NSC LM2671M-3.3, LM2671M-12, LM2671N-ADJ, LM2671N-5.0, LM2671N-12 Datasheet
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September 1998
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 regulators. Because of its very high efficiency (>90%), the copper 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. External shutdown is included, featuring typically 50 µA 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.
Features
nEfficiency up to 96%
nAvailable in SO-8 and 8-pin DIP packages
nComputer Design Software LM267X Made Simple
nSimple and easy to design with
nRequires only 5 external components
nUses readily available standard inductors
n3.3V, 5.0V, 12V, and adjustable output versions
nAdjustable version output voltage range: 1.21V to 37V
n±1.5% max output voltage tolerance over line and load conditions
nGuaranteed 500mA output load current
n0.25Ω DMOS Output Switch
nWide input voltage range: 8V to 40V
n260 kHz fixed frequency internal oscillator
nTTL shutdown capability, low power standby mode
nSoft-start and frequency synchronization
nThermal shutdown and current limit protection
Typical Applications
nSimple High Efficiency (>90%) Step-Down (Buck) Regulator
nEfficient Pre-Regulator for Linear Regulators
Typical Application (Fixed Output Voltage Versions)
DS100042-1
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation. Windows® is a registered trademark of Microsoft Corporation.
Voltage Down-Step 500mA Efficiency High Converter Power SWITCHER SIMPLE LM2671
Features with Regulator
© 1998 National Semiconductor Corporation |
DS100042 |
www.national.com |
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 |
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−0.1V ≤ VSH ≤ 6V |
ON/OFF |
Pin Voltage |
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Switch Voltage to Ground |
−1V |
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Boost Pin Voltage |
VSW + 8V |
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Feedback Pin Voltage |
−0.3V ≤ VFB ≤ 14V |
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ESD Susceptibility |
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Human Body Model (Note 2) |
2 kV |
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Power Dissipation |
Internally Limited |
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Storage Temperature Range |
−65ÊC to +150ÊC |
Lead Temperature |
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M Package |
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Vapor Phase (60s) |
+215ÊC |
Infrared (15s) |
+220ÊC |
N Package (Soldering, 10s) |
+260ÊC |
Maximum Junction Temperature |
+150ÊC |
Operating Ratings
Supply Voltage |
6.5V to 40V |
Temperature Range |
−40ÊC ≤ TJ ≤ +125ÊC |
Electrical Characteristics Specifications with standard type face are for TJ = 25ÊC, and those in bold type face apply over full Operating Temperature Range.
LM2671-3.3
Symbol |
Parameter |
Conditions |
Typical |
Min |
Max |
Units |
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(Note 4) |
(Note 5) |
(Note 5) |
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SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3) |
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VOUT |
Output Voltage |
VIN = 8V to 40V, ILOAD = 20 mA to 500 mA |
3.3 |
3.251/3.201 |
3.350/3.399 |
V |
VOUT |
Output Voltage |
VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA |
3.3 |
3.251/3.201 |
3.350/3.399 |
V |
η |
Efficiency |
VIN = 12V, ILOAD = 500 mA |
86 |
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LM2671-5.0
Symbol |
Parameter |
Conditions |
Typical |
Min |
Max |
Units |
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(Note 4) |
(Note 5) |
(Note 5) |
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SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3) |
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VOUT |
Output Voltage |
VIN = 8V to 40V, ILOAD = 20 mA to 500 mA |
5.0 |
4.925/4.850 |
5.075/5.150 |
V |
VOUT |
Output Voltage |
VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA |
5.0 |
4.925/4.850 |
5.075/5.150 |
V |
η |
Efficiency |
VIN = 12V, ILOAD = 500 mA |
90 |
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LM2671-12
Symbol |
Parameter |
Conditions |
Typical |
Min |
Max |
Units |
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(Note 4) |
(Note 5) |
(Note 5) |
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SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3) |
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VOUT |
Output Voltage |
VIN = 15V to 40V, ILOAD = 20 mA to 500 mA |
12 |
11.82/11.64 |
12.18/12.36 |
V |
η |
Efficiency |
VIN = 24V, ILOAD = 500 mA |
94 |
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% |
LM2671-ADJ
Symbol |
Parameter |
Conditions |
Typ |
Min |
Max |
Units |
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(Note 4) |
(Note 5) |
(Note 5) |
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SYSTEM PARAMETERS Test Circuit Figure 3 (Note 3) |
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VFB |
Feedback |
VIN = 8V to 40V, ILOAD = 20 mA to 500 mA |
1.210 |
1.192/1.174 |
1.228/1.246 |
V |
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Voltage |
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VOUT Programmed for 5V |
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(see Circuit of Figure 3) |
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VFB |
Feedback |
VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA |
1.210 |
1.192/1.174 |
1.228/1.246 |
V |
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Voltage |
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VOUT Programmed for 5V |
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(see Circuit of Figure 3) |
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www.national.com |
2 |
LM2671-ADJ (Continued)
Symbol |
Parameter |
Conditions |
Typ |
Min |
Max |
Units |
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(Note 4) |
(Note 5) |
(Note 5) |
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SYSTEM PARAMETERS Test Circuit Figure 3 (Note 3) |
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η |
Efficiency |
VIN = 12V, ILOAD = 500 mA |
90 |
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% |
All Output Voltage Versions
Electrical Characteristics
Specifications with standard type face are for TJ = 25ÊC, and those in bold type face apply over full Operating Temperature Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable versions and VIN = 24V for the 12V version, and ILOAD = 100 mA.
