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LM2673 SIMPLE SWITCHER 3A Step-Down Voltage Regulator with Adjustable Current Limit
August 2002
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 characteris-
tics. 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 adjust-
able 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 mΩ 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 +125˚C 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.
© 2002 National Semiconductor Corporation
DS100913
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LM2673
Connection Diagrams and Ordering Information
TO-263 Package
Top View
TO-220 Package
Top View
10091301
10091302
Order Number
LM2673S-3.3, LM2673S-5.0,
LM2673S-12 or LM2673S-ADJ
See NSC Package Number TS7B
Top View
Order Number
LM2673T-3.3, LM2673T-5.0,
LM2673T-12 or LM2673T-ADJ
See NSC Package Number TA07B
10091335
LLP-14
See NS package Number LDC14A
Ordering Information for LLP Package
Output Voltage
12
12
3.3
3.3
5.0
5.0
ADJ
ADJ
Order Information
LM2673LD-12
LM2673LDX-12
LM2673LD-3.3
LM2673LDX-3.3
LM2673LD-5.0
LM2673LDX-5.0
LM2673LD-ADJ
LM2673LDX-ADJ
Package Marking
S0000AB
S0000AB
S00008B
S00008B
S00009B
S00009B
S0000BB
S0000BB
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
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2
LM2673
Absolute Maximum Ratings
(Note 1)
Storage Temperature Range
Soldering Temperature
Wave
Infrared
Vapor Phase
−65˚C to 150˚C
4 sec, 260˚C
10 sec, 240˚C
75 sec, 219˚C
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Supply Voltage
Softstart Pin Voltage
Switch Voltage to Ground
Boost Pin Voltage
Feedback Pin Voltage
Power Dissipation
ESD (Note 2)
45V
−0.1V to 6V
−1V to V
IN
V
SW
+ 8V
−0.3V to 14V
Internally Limited
2 kV
Operating Ratings
Supply Voltage
Junction Temperature Range (T
J
)
8V to 40V
−40˚C to 125˚C
Electrical Characteristics
LM2673-3.3
Symbol
V
OUT
η
Parameter
Output Voltage
Efficiency
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 T
A
= T
J
= 25˚C. R
ADJ
= 8.2KΩ
Conditions
V
IN
= 8V to 40V, 100mA
≤
I
OUT
≤
3A
V
IN
= 12V, I
LOAD
= 3A
Typical
(Note 3)
3.3
86
Min
(Note 4)
3.234/3.201
Max
(Note 4)
3.366/3.399
Units
V
%
LM2673-5.0
Symbol
V
OUT
η
Parameter
Output Voltage
Efficiency
Conditions
V
IN
= 8V to 40V, 100mA
≤
I
OUT
≤
3A
V
IN
= 12V, I
LOAD
= 3A
Typical
(Note 3)
5.0
88
Min
(Note 4)
4.900/4.850
Max
(Note 4)
5.100/5.150
V
%
Units
LM2673-12
Symbol
V
OUT
η
Parameter
Output Voltage
Efficiency
Conditions
V
IN
= 15V to 40V, 100mA
≤
I
OUT
≤
3A
V
IN
= 24V, I
LOAD
= 3A
Typical
(Note 3)
12
94
Min
(Note 4)
11.76/11.64
Max
(Note 4)
12.24/12.36
V
%
Units
LM2673-ADJ
Symbol
V
FB
η
Parameter
Feedback
Voltage
Efficiency
Conditions
V
IN
= 8V to 40V, 100mA
≤
I
OUT
≤
3A
V
OUT
Programmed for 5V
V
IN
= 12V, I
LOAD
= 3A
Typ
(Note 3)
1.21
88
Min
(Note 4)
1.186/1.174
Max
(Note 4)
1.234/1.246
V
%
Units
3
www.national.com
LM2673
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 T
A
= T
J
= 25˚C. Unless otherwise specified, R
ADJ
= 8.2KΩ, V
IN
=12V for the 3.3V, 5V
and Adjustable versions and V
IN
=24V for the 12V version.
Symbol
I
Q
Parameter
Quiescent
Current
V
FEEDBACK
= 8V
For 3.3V, 5.0V, and ADJ Versions
V
FEEDBACK
= 15V
For 12V Versions
V
ADJ
I
CL
I
L
Current Limit
Adjust Voltage
Current Limit
Output Leakage
Current
Switch
On-Resistance
Oscillator
Frequency
Duty Cycle
Feedback Bias
Current
Softstart
Threshold
Voltage
Softstart Pin
Current
Thermal
Resistance
Softstart Pin = 0V
T Package, Junction to Ambient
(Note 6)
T Package, Junction to Ambient
(Note 7)
θ
JC
θ
JA
θ
JA
θ
JA
θ
JC
θ
JA
θ
JA
T Package, Junction to Case
S Package, Junction to Ambient
(Note 8)
S Package, Junction to Ambient
(Note 9)
S Package, Junction to Ambient
(Note 10)
S Package, Junction to Case
LD Package, Junction to Ambient
(Note 11)
LD Package, Junction to Ambient
(Note 12)
29
2
55
˚C/W
++
26
35
2
56
˚C/W
45
R
ADJ
= 8.2KΩ, (Note 5)
V
IN
= 40V, Softstart Pin = 0V
V
SWITCH
= 0V
V
SWITCH
= −1V
I
SWITCH
= 3A
Measured at Switch Pin
Maximum Duty Cycle
Minimum Duty Cycle
I
BIAS
V
SFST
V
FEEDBACK
= 1.3V
ADJ Version Only
1.21
4.5
1.0
6
0.15
260
91
0
85
225
1.181/1.169
3.8/3.6
1.229/1.246
5.25/5.4
1.5
15
0.17/0.29
280
V
A
mA
mA
Ω
kHz
%
%
nA
Conditions
Typ
4.2
Min
Max
6
Units
mA
DEVICE PARAMETERS
R
DS(ON)
f
O
D
0.63
0.53
0.74
V
I
SFST
θ
JA
θ
JA
3.7
65
6.9
µA
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