Texas Instruments SLVU013 User Manual

Size:
709.05 Kb
Download

e S

e e e T S

e

User's Guide

June 1999

Mixed-SignalLinear Products

SLVU013

IMPORTANT NOTICE

Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability.

TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with TI's standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements.

CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF DEATH, PERSONAL INJURY, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE (ªCRITICAL APPLICATIONSº). TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, AUTHORIZED, OR WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORTDEVICES OR SYSTEMS OR OTHER CRITICAL APPLICATIONS. INCLUSION OF TI PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE FULLY AT THE CUSTOMER'S RISK.

In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards.

TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right of TI covering or relating to any combination, machine, or process in which such semiconductor products or services might be or are used. TI's publication of information regarding any third party's products or services does not constitute TI's approval, warranty or endorsement thereof.

Copyright 1999, Texas Instruments Incorporated

Information About Cautions and Warnings

Preface

Read This First

About This Manual

This user's guide describes techniques for designing synchronous buck converters using TI's SLVP1111±114 evaluation modules (EVM) and TPS56xx ripple regulator controllers.

How to Use This Manual

This document contains the following chapters:

Chapter 1 Introduction

Chapter 2 Design Procedure

Chapter 3 Test Results

Information About Cautions and Warnings

This book may contain cautions and warnings.

This is an example of a caution statement.

A caution statement describes a situation that could potentially damage your software or equipment.

This is an example of a warning statement.

A warning statement describes a situation that could potentially cause harm to you.

The information in a caution or a warning is provided for your protection. Please read each caution and warning carefully.

Read This First

iii

Trademarks

Related Documentation From Texas Instruments

Synchronous Buck Converter Design Using TPS56xx Controllers in SLVP10x EVMs User's Guide (literature number SLVU007).

TPS56xx data sheet (literature number SLVS177A)

Designer's Notebook The TPS56xx Family of Power Supply Controllers

(literature number SLVT140A)

Designing Fast Response Synchronous Buck Regulators Using the TPS5210 (literaure number SLVA044).

FCC Warning

This equipment is intended for use in a laboratory test environment only. It generates, uses, and can radiate radio frequency energy and has not been tested for compliance with the limits of computing devices pursuant to subpart J of part 15 of FCC rules, which are designed to provide reasonable protection against radio frequency interference. Operation of this equipment in other environments may cause interference with radio communications, in which case the user at his own expense will be required to take whatever measures may be required to correct this interference.

Trademarks

TI is a trademark of Texas Instruments Incorporated.

iv

Running TitleÐAttribute Reference

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-1

1.1

Synchronous Buck Regulator Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-2

1.2

Hysteretic Control Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-3

1.3

Design Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-4

1.4

Design Specification Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-5

1.5

Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-7

1.6

Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-8

1.7

Board Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-10

2 Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-1

2.1

TPS56xx Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-2

 

2.1.1

VCC Undervoltage Lockout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-3

 

2.1.2

Inhibit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-4

 

2.1.3

Slowstart Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-4

 

2.1.4

Hysteresis Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-5

 

2.1.5

Noise Suppression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-7

 

2.1.6

Overcurrent Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-7

 

2.1.7

Overvoltage Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-10

 

2.1.8

Power Good . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-10

 

2.1.9

Bias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-10

 

2.1.10

Gate Drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-10

2.2

External Component Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-14

 

2.2.1

Duty Cycle Estimate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-14

 

2.2.2

Input Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-14

 

2.2.3

Output Filter Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-14

 

2.2.4

Switching Frequency Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-17

 

2.2.5

Power MOSFET Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-20

3 Test Results .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-1

3.1

Test Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-2

 

3.1.1 Static Line and Load Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-2

 

3.1.2

Output Voltage Ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-2

 

3.1.3 Efficiency and Power Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-2

 

3.1.4 Output Start-Upand Overshoot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-2

 

3.1.5

Frequency Variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-3

 

3.1.6 Load Current Transient Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-3

 

3.1.7

Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-3

 

3.1.8

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-4

3.2

Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-5

3.3

Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-7

Chapter TitleÐAttribute Reference

v

Running TitleÐAttribute Reference

Figures

1±1 Simplified Synchronous Buck Converter Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-21±2 Simplified Hysteretic Controlled Output Voltage Waveform . . . . . . . . . . . . . . . . . . . . . . . . . .1-31±3 SLVP111±114 EVM Converter Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-71±4 Top Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-101±5 Bottom Assembly (Top View) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-101±6 Top Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-101±7 Bottom Layer (Top VIew) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-112±1 TPS56xx Functional Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-32±2 Block Diagram Showing Noise Suppression Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-7

2±3 VDS Sensing Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-82±4 Gate Driver Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-11

