TEXAS INSTRUMENTS LM 2671 M5,0 Instructions

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

LM2671 SIMPLE SWITCHER®Power Converter High Efficiency 500-mA

Step-Down Voltage Regulator With Features

LM2671

1 Features

• Efficiency up to 96%

• Available in 8-Pin SOIC, PDIP, and WSON Packages

• Simple and Easy to Design With

• Requires Only 5 External Components

• Uses Readily Available Standard Inductors

• 3.3-V, 5-V, 12-V, and Adjustable Output Versions

• Adjustable Version Output Voltage Range: 1.21 V to 37 V

• ±1.5% Maximum Output Voltage Tolerance Over Line and Load Conditions

• Ensured 500-mA Output Load Current

• 0.25-Ω DMOS Output Switch

• Wide Input Voltage Range: 8 V to 40 V

• 260-kHz Fixed Frequency Internal Oscillator

• TTL Shutdown Capability, Low Power Standby Mode

• Soft-Start and Frequency Synchronization

• Thermal Shutdown and Current-Limit Protection

2 Applications

• Simple High Efficiency (> 90%) Step-Down (Buck) Regulators

• Efficient Preregulator for Linear Regulators

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

PART NUMBER PACKAGE BODY SIZE (NOM)

SOIC (8) 4.90 mm × 3.91 mm

LM2674

(1) For all available packages, see the orderable addendum at

the end of the data sheet.

PDIP (8) 9.81 mm × 6.35 mm WSON (16) 5.00 mm × 5.00 mm

(1)

Typical Application

For fixed output voltage versions

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications, intellectual property matters and other important disclaimers. PRODUCTION DATA.

LM2671

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

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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

Product Folder Links: LM2671

Not to scale

DAP

VSW

VIN

GND

SYNC

GND

ON/OFF

16 15 14 13 12 11 10

Not to scale

1CB 8 VSW

2SS 7 VIN

3SYNC 6 GND

4FB 5 ON/OFF

LM2671

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

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

NAME SOIC, PDIP WSON

I/O DESCRIPTION

CB 1 1 I

SS 2 4 I

SYNC 3 6 I

FB 4 8 I

ON/OFF 5 9 I

VSW 8 15, 16 O

GND 6 11, 12 —

VIN 7 14 I

NC —

2, 3, 5, 7,

10, 13

Pin Functions

Bootstrap capacitor connection for high-side driver. Connect a high-quality, 100-nF capacitor from CB to VSW Pin.

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.

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.

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.

Enable input to the voltage regulator. High = ON and low = OFF. Pull this pin high or float to enable the regulator

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.

Power ground pins. Connect to system ground. Ground pins of CINand C Path to CINmust be as short as possible.

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 C and GND must be as short as possible.

— No connect pins

NHN Package 16-Pin WSON

Top View

Connect DAP to pin 11 and 12

OUT

Product Folder Links: LM2671

LM2671

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

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7 Specifications

7.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted)

Supply voltage 45 V ON/OFF pin voltage, V Switch voltage to ground –1 V Boost pin voltage VSW+ 8 V Feedback pin voltage, V Power dissipation Internally Limited

Lead temperature

Maximum junction temperature 150 °C Storage temperature, T

(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.

D package

Vapor phase (60 s) 215

Infrared (15 s) 220 P package (soldering, 10 s) 260 WSON package See AN-1187

stg

(1)(2)

MIN MAX UNIT

−0.1 6 V

−0.3 14 V

°C

−65 150 °C

7.2 ESD Ratings

VALUE UNIT

(ESD)

Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001

(1)(2)

±2000 V

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. (2) The human body model is a 100-pF capacitor discharged through a 1.5-kΩ resistor into each pin.

7.3 Recommended Operating Conditions

MIN MAX UNIT

Supply voltage 6.5 40 V Junction temperature, T

–40 125 °C

7.4 Thermal Information

LM2674

THERMAL METRIC

θJA

Junction-to-ambient thermal resistance

(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 R 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).

(1)

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

8 PINS 8 PINS 16 PINS

(2)

for the WSON (NHN) package is specifically dependent on PCB trace

θJA

105 95 — °C/W

Product Folder Links: LM2671

LM2671

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

7.5 Electrical Characteristics – 3.3 V

Specifications are for TJ= 25°C (unless otherwise noted).

PARAMETER TEST CONDITIONS MIN

SYSTEM PARAMETERS

Output voltage

OUT

η Efficiency VIN= 12 V, I

(3)

VIN= 8 V to 40 V, I

= 20 mA to 500 mA

LOAD

VIN= 6.5 V to 40 V, I

= 20 mA to 250 mA

LOAD

TJ= 25°C 3.251 3.3 3.35 Over full operating temperature

range TJ= 25°C 3.251 3.3 3.35 Over full operating temperature

range

= 500 mA 86%

(1)

3.201 3.399

(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.

