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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
•
1 Efficiency up to 96% The LM2671 series of regulators are monolithic
integrated circuits built with a LMDMOS process.
• Available in 8-Pin SOIC, PDIP, and WSON These regulators provide all the active functions for a
Packages step-down (buck) switching regulator, capable of
• Simple and Easy to Design With driving a 500-mA load current with excellent line and
• Requires Only 5 External Components load regulation. These devices are available in fixed
output voltages of 3.3 V, 5 V, 12 V, and an adjustable
• Uses Readily Available Standard Inductors
output version.
• 3.3-V, 5-V, 12-V, and Adjustable Output Versions
Requiring a minimum number of external
• Adjustable Version Output Voltage Range: 1.21 V components, these regulators are simple to use and
to 37 V include patented internal frequency compensation,
• ±1.5% Maximum Output Voltage Tolerance Over fixed frequency oscillator, external shutdown, soft
Line and Load Conditions start, and frequency synchronization.
• Ensured 500-mA Output Load Current The LM2671 series operates at a switching frequency
• 0.25-Ω DMOS Output Switch of 260 kHz, thus allowing smaller sized filter
• Wide Input Voltage Range: 8 V to 40 V components than what is required with lower
frequency switching regulators. Because of its very
• 260-kHz Fixed Frequency Internal Oscillator high efficiency (> 90%), the copper traces on the
• TTL Shutdown Capability, Low Power Standby printed-circuit board are the only heat sinking
Mode required.
• Soft-Start and Frequency Synchronization A family of standard inductors for use with the
• Thermal Shutdown and Current-Limit Protection LM2671 are available from several different
manufacturers. This feature greatly simplifies the
2 Applications design of switch-mode power supplies using these
advanced ICs. Also included in the data sheet are
• Simple High Efficiency (> 90%) Step-Down (Buck) selector guides for diodes and capacitors designed to
Regulators work in switch-mode power supplies.
• Efficient Preregulator for Linear Regulators
Device Information(1)
PART NUMBER PACKAGE BODY SIZE (NOM)
SOIC (8) 4.90 mm × 3.91 mm
LM2674 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

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.
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Table of Contents
1 Features .................................................................. 1 8.2 Functional Block Diagram ....................................... 10
2 Applications ........................................................... 1 8.3 Feature Description................................................. 10
3 Description ............................................................. 1 8.4 Device Functional Modes........................................ 11
4 Revision History..................................................... 2 9 Application and Implementation ........................ 13
9.1 Application Information............................................ 13
5 Description (continued)......................................... 3
9.2 Typical Applications ................................................ 14
6 Pin Configuration and Functions ......................... 3
10 Power Supply Recommendations ..................... 26
7 Specifications......................................................... 4
7.1 Absolute Maximum Ratings ...................................... 4 11 Layout................................................................... 27
11.1 Layout Guidelines ................................................. 27
7.2 ESD Ratings.............................................................. 4
11.2 Layout Examples................................................... 27
7.3 Recommended Operating Conditions....................... 4
7.4 Thermal Information .................................................. 4 12 Device and Documentation Support ................. 28
7.5 Electrical Characteristics – 3.3 V .............................. 5 12.1 Documentation Support ........................................ 28
7.6 Electrical Characteristics – 5 V ................................. 5 12.2 Receiving Notification of Documentation Updates 28
7.7 Electrical Characteristics – 12 V ............................... 5 12.3 Community Resources.......................................... 28
7.8 Electrical Characteristics – Adjustable...................... 6 12.4 Trademarks ........................................................... 28
7.9 Electrical Characteristics – All Output Voltage 12.5 Electrostatic Discharge Caution ............................ 28
Versions ..................................................................... 6 12.6 Glossary ................................................................ 28
7.10 Typical Characteristics ............................................ 7 13 Mechanical, Packaging, and Orderable
8 Detailed Description ............................................ 10 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 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 NHN Package

8-Pin SOIC or PDIP 16-Pin WSON
Top View Top View

CB 1 16 VSW
CB 1 8 VSW 15 VSW
NC 2
SS 2 7 VIN NC 3 14 VIN
SS 4 13 NC
SYNC 3 6 GND NC 5
DAP
12 GND
FB 4 5 ON/OFF SYNC 6 11 GND
NC 7 10 NC
FB 8 9 ON/OFF
Not to scale

