LM2671
SIMPLE SWITCHER
Power Converter High Efficiency
500mA Step-Down Voltage Regulator with Features
General Description
The LM2671 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 500mA 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), fixed frequency oscillator, external shutdown,
soft-start, and frequency synchronization.
The LM2671 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 LM2671 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 LM2671 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
Soft-start and frequency synchronization
n
Thermal shutdown and current limit protection
Applications
n
Simple High Efficiency (
>
90%) Step-Down (Buck)
Regulator
n
Efficient Pre-Regulator for Linear Regulators
Typical Application
(Fixed Output Voltage Versions)
10004201
SIMPLE SWITCHER
is a registered trademark of National Semiconductor Corporation.
Windows
is a registered trademark of Microsoft Corporation.
February 2005
LM2671
SIMPLE
SWITCHER
Power
Converter
High
Efficiency
500mA
Step-Down
V
oltage
Regulator
with
Features
2005 National Semiconductor Corporation
DS100042
www.national.com
Connection Diagrams
16-Lead LLP Surface Mount Package
Top View
8-Lead Package
Top View
10004241
LLP Package
See NSC Package Drawing Number LDA16A
10004202
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
LM2671LD-12
S0005B
1000 Units on Tape and Reel
12
LM2671LDX-12
S0005B
4500 Units on Tape and Reel
3.3
LM2671LD-3.3
S0006B
1000 Units on Tape and Reel
3.3
LM2671LDX-3.3
S0006B
4500 Units on Tape and Reel
5.0
LM2671LD-5.0
S0007B
1000 Units on Tape and Reel
5.0
LM2671LDX-5.0
S0007B
4500 Units on Tape and Reel
ADJ
LM2671LD-ADJ
S0008B
1000 Units on Tape and Reel
ADJ
LM2671LDX-ADJ
S0008B
4500 Units on Tape and Reel
SO-8
12
LM2671M-12
2671M-12
Shipped in Anti-Static Rails
12
LM2671MX-12
2671M-12
2500 Units on Tape and Reel
3.3
LM2671M-3.3
2671M-3.3
Shipped in Anti-Static Rails
3.3
LM2671MX-3.3
2671M-3.3
2500 Units on Tape and Reel
5.0
LM2671M-5.0
2671M-5.0
Shipped in Anti-Static Rails
5.0
LM2671MX-5.0
2671M-5.0
2500 Units on Tape and Reel
ADJ
LM2671M-ADJ
2671M-ADJ
Shipped in Anti-Static Rails
ADJ
LM2671MX-ADJ
2671M-ADJ
2500 Units on Tape and Reel
DIP
12
LM2671N-12
LM2671N-12
Shipped in Anti-Static Rails
3.3
LM2671N-3.3
LM2671N-3.3
Shipped in Anti-Static Rails
5.0
LM2671N-5.0
LM2671N-5.0
Shipped in Anti-Static Rails
ADJ
LM2671N-ADJ
LM2671N-ADJ
Shipped in Anti-Static Rail
LM2671
www.national.com
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
Temperature Range
-40C
T
J
+125C
Electrical Characteristics
LM2671-3.3
Specifications with standard type face are for T
J
= 25C, and those in 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
%
LM2671-5.0
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
%
LM2671-12
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
%
LM2671-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
1.210
1.192/1.174
1.228/1.246
V
V
OUT
Programmed for 5V
(see Circuit of Figure 3)
LM2671
www.national.com
3
LM2671-ADJ
(Continued)
Symbol
Parameter
Conditions
Typ
Min
Max
Units
(Note 4)
(Note 5)
(Note 5)
V
FB
Feedback
Voltage
V
IN
= 6.5V to 40V, I
LOAD
= 20 mA to 250 mA
1.210
1.192/1.174
1.228/1.246
V
V
OUT
Programmed for 5V
(see Circuit of Figure 3)
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 in bold type face apply over full Operating Temperature
Range. Unless otherwise specified, V
IN
= 12V for the 3.3V, 5V, and Adjustable versions and V
IN
= 24V for the 12V version,
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
1
25
A
V
SWITCH
= 0V
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
V
FEEDBACK
= 1.3V
85
nA
Current
ADJ Version Only
V
S/D
ON/OFF Pin
1.4
0.8
2.0
V
Voltage Thesholds
I
S/D
ON/OFF Pin Current
ON/OFF Pin = 0V
20
7
37
A
F
SYNC
Synchronization Frequency
V
SYNC
= 3.5V, 50% duty cycle
400
kHz
V
SYNC
Synchronization Threshold
Voltage
1.4
V
V
SS
Soft-Start Voltage
0.63
0.53
0.73
V
I
SS
Soft-Start Current
4.5
1.5
6.9
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 LM2671 is used as shown in Figure 2 and Figure 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.
LM2671
www.national.com
4
Typical Performance Characteristics
Normalized
Output Voltage
Line Regulation
10004203
10004204
Efficiency
Drain-to-Source
Resistance
10004205
10004206
Switch Current Limit
Operating
Quiescent Current
10004207
10004208
LM2671
www.national.com
5
PDF 
ZIP