TI1 LM2671M-3.3/NOPB Lm2671 simple switcherâ® power converter high efficiency 500-ma step-down voltage regulator with feature Datasheet

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LM2671
SNVS008L – SEPTEMBER 1998 – REVISED JUNE 2016
LM2671 SIMPLE SWITCHER® Power Converter High Efficiency 500-mA
Step-Down Voltage Regulator With Features
1 Features
3 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 500-mA load current with excellent line and
load regulation. These devices are available in fixed
output voltages of 3.3 V, 5 V, 12 V, and an adjustable
output version.
1
•
•
•
•
•
•
•
•
•
•
•
•
•
Efficiency up to 96%
Available in 8-Pin SOIC, PDIP, and WSON
Packages
Simple and Easy to Design With
Requires Only 5 External Components
Uses Readily Available Standard Inductors
3.3-V, 5-V, 12-V, and Adjustable Output Versions
Adjustable Version Output Voltage Range: 1.21 V
to 37 V
±1.5% Maximum Output Voltage Tolerance Over
Line and Load Conditions
Ensured 500-mA Output Load Current
0.25-Ω DMOS Output Switch
Wide Input Voltage Range: 8 V to 40 V
260-kHz Fixed Frequency Internal Oscillator
TTL Shutdown Capability, Low Power Standby
Mode
Soft-Start and Frequency Synchronization
Thermal Shutdown and Current-Limit Protection
2 Applications
•
•
Simple High Efficiency (> 90%) Step-Down (Buck)
Regulators
Efficient Preregulator for Linear Regulators
Requiring a minimum number of external
components, these regulators are simple to use and
include patented internal frequency compensation,
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 is required 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
required.
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 data sheet are
selector guides for diodes and capacitors designed to
work in switch-mode power supplies.
Device Information(1)
PART NUMBER
LM2674
PACKAGE
BODY SIZE (NOM)
SOIC (8)
4.90 mm × 3.91 mm
PDIP (8)
9.81 mm × 6.35 mm
WSON (16)
5.00 mm × 5.00 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Typical Application
For fixed output voltage versions
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM2671
SNVS008L – SEPTEMBER 1998 – REVISED JUNE 2016
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Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Description (continued).........................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
3
4
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
4
4
4
4
5
5
5
6
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics – 3.3 V ..............................
Electrical Characteristics – 5 V .................................
Electrical Characteristics – 12 V ...............................
Electrical Characteristics – Adjustable......................
Electrical Characteristics – All Output Voltage
Versions .....................................................................
7.10 Typical Characteristics ............................................
8
6
7
8.2 Functional Block Diagram ....................................... 10
8.3 Feature Description................................................. 10
8.4 Device Functional Modes........................................ 11
9
Application and Implementation ........................ 13
9.1 Application Information............................................ 13
9.2 Typical Applications ................................................ 14
10 Power Supply Recommendations ..................... 26
11 Layout................................................................... 27
11.1 Layout Guidelines ................................................. 27
11.2 Layout Examples................................................... 27
12 Device and Documentation Support ................. 28
12.1
12.2
12.3
12.4
12.5
12.6
Documentation Support ........................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
28
28
28
28
28
28
Detailed Description ............................................ 10
13 Mechanical, Packaging, and Orderable
Information ........................................................... 28
8.1 Overview ................................................................. 10
13.1 DAP (WSON Package) ......................................... 28
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision K (April 2013) to Revision L
Page
•
Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation
section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and
Mechanical, Packaging, and Orderable Information section .................................................................................................. 1
•
Removed all references to Computer Design Software LM267X Made Simple (Version 6.0).............................................. 1
Changes from Revision J (April 2013) to Revision K
•
2
Page
Changed layout of National Data Sheet to TI format ........................................................................................................... 27
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5 Description (continued)
Other features include a ensured ±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
standby current. The output switch includes current limiting, as well as thermal shutdown for full protection under
fault conditions.
6 Pin Configuration and Functions
D or P Package
8-Pin SOIC or PDIP
Top View
CB
1
SS
2
8
7
NHN Package
16-Pin WSON
Top View
VSW
VIN
SYNC
3
6
GND
FB
4
5
ON/OFF
CB
NC
1
16
VSW
2
15
VSW
NC
SS
3
14
13
VIN
NC
12
11
GND
GND
10
9
NC
ON/OFF
NC
SYNC
4
5
DAP
6
NC
7
FB
8
Not to scale
Not to scale
Connect DAP to pin 11 and 12
Pin Functions
PIN
NAME
I/O
DESCRIPTION
SOIC, PDIP
WSON
CB
1
1
I
Bootstrap capacitor connection for high-side driver. Connect a high-quality,
100-nF capacitor from CB to VSW Pin.
SS
2
4
I
Soft-start Pin. Connect a capacitor from this pin to GND to control the output
voltage ramp. If the feature not desired, the pin can be left floating.
SYNC
3
6
I
This input allows control of the switching clock frequency. If left open-circuited
the regulator is switched at the internal oscillator frequency, typically 260 kHz.
FB
4
8
I
Feedback sense input pin. Connect to the midpoint of feedback divider to set
VOUT for ADJ version or connect this pin directly to the output capacitor for a
fixed output version.
ON/OFF
5
9
I
Enable input to the voltage regulator. High = ON and low = OFF. Pull this pin
high or float to enable the regulator
VSW
8
15, 16
O
Source pin of the internal high-side FET. This is a switching node. Attached this
pin to an inductor and the cathode of the external diode.
GND
6
11, 12
—
Power ground pins. Connect to system ground. Ground pins of CIN and COUT.
Path to CIN must be as short as possible.
VIN
7
14
I
NC
—
2, 3, 5, 7,
10, 13
—
Supply input pin to collector pin of high-side FET. Connect to power supply and
input bypass capacitors CIN. Path from VIN pin to high frequency bypass CIN
and GND must be as short as possible.
No connect pins
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7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1) (2)
MIN
MAX
UNIT
45
V
Supply voltage
−0.1
ON/OFF pin voltage, VSH
6
V
–1
V
VSW + 8
V
14
V
Switch voltage to ground
Boost pin voltage
−0.3
Feedback pin voltage, VFB
Power dissipation
Internally Limited
D package
Lead temperature
Vapor phase (60 s)
215
Infrared (15 s)
220
P package (soldering, 10 s)
WSON package
See AN-1187
Maximum junction temperature
−65
Storage temperature, Tstg
(1)
(2)
°C
260
150
°C
150
°C
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
7.2 ESD Ratings
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1) (2)
VALUE
UNIT
±2000
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
The human body model is a 100-pF capacitor discharged through a 1.5-kΩ resistor into each pin.
7.3 Recommended Operating Conditions
MIN
MAX
Supply voltage
6.5
40
UNIT
V
Junction temperature, TJ
–40
125
°C
7.4 Thermal Information
LM2674
THERMAL METRIC
RθJA
(1)
(2)
4
(1)
Junction-to-ambient thermal resistance (2)
D (SOIC)
P (PDIP)
NHN (WSON)
8 PINS
8 PINS
16 PINS
105
95
—
UNIT
°C/W
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
Junction to ambient thermal resistance with approximately 1 square inch of printed-circuit board copper surrounding the leads. Additional
copper area lowers thermal resistance further. The value RθJA for the WSON (NHN) 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 WSON
package, see AN-1187 Leadless Leadframe Package (LLP).
