LM2671MX-ADJ - Texas Instruments High-Performance Analog

LM2671

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LM2671 SIMPLE SWITCHER

Power Converter High Efficiency 500mA Step-Down Voltage

Regulator with Features

Check for Samples: LM2671

1FEATURES

234• Efficiency up to 96% DESCRIPTION

The LM2671 series of regulators are monolithic

• Available in SOIC, 8-pin PDIP and WSON integrated circuits built with a LMDMOS process.

Packages These regulators provide all the active functions for a

• Computer Design Software LM267X Made step-down (buck) switching regulator, capable of

Simple (version 6.0) driving a 500mA load current with excellent line and

• Simple and Easy to Design With load regulation. These devices are available in fixed

output voltages of 3.3V, 5.0V, 12V, and an adjustable

• Requires Only 5 external Components output version.

• Uses Readily Available Standard Inductors Requiring a minimum number of external

• 3.3V, 5.0V, 12V, and Adjustable Output components, these regulators are simple to use and

Versions include patented internal frequency compensation

• Adjustable Version Output Voltage Range: (Patent Nos. 5,382,918 and 5,514,947), fixed

1.21V to 37V frequency oscillator, external shutdown, soft-start,

and frequency synchronization.

• ±1.5% Max Output Voltage Tolerance Over

Line and Load Conditions The LM2671 series operates at a switching frequency

• Ensured 500mA Output Load Current of 260 kHz, thus allowing smaller sized filter

components than what would be needed with lower

• 0.25ΩDMOS Output Switch frequency switching regulators. Because of its very

• Wide Input Voltage Range: 8V to 40V high efficiency (>90%), the copper traces on the

• 260 kHz Fixed Frequency Internal Oscillator printed circuit board are the only heat sinking needed.

• TTL Shutdown Capability, Low Power Standby A family of standard inductors for use with the

Mode LM2671 are available from several different

manufacturers. This feature greatly simplifies the

• Soft-Start and Frequency Synchronization design of switch-mode power supplies using these

• Thermal Shutdown and Current Limit advanced ICs. Also included in the datasheet are

Protection selector guides for diodes and capacitors designed to

work in switch-mode power supplies.

APPLICATIONS Other features include a ensured ±1.5% tolerance on

• Simple High Efficiency (>90%) Step-Down output voltage within specified input voltages and

(Buck) Regulator output load conditions, and ±10% on the oscillator

• Efficient Pre-Regulator for Linear Regulators frequency. External shutdown is included, featuring

typically 50 μA stand-by current. The output switch

includes current limiting, as well as thermal shutdown

for full protection under fault conditions.

To simplify the LM2671 buck regulator design

procedure, there exists computer design software,

LM267X Made Simple (version 6.0).

1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

2SIMPLE SWITCHER, WEBENCH are registered trademarks of Texas Instruments.

3Windows is a registered trademark of Microsoft Corporation.

4All other trademarks are the property of their respective owners.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

6 11

SYNC

VSW

VIN

GND

ON/OFF

* No Connections

DAP**

**Connect to Pins 11, 12 on PCB

LM2671

SNVS008K –SEPTEMBER 1998–REVISED APRIL 2013

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Typical Application

Figure 1. Fixed Output Voltage Versions

Connection Diagram

Figure 2. 16-Lead WSON Surface Mount Package

Top View

See Package Drawing Number NHN0016A

Figure 3. SOIC/PDIP Package

8-Lead Package

Top View

See Package Drawing Number D0008A/P0008E

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.

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Absolute Maximum Ratings(1)(2)

Supply Voltage 45V

ON/OFF Pin Voltage −0.1V ≤VSH ≤6V

Switch Voltage to Ground −1V

Boost Pin Voltage VSW + 8V

Feedback Pin Voltage −0.3V ≤VFB ≤14V

ESD Susceptibility

Human Body Model (3) 2 kV

Power Dissipation Internally Limited

Storage Temperature Range −65°C to +150°C

Lead Temperature

D Package

Vapor Phase (60s) +215°C

Infrared (15s) +220°C

P Package (Soldering, 10s) +260°C

WSON Package (See AN-1187)

Maximum Junction Temperature +150°C

(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for

which the device is intended to be functional, but device parameter specifications may not be ensured under these conditions. For

ensured specifications and test conditions, see the Electrical Characteristics.

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

specifications.

(3) The human body model is a 100 pF capacitor discharged through a 1.5 kΩresistor into each pin.

Operating Ratings

Supply Voltage 6.5V to 40V

Temperature Range −40°C ≤TJ≤+125°C

Electrical Characteristics LM2671-3.3

Specifications with standard type face are for TJ= 25°C, and those in bold type face apply over full Operating Temperature

Range.

Typical Min (2) Max (2)

Symbol Parameter Conditions Units

(1)

SYSTEM PARAMETERS Test Circuit Figure 22 (3)

VOUT Output Voltage VIN = 8V to 40V, ILOAD = 20 mA to 500 mA 3.3 3.251/3.201 3.350/3.399 V

VOUT Output Voltage VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA 3.3 3.251/3.201 3.350/3.399 V

ηEfficiency VIN = 12V, ILOAD = 500 mA 86 %

(1) Typical numbers are at 25°C and represent the most likely norm.