TYP

(2)

MAX

(1)

7.6 Electrical Characteristics – 5 V

Specifications are for TJ= 25°C (unless otherwise noted).

PARAMETER TEST CONDITIONS MIN

SYSTEM PARAMETERS

Output voltage

OUT

η Efficiency VIN= 12 V, I

(3)

VIN= 8 V to 40 V, I

= 20 mA to 500 mA

LOAD

VIN= 6.5 V to 40 V, I

= 20 mA to 250 mA

LOAD

TJ= 25°C 4.925 5 5.075 Over full operating temperature

range TJ= 25°C 4.925 5 5.075 Over full operating temperature

range

= 500 mA 90%

(1)

4.85 5.15

(1) All room temperature limits are 100% production tested. All limits at temperature extremes are ensured through correlation using

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.

TYP

(2)

MAX

(1)

UNIT

7.7 Electrical Characteristics – 12 V

Specifications are for TJ= 25°C (unless otherwise noted).

PARAMETER TEST CONDITIONS MIN

SYSTEM PARAMETERS

Output voltage

OUT

η Efficiency VIN= 24 V, I

(3)

VIN= 15 V to 40 V, I

= 20 mA to 500 mA

LOAD

TJ= 25°C 11.82 12 12.18 Over full operating

temperature range

= 500 mA 94%

(1)

11.64 12.36

(1) All room temperature limits are 100% production tested. All limits at temperature extremes are ensured through correlation using

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.

Product Folder Links: LM2671

TYP

(2)

MAX

(1)

UNIT

LM2671

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

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7.8 Electrical Characteristics – Adjustable

Specifications are for TJ= 25°C (unless otherwise noted).

PARAMETER TEST CONDITIONS MIN

SYSTEM PARAMETERS

Feedback

voltage

η Efficiency VIN= 12 V, I

(3)

VIN= 8 V to 40 V, I

= 20 mA to 500 mA

LOAD

programmed for 5 V

OUT

VIN= 6.5 V to 40 V, I

= 20 mA to 250 mA

LOAD

programmed for 5 V

OUT

LOAD

TJ= 25°C 1.192 1.21 1.228 Over full operating

temperature range TJ= 25°C 1.192 1.21 1.228 Over full operating

temperature range

= 500 mA 90%

(1)

1.174 1.246

(1) All room temperature limits are 100% production tested. All limits at temperature extremes are ensured through correlation using

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.

TYP

(2)

MAX

(1)

UNIT

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 I

DEVICE PARAMETERS

STBY

DS(ON)

BIAS

S/D

SYNC

= 100 mA (unless otherwise noted).

LOAD

PARAMETERS TEST CONDITIONS MIN TYP MAX UNIT

Quiescent current

Standby quiescent current ON/OFF pin = 0 V

Current limit

Output leakage current

Switch ON-resistance I

Oscillator frequency Measured at switch pin

Maximum duty cycle 95% Minimum duty cycle 0% Feedback bias current V

ON/OFF pin voltage thresholds

ON/OFF pin current ON/OFF pin = 0 V

Synchronization frequency V Synchronization threshold voltage 1.4 V

Soft-start voltage

Soft-start current

for 3.3-V, 5-V, and adjustable versions V

for 12-V versions

TJ= 25°C 0.62 0.8 1.2 Over full operating temperature range 0.575 1.25 VIN= 40 V, ON/OFF pin = 0 V

V V

SWITCH

TJ= 25°C 1.4 Over full operating temperature range 0.8 2

TJ= 25°C 0.63 Over full operating temperature range 0.53 0.73 TJ= 25°C 4.5 Over full operating temperature range 1.5 6.9

= 8 V

FEEDBACK

= 15 V

FEEDBACK

TJ= 25°C 50 100 Over full operating temperature

range

= 0 V

SWITCH

= −1 V, ON/OFF pin = 0 V 6 15 mA

SWITCH

TJ= 25°C 0.25 0.4

= 500 mA

= 1.3 V (adjustable version only) 85 nA

FEEDBACK

= 3.5 V, 50% duty cycle 400 kHz

SYNC

Over full operating temperature range

TJ= 25°C 260 Over full operating temperature

range

TJ= 25°C 20 Over full operating temperature

range

225 275

2.5 3.6

2.5

1 25 μA

7 37

150

0.6

μA

kHz

μA

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7.10 Typical Characteristics

LM2671

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

Figure 1. Normalized Output Voltage

Figure 3. Efficiency

Figure 2. Line Regulation

Figure 4. Drain-to-Source Resistance

Figure 5. Switch Current Limit

Product Folder Links: LM2671

Figure 6. Operating Quiescent Current

LM2671

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

Typical Characteristics (continued)

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Figure 7. Standby Quiescent Current

Figure 9. ON/OFF Pin Current (Sourcing) Figure 10. Switching Frequency

Figure 8. ON/OFF Threshold Voltage

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

LM2671

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

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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 VSWpin cycles between VIN(switch ON) and below ground by the voltage drop of the external Schottky diode (switch OFF).