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7.5 Electrical Characteristics – 3.3 V
Specifications are for TJ = 25°C (unless otherwise noted).
PARAMETER
MIN (1)
TYP (2)
TJ = 25°C
3.251
3.3
Over full operating temperature
range
3.201
TJ = 25°C
3.251
Over full operating temperature
range
3.201
TEST CONDITIONS
MAX (1) UNIT
SYSTEM PARAMETERS (3)
VIN = 8 V to 40 V,
ILOAD = 20 mA to 500 mA
VOUT
Output voltage
VIN = 6.5 V to 40 V,
ILOAD = 20 mA to 250 mA
Efficiency
η
(1)
(2)
(3)
VIN = 12 V, ILOAD = 500 mA
3.35
3.399
3.3
V
3.35
3.399
V
86%
All room temperature limits are 100% production tested. All limits at temperature extremes are ensured through correlation using
standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
Typical numbers are at 25°C and represent the most likely norm.
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 15 and Figure 21 test circuits, system performance is as
specified by the system parameters section of the Electrical Characteristics.
7.6 Electrical Characteristics – 5 V
Specifications are for TJ = 25°C (unless otherwise noted).
PARAMETER
SYSTEM PARAMETERS
TEST CONDITIONS
VIN = 8 V to 40 V,
ILOAD = 20 mA to 500 mA
VOUT
Output voltage
VIN = 6.5 V to 40 V,
ILOAD = 20 mA to 250 mA
Efficiency
η
(1)
(2)
(3)
MIN (1)
TYP (2)
4.925
5
MAX (1) UNIT
(3)
TJ = 25°C
Over full operating temperature
range
TJ = 25°C
Over full operating temperature
range
4.85
4.925
5.15
5
4.85
VIN = 12 V, ILOAD = 500 mA
5.075
V
5.075
5.15
V
90%
All room temperature limits are 100% production tested. All limits at temperature extremes are ensured through correlation using
standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
Typical numbers are at 25°C and represent the most likely norm.
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 15 and Figure 21 test circuits, system performance is as
specified by the system parameters section of the Electrical Characteristics.
7.7 Electrical Characteristics – 12 V
Specifications are for TJ = 25°C (unless otherwise noted).
PARAMETER
SYSTEM PARAMETERS
VOUT
Output voltage
VIN = 15 V to 40 V,
ILOAD = 20 mA to 500 mA
η
Efficiency
VIN = 24 V, ILOAD = 500 mA
(1)
(2)
(3)
MIN (1)
TYP (2)
TJ = 25°C
11.82
12
Over full operating
temperature range
11.64
TEST CONDITIONS
MAX (1) UNIT
(3)
12.18
12.36
V
94%
All room temperature limits are 100% production tested. All limits at temperature extremes are ensured through correlation using
standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
Typical numbers are at 25°C and represent the most likely norm.
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 15 and Figure 21 test circuits, system performance is as
specified by the system parameters section of the Electrical Characteristics.
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7.8 Electrical Characteristics – Adjustable
Specifications are for TJ = 25°C (unless otherwise noted).
PARAMETER
TEST CONDITIONS
MIN (1)
TYP (2)
1.21
MAX (1) UNIT
SYSTEM PARAMETERS (3)
Feedback
voltage
VFB
Efficiency
η
(1)
(2)
(3)
VIN = 8 V to 40 V,
ILOAD = 20 mA to 500 mA
VOUT programmed for 5 V
TJ = 25°C
1.192
Over full operating
temperature range
1.174
VIN = 6.5 V to 40 V,
ILOAD = 20 mA to 250 mA
VOUT programmed for 5 V
TJ = 25°C
1.192
Over full operating
temperature range
1.174
VIN = 12 V, ILOAD = 500 mA
1.228
1.246
1.21
V
1.228
1.246
V
90%
All room temperature limits are 100% production tested. All limits at temperature extremes are ensured through correlation using
standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
Typical numbers are at 25°C and represent the most likely norm.
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 15 and Figure 21 test circuits, system performance is as
specified by the system parameters section of the Electrical Characteristics.
7.9 Electrical Characteristics – All Output Voltage Versions
Specifications are for TJ = 25°C, VIN = 12 V for the 3.3-V, 5-V, and Adjustable versions and VIN = 24 V for the 12-V version,
and ILOAD = 100 mA (unless otherwise noted).
PARAMETERS
TEST CONDITIONS
MIN
TYP
MAX
VFEEDBACK = 8 V
for 3.3-V, 5-V, and adjustable versions
2.5
3.6
VFEEDBACK = 15 V
for 12-V versions
2.5
UNIT
DEVICE PARAMETERS
IQ
Quiescent current
mA
TJ = 25°C
ISTBY
Standby quiescent current
ICL
Current limit
IL
Output leakage current
ON/OFF pin = 0 V
50
Over full operating temperature
range
TJ = 25°C
150
0.62
Over full operating temperature range
TJ = 25°C
ISWITCH = 500 mA
fO
Oscillator frequency
Measured at switch pin
IBIAS
225
275
85
TJ = 25°C
1.4
ON/OFF pin current
ON/OFF pin = 0 V
FSYNC
Synchronization frequency
VSYNC = 3.5 V, 50% duty cycle
VSYNC
Synchronization threshold voltage
Over full operating temperature range
0.8
TJ = 25°C
6
Ω
kHz
0%
IS/D
Soft-start current
mA
VFEEDBACK = 1.3 V (adjustable version only)
ON/OFF pin voltage thresholds
ISS
15
0.4
95%
VS/D
Soft-start voltage
6
0.25
260
Over full operating temperature
range
Minimum duty cycle
VSS
A
μA
0.6
Maximum duty cycle
Feedback bias current
μA
25
Over full operating temperature
range
TJ = 25°C
D
1.2
1.25
1
VSWITCH = −1 V, ON/OFF pin = 0 V
Switch ON-resistance
0.8
0.575
VIN = 40 V, ON/OFF pin = 0 V
VSWITCH = 0 V
RDS(ON)
100
nA
2
20
Over full operating temperature
range
7
TJ = 25°C
37
kHz
1.4
V
0.53
TJ = 25°C
0.73
4.5
Over full operating temperature range
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1.5
μA
400
0.63
Over full operating temperature range
V
6.9
V
μA
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7.10 Typical Characteristics
Figure 1. Normalized Output Voltage
Figure 2. Line Regulation
Figure 3. Efficiency
Figure 4. Drain-to-Source Resistance
Figure 5. Switch Current Limit
Figure 6. Operating Quiescent Current
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Typical Characteristics (continued)
8
Figure 7. Standby Quiescent Current
Figure 8. ON/OFF Threshold Voltage
Figure 9. ON/OFF Pin Current (Sourcing)
Figure 10. Switching Frequency
Figure 11. Feedback Pin Bias Current
Figure 12. Peak Switch Current
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Typical Characteristics (continued)
Figure 13. Dropout Voltage – 3.3-V Option
Figure 14. Dropout Voltage – 5-V Option
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8 Detailed Description
8.1 Overview
The LM2671 provides all of the active functions required for a step-down (buck) switching regulator. The internal
power switch is a DMOS power MOSFET to provide power supply designs with high current capability, up to
0.5 A, and highly efficient operation.
The LM2671 is part of the SIMPLE SWITCHER® family of power converters. A complete design uses a minimum
number of external components, which have been predetermined from a variety of manufacturers. Using either
this data sheet or TI's WEBENCH® design tool, a complete switching power supply can be designed quickly.
