LICENSE, WHETHER EXPRESS,
IMPLIED, ARISING BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS
DOCUMENT.
TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT
NATIONAL’S PRODUCT WARRANTY. EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS, TESTING OF ALL
PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED. NATIONAL ASSUMES NO LIABILITY FOR
APPLICATIONS ASSISTANCE OR BUYER PRODUCT DESIGN. BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND
APPLICATIONS USING NATIONAL COMPONENTS. PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE
NATIONAL COMPONENTS, BUYERS SHOULD PROVIDE ADEQUATE DESIGN, TESTING AND OPERATING SAFEGUARDS.
EXCEPT AS PROVIDED IN NATIONAL’S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, NATIONAL ASSUMES NO
LIABILITY WHATSOEVER, AND NATIONAL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY RELATING TO THE SALE
AND/OR USE OF NATIONAL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR
PURPOSE, MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY
RIGHT.
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR
SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF THE CHIEF EXECUTIVE OFFICER AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
Life support devices or systems are devices 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. A critical component is any component in a life support device or system whose failure to perform
can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness.
National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation. All other
brand or product names may be trademarks or registered trademarks of their respective holders.
Copyright© 2008 National Semiconductor Corporation
For the most current product information visit us at www.national.com
National Semiconductor
Americas Technical
Support Center
Email:
new.feedback@nsc.com
Tel: 1-800-272-9959
National Semiconductor Europe
Technical Support Center
Email: europe.support@nsc.com
German Tel: +49 (0) 180 5010 771
English Tel: +44 (0) 870 850 4288
National Semiconductor Asia
Pacific Technical Support Center
Email: ap.support@nsc.com
National Semiconductor Japan
Technical Support Center
Email: jpn.feedback@nsc.com
www.national.com
相关型号：
LM2673SX-5.0/NOPB
8V to 40V, 3A SIMPLE SWITCHER® buck converter with adjustable current limit 7-DDPAK/TO-263 -40 to 125
TI
©2020 ICPDF网 联系我们和版权申明