Product Folder Links: LM2671

LM2671

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

Feature Description (continued)

8.3.2 Input

The input voltage for the power supply is connected to the VINpin. 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 VINpin 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 VSWpin. This capacitor boosts the gate drive to the internal MOSFET above VINto fully turn it ON. This minimizes conduction losses in the power switch to maintain high efficiency. The recommended value for C Boost is 0.01 μF.

8.3.4 Ground

This is the ground reference connection for all components in the power supply. In fast-switching, high-current applications such as those implemented with the LM2671, TI recommends that a broad ground plane be used to minimize signal coupling throughout the circuit.

8.3.5 Sync

This input allows control of the switching clock frequency. If left open-circuited the regulator is switched at the internal oscillator frequency, typically 260 kHz. An external clock can be used to force the switching frequency and thereby control the output ripple frequency of the regulator. This capability provides for consistent filtering of the output ripple from system to system as well as precise frequency spectrum positioning of the ripple frequency which is often desired in communications and radio applications. This external frequency must be greater than the LM2671 internal oscillator frequency, which could be as high as 275 kHz, to prevent an erroneous reset of the internal ramp oscillator and PWM control of the power switch. The ramp oscillator is reset on the positive going edge of the sync input signal. TI recommends that the external TTL or CMOS compatible clock (between 0 V and a level greater than 3 V) be ac coupled to the SYNC pin through a 100-pF capacitor and a 1-kΩ resistor to ground.

When the SYNC function is used, current limit frequency foldback is not active. Therefore, the device may not be fully protected against extreme output short-circuit conditions.

8.3.6 Feedback

This is the input to a two-stage high gain amplifier, which drives the PWM controller. Connect the FB pin directly to the output for proper regulation. For the fixed output devices (3.3-V, 5-V and 12-V outputs), a direct wire connection to the output is all that is required as internal gain setting resistors are provided inside the LM2671. For the adjustable output version two external resistors are required to set the DC output voltage. For stable operation of the power supply it is important to prevent coupling of any inductor flux to the feedback input.

8.3.7 ON/OFF

This input provides an electrical ON/OFF control of the power supply. Connecting this pin to ground or to any voltage less than 0.8 V is completely turn OFF the regulator. The current drain from the input supply when OFF is only 50 μA. The ON/OFF input has an internal pullup current source of approximately 20 μA and a protection clamp Zener diode of 7 V to ground. When electrically driving the ON/OFF pin the high voltage level for the ON condition must not exceed the 6 V absolute maximum limit. When ON/OFF control is not required this pin must be left open.

8.4 Device Functional Modes

8.4.1 Shutdown Mode

The ON/OFF pin provides electrical ON and OFF control for the LM2671. When the voltage of this pin is lower than 1.4 V, the device enters shutdown mode. The typical standby current in this mode is 50 μA.

Product Folder Links: LM2671

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

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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.

Product Folder Links: LM2671

LM2671

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

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 C

= 47 µF, L = 22 µH.

OUT

NOTE

Even with these components, for a device’s current limit of ICLIM, the maximum load current under which the possibility of the large current limit hysteresis can be minimized is ICLIM/2.

For example, if the input is 24 V and the set output voltage is 18 V, then for a desired maximum current of 1.5 A, the current limit of the chosen switcher must be confirmed to be at least 3 A. Under extreme overcurrent or shortcircuit conditions, the LM267X employs frequency foldback in addition to the current limit. If the cycle-by-cycle inductor current increases above the current limit threshold (due to short circuit or inductor saturation for example) the switching frequency is automatically reduced to protect the IC. Frequency below 100 kHz is typical for an extreme short-circuit condition.

Product Folder Links: LM2671

LM2671

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

9.2 Typical Applications

9.2.1 Fixed Output Voltage Version

CIN= 22-μF, 50-V Tantalum, Sprague 199D Series C

= 47-μF, 25-V Tantalum, Sprague 595D Series

OUT

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.