(2) All limits ensured at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits

are 100% production tested. All limits at temperature extremes are ensured via correlation using standard Statistical Quality Control

(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

(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 22 and Figure 23 test circuits, system performance will

be as specified by the system parameters section of the Electrical Characteristics.

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Electrical Characteristics LM2671-5.0

Symbol Parameter Conditions Typical (1) Min (2) Max (2) Units

SYSTEM PARAMETERS Test Circuit Figure 22 (3)

VOUT Output Voltage VIN = 8V to 40V, ILOAD = 20 mA to 500 mA 5.0 4.925/4.850 5.075/5.150 V

VOUT Output Voltage VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA 5.0 4.925/4.850 5.075/5.150 V

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

(1) Typical numbers are at 25°C and represent the most likely norm.

(2) All limits ensured at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits

are 100% production tested. All limits at temperature extremes are ensured via correlation using standard Statistical Quality Control

(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

(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 22 and Figure 23 test circuits, system performance will

be as specified by the system parameters section of the Electrical Characteristics.

Electrical Characteristics LM2671-12

Symbol Parameter Conditions Typical (1) Min (2) Max (2) Units

SYSTEM PARAMETERS Test Circuit Figure 22 (3)

VOUT Output Voltage VIN = 15V to 40V, ILOAD = 20 mA to 500 mA 12 11.82/11.64 12.18/12.36 V

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

(1) Typical numbers are at 25°C and represent the most likely norm.

(2) All limits ensured at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits

are 100% production tested. All limits at temperature extremes are ensured via correlation using standard Statistical Quality Control

(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

(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 22 and Figure 23 test circuits, system performance will

be as specified by the system parameters section of the Electrical Characteristics.

Electrical Characteristics LM2671-ADJ

Symbol Parameter Conditions Typ (1) Min (2) Max (2) Units

SYSTEM PARAMETERS Test Circuit Figure 23 (3)

VFB Feedback Voltage VIN = 8V to 40V, ILOAD = 20 mA to 500 mA

VOUT Programmed for 5V 1.210 1.192/1.174 1.228/1.246 V

(see Circuit of Figure 23)

VFB Feedback Voltage VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA

VOUT Programmed for 5V 1.210 1.192/1.174 1.228/1.246 V

(see Circuit of Figure 23)

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

(1) Typical numbers are at 25°C and represent the most likely norm.

(2) All limits ensured at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits

are 100% production tested. All limits at temperature extremes are ensured via correlation using standard Statistical Quality Control

(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

(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 22 and Figure 23 test circuits, system performance will

be as specified by the system parameters section of the Electrical Characteristics.

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All Output Voltage Versions

Specifications with standard type face are for TJ= 25°C, and those in bold type face apply over full Operating Temperature

Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable versions and VIN = 24V for the 12V version,

and ILOAD = 100 mA.

Symbol Parameters Conditions Typ Min Max Units

DEVICE PARAMETERS

IQQuiescent Current VFEEDBACK = 8V 2.5 3.6 mA

For 3.3V, 5.0V, and ADJ Versions

VFEEDBACK = 15V 2.5 mA

For 12V Versions

ISTBY Standby Quiescent Current ON/OFF Pin = 0V 50 100/150 μA

ICL Current Limit 0.8 0.62/0.575 1.2/1.25 A

ILOutput Leakage Current VIN = 40V, ON/OFF Pin = 0V 1 25 μA

VSWITCH = 0V

VSWITCH =−1V, ON/OFF Pin = 0V 6 15 mA

RDS(ON) Switch On-Resistance ISWITCH = 500 mA 0.25 0.40/0.60 Ω

fOOscillator Frequency Measured at Switch Pin 260 225 275 kHz

D Maximum Duty Cycle 95 %

Minimum Duty Cycle 0 %

IBIAS Feedback Bias Current VFEEDBACK = 1.3V ADJ Version Only 85 nA

VS/D ON/OFF Pin Voltage Thesholds 1.4 0.8 2.0 V

IS/D ON/OFF Pin Current ON/OFF Pin = 0V 20 7 37 μA

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

VSYNC Synchronization Threshold 1.4 V

Voltage

VSS Soft-Start Voltage 0.63 0.53 0.73 V

ISS Soft-Start Current 4.5 1.5 6.9 μA

θJA Thermal Resistance P Package, Junction to Ambient (1) 95 °C/W

D Package, Junction to Ambient (1) 105

(1) Junction to ambient thermal resistance with approximately 1 square inch of printed circuit board copper surrounding the leads. Additional

copper area will lower thermal resistance further. See Application Information section in the application note accompanying this

datasheet and the thermal model in LM267X Made Simple version 6.0 software. The value θJ−Afor 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, refer to Application Note AN-1187 SNOA401.

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Typical Performance Characteristics

Normalized

Output Voltage Line Regulation

Figure 4. Figure 5.

Drain-to-Source

Efficiency Resistance

Figure 6. Figure 7.

Operating

Switch Current Limit Quiescent Current

Figure 8. Figure 9.

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Typical Performance Characteristics (continued)

Standby ON/OFF Threshold

Quiescent Current Voltage

Figure 10. Figure 11.

ON/OFF Pin

Current (Sourcing) Switching Frequency

Figure 12. Figure 13.

Feedback Pin

Bias Current Peak Switch Current

Figure 14. Figure 15.