Not to scale

Connect DAP to pin 11 and 12

Pin Functions
PIN
I/O DESCRIPTION
NAME SOIC, PDIP WSON
Bootstrap capacitor connection for high-side driver. Connect a high-quality,
CB 1 1 I
100-nF capacitor from CB to VSW Pin.
Soft-start Pin. Connect a capacitor from this pin to GND to control the output
SS 2 4 I
voltage ramp. If the feature not desired, the pin can be left floating.
This input allows control of the switching clock frequency. If left open-circuited
SYNC 3 6 I
the regulator is switched at the internal oscillator frequency, typically 260 kHz.
Feedback sense input pin. Connect to the midpoint of feedback divider to set
FB 4 8 I VOUT for ADJ version or connect this pin directly to the output capacitor for a
fixed output version.
Enable input to the voltage regulator. High = ON and low = OFF. Pull this pin
ON/OFF 5 9 I
high or float to enable the regulator
Source pin of the internal high-side FET. This is a switching node. Attached this
VSW 8 15, 16 O
pin to an inductor and the cathode of the external diode.
Power ground pins. Connect to system ground. Ground pins of CIN and COUT.
GND 6 11, 12 —
Path to CIN must be as short as possible.
Supply input pin to collector pin of high-side FET. Connect to power supply and
VIN 7 14 I input bypass capacitors CIN. Path from VIN pin to high frequency bypass CIN
and GND must be as short as possible.
2, 3, 5, 7,
NC — — No connect pins
10, 13

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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
Supply voltage 45 V
ON/OFF pin voltage, VSH −0.1 6 V
Switch voltage to ground –1 V
Boost pin voltage VSW + 8 V
Feedback pin voltage, VFB −0.3 14 V
Power dissipation Internally Limited
Vapor phase (60 s) 215
D package
Infrared (15 s) 220
Lead temperature °C
P package (soldering, 10 s) 260
WSON package See AN-1187
Maximum junction temperature 150 °C
Storage temperature, Tstg −65 150 °C

(1) 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.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.

7.2 ESD Ratings

VALUE UNIT
V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1) (2) ±2000 V

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) 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 UNIT
Supply voltage 6.5 40 V
Junction temperature, TJ –40 125 °C

7.4 Thermal Information

LM2674
(1)
THERMAL METRIC D (SOIC) P (PDIP) NHN (WSON) UNIT
8 PINS 8 PINS 16 PINS
RθJA Junction-to-ambient thermal resistance (2) 105 95 — °C/W

(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
(2) 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 TEST CONDITIONS MIN (1) TYP (2) MAX (1) UNIT
SYSTEM PARAMETERS (3)
TJ = 25°C 3.251 3.3 3.35
VIN = 8 V to 40 V,
Over full operating temperature V
ILOAD = 20 mA to 500 mA 3.201 3.399
range
VOUT Output voltage
TJ = 25°C 3.251 3.3 3.35
VIN = 6.5 V to 40 V,
Over full operating temperature V
ILOAD = 20 mA to 250 mA 3.201 3.399
range
η Efficiency VIN = 12 V, ILOAD = 500 mA 86%

(1) 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).
(2) Typical numbers are at 25°C and represent the most likely norm.
(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 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 TEST CONDITIONS MIN (1) TYP (2) MAX (1) UNIT
(3)
SYSTEM PARAMETERS
TJ = 25°C 4.925 5 5.075
VIN = 8 V to 40 V,
Over full operating temperature V
ILOAD = 20 mA to 500 mA 4.85 5.15
range
VOUT Output voltage
TJ = 25°C 4.925 5 5.075
VIN = 6.5 V to 40 V,
Over full operating temperature V
ILOAD = 20 mA to 250 mA 4.85 5.15
range
η Efficiency VIN = 12 V, ILOAD = 500 mA 90%

(1) 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).
(2) Typical numbers are at 25°C and represent the most likely norm.
(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 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 TEST CONDITIONS MIN (1) TYP (2) MAX (1) UNIT
(3)
SYSTEM PARAMETERS
TJ = 25°C 11.82 12 12.18
VIN = 15 V to 40 V,
VOUT Output voltage Over full operating V
ILOAD = 20 mA to 500 mA 11.64 12.36
temperature range
η Efficiency VIN = 24 V, ILOAD = 500 mA 94%

