LM2674
SIMPLE SWITCHER
Power Converter High Efficiency
500 mA Step-Down Voltage Regulator
General Description
The LM2674 series of regulators are monolithic integrated
circuits built with a LMDMOS process. These regulators
provide all the active functions for a step-down (buck)
switching regulator, capable of driving a 500 mA load current
with excellent line and load regulation. These devices are
available in fixed output voltages of 3.3V, 5.0V, 12V, and an
adjustable output version.
Requiring a minimum number of external components, these
regulators are simple to use and include patented internal
frequency compensation (Patent Nos. 5,382,918 and
5,514,947) and a fixed frequency oscillator.
The LM2674 series operates at a switching frequency of
260 kHz, thus allowing smaller sized filter components than
what would be needed with lower frequency switching regu-
lators. Because of its very high efficiency (
>
90%), the cop-
per traces on the printed circuit board are the only heat
sinking needed.
A family of standard inductors for use with the LM2674 are
available from several different manufacturers. This feature
greatly simplifies the design of switch-mode power supplies
using these advanced ICs. Also included in the datasheet
are selector guides for diodes and capacitors designed to
work in switch-mode power supplies.
Other features include a guaranteed
1.5% tolerance on
output voltage within specified input voltages and output
load conditions, and
10% on the oscillator frequency. Ex-
ternal shutdown is included, featuring typically 50 A
stand-by current. The output switch includes current limiting,
as well as thermal shutdown for full protection under fault
conditions.
To simplify the LM2674 buck regulator design procedure,
there exists computer design software, LM267X Made
Simple (version 6.0).
Features
n
Efficiency up to 96%
n
Available in SO-8, 8-pin DIP and LLP packages
n
Computer Design Software LM267X Made Simple
(version 6.0)
n
Simple and easy to design with
n
Requires only 5 external components
n
Uses readily available standard inductors
n
3.3V, 5.0V, 12V, and adjustable output versions
n
Adjustable version output voltage range: 1.21V to 37V
n
1.5% max output voltage tolerance over line and load
conditions
n
Guaranteed 500mA output load current
n
0.25
DMOS Output Switch
n
Wide input voltage range: 8V to 40V
n
260 kHz fixed frequency internal oscillator
n
TTL shutdown capability, low power standby mode
n
Thermal shutdown and current limit protection
Typical Applications
n
Simple High Efficiency (
>
90%) Step-Down (Buck)
Regulator
n
Efficient Pre-Regulator for Linear Regulators
n
Positive-to-Negative Converter
Typical Application
10004101
SIMPLE SWITCHER
is a registered trademark of National Semiconductor Corporation.
Windows
is a registered trademark of Microsoft Corporation.
February 2005
LM2674
SIMPLE
SWITCHER
Power
Converter
High
Efficiency
500
mA
Step-Down
V
oltage
Regulator
2005 National Semiconductor Corporation
DS100041
www.national.com
Connection Diagrams
16-Lead LLP Surface Mount Package
Top View
8-Lead Package
Top View
10004138
LLP Package
See NSC Package Drawing Number LDA16A
10004102
SO-8/DIP Package
See NSC Package Drawing Number MO8A/N08E
TABLE 1. Package Marking and Ordering Information
Output Voltage
Order Information
Package Marking
Supplied as:
16 Lead LLP
12
LM2674LD-12
S0009B
1000 Units on Tape and Reel
12
LM2674LDX-12
S0009B
4500 Units on Tape and Reel
3.3
LM2674LD-3.3
S000AB
1000 Units on Tape and Reel
3.3
LM2674LDX-3.3
S000AB
4500 Units on Tape and Reel
5.0
LM2674LD-5.0
S000BB
1000 Units on Tape and Reel
