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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

LM2671 SIMPLE SWITCHER

Power Converter High Efficiency 500-mA

Step-Down Voltage Regulator With Features

1 Features

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-ΩDMOS 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

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.

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 PACKAGE BODY SIZE (NOM)

LM2674 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

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Table of Contents

1 Features.................................................................. 1

2 Applications ........................................................... 1

3 Description............................................................. 1

4 Revision History..................................................... 2

5 Description (continued)......................................... 3

6 Pin Configuration and Functions......................... 3

7 Specifications......................................................... 4

7.1 Absolute Maximum Ratings ...................................... 4

7.2 ESD Ratings.............................................................. 4

7.3 Recommended Operating Conditions....................... 4

7.4 Thermal Information.................................................. 4

7.5 Electrical Characteristics – 3.3 V.............................. 5

7.6 Electrical Characteristics – 5 V................................. 5

7.7 Electrical Characteristics – 12 V............................... 5

7.8 Electrical Characteristics – Adjustable...................... 6

7.9 Electrical Characteristics – All Output Voltage

Versions..................................................................... 6

7.10 Typical Characteristics............................................ 7

8 Detailed Description............................................ 10

8.1 Overview................................................................. 10

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 Documentation Support ........................................ 28

12.2 Receiving Notification of Documentation Updates 28

12.3 Community Resources.......................................... 28

12.4 Trademarks........................................................... 28

12.5 Electrostatic Discharge Caution............................ 28

12.6 Glossary................................................................ 28

13 Mechanical, Packaging, and Orderable

Information........................................................... 28

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

Not to scale

DAP

CB VSW

NC VSW

NC VIN

SS NC

NC GND

SYNC GND

NC NC

FB ON/OFF

Not to scale

1CB 8 VSW

2SS 7 VIN

3SYNC 6 GND

4FB 5 ON/OFF

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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

NHN Package

16-Pin WSON

Top View

Connect DAP to pin 11 and 12

Pin Functions

PIN I/O DESCRIPTION

NAME 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 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.

NC — 2, 3, 5, 7,

10, 13 — No connect pins

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(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 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

Lead temperature D package Vapor phase (60 s) 215

°C

Infrared (15 s) 220

P package (soldering, 10 s) 260

WSON package See AN-1187

Maximum junction temperature 150 °C

Storage temperature, Tstg −65 150 °C

(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-kΩresistor into each pin.

7.2 ESD Ratings VALUE UNIT

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

7.3 Recommended Operating Conditions MIN MAX UNIT

Supply voltage 6.5 40 V

Junction temperature, TJ–40 125 °C

(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).

7.4 Thermal Information

THERMAL METRIC(1) LM2674

UNITD (SOIC) P (PDIP) NHN (WSON)

8 PINS 8 PINS 16 PINS

RθJA Junction-to-ambient thermal resistance(2) 105 95 — °C/W

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(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.

7.5 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)

VOUT Output voltage

VIN = 8 V to 40 V,

ILOAD = 20 mA to 500 mA

TJ= 25°C 3.251 3.3 3.35 V

Over full operating temperature

range 3.201 3.399

VIN = 6.5 V to 40 V,

ILOAD = 20 mA to 250 mA

TJ= 25°C 3.251 3.3 3.35 V

Over full operating temperature

range 3.201 3.399

ηEfficiency 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

SYSTEM PARAMETERS(3)

VOUT Output voltage

VIN = 8 V to 40 V,

ILOAD = 20 mA to 500 mA

TJ= 25°C 4.925 5 5.075 V

Over full operating temperature

range 4.85 5.15

VIN = 6.5 V to 40 V,

ILOAD = 20 mA to 250 mA

TJ= 25°C 4.925 5 5.075 V

Over full operating temperature

range 4.85 5.15

ηEfficiency 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

SYSTEM PARAMETERS(3)

VOUT Output voltage VIN = 15 V to 40 V,

ILOAD = 20 mA to 500 mA

TJ= 25°C 11.82 12 12.18 V

Over full operating

temperature range 11.64 12.36

ηEfficiency VIN = 24 V, ILOAD = 500 mA 94%

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(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.

