Texas Instruments LM267 Series Manuel utilisateur

User's Guide

SNVA013D–December 2000–Revised April 2013

AN-1135 LM267X 3A, 5A Evaluation Boards

1 Introduction

The LM267X evaluation board was developed for the evaluation of LM267X SIMPLE SWITCHER series of

3 Amp and 5 Amp high efficiency step-down (Buck) switching voltage regulators. This application note

describes the printed circuit board, and provides example circuits and directions on setup and operation of

the LM2673S-5_EVAL and LM2679S-5_EVAL evaluation boards.

2 General Description

Many of our boards are intended to provide the user with device characterization and layout optimization

data. The LM267x evaluation board was intended to allow the user to experiment with a variety of circuit

topologies and components, and therefore not optimized for size. Please refer to the discussions of layout

optimization in the PCB Layout Optimization section.

This board was designed such that both through-hole and surface-mount components can be used for

construction. The regulator IC can be placed on the board as a surface-mount component only. The

ground plane serves as a heatsink.

Table 1 shows an overview of the family of devices with special features of each indicated. Consult the

device data sheet, or use the special power supply design software calledSwitchers Made Simple

version 6.X (available for free download from www.ti.com) to determine all necessary component values

for the particular device being used to accomplish a specific design and board layout considerations.

The printed circuit board, PCB, is labeled to indicate the location of all of the needed components for all

possible design options. Table 2 shows a complete list of the component labels and their functions.

Figure 1 identifies all components, but not all are necessary in every design.

Figure 2,Figure 3 and Figure 4 show the top, bottom and silk screen of the printed circuit board

respectively.

Table 1. LM267X Family of High-Current Regulators supported by the Evaluation Board

Device Maximum Load Current (A) Special Features

LM2670 3 ON/OFF, External Frequency Sync Capability

LM2673 3 Adjustable Current Limit, Softstart

LM2676 3 ON/OFF

LM2677 5 ON/OFF, External Frequncy Sync. Capability

LM2678 5 ON/OFF

LM2679 5 Adjustable Current Limit, Softstart

SNVA013D–December 2000–Revised April 2013 AN-1135 LM267X 3A, 5A Evaluation Boards

General Description

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Figure 1. Example Schematic Showing Connection for all Components.

Table 2. List of Component Labels and Functionality

Label Function

U1 LM267 Switching Regulator IC

CIN Input Capacitor(s); All devices.

CINX 0.47 µF, optional high frequency input bypass capacitor, recommended in all designs: All

devices.

CB Boost capacitor; All devices.

D1 Catch diode; All devices.

R1 Feedback resistor for adjustable output converters. This designator is left open (not

connected) for fixed output converters.

R2 Feedback resistor (typ. 1 kΩ) for adjustable output converters. This designator is left shorted

(replaced by a jumper wire) for fixed output voltage converters.

R3* Current limit resistor for LM2673, LM2679; Sync input resistor (1 kΩ) for LM2670 and

LM2677; Not inserted for LM2676 and LM2678.

L1 Inductor; All devices.

CSYNC Sync input capacitor (100 pF); LM2670 and LM2677only. Not inserted with other devices.

CSS Soft start capacitor; LM2673 and LM2679 only. Not inserted with other devices.

COUTX 0.47 µF, optional high frequency output bypass capacitor; All devices.

COUT Output capacitor(s); All devices.

2AN-1135 LM267X 3A, 5A Evaluation Boards SNVA013D–December 2000–Revised April 2013

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General Description

Figure 2. Top Layer Foil Pattern of Printed Circuit Board

Figure 3. Bottom Layer Foil Pattern of Printed Circuit Board

SNVA013D–December 2000–Revised April 2013 AN-1135 LM267X 3A, 5A Evaluation Boards

Special Notes

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Figure 4. Silkscreen Image of Printed Circuit Board

3Special Notes

The evaluation board was designed primarily for circuit implementation using all surface-mount

components. The small series "trace inductance", particularly from the Switch Output pin, can create a

high frequency (10's of MHz) ringing signal at the switch output. If problematic, this ringing can be reduced

or eliminated by the use of a series RC damper or snubber network from the switch output to ground. The

addition of these components is made at the locations labeled CD and RD. Values of 0.01 µF and 10Ωare

good starting values that may need to be varied depending on the magnitude of parasitic factors in a given

design. In an actual end application, these components are normally not required if proper care to

minimize trace lengths is taken in the PCB design.