5.0
LM2674LDX-5.0
S000BB
4500 Units on Tape and Reel
ADJ
LM2674LD-ADJ
S000CB
1000 Units on Tape and Reel
ADJ
LM2674LDX-ADJ
S000CB
4500 Units on Tape and Reel
SO-8
12
LM2674M-12
2674M-12
Shipped in Anti-Static Rails
12
LM2674MX-12
2674M-12
2500 Units on Tape and Reel
3.3
LM2674M-3.3
2674M-3.3
Shipped in Anti-Static Rails
3.3
LM2674MX-3.3
2674M-3.3
2500 Units on Tape and Reel
5.0
LM2674M-5.0
2674M-5.0
Shipped in Anti-Static Rails
5.0
LM2674MX-5.0
2674M-5.0
2500 Units on Tape and Reel
ADJ
LM2674M-ADJ
2674M-ADJ
Shipped in Anti-Static Rails
ADJ
LM2674MX-ADJ
2674M-ADJ
2500 Units on Tape and Reel
DIP
12
LM2674N-12
LM2674N-12
Shipped in Anti-Static Rails
3.3
LM2674N-3.3
LM2674N-3.3
Shipped in Anti-Static Rails
5.0
LM2674N-5.0
LM2674N-5.0
Shipped in Anti-Static Rails
ADJ
LM2674N-ADJ
LM2674N-ADJ
Shipped in Anti-Static Rails
LM2674
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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.
Supply Voltage
45V
ON/OFF Pin Voltage
-0.1V
V
SH
6V
Switch Voltage to Ground
-1V
Boost Pin Voltage
V
SW
+ 8V
Feedback Pin Voltage
-0.3V
V
FB
14V
ESD Susceptibility
Human Body Model (Note 2)
2 kV
Power Dissipation
Internally Limited
Storage Temperature Range
-65C to +150C
Lead Temperature
M Package
Vapor Phase (60s)
+215C
Infrared (15s)
+220C
N Package (Soldering, 10s)
+260C
LLP Package (See AN-1187)
Maximum Junction Temperature
+150C
Operating Ratings
Supply Voltage
6.5V to 40V
Junction Temperature Range
-40C
T
J
+125C
Electrical Characteristics
LM2674-3.3
Specifications with standard type face are for T
J
= 25C, and those with bold type face apply over full
Operating Temperature Range.
Symbol
Parameter
Conditions
Typical
Min
Max
Units
(Note 4)
(Note 5)
(Note 5)
SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)
V
OUT
Output Voltage
V
IN
= 8V to 40V, I
LOAD
= 20 mA to 500 mA
3.3
3.251/3.201
3.350/3.399
V
V
OUT
Output Voltage
V
IN
= 6.5V to 40V, I
LOAD
= 20 mA to 250 mA
3.3
3.251/3.201
3.350/3.399
V
Efficiency
V
IN
= 12V, I
LOAD
= 500 mA
86
%
LM2674-5.0
Symbol
Parameter
Conditions
Typical
Min
Max
Units
(Note 4)
(Note 5)
(Note 5)
SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)
V
OUT
Output Voltage
V
IN
= 8V to 40V, I
LOAD
= 20 mA to 500 mA
5.0
4.925/4.850
5.075/5.150
V
V
OUT
Output Voltage
V
IN
= 6.5V to 40V, I
LOAD
= 20 mA to 250 mA
5.0
4.925/4.850
5.075/5.150
V
Efficiency
V
IN
= 12V, I
LOAD
= 500 mA
90
%
LM2674-12
Symbol
Parameter
Conditions
Typical
Min
Max
Units
(Note 4)
(Note 5)
(Note 5)
SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3)
V
OUT
Output Voltage
V
IN
= 15V to 40V, I
LOAD
= 20 mA to 500 mA
12
11.82/11.64
12.18/12.36
V
Efficiency
V
IN
= 24V, I
LOAD
= 500 mA
94
%
LM2674-ADJ
Symbol
Parameter
Conditions
Typ
Min
Max
Units
(Note 4)
(Note 5)
(Note 5)
SYSTEM PARAMETERS Test Circuit Figure 3 (Note 3)
V
FB
Feedback
Voltage
V
IN
= 8V to 40V, I
LOAD
= 20 mA to 500 mA
V
OUT
Programmed for 5V
(see Circuit of Figure 3)
1.210
1.192/1.174
1.228/1.246
V
V
FB
Feedback
Voltage
V
IN
= 6.5V to 40V, I
LOAD
= 20 mA to 250 mA
V
OUT
Programmed for 5V
(see Circuit of Figure 3)
1.210
1.192/1.174
1.228/1.246
V
LM2674
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3
LM2674-ADJ
(Continued)
Symbol
Parameter
Conditions
Typ
Min
Max
Units
(Note 4)
(Note 5)
(Note 5)
Efficiency
V
IN
= 12V, I
LOAD
= 500 mA
90
%
All Output Voltage Versions
Specifications with standard type face are for T
J
= 25C, and those with bold type face apply over full Operating Tempera-
ture Range. Unless otherwise specified, V
IN
= 12V for the 3.3V, 5V, and Adjustable versions and V
IN
= 24V for the 12V ver-
sion, and I
LOAD
= 100 mA.