(1) 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).
(2) Typical numbers are at 25°C and represent the most likely norm.
(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 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) MAX (1) UNIT
SYSTEM PARAMETERS (3)
VIN = 8 V to 40 V, TJ = 25°C 1.192 1.21 1.228
ILOAD = 20 mA to 500 mA Over full operating V
VOUT programmed for 5 V 1.174 1.246
Feedback temperature range
VFB
voltage TJ = 25°C 1.192 1.21 1.228
VIN = 6.5 V to 40 V,
ILOAD = 20 mA to 250 mA Over full operating V
VOUT programmed for 5 V 1.174 1.246
temperature range
η Efficiency VIN = 12 V, ILOAD = 500 mA 90%

(1) 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).
(2) Typical numbers are at 25°C and represent the most likely norm.
(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 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 UNIT
DEVICE PARAMETERS
VFEEDBACK = 8 V
2.5 3.6
for 3.3-V, 5-V, and adjustable versions
IQ Quiescent current mA
VFEEDBACK = 15 V
2.5
for 12-V versions
TJ = 25°C 50 100
ISTBY Standby quiescent current ON/OFF pin = 0 V Over full operating temperature μA
150
range
TJ = 25°C 0.62 0.8 1.2
ICL Current limit A
Over full operating temperature range 0.575 1.25
VIN = 40 V, ON/OFF pin = 0 V
1 25 μA
IL Output leakage current VSWITCH = 0 V
VSWITCH = −1 V, ON/OFF pin = 0 V 6 15 mA
TJ = 25°C 0.25 0.4
RDS(ON) Switch ON-resistance ISWITCH = 500 mA Over full operating temperature Ω
0.6
range
TJ = 25°C 260
fO Oscillator frequency Measured at switch pin Over full operating temperature kHz
225 275
range
Maximum duty cycle 95%
D
Minimum duty cycle 0%
IBIAS Feedback bias current VFEEDBACK = 1.3 V (adjustable version only) 85 nA
TJ = 25°C 1.4
VS/D ON/OFF pin voltage thresholds V
Over full operating temperature range 0.8 2
TJ = 25°C 20
IS/D ON/OFF pin current ON/OFF pin = 0 V Over full operating temperature μA
7 37
range
FSYNC Synchronization frequency VSYNC = 3.5 V, 50% duty cycle 400 kHz
VSYNC Synchronization threshold voltage 1.4 V
TJ = 25°C 0.63
VSS Soft-start voltage V
Over full operating temperature range 0.53 0.73
TJ = 25°C 4.5
ISS Soft-start current μA
Over full operating temperature range 1.5 6.9

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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)

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).

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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.

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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 short-
circuit 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 electro-
magnetic 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.

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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. SCHOTTKY RENCO PULSE ENGINEERING COILCRAFT
INDUCTANCE CURRENT
REF. THROUGH SURFACE SURFACE THROUGH SURFACE SURFACE
(μH) (A) THROUGH HOLE
DESG. HOLE MOUNT MOUNT HOLE MOUNT MOUNT
L2 150 0.21 67143920 67144290 RL-5470-4 RL1500-150 PE-53802 PE-53802-S DO1608-154
L3 100 0.26 67143930 67144300 RL-5470-5 RL1500-100 PE-53803 PE-53803-S DO1608-104
L4 68 0.32 67143940 67144310 RL-1284-68-43 RL1500-68 PE-53804 PE-53804-S DO1608-683
L5 47 0.37 67148310 67148420 RL-1284-47-43 RL1500-47 PE-53805 PE-53805-S DO1608-473
L6 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 SURFACE MOUNT THROUGH HOLE
INDUCTANCE
VOLTAGE
(μH) SPRAGUE AVX TPS NICHICON PANASONIC
(V) SANYO OS-CON SANYO MV-GX
594D SERIES SERIES PL SERIES HFQ SERIES
SA SERIES (μF/V) SERIES (μF/V)
(μF/V) (μF/V) (μF/V) (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
3.3
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
5
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
12 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