4 Example Circuit Designs

Example 1: 5V/3A Converter with Surface Mount Components.

In this example, it is desired to convert a voltage range of between 8V and 12V, to 5VDC with load current

of 3A. It is also desired to implement the design with surface mount components only. Softstart duration

will be set to between 1 and 1.5 ms.

Table 3. Target Design Specifications

VIN min. 8V

VIN max. 16V

VOUT 5V

ILOAD 3A

ICL 5.0A (approx.)

TSS 1 to 1.5 ms

Table 4. Component Values for an 8-12V in, 5V/3A Out LM2673S-5.0 Buck Converter

Component Value Suggested Part Number

U1 Texas Instruments LM2673

CIN 2 x 33 µF/35V Vishay 594D336X0035R2T

CINX 0.47 µF Vishay VJ1210U474ZXAA

4AN-1135 LM267X 3A, 5A Evaluation Boards SNVA013D–December 2000–Revised April 2013

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Example Circuit Designs

Table 4. Component Values for an 8-12V in, 5V/3A Out LM2673S-5.0 Buck Converter (continued)

Component Value Suggested Part Number

CB 0.01 µF/50V Vishay VJ1206Y103MXXA

D1 3A/60V Schottky (450 mV at 3A) Motorola MBRD360

R3* 7.15 kΩVishay CRCW12067151J

(5.19A current limit)

L1 22 µH (L41) SUMIDA ELECTRIC CO. CDRH127-220

CSS 3.3 nF/100V (softstart) Vishay VJ1206Y33ZJXBAB

COUTX 0.47 µF Vishay VJ1210U474ZXAA

COUT 2 x 18 0µF/16V Vishay 594D187X0016R2T

Figure 5 below shows the 5V/3A design circuit. This solution is available as evaluation board LM2673S-

5_EVAL.

Figure 6 through Figure 9 show the output waveforms for output voltage with 500 mA load, output voltage

with 1A load, output ripple with 1A load, output voltage with 3A load, output ripple with 3A load, output

response to 1A transient load and output response to 3A transient load respectively.

Figure 5. 5V/3A Design Circuit

A: OUTPUT VOLTAGE: VOUT; 2V/DIV

B: LOAD CURRENT: ILOAD = 500 mA; 500 mA/DIV

Figure 6. Output Voltage with 500 mA Load

SNVA013D–December 2000–Revised April 2013 AN-1135 LM267X 3A, 5A Evaluation Boards

Example Circuit Designs

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A: OUTPUT RIPPLE; 10 mV/DIV

B: LOAD CURRENT: ILOAD = 0.5A; 1A/DIV

Figure 7. Output Ripple with 500 mA Load

A: OUTPUT VOLTAGE: VOUT; 2V/DIV

B: LOAD CURRENT: ILOAD = 1A; 500 mA/DIV

Figure 8. Output Voltage with 1A Load

A: OUTPUT RIPPLE; 10 mV/DIV

B: LOAD CURRENT: ILOAD = 1A; 1A/DIV

Figure 9. Output Ripple with 1 Amp Load

6AN-1135 LM267X 3A, 5A Evaluation Boards SNVA013D–December 2000–Revised April 2013

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Example Circuit Designs

A: OUTPUT VOLTAGE: VOUT; 2V/DIV

B: LOAD CURRENT: ILOAD = 3A; 1A/DIV

Figure 10. Output Voltage with 3A Load

A: OUTPUT RIPPLE; 10 mV/DIV

B: LOAD CURRENT: ILOAD = 3A; 1A/DIV

Figure 11. Output Ripple with 3 Amp Load

A: OUTPUT RESPONSE; 1V/DIV

B: TRANSIENT LOAD CURRENT: 1A/DIV

Figure 12. Output Response to 0∼∼1A Transient Load

SNVA013D–December 2000–Revised April 2013 AN-1135 LM267X 3A, 5A Evaluation Boards