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Table 1. Design Parameters

PARAMETER VALUE

Regulated output voltage (3.3 V, 5 V, or 12 V), V

Maximum DC input voltage, VIN(max) 12 V

Maximum load current, I

(max) 500 mA

LOAD

OUT

5 V

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.

Product Folder Links: LM2671

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

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.

INDUCTANCE

REF.

DESG.

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

(μH)

CURRENT

(A)

SCHOTTKY RENCO PULSE ENGINEERING COILCRAFT

THROUGH

HOLE

SURFACE

MOUNT

THROUGH HOLE

SURFACE

MOUNT

THROUGH

HOLE

SURFACE

MOUNT

SURFACE

MOUNT

9.2.1.2.2 Output Capacitor Selection (C

OUT

)

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.

Product Folder Links: LM2671

LM2671

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

OUTPUT

VOLTAGE

(V)

3.3

INDUCTANCE

(μH)

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

SURFACE MOUNT THROUGH HOLE

SPRAGUE

594D SERIES

(μF/V)

Table 3. Output Capacitor Table

OUTPUT CAPACITOR

AVX TPS

SERIES

(μF/V)

SANYO OS-CON

SA SERIES (μF/V)

SANYO MV-GX

SERIES (μF/V)

NICHICON

PL SERIES

(μF/V)

www.ti.com

PANASONIC HFQ SERIES

(μF/V)

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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LM2671

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

Table 4. Schottky Diode Selection Table

20 V

30 V

40 V

50 V

SURFACE MOUNT THROUGH HOLE SURFACE MOUNT THROUGH HOLE

SK12 1N5817 SK32 1N5820

B120 SR102 — SR302

SK13 1N5818 SK33 1N5821

B130 11DQ03 30WQ03F 31DQ03

MBRS130 SR103 — —

SK14 1N5819 SK34 1N5822

B140 11DQ04 30BQ040 MBR340

MBRS140 SR104 30WQ04F 31DQ04

10BQ040 — MBRS340 SR304 10MQ040 — MBRD340 — 15MQ040 — — —

SK15 MBR150 SK35 MBR350

B150 11DQ05 30WQ05F 31DQ05

10BQ050 SR105 — SR305

9.2.1.2.4 Input Capacitor (CIN)

1-A DIODES 3-A DIODES

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

3.3 6.3 5 10

10 20 12 25 15 35

Product Folder Links: LM2671

85°C RATING

VOLTAGE

RATING

LM2671

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

RECOMMENDED

APPLICATION VOLTAGE

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Table 6. Sprague 594D

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 V pin. The important parameters for the input capacitor are the input voltage rating and the RMS current rating. With a maximum input voltage of 12 V, an aluminum electrolytic capacitor with a voltage rating greater than 15 V (1.25 × VIN) is required. The next higher capacitor voltage rating is 16 V.

The RMS current rating requirement for the input capacitor in a buck regulator is approximately ½ the DC load current. In this example, with a 500-mA load, a capacitor with a RMS current rating of at least 250 mA is required. The curves shown in Figure 16 can be used to select an appropriate input capacitor. From the curves, locate the 16-V line and note which capacitor values have RMS current ratings greater than 250 mA.

Figure 16. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical)

For a through-hole design, a 100-μF, 16-V electrolytic capacitor (Panasonic HFQ series, Nichicon PL, Sanyo MVGX series or equivalent) would be adequate. Other types or other manufacturers' capacitors can be used provided the RMS ripple current ratings are adequate. Additionally, for a complete surface mount design, electrolytic capacitors such as the Sanyo CV-C or CV-BS and the Nichicon WF or UR and the NIC Components NACZ series could be considered.

For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating and voltage rating. In this example, checking the Sprague 594D series datasheet, a Sprague 594D 15-μF, 25-V capacitor is adequate.

9.2.1.2.5 Boost Capacitor (CB)

This capacitor develops the necessary voltage to turn the switch gate on fully. All applications must use a

0.01-μF, 50-V ceramic capacitor. For this application, and all applications, use a 0.01-μF, 50-V ceramic capacitor.

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9.2.1.2.6 Soft-Start Capacitor (CSS) – Optional

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

This capacitor controls the rate at which the device starts up. The formula for the soft-start capacitor CSSis

Equation 1.

where

• ISS= soft-start current (4.5 μA typical)

• tSS= soft-start time (selected)

• V

• VIN= input voltage (selected) (1)

= soft-start threshold voltage (0.63 V typical)

SSTH

= output voltage (selected)

OUT SCHOTTKY

= schottky diode voltage drop (0.4 V typical)

For this application, selecting a start-up time of 10 ms and using Equation 2 for CSS.