2±5 I±V Characteristic Curve for Low-SideGate Drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-122±6 Output Ripple Voltage Detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-183±1 Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-63±2 SLVP111 Measured Load Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-73±3 SLVP111Measured Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-73±4 SLVP111Measured Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-83±5 SLVP111Measured Switching Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-83±6 SLVP111 Measured Switching Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-93±7 SLVP111MeasuredStart-Up(INHIBIT) Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-9

3±8 SLVP111 Measured Start-Up(VCC) Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-103±9 SLVP111MeasuredStart-Up(VIN) Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-103±10 SLVP111 Measured Load Transient Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-11

3±11 SLVP112 Measured Load Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-113±12 SLVP112 Measured Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-123±13 SLVP112 Measured Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-123±14 SLVP112 Measured Switching Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-133±15 SLVP112 Measured Switching Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-133±16 SLVP112 MeasuredStart-Up(INHIBIT) Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-14

3±17 SLVP112 Measured Start-Up(VCC) Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-143±18 SLVP112 MeasuredStart-Up(VIN) Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-153±19 SLVP112 Measured Load Transient Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-15

3±20 SLVP113 Measured Load Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-163±21 SLVP113 Measured Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-163±22 SLVP113 Measured Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-173±23 SLVP113 Measured Switching Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-173±24 SLVP113 Measured Switching Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-183±25 SLVP113 MeasuredStart-Up(INHIBIT) Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-183±26 SLVP113 MeasuredStart-Up(VCC) Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-19

vi

Running TitleÐAttribute Reference

3±27 SLVP113 Measured Start-Up(VIN) Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-19

3±28 SLVP113 Measured Load Transient Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-20

3±29 SLVP114 Measured Load Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-20

3±30 SLVP114 Measured Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-21

3±31 SLVP114 Measured Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-21

3±32 SLVP114 Measured Switching Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-22

3±33 SLVP114 Measured Switching Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-22

3±34 SLVP114 Measured Start-Up(INHIBIT) Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-23

3±35 SLVP114 Measured Start-Up(VCC) Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-23

3±36 SLVP114 Measured Start-Up(VIN) Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-24

3±37 SLVP114 Measured Load Transient Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-24

Tables

1±1 Summary of EVM Converter Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-41±2 EVM Converter Operating Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-51±3 SLVP111±114 EVMs Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-8

Contents vii

viii

Chapter 1

Introduction

The SLVP111/112/113/114 evaluation modules (EVMs) have been designed and tested using the TPS56xx hysteretic controllers. These boards are synchronous dc-dcbuck converters with fixed output voltages of 3.3 V, 2.5 V, 1.8 V and 1.5 V respectively. They use only surface mount components and are design examples of how to use TI's TPS56xx controllers in high density, low loss applications with tight static and dynamic output voltage requirements. Detailed test results taken from the EVMs are presented.

Design simplicity, low component count, and lower cost make buck converters popular solutions where low input voltages are available for the converter and where isolation is not a requirement.

This user's guide describes techniques for designing synchronous buck converters using TI's SLVP111±114 EVMs and TPS56xx ripple regulator controllers. Synchronous buck converters provide an elegant power supply solution for rapidly transitioning DSP loads (such as the Texas Instruments TMS320C62x/67x family), fast memory, and similar processors. An order of magnitude improvement in dynamic response of this converter over standard control methods reduces hold-upcapacitance needs near the transitioning loads, thus saving cost and board space.

Topic

 

Page

 

 

 

1.1

Synchronous Buck Regulator Operation . . . . . . . . . . . . . . . . . . . . . .

. . 1±2

1.2

Hysteretic Control Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . 1±3

1.3

Design Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . 1±4

1.4

Design Specification Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. 1±5

1.5

Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. 1±7

1.6

Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. 1±8

1.7

Board Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1±10

 

 

 

 

Introduction

1-1

Synchronous Buck Regulator Operation

1.1 Synchronous Buck Regulator Operation

The synchronous buck converter is a variation of the traditional buck converter. The main switching device is usually a power MOSFET and is driven in the same manner as in a traditional buck converter. The freewheeling rectifier, usually a Schottky device, is replaced by a power MOSFET and is driven in a complementary or synchronous fashion relative to the main switching device; when one MOSFET is on, the other is off. The freewheeling MOSFET is selected so that its ON voltage drop is less than the forward drop of the original freewheeling rectifier, thus increasing conversion efficiency. A very important design issue when using a synchronous buck converter is preventing cross-conductionof the two power MOSFETs, i.e., preventing both MOSFETs from being on simultaneously. A small amount of deadtime is necessary.

Figure 1 shows a simplified schematic of a synchronous buck converter. The TPS56xx senses the output voltage and then drives Q1 and Q2 depending on the sensed voltage. The TPS56xx senses the voltage at the junction of Q1, Q2, and L1 and uses it to actively prevent simultaneous conduction of Q1 and Q2.

Figure 1±1. Simplified Synchronous Buck Converter Schematic

VI

 

Q1

+

 

L1

TPS56xx

VO

 

Q2

+

 

 

C

1-2