1-A DIODES 3-A DIODES
VR
SURFACE MOUNT THROUGH HOLE SURFACE MOUNT THROUGH HOLE
SK12 1N5817 SK32 1N5820
20 V
B120 SR102 — SR302
SK13 1N5818 SK33 1N5821
30 V B130 11DQ03 30WQ03F 31DQ03
MBRS130 SR103 — —
SK14 1N5819 SK34 1N5822
B140 11DQ04 30BQ040 MBR340
MBRS140 SR104 30WQ04F 31DQ04
40 V
10BQ040 — MBRS340 SR304
10MQ040 — MBRD340 —
15MQ040 — — —
SK15 MBR150 SK35 MBR350
50 V 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 VOLTAGE
APPLICATION 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 VOLTAGE
APPLICATION 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 MV-
GX 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 500-
mA 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

CASE OUTPUT INDUCTANCE (μH)
STYLE (1) 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. SURFACE MOUNT THROUGH HOLE
REF.
DESG. SPRAGUE 594D AVX TPS SERIES SANYO OS-CON SA SANYO MV-GX NICHICON PL PANASONIC HFQ
# SERIES (μF/V) (μF/V) SERIES (μF/V) SERIES (μF/V) SERIES (μF/V) 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
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
(1)
C18 68/25 (2×) 33/25 47/25 220/35 220/35 220/35
(1)
C19 33/25 33/25 33/25 150/35 150/35 150/35
(1)
C20 33/25 33/25 33/25 120/35 120/35 120/35
(2)
C21 33/35 (2×) 22/25 150/35 150/35 150/35
(2)
C22 33/35 22/35 120/35 120/35 120/35
(2) (2) (2)
C23 220/50 100/50 120/50
(2) (2) (2)
C24 150/50 100/50 120/50
(2) (2) (2)
C25 150/50 82/50 82/50

(1) The SC series of Os-Con capacitors (others are SA series)

(2) 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 1-
A, 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 VOLTAGE
APPLICATION VOLTAGE RATING
85°C RATING
3.3 6.3
5 10
10 20
12 25
15 35

Table 11. Sprague 594D

RECOMMENDED VOLTAGE
APPLICATION 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.

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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 MV-
GX 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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LM2671
SNVS008L – SEPTEMBER 1998 – REVISED JUNE 2016 www.ti.com

9.2.2.3 Application Curves

Continuous Mode Switching Waveforms, VIN = 20 V, VOUT = 5 V, Discontinuous Mode Switching Waveforms, VIN = 20 V,
ILOAD = 500 mA, L = 100 μH, COUT = 100 μF, COUTESR = 0.1 Ω VOUT = 5 V, ILOAD = 300 mA, L = 15 μH, COUT = 68 μF (2×),
A: VSW pin voltage, 10 V/div. COUTESR = 25 mΩ
B: Inductor current, 0.2 A/div A: VSW pin voltage, 10 V/div.
C: Output ripple voltage, 50 mV/div ac-coupled B: Inductor current, 0.5 A/div
C: Output ripple voltage, 20 mV/div ac-coupled

Figure 23. Horizontal Time Base: 1 μs/div Figure 24. Horizontal Time Base: 1 μs/div

Load Transient Response for Continuous Mode, VIN = 20 V, Load Transient Response for Discontinuous Mode, VIN = 20 V,
VOUT = 5 V, L = 100 μH, COUT = 100 μF, COUTESR = 0.1 Ω VOUT = 5 V, L = 47 μH, COUT = 68 μF, COUTESR = 50 mΩ
A: Output voltage, 100 mV/div, ac-coupled A: Output voltage, 100 mV/div, ac-coupled
B: Load current: 100-mA to 500-mA load pulse 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 Submit Documentation Feedback Copyright © 1998–2016, Texas Instruments Incorporated

Product Folder Links: LM2671

 LM2671
www.ti.com 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)

Copyright © 1998–2016, Texas Instruments Incorporated Submit Documentation Feedback 27

Product Folder Links: LM2671
LM2671
SNVS008L – SEPTEMBER 1998 – REVISED JUNE 2016 www.ti.com

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 Submit Documentation Feedback Copyright © 1998–2016, Texas Instruments Incorporated

Product Folder Links: LM2671

 PACKAGE OPTION ADDENDUM

www.ti.com 23-May-2025

PACKAGING INFORMATION

Orderable part number Status Material type Package | Pins Package qty | Carrier RoHS Lead finish/ MSL rating/ Op temp (°C) Part marking
(1) (2) (3) Ball material Peak reflow (6)
(4) (5)

