LM2673
SIMPLE SWITCHER
3A Step-Down Voltage Regulator
with Adjustable Current Limit
General Description
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.
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.
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.
Features
n
Efficiency up to 94%
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.
n
150 m
DMOS output switch
n
3.3V, 5V and 12V fixed output and adjustable (1.2V to
37V ) versions
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 +125C operating junction temperature range
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.
April 2003
LM2673
SIMPLE
SWITCHER
3A
Step-Down
V
oltage
Regulator
with
Adjustable
Current
Limit
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
LM2673S-3.3, LM2673S-5.0,
LM2673S-12 or LM2673S-ADJ
See NSC Package Number TS7B
10091302
Order Number
LM2673T-3.3, LM2673T-5.0,
LM2673T-12 or LM2673T-ADJ
See NSC Package Number TA07B
Top View
10091335
LLP-14
See NS package Number LDC14A
Ordering Information for LLP Package
Output Voltage
Order Information
Package Marking
Supplied As
12
LM2673LD-12
S0000AB
250 Units on Tape and Reel
12
LM2673LDX-12
S0000AB
2500 Units on Tape and Reel
3.3
LM2673LD-3.3
S00008B
250 Units on Tape and Reel
3.3
LM2673LDX-3.3
S00008B
2500 Units on Tape and Reel
5.0
LM2673LD-5.0
S00009B
250 Units on Tape and Reel
5.0
LM2673LDX-5.0
S00009B
2500 Units on Tape and Reel
ADJ
LM2673LD-ADJ
S0000BB
250 Units on Tape and Reel
ADJ
LM2673LDX-ADJ
S0000BB
2500 Units on Tape and Reel
LM2673
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2
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Supply Voltage
45V
Softstart Pin Voltage
-0.1V to 6V
Switch Voltage to Ground
-1V to V
IN
Boost Pin Voltage
V
SW
+ 8V
Feedback Pin Voltage
-0.3V to 14V
Power Dissipation
Internally Limited
ESD (Note 2)
2 kV
Storage Temperature Range
-65C to 150C
Soldering Temperature
Wave
4 sec, 260C
Infrared
10 sec, 240C
Vapor Phase
75 sec, 219C
Operating Ratings
Supply Voltage
8V to 40V
Junction Temperature Range (T
J
)
-40C to 125C
Electrical Characteristics
Limits appearing in bold type face apply over the entire junction temperature
range of operation, -40C to 125C. Specifications appearing in normal type apply for T
A
= T
J
= 25C. R
ADJ
= 8.2K
LM2673-3.3
Symbol
Parameter
Conditions
Typical
Min
Max
Units
(Note 3)
(Note 4)
(Note 4)
V
OUT
Output Voltage
V
IN
= 8V to 40V, 100mA
I
OUT
3A
3.3
3.234/3.201
3.366/3.399
V
Efficiency
V
IN
= 12V, I
LOAD
= 3A
86
%
LM2673-5.0
Symbol
Parameter
Conditions
Typical
Min
Max
Units
(Note 3)
(Note 4)
(Note 4)
V
OUT
Output Voltage
V
IN
= 8V to 40V, 100mA
I
OUT
3A
5.0
4.900/4.850
5.100/5.150
V
Efficiency
V
IN
= 12V, I
LOAD
= 3A
88
%
LM2673-12
Symbol
Parameter
Conditions
Typical
Min
Max
Units
(Note 3)
(Note 4)
(Note 4)
V
OUT
Output Voltage
V
IN
= 15V to 40V, 100mA
I
OUT
3A
12
11.76/11.64
12.24/12.36
V
Efficiency
V
IN
= 24V, I
LOAD
= 3A
94
%
LM2673-ADJ
Symbol
Parameter
Conditions
Typ
Min
Max
Units
(Note 3)
(Note 4)
(Note 4)
V
FB
Feedback
Voltage
V
IN
= 8V to 40V, 100mA
I
OUT
3A
V
OUT
Programmed for 5V
1.21
1.186/1.174
1.234/1.246
V
Efficiency
V
IN
= 12V, I
LOAD
= 3A
88
%
LM2673
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3
All Output Voltage Versions
Electrical Characteristics
Limits appearing in bold type face apply over the entire junction temperature range of operation, -40C to 125C. Specifica-
tions appearing in normal type apply for T
A
= T
J
= 25C. Unless otherwise specified, R
ADJ
= 8.2K
, V
IN
=12V for the 3.3V, 5V
and Adjustable versions and V
IN
=24V for the 12V version.
Symbol
Parameter
Conditions
Typ
Min
Max
Units
DEVICE PARAMETERS
I
Q
Quiescent
Current
V
FEEDBACK
= 8V
4.2
6
mA
For 3.3V, 5.0V, and ADJ Versions
V
FEEDBACK
= 15V
For 12V Versions
V
ADJ
Current Limit
Adjust Voltage
1.21
1.181/1.169
1.229/1.246
V
I
CL
Current Limit
R
ADJ
= 8.2K
, (Note 5)
4.5
3.8/3.6
5.25/5.4
A
I
L
Output Leakage
Current
V
IN
= 40V, Softstart Pin = 0V
V
SWITCH
= 0V
V
SWITCH
= -1V
1.0
6
1.5
15
mA
mA
R
DS(ON)
Switch
On-Resistance
I
SWITCH
= 3A
0.15
0.17/0.29
f
O
Oscillator
Frequency
Measured at Switch Pin
260
225
280
kHz
D
Duty Cycle
Maximum Duty Cycle
91
%
Minimum Duty Cycle
0
%
I
BIAS
Feedback Bias
Current
V
FEEDBACK
= 1.3V
ADJ Version Only
85
nA
V
SFST
Softstart
Threshold
Voltage
0.63
0.53
0.74
V
I
SFST
Softstart Pin
Current
Softstart Pin = 0V
3.7
6.9
A
JA
Thermal
Resistance
T Package, Junction to Ambient
65
(Note 6)
JA
T Package, Junction to Ambient
45
(Note 7)
JC
T Package, Junction to Case
2
JA
S Package, Junction to Ambient
56
C/W
(Note 8)
JA
S Package, Junction to Ambient
35
(Note 9)
JA
S Package, Junction to Ambient
26
(Note 10)
JC
S Package, Junction to Case
2
++
JA
LD Package, Junction to Ambient
55
C/W
(Note 11)
JA
LD Package, Junction to Ambient
29
(Note 12)
LM2673
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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 k
resistor into each pin.
Note 3: Typical values are determined with T
A
= T
J
= 25C 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 T
A
= T
J
= 25C. 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: I
CL
=37,125/ R
ADJ
.
Note 6: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with
1
/
2
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
1
/
2
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.
LM2673
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