Also, see LM2670 SIMPLE SWITCHER® High Efficiency 3A Step-Down Voltage Regulator with Sync for
additional applications information.
8.2 Functional Block Diagram
8.3 Feature Description
8.3.1 Switch Output
This is the output of a power MOSFET switch connected directly to the input voltage. The switch provides energy
to an inductor, an output capacitor and the load circuitry under control of an internal pulse-width-modulator
(PWM). The PWM controller is internally clocked by a fixed 260-kHz oscillator. In a standard step-down
application the duty cycle (Time ON/Time OFF) of the power switch is proportional to the ratio of the power
supply output voltage to the input voltage. The voltage on the VSW pin cycles between VIN (switch ON) and below
ground by the voltage drop of the external Schottky diode (switch OFF).
10
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Feature Description (continued)
8.3.2 Input
The input voltage for the power supply is connected to the VIN pin. In addition to providing energy to the load the
input voltage also provides bias for the internal circuitry of the LM2671. For ensured performance the input
voltage must be in the range of 6.5 V to 40 V. For best performance of the power supply the VIN pin must always
be bypassed with an input capacitor placed close to this pin and GND.
8.3.3 C Boost
A capacitor must be connected from the CB pin to the VSW pin. This capacitor boosts the gate drive to the internal
MOSFET above VIN to fully turn it ON. This minimizes conduction losses in the power switch to maintain high
efficiency. The recommended value for C Boost is 0.01 μF.
8.3.4 Ground
This is the ground reference connection for all components in the power supply. In fast-switching, high-current
applications such as those implemented with the LM2671, TI recommends that a broad ground plane be used to
minimize signal coupling throughout the circuit.
8.3.5 Sync
This input allows control of the switching clock frequency. If left open-circuited the regulator is switched at the
internal oscillator frequency, typically 260 kHz. An external clock can be used to force the switching frequency
and thereby control the output ripple frequency of the regulator. This capability provides for consistent filtering of
the output ripple from system to system as well as precise frequency spectrum positioning of the ripple frequency
which is often desired in communications and radio applications. This external frequency must be greater than
the LM2671 internal oscillator frequency, which could be as high as 275 kHz, to prevent an erroneous reset of
the internal ramp oscillator and PWM control of the power switch. The ramp oscillator is reset on the positive
going edge of the sync input signal. TI recommends that the external TTL or CMOS compatible clock (between
0 V and a level greater than 3 V) be ac coupled to the SYNC pin through a 100-pF capacitor and a 1-kΩ resistor
to ground.
When the SYNC function is used, current limit frequency foldback is not active. Therefore, the device may not be
fully protected against extreme output short-circuit conditions.
8.3.6 Feedback
This is the input to a two-stage high gain amplifier, which drives the PWM controller. Connect the FB pin directly
to the output for proper regulation. For the fixed output devices (3.3-V, 5-V and 12-V outputs), a direct wire
connection to the output is all that is required as internal gain setting resistors are provided inside the LM2671.
For the adjustable output version two external resistors are required to set the DC output voltage. For stable
operation of the power supply it is important to prevent coupling of any inductor flux to the feedback input.
8.3.7 ON/OFF
This input provides an electrical ON/OFF control of the power supply. Connecting this pin to ground or to any
voltage less than 0.8 V is completely turn OFF the regulator. The current drain from the input supply when OFF
is only 50 μA. The ON/OFF input has an internal pullup current source of approximately 20 μA and a protection
clamp Zener diode of 7 V to ground. When electrically driving the ON/OFF pin the high voltage level for the ON
condition must not exceed the 6 V absolute maximum limit. When ON/OFF control is not required this pin must
be left open.
8.4 Device Functional Modes
8.4.1 Shutdown Mode
The ON/OFF pin provides electrical ON and OFF control for the LM2671. When the voltage of this pin is lower
than 1.4 V, the device enters shutdown mode. The typical standby current in this mode is 50 μA.
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Device Functional Modes (continued)
8.4.2 Active Mode
When the voltage of the ON/OFF pin is higher than 1.4 V, the device starts switching and the output voltage rises
until it reaches a normal regulation voltage.
12
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9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The LM2671 is a step-down DC-DC regulator. The device is typically used to convert a higher DC voltage to a
lower DC voltage with a maximum output current of 0.5 A. The following design procedure can be used to select
components for the LM2671. Alternately, the WEBENCH® software may be used to generate complete designs.
When generating a design, the WEBENCH software uses iterative design procedure and accesses
comprehensive databases of components. See ti.com for more details.
When the output voltage is greater than approximately 6 V, and the duty cycle at minimum input voltage is
greater than approximately 50%, the designer must exercise caution in selection of the output filter components.
When an application designed to these specific operating conditions is subjected to a current limit fault condition,
it may be possible to observe a large hysteresis in the current limit. This can affect the output voltage of the
device until the load current is reduced sufficiently to allow the current limit protection circuit to reset itself.
Under current limiting conditions, the LM267x is designed to respond in the following manner:
1. At the moment when the inductor current reaches the current limit threshold, the ON-pulse is immediately
terminated. This happens for any application condition.
2. However, the current limit block is also designed to momentarily reduce the duty cycle to below 50% to avoid
subharmonic oscillations, which could cause the inductor to saturate.
3. Therefore, once the inductor current falls below the current limit threshold, there is a small relaxation time
during which the duty cycle progressively rises back above 50% to the value required to achieve regulation.
If the output capacitance is sufficiently large, it might be possible that as the output tries to recover, the output
capacitor charging current is large enough to repeatedly re-trigger the current limit circuit before the output has
fully settled. This condition is exacerbated with higher output voltage settings because the energy requirement of
the output capacitor varies as the square of the output voltage (½ CV2), thus requiring an increased charging
current. A simple test to determine if this condition might exist for a suspect application is to apply a short circuit
across the output of the converter, and then remove the shorted output condition. In an application with properly
selected external components, the output recovers smoothly. Practical values of external components that have
been experimentally found to work well under these specific operating conditions are COUT = 47 µF, L = 22 µH.
NOTE
Even with these components, for a device’s current limit of ICLIM, the maximum load
current under which the possibility of the large current limit hysteresis can be minimized is
ICLIM/2.
For example, if the input is 24 V and the set output voltage is 18 V, then for a desired maximum current of 1.5 A,
the current limit of the chosen switcher must be confirmed to be at least 3 A. Under extreme overcurrent or shortcircuit conditions, the LM267X employs frequency foldback in addition to the current limit. If the cycle-by-cycle
inductor current increases above the current limit threshold (due to short circuit or inductor saturation for
example) the switching frequency is automatically reduced to protect the IC. Frequency below 100 kHz is typical
for an extreme short-circuit condition.