Example 2: 5V/5A Design with Surface Mount Components

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A: OUTPUT RESPONSE; 1V/DIV

B: TRANSIENT LOAD CURRENT: 2A/DIV

Figure 13. Output Response to 0∼∼3A Load Transient

5 Example 2: 5V/5A Design with Surface Mount Components

For this example, it is desired to design a power supply to convert an input voltage within the range of 14V

and 28V to an output voltage of 5V with a maximum load current of 5A using only surface mount

components. In addition, the current limit of the regulator will be set to approximately 7.0A, and the

softstart time will be set to approximately 1.0 ms to limit the startup surge current.

Table 5. Target Design Specifications:

VIN min. 14V

VINmax. 28V

VOUT 5V

ILOAD 5A

ICL 7.0A (approx.)

TSS 1.0 ms (approx.)

Table 6. Component Values for an 14V-28V in, 5V/5A Out LM2679S-5.0 Buck Converter

Component Value Suggested Part Number

U1 Texas Instruments LM2679

CIN 3 x 15 µF/50V Vishay 594D156X0050R2T

CINX 0.47µF Vishay VJ1210U474ZXAA

CB 0.01µF/50V Vishay VJ1206Y103ZXXA

D1 8A/35V Schottky (500 mV at 5A) Motorola MBRD835L

R3* 4.99 kΩ(7.19A current limit) Vishay CRCW12064991J

L1 15 µH Coilcraft D05022P-153

CSS 4.7 nF/100V (1.0 ms softstart) Vishay VJ1206Y47ZJXBAB

COUTX 0.47 µF Vishay VJ1210U474ZXAA

COUT 2 x 180 µF/16V Vishay 594D187X0016R2T

Figure 14 below shows the circuit for the 5V/5A design. This solution is available as evaluation board

LM2679S-5_EVAL.

Figure 14 through Figure 23 show the output waveforms for output voltage with 500 mA load, output

voltage with 2.5A load, output ripple with 2.5A load, output voltage with 5A load, output ripple with 5A

load, output response to 500 mA transient load, output response to 2.5A transient load and output

response to 5A transient load respectively.

8AN-1135 LM267X 3A, 5A Evaluation Boards SNVA013D–December 2000–Revised April 2013

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Example 2: 5V/5A Design with Surface Mount Components

Figure 14. 5V/5A Design Circuit

A: OUTPUT VOLTAGE: VOUT; 2V/DIV

B: LOAD CURRENT: ILOAD = 500 mA; 500 mA/DIV

Figure 15. Output Voltage with 500 mA Load

A: OUTPUT RIPPLE; 100 mV/DIV

B: LOAD CURRENT: ILOAD = 500 mA; 1A/DIV

Figure 16. Output Ripple with 500 mA Load

SNVA013D–December 2000–Revised April 2013 AN-1135 LM267X 3A, 5A Evaluation Boards

Example 2: 5V/5A Design with Surface Mount Components

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A: OUTPUT VOLTAGE: VOUT; 2V/DIV

B: LOAD CURRENT: ILOAD = 2.5A; 1A/DIV

Figure 17. Output Voltage with 2.5A Load

A: OUTPUT RIPPLE; 100 mV/DIV

B: LOAD CURRENT: ILOAD = 2.5A; 2A/DIV

Figure 18. Output Ripple with 2.5A Load

A: OUTPUT VOLTAGE: VOUT; 2V/DIV

B: LOAD CURRENT: ILOAD = 5A; 2A/DIV

Figure 19. Output Voltage with 5A Load

10 AN-1135 LM267X 3A, 5A Evaluation Boards SNVA013D–December 2000–Revised April 2013

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