Symbol
Parameters
Conditions
Typ
Min
Max
Units
DEVICE PARAMETERS
I
Q
Quiescent Current
V
FEEDBACK
= 8V
2.5
3.6
mA
For 3.3V, 5.0V, and ADJ Versions
V
FEEDBACK
= 15V
2.5
mA
For 12V Versions
I
STBY
Standby Quiescent
Current
ON/OFF Pin = 0V
50
100/150
A
I
CL
Current Limit
0.8
0.62/0.575
1.2/1.25
A
I
L
Output Leakage Current
V
IN
= 40V, ON/OFF Pin = 0V
V
SWITCH
= 0V
1
25
A
V
SWITCH
= -1V, ON/OFF Pin = 0V
6
15
mA
R
DS(ON)
Switch On-Resistance
I
SWITCH
= 500 mA
0.25
0.40/0.60
f
O
Oscillator Frequency
Measured at Switch Pin
260
225
275
kHz
D
Maximum Duty Cycle
95
%
Minimum Duty Cycle
0
%
I
BIAS
Feedback Bias
Current
V
FEEDBACK
= 1.3V
ADJ Version Only
85
nA
V
S/D
ON/OFF Pin
Voltage Thesholds
1.4
0.8
2.0
V
I
S/D
ON/OFF Pin Current
ON/OFF Pin = 0V
20
7
37
A
JA
Thermal Resistance
N Package, Junction to Ambient (Note 6)
95
C/W
M Package, Junction to Ambient (Note 6)
105
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but device parameter specifications may not be guaranteed under these conditions. For guaranteed specifications and test conditions, see
the Electrical Characteristics.
Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 k
resistor into each pin.
Note 3: External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator
performance. When the LM2674 is used as shown in Figures 2, 3 test circuits, system performance will be as specified by the system parameters section of the
Electrical Characteristics.
Note 4: Typical numbers are at 25C and represent the most likely norm.
Note 5: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%
production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used
to calculate Average Outgoing Quality Level (AOQL).
Note 6: Junction to ambient thermal resistance with approximately 1 square inch of printed circuit board copper surrounding the leads. Additional copper area will
lower thermal resistance further. See Application Information section in the application note accompanying this datasheet and the thermal model in LM267X Made
Simple (version 6.0) software. The value
J-A
for the LLP (LD) package is specifically dependent on PCB trace area, trace material, and the number of layers and
thermal vias. For improved thermal resistance and power dissipation for the LLP package, refer to Application Note AN-1187.
LM2674
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4
Typical Performance
Characteristics
Normalized
Output Voltage
Line Regulation
10004103
10004104
Efficiency
Drain-to-Source
Resistance
10004105
10004106
Switch Current Limit
Operating
Quiescent Current
10004107
10004108
LM2674
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5
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