7.8 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)

VFB Feedback

voltage

VIN = 8 V to 40 V,

ILOAD = 20 mA to 500 mA

VOUT programmed for 5 V

TJ= 25°C 1.192 1.21 1.228 V

Over full operating

temperature range 1.174 1.246

VIN = 6.5 V to 40 V,

ILOAD = 20 mA to 250 mA

VOUT programmed for 5 V

TJ= 25°C 1.192 1.21 1.228 V

Over full operating

temperature range 1.174 1.246

ηEfficiency VIN = 12 V, ILOAD = 500 mA 90%

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

IQQuiescent current

VFEEDBACK = 8 V

for 3.3-V, 5-V, and adjustable versions 2.5 3.6 mA

VFEEDBACK = 15 V

for 12-V versions 2.5

ISTBY Standby quiescent current ON/OFF pin = 0 V TJ= 25°C 50 100

μA

Over full operating temperature

range 150

ICL Current limit TJ= 25°C 0.62 0.8 1.2 A

Over full operating temperature range 0.575 1.25

ILOutput leakage current VIN = 40 V, ON/OFF pin = 0 V

VSWITCH = 0 V 1 25 μA

VSWITCH =−1 V, ON/OFF pin = 0 V 6 15 mA

RDS(ON) Switch ON-resistance ISWITCH = 500 mA TJ= 25°C 0.25 0.4

Over full operating temperature

range 0.6

fOOscillator frequency Measured at switch pin TJ= 25°C 260 kHz

Over full operating temperature

range 225 275

DMaximum duty cycle 95%

Minimum duty cycle 0%

IBIAS Feedback bias current VFEEDBACK = 1.3 V (adjustable version only) 85 nA

VS/D ON/OFF pin voltage thresholds TJ= 25°C 1.4 V

Over full operating temperature range 0.8 2

IS/D ON/OFF pin current ON/OFF pin = 0 V TJ= 25°C 20

μA

Over full operating temperature

range 7 37

FSYNC Synchronization frequency VSYNC = 3.5 V, 50% duty cycle 400 kHz

VSYNC Synchronization threshold voltage 1.4 V

VSS Soft-start voltage TJ= 25°C 0.63 V

Over full operating temperature range 0.53 0.73

ISS Soft-start current TJ= 25°C 4.5 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 CBpin 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-kΩresistor

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 5 V

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.

REF.

DESG.

INDUCTANCE

(μH) CURRENT

(A)

SCHOTTKY RENCO PULSE ENGINEERING COILCRAFT

THROUGH

HOLE SURFACE

MOUNT THROUGH HOLE SURFACE

MOUNT THROUGH

HOLE SURFACE

MOUNT SURFACE

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

VOLTAGE

(V)

INDUCTANCE

(μH)

OUTPUT CAPACITOR

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)

3.3

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

VR1-A DIODES 3-A DIODES

SURFACE MOUNT THROUGH HOLE SURFACE MOUNT THROUGH HOLE

20 V SK12 1N5817 SK32 1N5820

B120 SR102 — SR302

30 V SK13 1N5818 SK33 1N5821

B130 11DQ03 30WQ03F 31DQ03

MBRS130 SR103 — —

40 V

SK14 1N5819 SK34 1N5822

B140 11DQ04 30BQ040 MBR340

MBRS140 SR104 30WQ04F 31DQ04

10BQ040 — MBRS340 SR304

10MQ040 — MBRD340 —

15MQ040 — — —

50 V 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 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-kΩresistor and a

100-pF capacitor are suitable values.

For all applications, use a 1-kΩresistor 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 R1and R2, as shown in Figure 21.

Use the following formula to select the appropriate resistor values.

where

• VREF = 1.21 V (3)

Select R1to be 1 kΩ, 1%. Solve for R2.

(4)

Select a value for R1between 240 Ωand 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=1kΩ(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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(1) SM - Surface Mount, TH - Through Hole

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

STYLE (1) OUTPUT

VOLTAGE (V) INDUCTANCE (μH)

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

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(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.

Table 9. Output Capacitor Selection Table

OUTPUT CAPACITOR

CAP.

REF.

DESG.

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)

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

C18 68/25 (2×) 33/25 47/25 (1) 220/35 220/35 220/35

C19 33/25 33/25 33/25 (1) 150/35 150/35 150/35

C20 33/25 33/25 33/25 (1) 120/35 120/35 120/35

C21 33/35 (2×) 22/25 (2) 150/35 150/35 150/35

C22 33/35 22/35 (2) 120/35 120/35 120/35

C23 (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

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

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.

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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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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

Figure 23. Horizontal Time Base: 1 μs/div

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

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

Figure 25. Horizontal Time Base: 50 μs/div

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 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.

LM2671

www.ti.com

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

Product Folder Links: LM2671

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)

LM2671

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

www.ti.com

Product Folder Links: LM2671

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).