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9.2 Typical Applications
9.2.1 Fixed Output Voltage Version
CIN = 22-μF, 50-V Tantalum, Sprague 199D Series
COUT = 47-μF, 25-V Tantalum, Sprague 595D Series
D1 = 3.3-A, 50-V Schottky Rectifier, IR 30WQ05F
L1 = 68-μH Sumida #RCR110D-680L
CB = 0.01-μF, 50-V ceramic
Figure 15. Typical Application for Fixed Output Voltage Versions
9.2.1.1 Design Requirements
Table 1 lists the design parameters for this example.
Table 1. Design Parameters
PARAMETER
VALUE
Regulated output voltage (3.3 V, 5 V, or 12 V), VOUT
5V
Maximum DC input voltage, VIN(max)
12 V
Maximum load current, ILOAD(max)
500 mA
9.2.1.2 Detailed Design Procedure
9.2.1.2.1 Inductor Selection (L1)
1. Select the correct inductor value selection guide from Figure 17 and Figure 18 or Figure 19 (output voltages
of 3.3 V, 5 V, or 12 V respectively). For all other voltages, see the design procedure for the adjustable
version. Use the inductor selection guide for the 5-V version shown in Figure 18.
2. From the inductor value selection guide, identify the inductance region intersected by the maximum input
voltage line and the maximum load current line. Each region is identified by an inductance value and an
inductor code (LXX). From the inductor value selection guide shown in Figure 18, the inductance region
intersected by the 12-V horizontal line and the 500-mA vertical line is 47 μH, and the inductor code is L13.
3. Select an appropriate inductor from the four manufacturer's part numbers listed in Table 2. Each
manufacturer makes a different style of inductor to allow flexibility in meeting various design requirements.
See the following for some of the differentiating characteristics of each manufacturer's inductors:
– Schottky: ferrite EP core inductors; these have very low leakage magnetic fields to reduce electromagnetic interference (EMI) and are the lowest power loss inductors
– Renco: ferrite stick core inductors; benefits are typically lowest cost inductors and can withstand E•T and
transient peak currents above rated value. Be aware that these inductors have an external magnetic field
which may generate more EMI than other types of inductors.
– Pulse: powered iron toroid core inductors; these can also be low cost and can withstand larger than
normal E•T and transient peak currents. Toroid inductors have low EMI.
– Coilcraft: ferrite drum core inductors; these are the smallest physical size inductors, available only as
SMT components. Be aware that these inductors also generate EMI—but less than stick inductors.
Complete specifications for these inductors are available from the respective manufacturers.
14
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The inductance value required is 47 μH. From the table in Table 2, go to the L13 line and choose an inductor
part number from any of the four manufacturers shown. In most instances, both through hole and surface mount
inductors are available.
Table 2. Inductor Manufacturers' Part Numbers
IND.
REF.
DESG.
INDUCTANCE
(μH)
CURRENT
(A)
L2
150
L3
100
L4
SCHOTTKY
RENCO
THROUGH
HOLE
SURFACE
MOUNT
0.21
67143920
0.26
67143930
68
0.32
L5
47
L6
PULSE ENGINEERING
COILCRAFT
THROUGH HOLE
SURFACE
MOUNT
THROUGH
HOLE
SURFACE
MOUNT
SURFACE
MOUNT
67144290
RL-5470-4
RL1500-150
PE-53802
PE-53802-S
DO1608-154
67144300
RL-5470-5
RL1500-100
PE-53803
PE-53803-S
DO1608-104
67143940
67144310
RL-1284-68-43
RL1500-68
PE-53804
PE-53804-S
DO1608-683
0.37
67148310
67148420
RL-1284-47-43
RL1500-47
PE-53805
PE-53805-S
DO1608-473
33
0.44
67148320
67148430
RL-1284-33-43
RL1500-33
PE-53806
PE-53806-S
DO1608-333
L7
22
0.52
67148330
67148440
RL-1284-22-43
RL1500-22
PE-53807
PE-53807-S
DO1608-223
L9
220
0.32
67143960
67144330
RL-5470-3
RL1500-220
PE-53809
PE-53809-S
DO3308-224
L10
150
0.39
67143970
67144340
RL-5470-4
RL1500-150
PE-53810
PE-53810-S
DO3308-154
L11
100
0.48
67143980
67144350
RL-5470-5
RL1500-100
PE-53811
PE-53811-S
DO3308-104
L12
68
0.58
67143990
67144360
RL-5470-6
RL1500-68
PE-53812
PE-53812-S
DO3308-683
L13
47
0.7
67144000
67144380
RL-5470-7
RL1500-47
PE-53813
PE-53813-S
DO3308-473
L14
33
0.83
67148340
67148450
RL-1284-33-43
RL1500-33
PE-53814
PE-53814-S
DO3308-333
L15
22
0.99
67148350
67148460
RL-1284-22-43
RL1500-22
PE-53815
PE-53815-S
DO3308-223
L18
220
0.55
67144040
67144420
RL-5471-2
RL1500-220
PE-53818
PE-53818-S
DO3316-224
L19
150
0.66
67144050
67144430
RL-5471-3
RL1500-150
PE-53819
PE-53819-S
DO3316-154
L20
100
0.82
67144060
67144440
RL-5471-4
RL1500-100
PE-53820
PE-53820-S
DO3316-104
L21
68
0.99
67144070
67144450
RL-5471-5
RL1500-68
PE-53821
PE-53821-S
DO3316-683
9.2.1.2.2 Output Capacitor Selection (COUT)
Select an output capacitor from the output capacitor table in Table 9. Using the output voltage and the
inductance value found in the inductor selection guide, step 1, locate the appropriate capacitor value and voltage
rating.
Use the 5-V section in the output capacitor table in Table 9. Choose a capacitor value and voltage rating from
the line that contains the inductance value of 47 μH. The capacitance and voltage rating values corresponding to
the 47-μH inductor are:
• Surface mount:
– 68-μF, 10-V Sprague 594D series
– 100-μF, 10-V AVX TPS series
• Through hole:
– 68-μF, 10-V Sanyo OS-CON SA series
– 150-μF, 35-V Sanyo MV-GX series
– 150-μF, 35-V Nichicon PL series
– 150-μF, 35-V Panasonic HFQ series
The capacitor list contains through-hole electrolytic capacitors from four different capacitor manufacturers and
surface mount tantalum capacitors from two different capacitor manufacturers. TI recommends that both the
manufacturers and the manufacturer's series that are listed in the table be used.