(2)

If this feature is not desired, leave this pin open. With certain soft-start capacitor values and operating conditions, the LM2671 can exhibit an overshoot on the output voltage during turnon. Especially when starting up into no load or low load, the soft-start function may not be effective in preventing a larger voltage overshoot on the output. With larger loads or lower input voltages during start-up this effect is minimized. In particular, avoid using soft-start capacitors between 0.033 µF and 1 µF.

9.2.1.2.7 Frequency Synchronization (optional)

The LM2671 (oscillator) can be synchronized to run with an external oscillator, using the sync pin (pin 3). By doing so, the LM2671 can be operated at higher frequencies than the standard frequency of 260 kHz. This allows for a reduction in the size of the inductor and output capacitor.

As shown in the drawing below, a signal applied to a RC filter at the sync pin causes the device to synchronize to the frequency of that signal. For a signal with a peak-to-peak amplitude of 3 V or greater, a 1-kΩ resistor and a 100-pF capacitor are suitable values.

For all applications, use a 1-kΩ resistor and a 100-pF capacitor for the RC filter.

Product Folder Links: LM2671

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

9.2.1.3 Application Curves

for continuous mode operation

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Figure 17. LM2671-3.3

Figure 19. LM2671-12

9.2.2 Adjustable Output Voltage Version

Figure 18. LM2671-5

Figure 20. LM2671-ADJ

CIN= 22-μF, 50-V Tantalum, Sprague 199D Series C

= 47-μF, 25-V Tantalum, Sprague 595D Series

OUT

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, V

Maximum input voltage, VIN(max) 28 V

Maximum load current, I

Switching frequency, F Fixed at a nominal 260 kHz

OUT

(max) 500 mA

LOAD

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

• V

= 1.21 V (3)

REF

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

LM2671

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

20 V

(4)

Select a value for R1between 240 Ω and 1.5 kΩ. The lower resistor values minimize noise pickup in the sensitive feedback pin. For the lowest temperature coefficient and the best stability with time, use 1% metal film resistors.

(5)

R2= 1 kΩ (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ. R2= 15.4 kΩ.

9.2.2.2.2 Inductor Selection (L1)

1. Calculate the inductor Volt • microsecond constant E • T (V • μs) from Equation 6.

where

• V

• VD= diode forward voltage drop = 0.5 V (6)

= internal switch saturation voltage = 0.25 V

SAT

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.

(max) = 500 mA (9)

LOAD

4. Identify the inductance region intersected by the E • T value and the maximum load current value. Each region is identified by an inductance value and an inductor code (LXX). From the inductor value selection guide shown in Figure 20, the inductance region intersected by the 21.6 (V • μs) horizontal line and the 500mA vertical line is 100 μH, and the inductor code is L20.

5. Select an appropriate inductor from the four manufacturer's part numbers listed in Table 2. For information

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

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.

www.ti.com

9.2.2.2.3 Output Capacitor Selection (C

OUT

)

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

(1)

STYLE

SM and TH 1.21–2.5 — — — — C1 C2 C3 SM and TH 2.5–3.75 — — — C1 C2 C3 C3 SM and TH 3.75–5 — — C4 C5 C6 C6 C6 SM and TH 5–6.25 — C4 C7 C6 C6 C6 C6 SM and TH 6.25–7.5 C8 C4 C7 C6 C6 C6 C6 SM and TH 7.5–10 C9 C10 C11 C12 C13 C13 C13 SM and TH 10–12.5 C14 C11 C12 C12 C13 C13 C13 SM and TH 12.5–15 C15 C16 C17 C17 C17 C17 C17 SM and TH 15–20 C18 C19 C20 C20 C20 C20 C20 SM and TH 20–30 C21 C22 C22 C22 C22 C22 C22

TH 30–37 C23 C24 C24 C25 C25 C25 C25

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

OUTPUT

VOLTAGE (V)

22 33 47 68 100 150 220

INDUCTANCE (μH)

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

Table 9. Output Capacitor Selection Table

OUTPUT CAPACITOR

CAP. REF.

DESG.

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 C19 33/25 33/25 33/25 C20 33/25 33/25 33/25 C21 33/35 (2×) 22/25 C22 33/35 22/35 C23 C24 C25

(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.