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Typical Performance Characteristics (continued)

Dropout Voltage—3.3V Option Dropout Voltage—5.0V Option

Figure 16. Figure 17.

BLOCK DIAGRAM

* Patent Number 5,514,947

† Patent Number 5,382,918

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Typical Performance Characteristics

(Circuit of Figure 22)

Continuous Mode Switching Waveforms Discontinuous Mode Switching Waveforms

VIN = 20V, VOUT = 5V, ILOAD = 500 mA VIN = 20V, VOUT = 5V, ILOAD = 300 mA

L = 100 μH, COUT = 100 μF, COUTESR = 0.1ΩL = 15 μH, COUT = 68 μF (2×), COUTESR = 25 mΩ

A: VSW Pin Voltage, 10 V/div. A: VSW Pin Voltage, 10 V/div.

B: Inductor Current, 0.2 A/div B: Inductor Current, 0.5 A/div

C: Output Ripple Voltage, 50 mV/div AC-Coupled C: Output Ripple Voltage, 20 mV/div AC-Coupled

Figure 18. Horizontal Time Base: 1 μs/div Figure 19. Horizontal Time Base: 1 μs/div

Load Transient Response for Continuous Mode Load Transient Response for Discontinuous Mode

VIN = 20V, VOUT = 5V VIN = 20V, VOUT = 5V,

L = 100 μH, COUT = 100 μF, COUTESR = 0.1ΩL = 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 20. Horizontal Time Base: 50 μs/div Figure 21. Horizontal Time Base: 200 μs/div

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TEST CIRCUIT AND LAYOUT GUIDELINES

CIN - 22 μF, 50V Tantalum, Sprague “199D Series”

COUT - 47 μF, 25V Tantalum, Sprague “595D Series”

D1 - 3.3A, 50V Schottky Rectifier, IR 30WQ05F

L1 - 68 μH Sumida #RCR110D-680L

CB- 0.01 μF, 50V Ceramic

Figure 22. Standard Test Circuits and Layout Guides

Fixed Output Voltage Versions

CIN - 22 μF, 50V Tantalum, Sprague “199D Series”

COUT - 47 μF, 25V Tantalum, Sprague “595D Series”

D1 - 3.3A, 50V Schottky Rectifier, IR 30WQ05F

L1 - 68 μH Sumida #RCR110D-680L

R1 - 1.5 kΩ, 1%

CB- 0.01 μF, 50V Ceramic

For a 5V output, select R2 to be 4.75 kΩ, 1%

where VREF = 1.21V

Use a 1% resistor for best stability.

Figure 23. Standard Test Circuits and Layout Guides

Adjustable Output Voltage Versions

Application Hints

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

0.5A, and highly efficient operation.

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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 pre-determined 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, refer to the LM2670 data sheet for additional applications information.

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 260kHz 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).

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 6.5V to 40V. For best performance of the power supply the VIN pin should always

be bypassed with an input capacitor located close to this pin and GND.

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 0.01μF.

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, it is recommended that a broad ground plane be used

to minimize signal coupling throughout the circuit

SYNC

This input allows control of the switching clock frequency. If left open-circuited the regulator will be 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. It is recommended that the external TTL or CMOS compatible

clock (between 0V and a level greater than 3V) be ac coupled to the SYNC pin through a 100pF capacitor and a

1KΩresistor 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.

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 (3.3V, 5V and 12V 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.

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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 0.8V will completely turn OFF the regulator. The current drain from the input supply when OFF

is only 50μA. The ON/OFF input has an internal pull-up current source of approximately 20μA and a protection

clamp zener diode of 7V to ground. When electrically driving the ON/OFF pin the high voltage level for the ON

condition should not exceed the 6V absolute maximum limit. When ON/OFF control is not required this pin

should be left open.

DAP (WSON PACKAGE)

The Die Attach Pad (DAP) can and should be connected to the PCB Ground plane/island. For CAD and

assembly guidelines refer to Application Note SNOA401.

LM2671 Series Buck Regulator Design Procedure (Fixed Output)

PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)

To simplify the buck regulator design procedure, Texas Instruments

is making available computer design software to be used with the

SIMPLE SWITCHER line of switching regulators.LM267X Made

Simple (version 6.0) is available on Windows®3.1, NT, or 95

operating systems.

Given: Given:

VOUT = Regulated Output Voltage (3.3V, 5V, or 12V) VOUT = 5V

VIN(max) = Maximum DC Input Voltage VIN(max) = 12V

ILOAD(max) = Maximum Load Current ILOAD(max) = 500 mA

1. Inductor Selection (L1) 1. Inductor Selection (L1)

A. Select the correct inductor value selection guide from Figure 24 A. Use the inductor selection guide for the 5V version shown in

and Figure 25 or Figure 26 (output voltages of 3.3V, 5V, or 12V Figure 25.

respectively). For all other voltages, see the design procedure for the

adjustable version.

B. From the inductor value selection guide, identify the inductance B. From the inductor value selection guide shown in Figure 25, the

region intersected by the Maximum Input Voltage line and the inductance region intersected by the 12V horizontal line and the 500

Maximum Load Current line. Each region is identified by an mA vertical line is 47 μH, and the inductor code is L13.

inductance value and an inductor code (LXX).