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Table 3. Output Capacitor Table
OUTPUT CAPACITOR
OUTPUT
VOLTAGE
(V)
3.3
5
12
INDUCTANCE
(μH)
SURFACE MOUNT
THROUGH HOLE
SPRAGUE
594D SERIES
(μF/V)
AVX TPS
SERIES
(μF/V)
SANYO OS-CON
SA SERIES (μF/V)
SANYO MV-GX
SERIES (μF/V)
NICHICON
PL SERIES
(μF/V)
PANASONIC
HFQ SERIES
(μF/V)
22
120/6.3
100/10
100/10
330/35
330/35
330/35
33
120/6.3
100/10
68/10
220/35
220/35
220/35
47
68/10
100/10
68/10
150/35
150/35
150/35
68
120/6.3
100/10
100/10
120/35
120/35
120/35
100
120/6.3
100/10
100/10
120/35
120/35
120/35
150
120/6.3
100/10
100/10
120/35
120/35
120/35
22
100/16
100/10
100/10
330/35
330/35
330/35
33
68/10
10010
68/10
220/35
220/35
220/35
47
68/10
100/10
68/10
150/35
150/35
150/35
68
100/16
100/10
100/10
120/35
120/35
120/35
100
100/16
100/10
100/10
120/35
120/35
120/35
150
100/16
100/10
100/10
120/35
120/35
120/35
22
120/20
(2×) 68/20
68/20
330/35
330/35
330/35
33
68/25
68/20
68/20
220/35
220/35
220/35
47
47/20
68/20
47/20
150/35
150/35
150/35
68
47/20
68/20
47/20
120/35
120/35
120/35
100
47/20
68/20
47/20
120/35
120/35
120/35
150
47/20
68/20
47/20
120/35
120/35
120/35
220
47/20
68/20
47/20
120/35
120/35
120/35
9.2.1.2.3 Catch Diode Selection (D1)
1. In normal operation, the average current of the catch diode is the load current times the catch diode duty
cycle, 1-D (D is the switch duty cycle, which is approximately the output voltage divided by the input voltage).
The largest value of the catch diode average current occurs at the maximum load current and maximum
input voltage (minimum D). For normal operation, the catch diode current rating must be at least 1.3 times
greater than its maximum average current. However, if the power supply design must withstand a continuous
output short, the diode must have a current rating equal to the maximum current limit of the LM2671. The
most stressful condition for this diode is a shorted output condition (refer to Table 4). In this example, a 1-A,
20-V Schottky diode provides the best performance. If the circuit must withstand a continuous shorted output,
TI recommends a higher-current Schottky diode.
2. The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage.
3. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best
performance and efficiency. This Schottky diode must be placed close to the LM2671 using short leads and
short printed-circuit traces.
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Table 4. Schottky Diode Selection Table
VR
20 V
30 V
40 V
50 V
1-A DIODES
3-A DIODES
SURFACE MOUNT
THROUGH HOLE
SURFACE MOUNT
THROUGH HOLE
SK12
1N5817
SK32
1N5820
B120
SR102
—
SR302
SK13
1N5818
SK33
1N5821
B130
11DQ03
30WQ03F
31DQ03
MBRS130
SR103
—
—
SK14
1N5819
SK34
1N5822
B140
11DQ04
30BQ040
MBR340
MBRS140
SR104
30WQ04F
31DQ04
10BQ040
—
MBRS340
SR304
10MQ040
—
MBRD340
—
15MQ040
—
—
—
SK15
MBR150
SK35
MBR350
B150
11DQ05
30WQ05F
31DQ05
10BQ050
SR105
—
SR305
9.2.1.2.4 Input Capacitor (CIN)
A low ESR aluminum or tantalum bypass capacitor is required between the input pin and ground to prevent large
voltage transients from appearing at the input. This capacitor must be placed close to the IC using short leads. In
addition, the RMS current rating of the input capacitor must be selected to be at least ½ the DC load current. The
capacitor manufacturer data sheet must be checked to assure that this current rating is not exceeded. The
curves shown in Figure 16 show typical RMS current ratings for several different aluminum electrolytic capacitor
values. A parallel connection of two or more capacitors may be required to increase the total minimum RMS
current rating to suit the application requirements.
For an aluminum electrolytic capacitor, the voltage rating must be at least 1.25 times the maximum input voltage.
Caution must be exercised if solid tantalum capacitors are used. The tantalum capacitor voltage rating must be
twice the maximum input voltage. Table 5 and Table 6 show the recommended application voltage for AVX TPS
and Sprague 594D tantalum capacitors. TI also recommends that they be surge current tested by the
manufacturer. The TPS series available from AVX, and the 593D and 594D series from Sprague are all surge
current tested. Another approach to minimize the surge current stresses on the input capacitor is to add a small
inductor in series with the input supply line.
Table 5. AVX TPS
RECOMMENDED
APPLICATION VOLTAGE
VOLTAGE
RATING
85°C RATING
3.3
6.3
5
10
10
20
12
25
15
35
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Table 6. Sprague 594D
RECOMMENDED
APPLICATION VOLTAGE
VOLTAGE
RATING
85°C RATING
2.5
4
3.3
6.3
5
10
8
16
12
20
18
25
24
35
29
50
Use caution when using ceramic capacitors for input bypassing, because it may cause severe ringing at the VIN
pin. The important parameters for the input capacitor are the input voltage rating and the RMS current rating.
With a maximum input voltage of 12 V, an aluminum electrolytic capacitor with a voltage rating greater than 15 V
(1.25 × VIN) is required. The next higher capacitor voltage rating is 16 V.
The RMS current rating requirement for the input capacitor in a buck regulator is approximately ½ the DC load
current. In this example, with a 500-mA load, a capacitor with a RMS current rating of at least 250 mA is
required. The curves shown in Figure 16 can be used to select an appropriate input capacitor. From the curves,
locate the 16-V line and note which capacitor values have RMS current ratings greater than 250 mA.
Figure 16. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical)
For a through-hole design, a 100-μF, 16-V electrolytic capacitor (Panasonic HFQ series, Nichicon PL, Sanyo MVGX series or equivalent) would be adequate. Other types or other manufacturers' capacitors can be used
provided the RMS ripple current ratings are adequate. Additionally, for a complete surface mount design,
electrolytic capacitors such as the Sanyo CV-C or CV-BS and the Nichicon WF or UR and the NIC Components
NACZ series could be considered.
For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to
the capacitor surge current rating and voltage rating. In this example, checking the Sprague 594D series
datasheet, a Sprague 594D 15-μF, 25-V capacitor is adequate.
9.2.1.2.5 Boost Capacitor (CB)
This capacitor develops the necessary voltage to turn the switch gate on fully. All applications must use a
0.01-μF, 50-V ceramic capacitor. For this application, and all applications, use a 0.01-μF, 50-V ceramic capacitor.
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9.2.1.2.6 Soft-Start Capacitor (CSS) – Optional
This capacitor controls the rate at which the device starts up. The formula for the soft-start capacitor CSS is
Equation 1.
where
•
•
•
•
•
•
ISS= soft-start current (4.5 μA typical)
tSS= soft-start time (selected)
VSSTH= soft-start threshold voltage (0.63 V typical)
VOUT= output voltage (selected)
VSCHOTTKY= schottky diode voltage drop (0.4 V typical)
VIN= input voltage (selected)
(1)
For this application, selecting a start-up time of 10 ms and using Equation 2 for CSS.
(2)
If this feature is not desired, leave this pin open. With certain soft-start capacitor values and operating conditions,
the LM2671 can exhibit an overshoot on the output voltage during turnon. Especially when starting up into no
load or low load, the soft-start function may not be effective in preventing a larger voltage overshoot on the
output. With larger loads or lower input voltages during start-up this effect is minimized. In particular, avoid using
soft-start capacitors between 0.033 µF and 1 µF.