SPRAGUE 594D

SERIES (μF/V)

SURFACE MOUNT THROUGH HOLE

AVX TPS SERIES

(μF/V)

(2) (2) (2) (2) (2) (2) (2) (2) (2)

SANYO OS-CON SA

SERIES (μF/V)

(1) (1)

(1) (2) (2)

SANYO MV-GX

SERIES (μF/V)

220/35 220/35 220/35 150/35 150/35 150/35 120/35 120/35 120/35 150/35 150/35 150/35 120/35 120/35 120/35 220/50 100/50 120/50 150/50 100/50 120/50 150/50 82/50 82/50

NICHICON PL

SERIES (μF/V)

PANASONIC HFQ

SERIES (μF/V)

LM2671

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 V

OUT/VIN

). The largest value of the catch diode average current occurs at the maximum input voltage (minimum D). For normal operation, the catch diode current rating must be at least 1.3 times greater than its maximum average current. However, if the power supply design must withstand a continuous output short, the diode must have a current rating greater than the maximum current limit of the LM2671. The most stressful condition for this diode is a shorted output condition.

Refer to the table shown in Table 4. Schottky diodes provide the best performance, and in this example a 1A, 40-V Schottky diode would be a good choice. If the circuit must withstand a continuous shorted output, a higher current (at least 1.2 A) Schottky diode is recommended.

2. The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage.

3. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency. The Schottky diode must be placed close to the LM2671 using short leads and short printed-circuit traces.

Product Folder Links: LM2671

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

9.2.2.2.5 Input Capacitor (CIN)

www.ti.com

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

85°C RATING

3.3 6.3 5 10

10 20 12 25 15 35

VOLTAGE

RATING

Table 11. Sprague 594D

RECOMMENDED

APPLICATION VOLTAGE

85°C RATING

2.5 4

3.3 6.3 5 10 8 16

12 20 18 25 24 35 29 50

VOLTAGE

RATING

Use caution when using ceramic capacitors for input bypassing, because it may cause severe ringing at the V 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.

Product Folder Links: LM2671

LM2671

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

Figure 22. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical)

For a through-hole design, a 68-μF, 35-V electrolytic capacitor (Panasonic HFQ series, Nichicon PL, Sanyo MVGX series or equivalent) would be adequate. Other types or other manufacturers' capacitors can be used provided the RMS ripple current ratings are adequate. Additionally, for a complete surface mount design, electrolytic capacitors such as the Sanyo CV-C or CV-BS and the Nichicon WF or UR and the NIC Components NACZ series could be considered.

For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating and voltage rating. In this example, checking the Sprague 594D series data sheet, a Sprague 594D 15-μF, 50-V capacitor is adequate.

9.2.2.2.6 Boost Capacitor (CB)

This capacitor develops the necessary voltage to turn the switch gate on fully. All applications must use a

0.01-μF, 50-V ceramic capacitor. For this application, and all applications, use a 0.01-μF, 50-V ceramic capacitor. If the soft-start and frequency synchronization features are desired, look at steps 6 and 7 in Detailed Design

Procedure.

Product Folder Links: LM2671

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

9.2.2.3 Application Curves

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Continuous Mode Switching Waveforms, VIN= 20 V, V I

= 500 mA, L = 100 μH, C

LOAD

= 100 μF, C

OUT

ESR = 0.1 Ω

OUT

A: VSWpin 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

Load Transient Response for Continuous Mode, VIN= 20 V, V

= 5 V, L = 100 μH, C

OUT

= 100 μF, C

OUT

ESR = 0.1 Ω

OUT

A: Output voltage, 100 mV/div, ac-coupled B: Load current: 100-mA to 500-mA load pulse

= 5 V,

Discontinuous Mode Switching Waveforms, VIN= 20 V, V

= 5 V, I

OUT

ESR = 25 mΩ

OUT

= 300 mA, L = 15 μH, C

LOAD

= 68 μF (2×),

OUT

A: VSWpin 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 Discontinuous Mode, VIN= 20 V, V

= 5 V, L = 47 μH, C

OUT

= 68 μF, C

OUT

ESR = 50 mΩ

OUT

A: Output voltage, 100 mV/div, ac-coupled B: Load current: 100-mA to 400-mA load pulse

Figure 25. Horizontal Time Base: 50 μs/div

Figure 26. Horizontal Time Base: 200 μs/div

10 Power Supply Recommendations

The LM2671 is designed to operate from an input voltage supply up to 40 V. This input supply must be well regulated and able to withstand maximum input current and maintain a stable voltage.

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LM2671

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SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

11 Layout

11.1 Layout Guidelines

Layout is very important in switching regulator designs. Rapidly switching currents associated with wiring inductance can generate voltage transients which can cause problems. For minimal inductance and ground loops, the wires indicated by heavy lines (in Figure 15 and Figure 21) must be wide printed-circuit traces and must be kept as short as possible. For best results, external components must be placed as close to the switcher IC as possible using ground plane construction or single point grounding.