C. Select an appropriate inductor from the four manufacturer's part C. The inductance value required is 47 μH. From the table in

numbers listed in Table 1. Each manufacturer makes a different style Table 1, go to the L13 line and choose an inductor part number from

of inductor to allow flexibility in meeting various design requirements. any of the four manufacturers shown. (In most instances, both

Listed below are some of the differentiating characteristics of each through hole and surface mount inductors are available.)

manufacturer's inductors:

Schott: 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. A table listing the manufacturers' phone

numbers is located in Table 2.

2. Output Capacitor Selection (COUT) 2. Output Capacitor Selection (COUT)

A. Select an output capacitor from the output capacitor table in A. Use the 5.0V section in the output capacitor table in Table 10.

Table 10. Using the output voltage and the inductance value found in Choose a capacitor value and voltage rating from the line that

the inductor selection guide, step 1, locate the appropriate capacitor contains the inductance value of 47 μH. The capacitance and

value and voltage rating. voltage rating values corresponding to the 47 μH inductor are the:

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PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)

The capacitor list contains through-hole electrolytic capacitors from Surface Mount:

four different capacitor manufacturers and surface mount tantalum 68 μF/10V Sprague 594D Series.

capacitors from two different capacitor manufacturers. It is 100 μF/10V AVX TPS Series.

recommended that both the manufacturers and the manufacturer's Through Hole:

series that are listed in the table be used. A table listing the 68 μF/10V Sanyo OS-CON SA Series.

manufacturers' phone numbers is located in Table 4. 150 μF/35V Sanyo MV-GX Series.

150 μF/35V Nichicon PL Series.

150 μF/35V Panasonic HFQ Series.

3. Catch Diode Selection (D1) 3. Catch Diode Selection (D1)

A. In normal operation, the average current of the catch diode is the A. Refer to the table shown in Table 5. In this example, a 1A, 20V

load current times the catch diode duty cycle, 1-D (D is the switch Schottky diode will provide the best performance. If the circuit must

duty cycle, which is approximately the output voltage divided by the withstand a continuous shorted output, a higher current Schottky

input voltage). The largest value of the catch diode average current diode is recommended.

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 should 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.

B. The reverse voltage rating of the diode should be at least 1.25

times the maximum input voltage.

C. Because of their fast switching speed and low forward voltage

drop, Schottky diodes provide the best performance and efficiency.

This Schottky diode must be located close to the LM2671 using

short leads and short printed circuit traces.

4. Input Capacitor (CIN) 4. Input Capacitor (CIN)

A low ESR aluminum or tantalum bypass capacitor is needed The important parameters for the input capacitor are the input

between the input pin and ground to prevent large voltage transients voltage rating and the RMS current rating. With a maximum input

from appearing at the input. This capacitor should be located close voltage of 12V, an aluminum electrolytic capacitor with a voltage

to the IC using short leads. In addition, the RMS current rating of the rating greater than 15V (1.25 × VIN) would be needed. The next

input capacitor should be selected to be at least ½ the DC load higher capacitor voltage rating is 16V.

current. The capacitor manufacturer data sheet must be checked to The RMS current rating requirement for the input capacitor in a buck

assure that this current rating is not exceeded. The curves shown in regulator is approximately ½ the DC load current. In this example,

Figure 28 show typical RMS current ratings for several different with a 500 mA load, a capacitor with a RMS current rating of at least

aluminum electrolytic capacitor values. A parallel connection of two 250 mA is needed. The curves shown in Figure 28 can be used to

or more capacitors may be required to increase the total minimum select an appropriate input capacitor. From the curves, locate the

RMS current rating to suit the application requirements. 16V line and note which capacitor values have RMS current ratings

For an aluminum electrolytic capacitor, the voltage rating should be greater than 250 mA.

at least 1.25 times the maximum input voltage. Caution must be For a through hole design, a 100 μF/16V electrolytic capacitor

exercised if solid tantalum capacitors are used. The tantalum (Panasonic HFQ series, Nichicon PL, Sanyo MV-GX series or

capacitor voltage rating should be twice the maximum input voltage. equivalent) would be adequate. Other types or other manufacturers'

The tables in Recommended Application Voltage for AVX TPS and capacitors can be used provided the RMS ripple current ratings are

Sprague 594D Tantalum Chip Capacitors Derated for 85°C. show adequate. Additionally, for a complete surface mount design,

the recommended application voltage for AVX TPS and Sprague electrolytic capacitors such as the Sanyo CV-C or CV-BS and the

594D tantalum capacitors. It is also recommended that they be surge Nichicon WF or UR and the NIC Components NACZ series could be

current tested by the manufacturer. The TPS series available from considered.

AVX, and the 593D and 594D series from Sprague are all surge For surface mount designs, solid tantalum capacitors can be used,

current tested. Another approach to minimize the surge current but caution must be exercised with regard to the capacitor surge

stresses on the input capacitor is to add a small inductor in series current rating and voltage rating. In this example, checking

with the input supply line. Recommended Application Voltage for AVX TPS and Sprague 594D

Use caution when using ceramic capacitors for input bypassing, Tantalum Chip Capacitors Derated for 85°C., and the Sprague 594D

because it may cause severe ringing at the VIN pin. series datasheet, a Sprague 594D 15 μF, 25V capacitor is adequate.