9.2.1.2.7 Frequency Synchronization (optional)
The LM2671 (oscillator) can be synchronized to run with an external oscillator, using the sync pin (pin 3). By
doing so, the LM2671 can be operated at higher frequencies than the standard frequency of 260 kHz. This
allows for a reduction in the size of the inductor and output capacitor.
As shown in the drawing below, a signal applied to a RC filter at the sync pin causes the device to synchronize to
the frequency of that signal. For a signal with a peak-to-peak amplitude of 3 V or greater, a 1-kΩ resistor and a
100-pF capacitor are suitable values.
For all applications, use a 1-kΩ resistor and a 100-pF capacitor for the RC filter.
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9.2.1.3 Application Curves
for continuous mode operation
Figure 17. LM2671-3.3
Figure 18. LM2671-5
Figure 19. LM2671-12
Figure 20. LM2671-ADJ
9.2.2 Adjustable Output Voltage Version
CIN = 22-μF, 50-V Tantalum, Sprague 199D Series
COUT = 47-μF, 25-V Tantalum, Sprague 595D Series
D1 = 3.3-A, 50-V Schottky Rectifier, IR 30WQ05F
L1 = 68-μH Sumida #RCR110D-680L
R1 =1.5 kΩ, 1%
CB = 0.01-μF, 50-V ceramic
Figure 21. Typical Application for Adjustable Output Voltage Versions
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9.2.2.1 Design Requirements
Table 7 lists the design parameters for this example.
Table 7. Design Parameters
PARAMETER
VALUE
Regulated output voltage, VOUT
20 V
Maximum input voltage, VIN(max)
28 V
Maximum load current, ILOAD(max)
500 mA
Switching frequency, F
Fixed at a nominal 260 kHz
9.2.2.2 Detailed Design Procedure
9.2.2.2.1
Programming Output Voltage
Select R1 and R2, as shown in Figure 21.
Use the following formula to select the appropriate resistor values.
where
•
VREF = 1.21 V
(3)
Select R1 to be 1 kΩ, 1%. Solve for R2.
(4)
Select a value for R1 between 240 Ω and 1.5 kΩ. The lower resistor values minimize noise pickup in the sensitive
feedback pin. For the lowest temperature coefficient and the best stability with time, use 1% metal film resistors.
(5)
R2 = 1 kΩ (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.
R2 = 15.4 kΩ.
9.2.2.2.2 Inductor Selection (L1)
1. Calculate the inductor Volt • microsecond constant E • T (V • μs) from Equation 6.
where
•
•
VSAT = internal switch saturation voltage = 0.25 V
VD = diode forward voltage drop = 0.5 V
(6)
Calculate the inductor Volt • microsecond constant (E • T) with Equation 7.
(7)
2. Use the E • T value from the previous formula and match it with the E • T number on the vertical axis of the
inductor value selection guide shown in Figure 20.
E • T = 21.6 (V • μs)
(8)
3. On the horizontal axis, select the maximum load current in Equation 9.
ILOAD(max) = 500 mA
(9)
4. Identify the inductance region intersected by the E • T value and the maximum load current value. Each
region is identified by an inductance value and an inductor code (LXX). From the inductor value selection
guide shown in Figure 20, the inductance region intersected by the 21.6 (V • μs) horizontal line and the 500mA vertical line is 100 μH, and the inductor code is L20.
5. Select an appropriate inductor from the four manufacturer's part numbers listed in Table 2. For information
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on the different types of inductors, see the inductor selection in the fixed output voltage design procedure.
From the table in Table 2, locate line L20, and select an inductor part number from the list of manufacturers'
part numbers.
9.2.2.2.3 Output Capacitor Selection (COUT)
1. Select an output capacitor from the capacitor code selection guide in Table 8. Using the inductance value
found in the inductor selection guide, step 1, locate the appropriate capacitor code corresponding to the
desired output voltage. Use the appropriate row of the capacitor code selection guide, in Table 8. For this
example, use the 15-V to 20-V row. The capacitor code corresponding to an inductance of 100 μH is C20.
2. Select an appropriate capacitor value and voltage rating, using the capacitor code, from the output capacitor
selection table in Table 9. There are two solid tantalum (surface mount) capacitor manufacturers and four
electrolytic (through hole) capacitor manufacturers to choose from. TI recommends using the manufacturers
and the manufacturer's series that are listed in the table.
From the output capacitor selection table in Table 9, choose a capacitor value (and voltage rating) that
intersects the capacitor code(s) selected in section A, C20.
The capacitance and voltage rating values corresponding to the capacitor code C20 are:
– Surface mount:
– 33-μF, 25-V Sprague 594D series
– 33-μF, 25-V AVX TPS series
– Through hole:
– 33-μF, 25-V Sanyo OS-CON SC series
– 120-μF, 35-V Sanyo MV-GX series
– 120-μF, 35-V Nichicon PL series
– 120-μF, 35-V Panasonic HFQ series
Other manufacturers or other types of capacitors may also be used, provided the capacitor specifications
(especially the 100-kHz ESR) closely match the characteristics of the capacitors listed in the output capacitor
table. See the capacitor manufacturers' data sheet for this information.
Table 8. Capacitor Code Selection Guide
INDUCTANCE (μH)
CASE
STYLE (1)
OUTPUT
VOLTAGE (V)
22
33
47
68
100
150
220
SM and TH
1.21–2.5
—
—
—
—
C1
C2
C3
SM and TH
2.5–3.75
—
—
—
C1
C2
C3
C3
SM and TH
3.75–5
—
—
C4
C5
C6
C6
C6
SM and TH
5–6.25
—
C4
C7
C6
C6
C6
C6
SM and TH
6.25–7.5
C8
C4
C7
C6
C6
C6
C6
SM and TH
7.5–10
C9
C10
C11
C12
C13
C13
C13
SM and TH
10–12.5
C14
C11
C12
C12
C13
C13
C13
SM and TH
12.5–15
C15
C16
C17
C17
C17
C17
C17
SM and TH
15–20
C18
C19
C20
C20
C20
C20
C20
SM and TH
20–30
C21
C22
C22
C22
C22
C22
C22
TH
30–37
C23
C24
C24
C25
C25
C25
C25
(1)
SM - Surface Mount, TH - Through Hole
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Table 9. Output Capacitor Selection Table
OUTPUT CAPACITOR
CAP.
REF.
DESG.