PACKAGE OPTION ADDENDUM

www.ti.com 11-Jan-2021

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead finish/

Ball material

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM2671LD-ADJ NRND WSON NHN 16 1000 Non-RoHS

& Green Call TI Call TI -40 to 125 S0008B

LM2671LD-ADJ/NOPB ACTIVE WSON NHN 16 1000 RoHS & Green SN Level-3-260C-168 HR -40 to 125 S0008B

LM2671M-12/NOPB ACTIVE SOIC D 8 95 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671

M-12

LM2671M-3.3/NOPB ACTIVE SOIC D 8 95 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671

M3.3

LM2671M-5.0 NRND SOIC D 8 95 Non-RoHS

& Green Call TI Call TI -40 to 125 2671

M5.0

LM2671M-5.0/NOPB ACTIVE SOIC D 8 95 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671

M5.0

LM2671M-ADJ NRND SOIC D 8 95 Non-RoHS

& Green Call TI Call TI -40 to 125 2671

MADJ

LM2671M-ADJ/NOPB ACTIVE SOIC D 8 95 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671

MADJ

LM2671MX-12/NOPB ACTIVE SOIC D 8 2500 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671

M-12

LM2671MX-3.3/NOPB ACTIVE SOIC D 8 2500 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671

M3.3

LM2671MX-5.0/NOPB ACTIVE SOIC D 8 2500 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671

M5.0

LM2671MX-ADJ/NOPB ACTIVE SOIC D 8 2500 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671

MADJ

LM2671N-12/NOPB ACTIVE PDIP P 8 40 RoHS & Green Call TI | SN Level-1-NA-UNLIM -40 to 125 LM2671

N-12

LM2671N-3.3/NOPB ACTIVE PDIP P 8 40 RoHS & Green Call TI | SN Level-1-NA-UNLIM -40 to 125 LM2671

N-3.3

LM2671N-5.0/NOPB ACTIVE PDIP P 8 40 RoHS & Green SN Level-1-NA-UNLIM -40 to 125 LM2671

N-5.0

LM2671N-ADJ/NOPB ACTIVE PDIP P 8 40 RoHS & Green SN Level-1-NA-UNLIM -40 to 125 LM2671

N-ADJ

(1) The marketing status values are defined as follows:

PACKAGE OPTION ADDENDUM

www.ti.com 11-Jan-2021

Addendum-Page 2

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.

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) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance

do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may

reference these types of products as "Pb-Free".

RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.

Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based

flame retardants must also meet the <=1000ppm threshold requirement.

(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 finish/Ball material - Orderable Devices 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.

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.

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device Package

Type Package

Drawing Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

(mm) B0

(mm) K0

(mm) P1

(mm) W

(mm) Pin1

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

PACKAGE MATERIALS INFORMATION

www.ti.com 29-Sep-2019

Pack Materials-Page 1

*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 210.0 185.0 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

PACKAGE MATERIALS INFORMATION

www.ti.com 29-Sep-2019

Pack Materials-Page 2

MECHANICAL DATA

NHN0016A

www.ti.com

LDA16A (REV A)

www.ti.com

PACKAGE OUTLINE

.228-.244 TYP

[5.80-6.19]

.069 MAX

[1.75]

6X .050

[1.27]

8X .012-.020

[0.31-0.51]

.150

[3.81]

.005-.010 TYP

[0.13-0.25]

0 - 8 .004-.010

[0.11-0.25]

.010

[0.25]

.016-.050

[0.41-1.27]

4X (0 -15 )

.189-.197

[4.81-5.00]

NOTE 3

B .150-.157

[3.81-3.98]

NOTE 4

4X (0 -15 )

(.041)

[1.04]

SOIC - 1.75 mm max heightD0008A

SMALL OUTLINE INTEGRATED CIRCUIT

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.

.010 [0.25] C A B

PIN 1 ID AREA

SEATING PLANE

.004 [0.1] C

SEE DETAIL A

DETAIL A

TYPICAL

SCALE 2.800

www.ti.com

EXAMPLE BOARD LAYOUT

.0028 MAX

[0.07]

ALL AROUND

.0028 MIN

[0.07]

ALL AROUND

(.213)

[5.4]

6X (.050 )

[1.27]

8X (.061 )

[1.55]

8X (.024)

[0.6]

(R.002 ) TYP

[0.05]

SOIC - 1.75 mm max heightD0008A

SMALL OUTLINE INTEGRATED CIRCUIT

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.

METAL SOLDER MASK

OPENING

NON SOLDER MASK

DEFINED

SOLDER MASK DETAILS

EXPOSED

METAL

OPENING

SOLDER MASK METAL UNDER

SOLDER MASK

DEFINED

EXPOSED

METAL

LAND PATTERN EXAMPLE

EXPOSED METAL SHOWN

SCALE:8X

SYMM

SEE

DETAILS

SYMM

www.ti.com

EXAMPLE STENCIL DESIGN

8X (.061 )

[1.55]

8X (.024)

[0.6]

6X (.050 )

[1.27] (.213)

[5.4]

(R.002 ) TYP

[0.05]

SOIC - 1.75 mm max heightD0008A

SMALL OUTLINE INTEGRATED CIRCUIT

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.

SOLDER PASTE EXAMPLE

BASED ON .005 INCH [0.125 MM] THICK STENCIL

SCALE:8X

SYMM

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