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Texas Instruments SLVP089 manual Introduction, 1. Typical Synchronous Buck Converter

Models: SLVP089

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1.1 Introduction

Introduction

1.1 Introduction

Synchronous buck converters provide the smaller size and higher efficiency required by electronic equipment, particularly portable battery-operated equipment. The synchronous buck converter reduces power losses associated with a standard buck converter by substituting a power MOSFET for the commutating diode. This reduces the typical 0.5-V to 1-V diode drop to 0.3 V or less and increases system efficiency by up to 10 percent. Continuous-current mode is desirable and is used in this EVM for the low peak-to-average current ratio. Figure 1–1 shows a typical synchronous buck converter.

Figure 1–1. Typical Synchronous Buck Converter

VI

R1

R2

R3

Controller

FB

R4

+

C1

Q1

L1

Q2

CR1

VO

+

C2

Transistor Q1 is the power switch and Q2 is the synchronous switch. A diode in parallel with Q2 allows inductor current flow during the dead time when both transistors are turned off. If dead time is not present in this configuration, high transient shoot-through currents will flow during the transition when one tran- sistor is turning on and the other is turning off, usually resulting in destruction of the power stage switches.

The SLVP089 evaluation module will supply a nominal 3.3-V output over a load range from 0 to 3 A using a dc input voltage of 5.5 V to 12 V. Full load efficiency is typically 90 percent.

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Texas Instruments SLVP089 manual Introduction, 1. Typical Synchronous Buck Converter

Contents

User’s Guide ConSLVverterP089SynchronousEvaluationModuleBuckMixed-Signal Linear Products 199807/98 Printed in U.S.ASLVU001A SLVP089 Synchronous Buck Converter Evaluation Module User’s Guide Literature Number SLVU001A JulyIMPORTANT NOTICE About This Manual How to Use This ManualRead This First Related Documentation From Texas InstrumentsFCC Warning If You Need AssistanceTrademarks 2.1 Introduction 2.2 Operating Specifications 2.3 Design Procedures Contents1.1 Introduction 1.2 Schematic 1.3 Input/Output Connections 2.3.1 Duty Cycle Estimate 2.3.2 Output Filter 2.3.3 Power SwitchFigures TablesPage HardwareChapter Topic1.1 Introduction Figure 1-1. Typical Synchronous Buck ConverterHardware 1.2 SchematicFigure 1-2. Schematic Diagram SchematicFigure 1-3. Input/Output Connections 1.3 Input/Output ConnectionsInput/Output Connections Board Layout 1.4 Board LayoutFigure 1-4. Board Layout Hardware1-5Table 1-1. Bill of Materials 1.5 Bill of MaterialsBill of Materials Table 1-3. Load Regulation and Ripple, 3.3-V 9-V Input 1.6 Test ResultsTable 1-2. Line/Load Regulation, 3.3-V Total Variation Figure 1-5. Efficiency Vs LoadTest Results Figure 1-6. Power Switch Turn-On and Delay from Q2 OffFigure 1-7. Power Switch Turn-Off and Delay to Q2 On V CC = 12Hardware1-9 Figure 1-8. Inductor and Output RippleTest Results 2-ACPage Page Design ProcedureChapter Topic2.1 Introduction Operating Specifications 2.2 Operating SpecificationsTable 2-1. Operating Specifications Design Procedure2.3.1 Duty Cycle Estimate 2.3 Design Procedures2.3.3 Power Switch 2.3.2 Output Filter2.3.5 Snubber Network 2.3.4 Synchronous Switch and Rectifier+ 3 W 1 mA 2.3.6 Controller Functions2.3.7 Loop Compensation 0.001Figure 2-1. Power Stage Bode Plot + DD V OFigure 2-2. Compensation Network Figure 2-3. Bode Plot Figure 2-4. Output Response