NSC LM2673T-ADJ, LM2673T-12, LM2673SX-ADJ, LM2673SX-3.3, LM2673SX-12 Datasheet
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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.Afamilyofstandardinductors 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 con-
trolled 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
SIMPLE SWITCHER®is a registered trademark of National Semiconductor Corporation.
DS100913-3
April 2000
LM2673 SIMPLE SWITCHER 3A Step-Down Voltage Regulator with Adjustable Current Limit
© 2000 National Semiconductor Corporation DS100913 www.national.com
Connection Diagram and Ordering Information
TO-263 Package
Top View
DS100913-1
Order Number
LM2673S-3.3, LM2673S-5.0,
LM2673S-12 or LM2673S-ADJ
See NSC Package Number TS7B
TO-220 Package
Top View
DS100913-2
Order Number
LM2673T-3.3, LM2673T-5.0,
LM2673T-12 or LM2673T-ADJ
See NSC Package Number TA07B
LM2673
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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 VSW+8V
Feedback Pin Voltage −0.3V to 14V
Power Dissipation Internally Limited
ESD (Note 2) 2 kV
Storage Temperature Range −65˚C to 150˚C
Soldering Temperature
Wave 4 sec, 260˚C
Infrared 10 sec, 240˚C
Vapor Phase 75 sec, 219˚C
Operating Ratings
Supply Voltage 8V to 40V
Junction Temperature Range (T
J
) −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 T
A=TJ
= 25˚C. R
ADJ
= 8.2KΩ
LM2673-3.3
Symbol Parameter Conditions Typical Min Max Units
(Note 3) (Note 4) (Note 4)
V
OUT
Output Voltage VIN= 8V to 40V, 100mA ≤ I
OUT
≤ 3A 3.3 3.234/3.201 3.366/3.399 V
η 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 VIN= 8V to 40V, 100mA ≤ I
OUT
≤ 3A 5.0 4.900/4.850 5.100/5.150 V
η 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 VIN= 15V to 40V, 100mA ≤ I
OUT
≤ 3A 12 11.76/11.64 12.24/12.36 V
η 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
VIN= 8V to 40V, 100mA ≤ I
OUT
≤ 3A
V
OUT
Programmed for 5V
1.21 1.186/1.174 1.234/1.246 V
η Efficiency V
IN
= 12V, I
LOAD
=3A 88 %
LM2673
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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.
Specifications appearing in normal type apply for TA=TJ= 25˚C. Unless otherwise specified, R
ADJ
= 8.2KΩ,VIN=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
= 8.2KΩ, (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 Ω
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 µA
θ
JA
Thermal
Resistance
T Package, Junction to Ambient 65
(Note 6)
θ
JA
T Package, Junction to Ambient 45
(Note 7)
θ
JC
T Package, Junction to Case 2
θ
JA
S Package, Junction to Ambient 56 ˚C/W
(Note 8)
θ
JA
S Package, Junction to Ambient 35
(Note 9)
θ
JA
S Package, Junction to Ambient 26
(Note 10)
θ
JC
S Package, Junction to Case 2 ++
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
A=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 T
A=TJ
= 25˚C. All limits at temperature extremes are guaranteed via correlation using standard standard Quality Control (SQC) meth-
ods. 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
⁄2inch 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
⁄2inch leads soldered to a PC board
containing approximately 4 square inches of (1 oz.) copper area surrounding the leads.
LM2673
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(Continued)
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.Additionalcopper area will reduce thermal resistance further.See the thermal model in Switchers Made
Simple
®
software.
LM2673
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Typical Performance Characteristics
Normalized
Output Voltage
DS100913-4
Line Regulation
DS100913-5
Efficiency vs Input Voltage
DS100913-6
Efficiency vs I
LOAD
DS100913-7
Switch Current Limit
DS100913-8
Operating Quiescent Current
DS100913-9
Switching Frequency
DS100913-12
Feedback Pin Bias Current
DS100913-13
LM2673
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Block Diagram
DS100913-14
* Active Inductor Patent Number 5,514,947
†
Active Capacitor Patent Number 5,382,918
LM2673
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Typical Performance Characteristics
Continuous Mode Switching Waveforms
V
IN
= 20V, V
OUT
=5V,I
LOAD
=3A
L = 33 µH, C
OUT
= 200 µF, C
OUT
ESR=26mΩ
DS100913-15
A: VSWPin Voltage, 10 V/div.
B: Inductor Current, 1 A/div
C: Output Ripple Voltage, 20 mV/div AC-Coupled
Horizontal Time Base: 1 µs/div
Discontinuous Mode Switching Waveforms
V
IN
= 20V, V
OUT
=5V,I
LOAD
= 500 mA
L = 10 µH, C
OUT
= 400 µF, C
OUT
ESR=13mΩ
DS100913-16
A: VSWPin Voltage, 10 V/div.
B: Inductor Current, 1 A/div
C: Output Ripple Voltage, 20 mV/div AC-Coupled
Horizontal Time Base: 1 µs//iv
Load Transient Response for Continuous Mode
V
IN
= 20V, V
OUT
=5V
L = 33 µH, C
OUT
= 200 µF, C
OUT
ESR=26mΩ
DS100913-17
A: Output Voltage, 100 mV//div, AC-Coupled.
B: Load Current: 500 mA to 3A Load Pulse
Horizontal Time Base: 100 µs/div
Load Transient Response for Discontinuous Mode
V
IN
= 20V, V
OUT
=5V,
L = 10 µH, C
OUT
= 400 µF, C
OUT
ESR=13mΩ
DS100913-18
A: Output Voltage, 100 mV/div, AC-Coupled.
B: Load Current: 200 mA to 3A Load Pulse
Horizontal Time Base: 200 µs/div
LM2673
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