#
SPRAGUE 594D
SERIES (μF/V)
AVX TPS SERIES
(μF/V)
SANYO OS-CON SA
SERIES (μF/V)
SANYO MV-GX
SERIES (μF/V)
NICHICON PL
SERIES (μF/V)
PANASONIC HFQ
SERIES (μF/V)
C1
120/6.3
100/10
100/10
220/35
220/35
220/35
C2
120/6.3
100/10
100/10
150/35
150/35
150/35
C3
120/6.3
100/10
100/35
120/35
120/35
120/35
C4
68/10
100/10
68/10
220/35
220/35
220/35
C5
100/16
100/10
100/10
150/35
150/35
150/35
C6
100/16
100/10
100/10
120/35
120/35
120/35
C7
68/10
100/10
68/10
150/35
150/35
150/35
C8
100/16
100/10
100/10
330/35
330/35
330/35
THROUGH HOLE
C9
100/16
100/16
100/16
330/35
330/35
330/35
C10
100/16
100/16
68/16
220/35
220/35
220/35
C11
100/16
100/16
68/16
150/35
150/35
150/35
C12
100/16
100/16
68/16
120/35
120/35
120/35
C13
100/16
100/16
100/16
120/35
120/35
120/35
C14
100/16
100/16
100/16
220/35
220/35
220/35
C15
47/20
68/20
47/20
220/35
220/35
220/35
C16
47/20
68/20
47/20
150/35
150/35
150/35
C17
47/20
68/20
47/20
120/35
120/35
120/35
C18
68/25
(2×) 33/25
47/25
(1)
220/35
220/35
220/35
150/35
150/35
150/35
120/35
120/35
120/35
C19
33/25
33/25
33/25
(1)
C20
33/25
33/25
33/25
(1)
C21
33/35
(2×) 22/25
(2)
150/35
150/35
150/35
22/35
(2)
C22
(1)
(2)
SURFACE MOUNT
120/35
120/35
120/35
C23
33/35
(2)
(2)
(2)
220/50
100/50
120/50
C24
(2)
(2)
(2)
150/50
100/50
120/50
C25
(2)
(2)
(2)
150/50
82/50
82/50
The SC series of Os-Con capacitors (others are SA series)
The voltage ratings of the surface mount tantalum chip and Os-Con capacitors are too low to work at these voltages.
9.2.2.2.4 Catch Diode Selection (D1)
1. In normal operation, the average current of the catch diode is the load current times the catch diode duty
cycle, 1-D (D is the switch duty cycle, which is approximately VOUT/VIN). The largest value of the catch diode
average current occurs at the maximum input voltage (minimum D). For normal operation, the catch diode
current rating must be at least 1.3 times greater than its maximum average current. However, if the power
supply design must withstand a continuous output short, the diode must have a current rating greater than
the maximum current limit of the LM2671. The most stressful condition for this diode is a shorted output
condition.
Refer to the table shown in Table 4. Schottky diodes provide the best performance, and in this example a 1A, 40-V Schottky diode would be a good choice. If the circuit must withstand a continuous shorted output, a
higher current (at least 1.2 A) Schottky diode is recommended.
2. The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage.
3. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best
performance and efficiency. The Schottky diode must be placed close to the LM2671 using short leads and
short printed-circuit traces.
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9.2.2.2.5 Input Capacitor (CIN)
A low ESR aluminum or tantalum bypass capacitor is required between the input pin and ground to prevent large
voltage transients from appearing at the input. This capacitor must be placed close to the IC using short leads. In
addition, the RMS current rating of the input capacitor must be selected to be at least ½ the DC load current. The
capacitor manufacturer data sheet must be checked to assure that this current rating is not exceeded. The
curves shown in Figure 16 show typical RMS current ratings for several different aluminum electrolytic capacitor
values. A parallel connection of two or more capacitors may be required to increase the total minimum RMS
current rating to suit the application requirements.
For an aluminum electrolytic capacitor, the voltage rating must be at least 1.25 times the maximum input voltage.
Caution must be exercised if solid tantalum capacitors are used. The tantalum capacitor voltage rating must be
twice the maximum input voltage. The Table 10 and Table 11 show the recommended application voltage for
AVX TPS and Sprague 594D tantalum capacitors. TI also recommends that they be surge current tested by the
manufacturer. The TPS series available from AVX, and the 593D and 594D series from Sprague are all surge
current tested. Another approach to minimize the surge current stresses on the input capacitor is to add a small
inductor in series with the input supply line.
Table 10. AVX TPS
RECOMMENDED
APPLICATION VOLTAGE
VOLTAGE
RATING
85°C RATING
3.3
6.3
5
10
10
20
12
25
15
35
Table 11. Sprague 594D
RECOMMENDED
APPLICATION VOLTAGE
VOLTAGE
RATING
85°C RATING
2.5
4
3.3
6.3
5
10
8
16
12
20
18
25
24
35
29
50
Use caution when using ceramic capacitors for input bypassing, because it may cause severe ringing at the VIN
pin.
The important parameters for the input capacitor are the input voltage rating and the RMS current rating. With a
maximum input voltage of 28 V, an aluminum electrolytic capacitor with a voltage rating of at least
35 V (1.25 × VIN) is required.
The RMS current rating requirement for the input capacitor in a buck regulator is approximately ½ the DC load
current. In this example, with a 500-mA load, a capacitor with a RMS current rating of at least 250 mA is
required. The curves shown in Figure 22 can be used to select an appropriate input capacitor. From the curves,
locate the 35-V line and note which capacitor values have RMS current ratings greater than 250 mA.
24
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Figure 22. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical)
For a through-hole design, a 68-μF, 35-V electrolytic capacitor (Panasonic HFQ series, Nichicon PL, Sanyo MVGX series or equivalent) would be adequate. Other types or other manufacturers' capacitors can be used
provided the RMS ripple current ratings are adequate. Additionally, for a complete surface mount design,
electrolytic capacitors such as the Sanyo CV-C or CV-BS and the Nichicon WF or UR and the NIC Components
NACZ series could be considered.
For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to
the capacitor surge current rating and voltage rating. In this example, checking the Sprague 594D series data
sheet, a Sprague 594D 15-μF, 50-V capacitor is adequate.
9.2.2.2.6 Boost Capacitor (CB)
This capacitor develops the necessary voltage to turn the switch gate on fully. All applications must use a
0.01-μF, 50-V ceramic capacitor. For this application, and all applications, use a 0.01-μF, 50-V ceramic capacitor.
If the soft-start and frequency synchronization features are desired, look at steps 6 and 7 in Detailed Design
Procedure.
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9.2.2.3 Application Curves
Continuous Mode Switching Waveforms, VIN = 20 V, VOUT = 5 V,
ILOAD = 500 mA, L = 100 μH, COUT = 100 μF, COUTESR = 0.1 Ω
A: VSW pin voltage, 10 V/div.
B: Inductor current, 0.2 A/div
C: Output ripple voltage, 50 mV/div ac-coupled
Discontinuous Mode Switching Waveforms, VIN = 20 V,
VOUT = 5 V, ILOAD = 300 mA, L = 15 μH, COUT = 68 μF (2×),
COUTESR = 25 mΩ
A: VSW pin voltage, 10 V/div.
B: Inductor current, 0.5 A/div
C: Output ripple voltage, 20 mV/div ac-coupled
Figure 24. Horizontal Time Base: 1 μs/div
Figure 23. Horizontal Time Base: 1 μs/div
Load Transient Response for Continuous Mode, VIN = 20 V,
VOUT = 5 V, L = 100 μH, COUT = 100 μF, COUTESR = 0.1 Ω
A: Output voltage, 100 mV/div, ac-coupled
B: Load current: 100-mA to 500-mA load pulse
Load Transient Response for Discontinuous Mode, VIN = 20 V,
VOUT = 5 V, L = 47 μH, COUT = 68 μF, COUTESR = 50 mΩ
A: Output voltage, 100 mV/div, ac-coupled
B: Load current: 100-mA to 400-mA load pulse
Figure 25. Horizontal Time Base: 50 μs/div
Figure 26. Horizontal Time Base: 200 μs/div
10 Power Supply Recommendations
The LM2671 is designed to operate from an input voltage supply up to 40 V. This input supply must be well
regulated and able to withstand maximum input current and maintain a stable voltage.