5. Boost Capacitor (CB) 5. Boost Capacitor (CB)

This capacitor develops the necessary voltage to turn the switch For this application, and all applications, use a 0.01 μF, 50V ceramic

gate on fully. All applications should use a 0.01 μF, 50V ceramic capacitor.

capacitor.

6. Soft-Start Capacitor (CSS - optional) 6. Soft-Start Capacitor (CSS - optional)

This capacitor controls the rate at which the device starts up. The For this application, selecting a start-up time of 10 ms and using the

formula for the soft-start capacitor CSS is: formula for CSS results in a value of:

(1) (2)

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PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)

where:

ISS = Soft-Start Current :4.5 μA typical.

tSS = Soft-Start Time :Selected.

VSSTH = Soft-Start Threshold Voltage :0.63V typical.

VOUT = Output Voltage :Selected.

VSCHOTTKY = Schottky Diode Voltage Drop :0.4V typical.

VIN = Input Voltage :Selected.

If this feature is not desired, leave this pin open. With certain

softstart capacitor values and operating conditions, the LM2671 can

exhibit an overshoot on the output voltage during turn on. Especially

when starting up into no load or low load, the softstart function may

not be effective in preventing a larger voltage overshoot on the

output. With larger loads or lower input voltages during startup this

effect is minimized. In particular, avoid using softstart capacitors

between 0.033µF and 1µF.

7. Frequency Synchronization (optional) 7. Frequency Synchronization (optional)

The LM2671 (oscillator) can be synchronized to run with an external For all applications, use a 1 kΩresistor and a 100 pF capacitor for

oscillator, using the sync pin (pin 3). By doing so, the LM2671 can the RC filter.

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 3V or greater, a

1 kΩresistor and a 100 pF capacitor are suitable values.

INDUCTOR VALUE SELECTION GUIDES

(For Continuous Mode Operation)

Figure 24. LM2671-3.3 Figure 25. LM2671-5.0

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Figure 26. LM2671-12 Figure 27. LM2671-ADJ

Table 1. Inductor Manufacturers' Part Numbers

Schott Renco Pulse Engineering Coilcraft

Ind. Inductan Current

Ref. ce Through Surface Through Surface Through Surface Surface

(A)

Desg. (μH) Hole Mount Hole 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 0.70 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

Table 2. Inductor Manufacturers' Phone Numbers

Coilcraft Inc. Phone (800) 322-2645

FAX (708) 639-1469

Coilcraft Inc., Europe Phone +44 1236 730 595

FAX +44 1236 730 627

Pulse Engineering Inc. Phone (619) 674-8100

FAX (619) 674-8262

Pulse Engineering Inc., Europe Phone +353 93 24 107

FAX +353 93 24 459

Renco Electronics Inc. Phone (800) 645-5828

FAX (516) 586-5562

Schott Corp. Phone (612) 475-1173

FAX (612) 475-1786

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Table 3. Output Capacitor Table

Output Capacitor

Surface Mount Through Hole

Output Inductance

Voltage Sprague AVX TPS Sanyo OS-CON Sanyo MV-GX Nichicon Panasonic

(μH)

(V) 594D Series Series SA Series Series PL Series HFQ Series

(μF/V) (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

5.0 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

Table 4. Capacitor Manufacturers' Phone Numbers

Nichicon Corp. Phone (847) 843-7500

FAX (847) 843-2798

Panasonic Phone (714) 373-7857

FAX (714) 373-7102

AVX Corp. Phone (845) 448-9411

FAX (845) 448-1943

Sprague/Vishay Phone (207) 324-4140

FAX (207) 324-7223

Sanyo Corp. Phone (619) 661-6322

FAX (619) 661-1055

Table 5. Schottky Diode Selection Table

1A Diodes 3A Diodes

VRSurface Through Surface Through

Mount Hole Mount Hole

20V SK12 1N5817 SK32 1N5820

B120 SR102 SR302

30V SK13 1N5818 SK33 1N5821

B130 11DQ03 30WQ03F 31DQ03

MBRS130 SR103

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Table 5. Schottky Diode Selection Table (continued)

1A Diodes 3A Diodes

VRSurface Through Surface Through

Mount Hole Mount Hole

40V SK14 1N5819 SK34 1N5822

B140 11DQ04 30BQ040 MBR340

MBRS140 SR104 30WQ04F 31DQ04

10BQ040 MBRS340 SR304

10MQ040 MBRD340

15MQ040

50V SK15 MBR150 SK35 MBR350

B150 11DQ05 30WQ05F 31DQ05

10BQ050 SR105 SR305

Table 6. Diode Manufacturers' Phone Numbers

International Rectifier Corp. Phone (310) 322-3331

FAX (310) 322-3332

Motorola, Inc. Phone (800) 521-6274

FAX (602) 244-6609

General Instruments Corp. Phone (516) 847-3000

FAX (516) 847-3236

Diodes, Inc. Phone (805) 446-4800

FAX (805) 446-4850

Figure 28. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical)

Recommended Application Voltage for AVX TPS and Sprague 594D Tantalum Chip Capacitors Derated

for 85°C.