LM2671LD-ADJ/NOPB Active Production WSON (NHN) | 16 1000 | SMALL T&R Yes SN Level-3-260C-168 HR -40 to 125 S0008B
LM2671LD-ADJ/NOPB.B Active Production WSON (NHN) | 16 1000 | SMALL T&R Yes SN Level-3-260C-168 HR -40 to 125 S0008B
LM2671M-12/NOPB Active Production SOIC (D) | 8 95 | TUBE Yes SN Level-1-260C-UNLIM -40 to 125 2671
M-12
LM2671M-12/NOPB.B Active Production SOIC (D) | 8 95 | TUBE Yes SN Level-1-260C-UNLIM -40 to 125 2671
M-12
LM2671M-3.3/NOPB Active Production SOIC (D) | 8 95 | TUBE Yes SN Level-1-260C-UNLIM -40 to 125 2671
M3.3
LM2671M-3.3/NOPB.B Active Production SOIC (D) | 8 95 | TUBE Yes SN Level-1-260C-UNLIM -40 to 125 2671
M3.3
LM2671M-5.0/NOPB Active Production SOIC (D) | 8 95 | TUBE Yes SN Level-1-260C-UNLIM -40 to 125 2671
M5.0
LM2671M-5.0/NOPB.B Active Production SOIC (D) | 8 95 | TUBE Yes SN Level-1-260C-UNLIM -40 to 125 2671
M5.0
LM2671M-ADJ/NOPB Active Production SOIC (D) | 8 95 | TUBE Yes SN Level-1-260C-UNLIM -40 to 125 2671
MADJ
LM2671M-ADJ/NOPB.B Active Production SOIC (D) | 8 95 | TUBE Yes SN Level-1-260C-UNLIM -40 to 125 2671
MADJ
LM2671MX-12/NOPB Active Production SOIC (D) | 8 2500 | LARGE T&R Yes SN Level-1-260C-UNLIM -40 to 125 2671
M-12
LM2671MX-12/NOPB.B Active Production SOIC (D) | 8 2500 | LARGE T&R Yes SN Level-1-260C-UNLIM -40 to 125 2671
M-12
LM2671MX-3.3/NOPB Active Production SOIC (D) | 8 2500 | LARGE T&R Yes SN Level-1-260C-UNLIM -40 to 125 2671
M3.3
LM2671MX-3.3/NOPB.B Active Production SOIC (D) | 8 2500 | LARGE T&R Yes SN Level-1-260C-UNLIM -40 to 125 2671
M3.3
LM2671MX-5.0/NOPB Active Production SOIC (D) | 8 2500 | LARGE T&R Yes SN Level-1-260C-UNLIM -40 to 125 2671
M5.0
LM2671MX-5.0/NOPB.B Active Production SOIC (D) | 8 2500 | LARGE T&R Yes SN Level-1-260C-UNLIM -40 to 125 2671
M5.0
LM2671MX-ADJ/NOPB Active Production SOIC (D) | 8 2500 | LARGE T&R Yes SN Level-1-260C-UNLIM -40 to 125 2671
MADJ

Addendum-Page 1
 PACKAGE OPTION ADDENDUM

www.ti.com 23-May-2025

Orderable part number Status Material type Package | Pins Package qty | Carrier RoHS Lead finish/ MSL rating/ Op temp (°C) Part marking
(1) (2) (3) Ball material Peak reflow (6)
(4) (5)