26
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SNVS008L – SEPTEMBER 1998 – REVISED JUNE 2016
11 Layout
11.1 Layout Guidelines
Layout is very important in switching regulator designs. Rapidly switching currents associated with wiring
inductance can generate voltage transients which can cause problems. For minimal inductance and ground
loops, the wires indicated by heavy lines (in Figure 15 and Figure 21) must be wide printed-circuit traces and
must be kept as short as possible. For best results, external components must be placed as close to the switcher
IC as possible using ground plane construction or single point grounding.
If open core inductors are used, take special care as to the location and positioning of this type of inductor.
Allowing the inductor flux to intersect sensitive feedback, IC ground path, and COUT wiring can cause problems.
When using the adjustable version, take special care as to the location of the feedback resistors and the
associated wiring. Physically place both resistors near the IC, and route the wiring away from the inductor,
especially an open core type of inductor.
11.2 Layout Examples
CIN = 15-μF, 25-V Solid Tantalum Sprague, 594D series
COUT = 68-μF, 10-V Solid Tantalum Sprague, 594D series
D1 = 1-A, 40-V Schottky Rectifier, surface mount
L1 = 47-μH, L13 Coilcraft DO3308
CB = 0.01-μF, 50-V ceramic
Figure 27. Typical Surface Mount PCB Layout, Fixed Output (4x Size)
CIN = 15 μF, 50 V Solid Tantalum Sprague, 594D series
COUT = 33 μF, 25 V Solid Tantalum Sprague, 594D series
D1 = 1-A, 40-V Schottky Rectifier, surface mount
L1 = 100-μH, L20 Coilcraft DO3316
CB = 0.01-μF, 50-V ceramic
R1 = 1 kΩ, 1%
R2 = Use formula in Detailed Design Procedure
Figure 28. Typical Surface Mount PCB Layout, Adjustable Output (4x Size)
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LM2671
SNVS008L – SEPTEMBER 1998 – REVISED JUNE 2016
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12 Device and Documentation Support
12.1 Documentation Support
12.1.1 Related Documentation
For related documentation see the following:
• AN-1187 Leadless Leadfram Package (LLP)
• LM2670 SIMPLE SWITCHER® High Efficiency 3A Step-Down Voltage Regulator with Sync
12.2 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
12.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
12.4 Trademarks
E2E is a trademark of Texas Instruments.
SIMPLE SWITCHER, WEBENCH are registered trademarks of Texas Instruments.
All other trademarks are the property of their respective owners.
12.5 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
12.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
13.1 DAP (WSON Package)
The die attach pad (DAP) can and must be connected to the PCB Ground plane. For CAD and assembly
guidelines refer to AN-1187 Leadless Leadfram Package (LLP).
28
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PACKAGE OPTION ADDENDUM
www.ti.com
16-Feb-2016
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
LM2671LD-ADJ
NRND
WSON
NHN
16
1000
TBD
Call TI
Call TI
-40 to 125
S0008B
LM2671LD-ADJ/NOPB
ACTIVE
WSON
NHN
16
1000
Green (RoHS
& no Sb/Br)
CU SN
Level-3-260C-168 HR
-40 to 125
S0008B
LM2671M-12/NOPB
ACTIVE
SOIC
D
8
95
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
2671
M-12
LM2671M-3.3/NOPB
ACTIVE
SOIC
D
8
95
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
2671
M3.3
LM2671M-5.0
NRND
SOIC
D
8
95
TBD
Call TI
Call TI
-40 to 125
2671
M5.0
LM2671M-5.0/NOPB
ACTIVE
SOIC
D
8
95
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
2671
M5.0
LM2671M-ADJ
NRND
SOIC
D
8
95
TBD
Call TI
Call TI
-40 to 125
2671
MADJ
LM2671M-ADJ/NOPB
ACTIVE
SOIC
D
8
95
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
2671
MADJ
LM2671MX-12/NOPB
ACTIVE
SOIC
D
8
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
2671
M-12
LM2671MX-3.3/NOPB
ACTIVE
SOIC
D
8
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
2671
M3.3
LM2671MX-5.0/NOPB
ACTIVE
SOIC
D
8
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
2671
M5.0
LM2671MX-ADJ/NOPB
ACTIVE
SOIC
D
8
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
2671
MADJ
LM2671N-12/NOPB
ACTIVE
PDIP
P
8
40
Green (RoHS
& no Sb/Br)
CU SN
Level-1-NA-UNLIM
-40 to 125
LM2671
N-12
LM2671N-3.3/NOPB
ACTIVE
PDIP
P
8
40
Green (RoHS
& no Sb/Br)
CU SN
Level-1-NA-UNLIM
-40 to 125
LM2671
N-3.3
LM2671N-5.0/NOPB
ACTIVE
PDIP
P
8
40
Green (RoHS
& no Sb/Br)
CU SN
Level-1-NA-UNLIM
-40 to 125
LM2671
N-5.0
LM2671N-ADJ/NOPB
ACTIVE
PDIP
P
8
40
Green (RoHS
& no Sb/Br)
CU SN
Level-1-NA-UNLIM
-40 to 125
LM2671
N-ADJ
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
16-Feb-2016
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
16-Feb-2016
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
LM2671LD-ADJ
WSON
NHN
16
1000
178.0
12.4
5.3
5.3
1.3
8.0
12.0
Q1
LM2671LD-ADJ/NOPB
WSON
NHN
16
1000
178.0
12.4
5.3
5.3
1.3
8.0
12.0
Q1
LM2671MX-12/NOPB
SOIC
D
8
2500
330.0
12.4
6.5
5.4
2.0
8.0
12.0
Q1
LM2671MX-3.3/NOPB
SOIC
D
8
2500
330.0
12.4
6.5
5.4
2.0
8.0
12.0
Q1
LM2671MX-5.0/NOPB
SOIC
D
8
2500
330.0
12.4
6.5
5.4
2.0
8.0
12.0
Q1
LM2671MX-ADJ/NOPB
SOIC
D
8
2500
330.0
12.4
6.5
5.4
2.0
8.0
12.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
16-Feb-2016
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM2671LD-ADJ
WSON
NHN
16
1000
210.0
185.0
35.0
LM2671LD-ADJ/NOPB
WSON
NHN
16
1000
213.0
191.0
55.0
LM2671MX-12/NOPB
SOIC
D
8
2500
367.0
367.0
35.0
LM2671MX-3.3/NOPB
SOIC
D
8
2500
367.0
367.0
35.0
LM2671MX-5.0/NOPB
SOIC
D
8
2500
367.0
367.0
35.0
LM2671MX-ADJ/NOPB
SOIC
D
8
2500
367.0
367.0
35.0
Pack Materials-Page 2
MECHANICAL DATA
NHN0016A
LDA16A (REV A)
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