Table 7. AVX TPS

Recommended Voltage

Application Voltage Rating

+85°C Rating

3.3 6.3

5 10

10 20

12 25

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Table 7. AVX TPS (continued)

Recommended Voltage

Application Voltage Rating

+85°C Rating

15 35

Table 8. 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

LM2671 Series Buck Regulator Design Procedure (Adjustable Output)

PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)

To simplify the buck regulator design procedure, Texas Instrumnets

is making available computer design software to be used with the

SIMPLE SWITCHER line of switching regulators.LM267X Made

Simple is available on (version 6.0) Windows®3.1, NT, or 95

operating systems.

Given: Given:

VOUT = Regulated Output Voltage VOUT = 20V

VIN(max) = Maximum Input Voltage VIN(max) = 28V

ILOAD(max) = Maximum Load Current ILOAD(max) = 500 mA

F = Switching Frequency (Fixed at a nominal 260 kHz). F = Switching Frequency (Fixed at a nominal 260 kHz).

1. Programming Output Voltage (Selecting R1and R2, as shown in 1. Programming Output Voltage (Selecting R1and R2, as shown in

Figure 23)Figure 23)

Use the following formula to select the appropriate resistor values. Select R1to be 1 kΩ, 1%. Solve for R2.

where VREF = 1.21V (3) (4)

Select a value for R1between 240Ωand 1.5 kΩ. The lower resistor R2= 1 kΩ(16.53 −1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.

values minimize noise pickup in the sensitive feedback pin. (For the R2= 15.4 kΩ.

lowest temperature coefficient and the best stability with time, use

1% metal film resistors.)

(5)

2. Inductor Selection (L1) 2. Inductor Selection (L1)

A. Calculate the inductor Volt • microsecond constant E • T (V • μs), A. Calculate the inductor Volt • microsecond constant (E • T),

from the following formula:

(6) (7)

where VSAT=internal switch saturation voltage=0.25V and VD= diode

forward voltage drop = 0.5V

B. Use the E • T value from the previous formula and match it with B. E • T = 21.6 (V • μs)

the E • T number on the vertical axis of the Inductor Value Selection

Guide shown in Figure 27.

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PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)

C. On the horizontal axis, select the maximum load current. C. ILOAD(max) = 500 mA

D. Identify the inductance region intersected by the E • T value and D. From the inductor value selection guide shown in Figure 27, the

the Maximum Load Current value. Each region is identified by an inductance region intersected by the 21.6 (V • μs) horizontal line and

inductance value and an inductor code (LXX). the 500 mA vertical line is 100 μH, and the inductor code is L20.

E. Select an appropriate inductor from the four manufacturer's part E. From the table in Table 1, locate line L20, and select an inductor

numbers listed in Table 1. For information on the different types of part number from the list of manufacturers' part numbers.

inductors, see the inductor selection in the fixed output voltage

design procedure.

3. Output Capacitor SeIection (COUT) 3. Output Capacitor SeIection (COUT)

A. Select an output capacitor from the capacitor code selection guide A. Use the appropriate row of the capacitor code selection guide, in

in Table 9. Using the inductance value found in the inductor Table 9. For this example, use the 15–20V row. The capacitor code

selection guide, step 1, locate the appropriate capacitor code corresponding to an inductance of 100 μH is C20.

corresponding to the desired output voltage.

B. Select an appropriate capacitor value and voltage rating, using B. From the output capacitor selection table in Table 10, choose a

the capacitor code, from the output capacitor selection table in capacitor value (and voltage rating) that intersects the capacitor

Table 10. There are two solid tantalum (surface mount) capacitor code(s) selected in section A, C20.

manufacturers and four electrolytic (through hole) capacitor The capacitance and voltage rating values corresponding to the

manufacturers to choose from. It is recommended that both the capacitor code C20 are the:

manufacturers and the manufacturer's series that are listed in the Surface Mount:

table be used. A table listing the manufacturers' phone numbers is 33 μF/25V Sprague 594D Series.

located in Table 4. 33 μF/25V AVX TPS Series.

Through Hole:

33 μF/25V Sanyo OS-CON SC Series.

120 μF/35V Sanyo MV-GX Series.

120 μF/35V Nichicon PL Series.

120 μF/35V 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. Refer to the capacitor manufacturers' data sheet for

this information.

4. Catch Diode Selection (D1) 4. Catch Diode Selection (D1)

A. In normal operation, the average current of the catch diode is the A. Refer to the table shown in Table 5. Schottky diodes provide the

load current times the catch diode duty cycle, 1-D (D is the switch best performance, and in this example a 1A, 40V Schottky diode

duty cycle, which is approximately VOUT/VIN). The largest value of would be a good choice. If the circuit must withstand a continuous

the catch diode average current occurs at the maximum input shorted output, a higher current (at least 1.2A) Schottky diode is

voltage (minimum D). For normal operation, the catch diode current recommended.

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 should 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.

B. The reverse voltage rating of the diode should be at least 1.25

times the maximum input voltage.

C. Because of their fast switching speed and low forward voltage

drop, Schottky diodes provide the best performance and efficiency.

The Schottky diode must be located close to the LM2671 using short

leads and short printed circuit traces.