If open core inductors are used, take special care as to the location and positioning of this type of inductor. Allowing the inductor flux to intersect sensitive feedback, IC ground path, and C

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

wiring can cause problems.

OUT

CIN= 15-μF, 25-V Solid Tantalum Sprague, 594D series C

= 68-μF, 10-V Solid Tantalum Sprague, 594D series

OUT

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 C

= 33 μF, 25 V Solid Tantalum Sprague, 594D series

OUT

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)

Product Folder Links: LM2671

LM2671

SNVS008L –SEPTEMBER 1998–REVISED JUNE 2016

www.ti.com

12 Device and Documentation Support

12.1 Documentation Support

12.1.1 Related Documentation

For related documentation see the following:

• AN-1187 Leadless Leadfram Package (LLP)

• LM2670 SIMPLE SWITCHER®High Efficiency 3A Step-Down Voltage Regulator with Sync

12.2 Receiving Notification of Documentation Updates

To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper right corner, click on Alert me to register and receive a weekly digest of any product information that has changed. For change details, review the revision history included in any revised document.

12.3 Community Resources

The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of

Use. TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration

among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help solve problems with fellow engineers.

Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and

contact information for technical support.

12.4 Trademarks

E2E is a trademark of Texas Instruments. SIMPLE SWITCHER, WEBENCH are registered trademarks of Texas Instruments. All other trademarks are the property of their respective owners.

12.5 Electrostatic Discharge Caution

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates.

12.6 Glossary

SLYZ022 — TI Glossary.

This glossary lists and explains terms, acronyms, and definitions.

13 Mechanical, Packaging, and Orderable Information

The following pages include mechanical, packaging, and orderable information. This information is the most current data available for the designated devices. This data is subject to change without notice and revision of this document. For browser-based versions of this data sheet, refer to the left-hand navigation.

13.1 DAP (WSON Package)

The die attach pad (DAP) can and must be connected to the PCB Ground plane. For CAD and assembly guidelines refer to AN-1187 Leadless Leadfram Package (LLP).

Product Folder Links: LM2671

PACKAGE OPTION ADDENDUM

www.ti.com

PACKAGING INFORMATION

Orderable Device Status

LM2671LD-ADJ NRND WSON NHN 16 1000 Non-RoHS

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

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

LM2671M-5.0 NRND SOIC D 8 95 Non-RoHS

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

LM2671M-ADJ NRND SOIC D 8 95 Non-RoHS

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

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

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

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

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

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

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

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

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

(1)

The marketing status values are defined as follows:

Package Type Package

(1)

Drawing

Pins Package

Qty

Eco Plan

(2)

& Green

Lead finish/

Ball material

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

Call TI Call TI -40 to 125 S0008B

Call TI Call TI -40 to 125 2671

11-Jan-2021

Samples

(4/5)

M-12

M3.3

M5.0

MADJ

M-12

M3.3

M5.0

MADJ

N-12

N-3.3

N-5.0

N-ADJ

Addendum-Page 1

PACKAGE OPTION ADDENDUM

www.ti.com

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.

11-Jan-2021

(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.

Addendum-Page 2

PACKAGE MATERIALS INFORMATION

www.ti.com 29-Sep-2019

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device Package

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

Type

Package Drawing

Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

(mm)B0(mm)K0(mm)P1(mm)W(mm)

Quadrant

Pin1

Pack Materials-Page 1

PACKAGE MATERIALS INFORMATION

www.ti.com 29-Sep-2019

*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

Pack Materials-Page 2

NHN0016A

MECHANICAL DATA

www.ti.com

LDA16A (REV A)

PACKAGE OUTLINE

.189-.197 [4.81-5.00]

NOTE 3

.228-.244 TYP [5.80-6.19]

B .150-.157

[3.81-3.98]

PIN 1 ID AREA

NOTE 4

SCALE 2.800

6X .050

[1.27]

.150 [3.81]

8X .012-.020 [0.31-0.51]

.010 [0.25] C A B

SOIC - 1.75 mm max heightD0008A

SMALL OUTLINE INTEGRATED CIRCUIT

SEATING PLANE

.004 [0.1] C

4X (0 -15 )

.069 MAX

[1.75]

.005-.010 TYP [0.13-0.25]

4X (0 -15 )

SEE DETAIL A

.010 [0.25]

0 - 8

.016-.050 [0.41-1.27]

(.041) [1.04]

DETAIL A

TYPICAL

.004-.010 [0.11-0.25]

4214825/C 02/2019

NOTES:

1. Linear dimensions are in inches [millimeters]. Dimensions in parenthesis are for reference only. Controlling dimensions are in inches. Dimensioning and tolerancing per ASME Y14.5M.