LM2671MX-ADJ/NOPB.B Active Production SOIC (D) | 8 2500 | LARGE T&R Yes SN Level-1-260C-UNLIM -40 to 125 2671
MADJ
LM2671N-12/NOPB Active Production PDIP (P) | 8 40 | TUBE Yes NIPDAU Level-1-NA-UNLIM -40 to 125 LM2671
N-12
LM2671N-12/NOPB.B Active Production PDIP (P) | 8 40 | TUBE Yes NIPDAU Level-1-NA-UNLIM -40 to 125 LM2671
N-12
LM2671N-3.3/NOPB Active Production PDIP (P) | 8 40 | TUBE Yes Call TI | Nipdau Level-1-NA-UNLIM -40 to 125 LM2671
N-3.3
LM2671N-3.3/NOPB.B Active Production PDIP (P) | 8 40 | TUBE Yes NIPDAU Level-1-NA-UNLIM -40 to 125 LM2671
N-3.3
LM2671N-5.0/NOPB Active Production PDIP (P) | 8 40 | TUBE Yes NIPDAU Level-1-NA-UNLIM -40 to 125 LM2671
N-5.0
LM2671N-5.0/NOPB.B Active Production PDIP (P) | 8 40 | TUBE Yes NIPDAU Level-1-NA-UNLIM -40 to 125 LM2671
N-5.0
LM2671N-ADJ/NOPB Active Production PDIP (P) | 8 40 | TUBE Yes NIPDAU Level-1-NA-UNLIM -40 to 125 LM2671
N-ADJ
LM2671N-ADJ/NOPB.B Active Production PDIP (P) | 8 40 | TUBE Yes NIPDAU Level-1-NA-UNLIM -40 to 125 LM2671
N-ADJ

(1)
Status: For more details on status, see our product life cycle.

(2)
Material type: When designated, preproduction parts are prototypes/experimental devices, and are not yet approved or released for full production. Testing and final process, including without limitation quality assurance,
reliability performance testing, and/or process qualification, may not yet be complete, and this item is subject to further changes or possible discontinuation. If available for ordering, purchases will be subject to an additional
waiver at checkout, and are intended for early internal evaluation purposes only. These items are sold without warranties of any kind.

(3)
RoHS values: Yes, No, RoHS Exempt. See the TI RoHS Statement for additional information and value definition.

(4)
Lead finish/Ball material: Parts may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two lines if the finish value exceeds the maximum
column width.

(5)
MSL rating/Peak reflow: The moisture sensitivity level ratings and peak solder (reflow) temperatures. In the event that a part has multiple moisture sensitivity ratings, only the lowest level per JEDEC standards is shown.
Refer to the shipping label for the actual reflow temperature that will be used to mount the part to the printed circuit board.

(6)
Part marking: There may be an additional marking, which relates to the logo, the lot trace code information, or the environmental category of the part.

Addendum-Page 2
 PACKAGE OPTION ADDENDUM

www.ti.com 23-May-2025

Multiple part markings will be inside parentheses. Only one part marking contained in parentheses and separated by a "~" will appear on a part. If a line is indented then it is a continuation of the previous line and the two
combined represent the entire part marking for that device.

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 3
 PACKAGE MATERIALS INFORMATION

www.ti.com 23-May-2025

TAPE AND REEL INFORMATION

REEL DIMENSIONS TAPE DIMENSIONS

K0 P1

B0 W
Reel
Diameter
Cavity A0
A0 Dimension designed to accommodate the component width
B0 Dimension designed to accommodate the component length
K0 Dimension designed to accommodate the component thickness
W Overall width of the carrier tape
P1 Pitch between successive cavity centers

Reel Width (W1)

QUADRANT ASSIGNMENTS FOR PIN 1 ORIENTATION IN TAPE

Sprocket Holes

Q1 Q2 Q1 Q2

Q3 Q4 Q3 Q4 User Direction of Feed

Pocket Quadrants

*All dimensions are nominal

Device Package Package Pins SPQ Reel Reel A0 B0 K0 P1 W Pin1
Type Drawing Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant
(mm) W1 (mm)
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 23-May-2025

TAPE AND REEL BOX DIMENSIONS

Width (mm)
H
W

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM2671LD-ADJ/NOPB WSON NHN 16 1000 208.0 191.0 35.0
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
 PACKAGE MATERIALS INFORMATION