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PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version)

5. Input Capacitor (CIN) 5. Input Capacitor (CIN)

A low ESR aluminum or tantalum bypass capacitor is needed The important parameters for the input capacitor are the input

between the input pin and ground to prevent large voltage transients voltage rating and the RMS current rating. With a maximum input

from appearing at the input. This capacitor should be located close voltage of 28V, an aluminum electrolytic capacitor with a voltage

to the IC using short leads. In addition, the RMS current rating of the rating of at least 35V (1.25 × VIN) would be needed.

input capacitor should be selected to be at least ½ the DC load The RMS current rating requirement for the input capacitor in a buck

current. The capacitor manufacturer data sheet must be checked to regulator is approximately ½ the DC load current. In this example,

assure that this current rating is not exceeded. The curves shown in with a 500 mA load, a capacitor with a RMS current rating of at least

Figure 28 show typical RMS current ratings for several different 250 mA is needed. The curves shown in Figure 28 can be used to

aluminum electrolytic capacitor values. A parallel connection of two select an appropriate input capacitor. From the curves, locate the

or more capacitors may be required to increase the total minimum 35V line and note which capacitor values have RMS current ratings

RMS current rating to suit the application requirements. greater than 250 mA.

For an aluminum electrolytic capacitor, the voltage rating should be For a through hole design, a 68 μF/35V electrolytic capacitor

at least 1.25 times the maximum input voltage. Caution must be (Panasonic HFQ series, Nichicon PL, Sanyo MV-GX series or

exercised if solid tantalum capacitors are used. The tantalum equivalent) would be adequate. Other types or other manufacturers'

capacitor voltage rating should be twice the maximum input voltage. capacitors can be used provided the RMS ripple current ratings are

The tables in Recommended Application Voltage for AVX TPS and adequate. Additionally, for a complete surface mount design,

Sprague 594D Tantalum Chip Capacitors Derated for 85°C. show electrolytic capacitors such as the Sanyo CV-C or CV-BS and the

the recommended application voltage for AVX TPS and Sprague Nichicon WF or UR and the NIC Components NACZ series could be

594D tantalum capacitors. It is also recommended that they be surge considered.

current tested by the manufacturer. The TPS series available from For surface mount designs, solid tantalum capacitors can be used,

AVX, and the 593D and 594D series from Sprague are all surge but caution must be exercised with regard to the capacitor surge

current tested. Another approach to minimize the surge current current rating and voltage rating. In this example, checking

stresses on the input capacitor is to add a small inductor in series Recommended Application Voltage for AVX TPS and Sprague 594D

with the input supply line. Tantalum Chip Capacitors Derated for 85°C., and the Sprague 594D

Use caution when using ceramic capacitors for input bypassing, series datasheet, a Sprague 594D 15 μF, 50V capacitor is adequate.

because it may cause severe ringing at the VIN pin.

6. Boost Capacitor (CB) 6. Boost Capacitor (CB)

This capacitor develops the necessary voltage to turn the switch For this application, and all applications, use a 0.01 μF, 50V ceramic

gate on fully. All applications should use a 0.01 μF, 50V ceramic capacitor.

capacitor.

If the soft-start and frequency synchronization features are desired,

look at steps 6 and 7 in the fixed output design procedure.

Table 9. Capacitor Code Selection Guide

Inductance (μH)

Case Output

Style (1) Voltage (V) 22 33 47 68 100 150 220

SM and TH 1.21–2.50 — — — — C1 C2 C3

SM and TH 2.50–3.75 — — — C1 C2 C3 C3

SM and TH 3.75–5.0 — — C4 C5 C6 C6 C6

SM and TH 5.0–6.25 — C4 C7 C6 C6 C6 C6

SM and TH 6.25–7.5 C8 C4 C7 C6 C6 C6 C6

SM and TH 7.5–10.0 C9 C10 C11 C12 C13 C13 C13

SM and TH 10.0–12.5 C14 C11 C12 C12 C13 C13 C13

SM and TH 12.5–15.0 C15 C16 C17 C17 C17 C17 C17

SM and TH 15.0–20.0 C18 C19 C20 C20 C20 C20 C20

SM and TH 20.0–30.0 C21 C22 C22 C22 C22 C22 C22

TH 30.0–37.0 C23 C24 C24 C25 C25 C25 C25

(1) SM - Surface Mount, TH - Through Hole

Table 10. Output Capacitor Selection Table

Output Capacitor

Surface Mount Through Hole

Cap. Sprague AVX TPS Sanyo OS-CON Sanyo MV-GX Nichicon Panasonic

Ref.

Desg. 594D Series Series SA Series Series PL Series HFQ Series

#(μF/V) (μF/V) (μF/V) (μF/V) (μF/V) (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

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Table 10. Output Capacitor Selection Table (continued)

Output Capacitor

Surface Mount Through Hole

Cap. Sprague AVX TPS Sanyo OS-CON Sanyo MV-GX Nichicon Panasonic

Ref.

Desg. 594D Series Series SA Series Series PL Series HFQ Series

#(μF/V) (μF/V) (μF/V) (μF/V) (μF/V) (μF/V)

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

(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.