2. This drawing is subject to change without notice.

3. This dimension does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, or gate burrs shall not exceed .006 [0.15] per side.

4. This dimension does not include interlead flash.

5. Reference JEDEC registration MS-012, variation AA.

www.ti.com

8X (.061 )

8X (.024)

6X (.050 )

[1.27]

[0.6]

[1.55]

SYMM

(.213)

[5.4]

LAND PATTERN EXAMPLE

EXPOSED METAL SHOWN

SCALE:8X

EXAMPLE BOARD LAYOUT

SOIC - 1.75 mm max heightD0008A

SMALL OUTLINE INTEGRATED CIRCUIT

SEE DETAILS

SYMM

(R.002 ) TYP

[0.05]

EXPOSED

METAL

NON SOLDER MASK

SOLDER MASK OPENING

.0028 MAX [0.07] ALL AROUND

DEFINED

SOLDER MASK

OPENING

EXPOSED

METAL

.0028 MIN [0.07] ALL AROUND

SOLDER MASK

DEFINED

SOLDER MASK DETAILS

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 UNDER SOLDER MASK

4214825/C 02/2019

www.ti.com

8X (.061 )

8X (.024)

[0.6]

6X (.050 )

[1.27]

[1.55]

EXAMPLE STENCIL DESIGN

SOIC - 1.75 mm max heightD0008A

SMALL OUTLINE INTEGRATED CIRCUIT

SYMM

(R.002 ) TYP

(.213)

[5.4]

[0.05]

BASED ON .005 INCH [0.125 MM] THICK STENCIL

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.

SCALE:8X

4214825/C 02/2019

SOLDER PASTE EXAMPLE

www.ti.com

IMPORTANT NOTICE AND DISCLAIMER

TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS” AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD PARTY INTELLECTUAL PROPERTY RIGHTS.

These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable standards, and any other safety, security, or other requirements. These resources are subject to change without notice. TI grants you permission to use these resources only for development of an application that uses the TI products described in the resource. Other reproduction and display of these resources is prohibited. No license is granted to any other TI intellectual property right or to any third party intellectual property right. TI disclaims responsibility for, and you will fully indemnify TI and its representatives against, any claims, damages, costs, losses, and liabilities arising out of your use of these resources.

TI’s products are provided subject to TI’s Terms of Sale (https:www.ti.com/legal/termsofsale.html) or other applicable terms available either on ti.com or provided in conjunction with such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s applicable warranties or warranty disclaimers for TI products.IMPORTANT NOTICE

Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265

TEXAS INSTRUMENTS LM 2671 M5,0 Instructions

Specifications and Main Features

Frequently Asked Questions

User Manual

1 Features

2 Applications

3 Description

Table of Contents

4 Revision History

5 Description (continued)

6 Pin Configuration and Functions

7 Specifications

7.1 Absolute Maximum Ratings

7.2 ESD Ratings

7.3 Recommended Operating Conditions

7.4 Thermal Information

7.5 Electrical Characteristics – 3.3 V

7.6 Electrical Characteristics – 5 V

7.7 Electrical Characteristics – 12 V

7.8 Electrical Characteristics – Adjustable

7.9 Electrical Characteristics – All Output Voltage Versions

7.10 Typical Characteristics

8 Detailed Description

8.1 Overview

8.2 Functional Block Diagram

8.3 Feature Description

8.3.1 Switch Output

8.3.2 Input

8.3.3 C Boost

8.3.4 Ground

8.3.5 Sync

8.3.6 Feedback

8.3.7 ON/OFF

8.4 Device Functional Modes

8.4.1 Shutdown Mode

8.4.2 Active Mode

9 Application and Implementation

9.1 Application Information

9.2 Typical Applications

9.2.1 Fixed Output Voltage Version

9.2.1.1 Design Requirements

9.2.1.2 Detailed Design Procedure

9.2.1.3 Application Curves

9.2.2 Adjustable Output Voltage Version

9.2.2.1 Design Requirements

9.2.2.2 Detailed Design Procedure

9.2.2.3 Application Curves

10 Power Supply Recommendations

11 Layout

11.1 Layout Guidelines

11.2 Layout Examples

12 Device and Documentation Support

12.1 Documentation Support

12.1.1 Related Documentation

12.2 Receiving Notification of Documentation Updates

12.3 Community Resources

12.4 Trademarks

12.5 Electrostatic Discharge Caution

12.6 Glossary

13 Mechanical, Packaging, and Orderable Information

13.1 DAP (WSON Package)