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Conditions |
Typ |
Min |
Max |
Units |
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DEVICE PARAMETERS |
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IQ |
Quiescent Current |
VFEEDBACK = 8V |
2.5 |
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3.6 |
mA |
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For 3.3V, 5.0V, and ADJ Versions |
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VFEEDBACK = 15V |
2.5 |
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mA |
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For 12V Versions |
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ISTBY |
Standby Quiescent Current |
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Pin = 0V |
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100/150 |
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ON/OFF |
50 |
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µA |
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ICL |
Current Limit |
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0.8 |
0.62/0.575 |
1.2/1.25 |
A |
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IL |
Output Leakage Current |
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VIN = 40V, ON/OFF |
Pin = 0V |
1 |
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25 |
µA |
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VSWITCH = 0V |
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VSWITCH = −1V, ON/OFF |
Pin = 0V |
6 |
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15 |
mA |
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RDS(ON) |
Switch On-Resistance |
ISWITCH = 500 mA |
0.25 |
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0.40/0.60 |
Ω |
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fO |
Oscillator Frequency |
Measured at Switch Pin |
260 |
225 |
275 |
kHz |
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D |
Maximum Duty Cycle |
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95 |
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% |
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Minimum Duty Cycle |
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0 |
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% |
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IBIAS |
Feedback Bias |
VFEEDBACK = 1.3V |
85 |
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nA |
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Current |
ADJ Version Only |
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VS/D |
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0.8 |
2.0 |
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ON/OFF |
Pin |
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1.4 |
V |
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Voltage Thesholds |
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IS/D |
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ON/OFF |
Pin Current |
ON/OFF Pin = 0V |
20 |
7 |
37 |
µA |
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FSYNC |
Synchronization Frequency |
VSYNC = 3.5V, 50% duty cycle |
400 |
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kHz |
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VSYNC |
Synchronization Threshold |
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1.4 |
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V |
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Voltage |
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VSS |
Soft-Start Voltage |
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0.63 |
0.53 |
0.73 |
V |
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ISS |
Soft-Start Current |
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4.5 |
1.5 |
6.9 |
µA |
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θJA |
Thermal Resistance |
N Package, Junction to Ambient (Note 6) |
95 |
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ÊC/W |
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M Package, Junction to Ambient (Note 6) |
105 |
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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 kΩ 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 25ÊC 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 1.0 software.
3 |
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Connection Diagram
8-Lead Package
Top View
DS100042-2
For Surface Mount Package
Order Number
LM2671M-3.3, LM2671M-5.0,
LM2671M-12 or LM2671M-ADJ
See NSC Package Number M08A
For DIP Package
Order Number
LM2671N-3.3, LM2671N-5.0,
LM2671N-12 or LM2671N-ADJ
See NSC Package Number N08E
Typical Performance Characteristics
Normalized |
Line Regulation |
Output Voltage |
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DS100042-4
DS100042-3
Efficiency
DS100042-5
www.national.com |
4 |
Typical Performance Characteristics (Continued)
Drain-to-Source |
Switch Current Limit |
Resistance |
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DS100042-7
DS100042-6
Operating
Quiescent Current
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DS100042-8 |
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Standby |
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ON/OFF Threshold |
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Quiescent Current |
Voltage |
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DS100042-9
DS100042-10
ON/OFF Pin
Current (Sourcing)
DS100042-11
5 |
www.national.com |
Typical Performance Characteristics (Continued)
Switching Frequency |
Feedback Pin |
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Bias Current |
DS100042-12
DS100042-13
Peak Switch Current
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DS100042-14 |
Dropout Voltage Ð 3.3V Option |
Dropout Voltage Ð 5.0V Option |
DS100042-15 |
DS100042-16 |
www.national.com |
6 |
Block Diagram
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DS100042-17 |
* Patent Number 5,514,947 |
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² Patent Number 5,382,918 |
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FIGURE 1. |
Typical Performance Characteristics (Circuit of Figure 2) |
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Continuous Mode Switching Waveforms |
Discontinuous Mode Switching Waveforms |
VIN = 20V, VOUT = 5V, ILOAD = 500 mA |
VIN = 20V, VOUT = 5V, ILOAD = 300 mA |
L = 100 µH, C OUT = 100 µF, C OUTESR = 0.1Ω |
L = 15 µH, C OUT = 68 µF (2x), C OUTESR = 25 mΩ |
DS100042-18 |
DS100042-19 |
A: VSW Pin Voltage, 10 V/div. |
A: VSW Pin Voltage, 10 V/div. |
B: Inductor Current, 0.2 A/div |
B: Inductor Current, 0.5 A/div |
C: Output Ripple Voltage, 50 mV/div AC-Coupled |
C: Output Ripple Voltage, 20 mV/div AC-Coupled |
Horizontal Time Base: 1 µs/div |
Horizontal Time Base: 1 µs/div |
7 |
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