Application Information

TYPICAL SURFACE MOUNT PC BOARD LAYOUT, FIXED OUTPUT (4X SIZE)

CIN - 15 μF, 25V, Solid Tantalum Sprague, “594D series”

COUT - 68 μF, 10V, Solid Tantalum Sprague, “594D series”

D1 - 1A, 40V Schottky Rectifier, Surface Mount

L1 - 47 μH, L13, Coilcraft DO3308

CB- 0.01 μF, 50V, Ceramic

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TYPICAL SURFACE MOUNT PC BOARD LAYOUT, ADJUSTABLE OUTPUT (4X SIZE)

CIN - 15 μF, 50V, Solid Tantalum Sprague, “594D series”

COUT - 33 μF, 25V, Solid Tantalum Sprague, “594D series”

D1 - 1A, 40V Schottky Rectifier, Surface Mount

L1 - 100 μH, L20, Coilcraft DO3316

CB- 0.01 μF, 50V, Ceramic

R1 - 1k, 1%

R2 - Use formula in Design Procedure

Figure 29. PC Board Layout

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 22 and Figure 23) should be wide printed circuit traces

and should be kept as short as possible. For best results, external components should be located as close to

the switcher IC as possible using ground plane construction or single point grounding.

If open core inductors are used, special care must be taken 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, special care must be taken as to the location of the feedback resistors and

the associated wiring. Physically locate both resistors near the IC, and route the wiring away from the inductor,

especially an open core type of inductor.

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REVISION HISTORY

Changes from Revision J (April 2013) to Revision K Page

• Changed layout of National Data Sheet to TI format .......................................................................................................... 22

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PACKAGE OPTION ADDENDUM

www.ti.com 1-Nov-2013

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead/Ball Finish

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM2671LD-ADJ NRND WSON NHN 16 1000 TBD Call TI Call TI -40 to 125 S0008B

LM2671LD-ADJ/NOPB ACTIVE WSON NHN 16 1000 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 S0008B

LM2671M-12/NOPB ACTIVE SOIC D 8 95 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 2671

M-12

LM2671M-3.3/NOPB ACTIVE SOIC D 8 95 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 2671

M3.3

LM2671M-5.0 NRND SOIC D 8 95 TBD Call TI Call TI -40 to 125 2671

M5.0

LM2671M-5.0/NOPB ACTIVE SOIC D 8 95 Green (RoHS

& no Sb/Br) SN | CU SN Level-1-260C-UNLIM -40 to 125 2671

M5.0

LM2671M-ADJ NRND SOIC D 8 95 TBD Call TI Call TI -40 to 125 2671

MADJ

LM2671M-ADJ/NOPB ACTIVE SOIC D 8 95 Green (RoHS

& no Sb/Br) SN | CU SN Level-1-260C-UNLIM -40 to 125 2671

MADJ

LM2671MX-12/NOPB ACTIVE SOIC D 8 2500 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 2671

M-12

LM2671MX-3.3/NOPB ACTIVE SOIC D 8 2500 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 2671

M3.3

LM2671MX-5.0 NRND SOIC D 8 2500 TBD Call TI Call TI -40 to 125 2671

M5.0

LM2671MX-5.0/NOPB ACTIVE SOIC D 8 2500 Green (RoHS

& no Sb/Br) SN | CU SN Level-1-260C-UNLIM -40 to 125 2671

M5.0

LM2671MX-ADJ/NOPB ACTIVE SOIC D 8 2500 Green (RoHS

& no Sb/Br) SN | CU SN Level-1-260C-UNLIM -40 to 125 2671

MADJ

LM2671N-12/NOPB ACTIVE PDIP P 8 40 Green (RoHS

& no Sb/Br) CU SN Level-1-NA-UNLIM -40 to 125 LM2671

N-12

LM2671N-3.3/NOPB ACTIVE PDIP P 8 40 Green (RoHS

& no Sb/Br) CU SN Level-1-NA-UNLIM -40 to 125 LM2671

N-3.3

LM2671N-5.0 NRND PDIP P 8 40 TBD Call TI Call TI -40 to 125 LM2671

N-5.0

LM2671N-5.0/NOPB ACTIVE PDIP P 8 40 Green (RoHS

& no Sb/Br) SN | CU SN Level-1-NA-UNLIM -40 to 125 LM2671

N-5.0

PACKAGE OPTION ADDENDUM

www.ti.com 1-Nov-2013

Addendum-Page 2

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead/Ball Finish

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM2671N-ADJ/NOPB ACTIVE PDIP P 8 40 Green (RoHS

& no Sb/Br) SN | CU SN Level-1-NA-UNLIM -40 to 125 LM2671

N-ADJ

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

ACTIVE: Product device recommended for new designs.

LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.

NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.

PREVIEW: Device has been announced but is not in production. Samples may or may not be available.

OBSOLETE: TI has discontinued the production of the device.

(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability

information and additional product content details.

TBD: The Pb-Free/Green conversion plan has not been defined.

Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that

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

Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between

the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.

Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight

in homogeneous material)

(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.

(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation

of the previous line and the two combined represent the entire Device Marking for that device.

(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish

value exceeds the maximum column width.

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information

provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and

continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.

TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

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 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 23-Sep-2013

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 213.0 191.0 55.0

LM2671MX-12/NOPB SOIC D 8 2500 367.0 367.0 35.0

LM2671MX-3.3/NOPB SOIC D 8 2500 367.0 367.0 35.0

LM2671MX-5.0 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 23-Sep-2013

Pack Materials-Page 2

MECHANICAL DATA

NHN0016A

www.ti.com

LDA16A (REV A)

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