www.ti.com 23-May-2025

TUBE

T - Tube
height L - Tube length

W - Tube
width

B - Alignment groove width

*All dimensions are nominal

Device Package Name Package Type Pins SPQ L (mm) W (mm) T (µm) B (mm)
LM2671M-12/NOPB D SOIC 8 95 495 8 4064 3.05
LM2671M-12/NOPB.B D SOIC 8 95 495 8 4064 3.05
LM2671M-3.3/NOPB D SOIC 8 95 495 8 4064 3.05
LM2671M-3.3/NOPB.B D SOIC 8 95 495 8 4064 3.05
LM2671M-5.0/NOPB D SOIC 8 95 495 8 4064 3.05
LM2671M-5.0/NOPB.B D SOIC 8 95 495 8 4064 3.05
LM2671M-ADJ/NOPB D SOIC 8 95 495 8 4064 3.05
LM2671M-ADJ/NOPB.B D SOIC 8 95 495 8 4064 3.05
LM2671N-12/NOPB P PDIP 8 40 502 14 11938 4.32
LM2671N-12/NOPB.B P PDIP 8 40 502 14 11938 4.32
LM2671N-3.3/NOPB P PDIP 8 40 502 14 11938 4.32
LM2671N-3.3/NOPB.B P PDIP 8 40 502 14 11938 4.32
LM2671N-5.0/NOPB P PDIP 8 40 502 14 11938 4.32
LM2671N-5.0/NOPB.B P PDIP 8 40 502 14 11938 4.32
LM2671N-ADJ/NOPB P PDIP 8 40 502 14 11938 4.32
LM2671N-ADJ/NOPB.B P PDIP 8 40 502 14 11938 4.32

Pack Materials-Page 3
 PACKAGE OUTLINE
D0008A SCALE 2.800
SOIC - 1.75 mm max height
SMALL OUTLINE INTEGRATED CIRCUIT

SEATING PLANE
.228-.244 TYP
[5.80-6.19]
.004 [0.1] C
A PIN 1 ID AREA
6X .050
[1.27]
8
1

.189-.197 2X
[4.81-5.00] .150
NOTE 3 [3.81]

4X (0 -15 )

4
5
8X .012-.020
B .150-.157 [0.31-0.51]
.069 MAX
[3.81-3.98] .010 [0.25] C A B [1.75]
NOTE 4

.005-.010 TYP
[0.13-0.25]

4X (0 -15 )

SEE DETAIL A
.010
[0.25]

.004-.010
0 -8 [0.11-0.25]
.016-.050
[0.41-1.27] DETAIL A
(.041) TYPICAL
[1.04]

4214825/C 02/2019

NOTES:

1. Linear dimensions are in inches [millimeters]. Dimensions in parenthesis are for reference only. Controlling dimensions are in inches.
Dimensioning and tolerancing per ASME Y14.5M.
2. This drawing is subject to change without notice.
3. This dimension does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, or gate burrs shall not
exceed .006 [0.15] per side.
4. This dimension does not include interlead flash.
5. Reference JEDEC registration MS-012, variation AA.

www.ti.com
 EXAMPLE BOARD LAYOUT
D0008A SOIC - 1.75 mm max height
SMALL OUTLINE INTEGRATED CIRCUIT

8X (.061 )
[1.55]
SYMM SEE
DETAILS
1
8

8X (.024)
[0.6] SYMM

(R.002 ) TYP
[0.05]
5
4
6X (.050 )
[1.27]
(.213)
[5.4]

LAND PATTERN EXAMPLE

EXPOSED METAL SHOWN
SCALE:8X

SOLDER MASK SOLDER MASK

METAL METAL UNDER
OPENING OPENING SOLDER MASK

EXPOSED
METAL EXPOSED
METAL
.0028 MAX .0028 MIN
[0.07] [0.07]
ALL AROUND ALL AROUND

NON SOLDER MASK SOLDER MASK

DEFINED DEFINED

SOLDER MASK DETAILS

4214825/C 02/2019

NOTES: (continued)

6. Publication IPC-7351 may have alternate designs.

7. Solder mask tolerances between and around signal pads can vary based on board fabrication site.

www.ti.com
 EXAMPLE STENCIL DESIGN
D0008A SOIC - 1.75 mm max height
SMALL OUTLINE INTEGRATED CIRCUIT

8X (.061 )
[1.55] SYMM

1
8

8X (.024)
[0.6] SYMM

(R.002 ) TYP
5 [0.05]
4
6X (.050 )
[1.27]
(.213)
[5.4]

SOLDER PASTE EXAMPLE

BASED ON .005 INCH [0.125 MM] THICK STENCIL
SCALE:8X

4214825/C 02/2019

NOTES: (continued)

8. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
9. Board assembly site may have different recommendations for stencil design.

www.ti.com
 MECHANICAL DATA
NHN0016A

LDA16A (REV A)

www.ti.com
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