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Application Report

SNVA206B–January 2007–Revised April 2013

AN-1563 Quick Start Guide for a 0.5 Amp Buck Regulator

Using The LM5574 and LM25574

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

ABSTRACT

This step-by-step guide provides an easy to use process to quickly select the external components

necessary to complete a design.

Contents

1 Introduction .................................................................................................................. 2

2 Quick Guide Design Worksheet ........................................................................................... 3

List of Figures

1 Application Schematic...................................................................................................... 2

List of Tables

1 Bill of Materials .............................................................................................................. 5

SNVA206B–January 2007–Revised April 2013 AN-1563 Quick Start Guide for a 0.5 Amp Buck Regulator Using The

LM5574 and LM25574

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Summary of content (6 pages)

PAGE 1
Application Report SNVA206B – January 2007 – Revised April 2013 AN-1563 Quick Start Guide for a 0.5 Amp Buck Regulator Using The LM5574 and LM25574 ..................................................................................................................................................... ABSTRACT This step-by-step guide provides an easy to use process to quickly select the external components necessary to complete a design. 1 2 Contents Introduction ..............................................
PAGE 2
Introduction 1 www.ti.com Introduction The LM5574 and LM25574 switching regulators feature all of the functions necessary to implement an efficient high voltage buck regulator using a minimum of external components. These easy to use regulators include either a 42V (LM25574) or a 75V (LM5574) N-Channel buck switch with an output current capability of 0.5 Amps. The operating frequency is programmable from 50kHz up to 1MHz.
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Quick Guide Design Worksheet www.ti.com 2 Quick Guide Design Worksheet Step 1. List the basic requirements: Output Current: 0 to 0.5 Amp Output Voltage: Input Voltage Min Spec: Input Voltage Max Spec: V [1] V [2] V [3] Step 2. If the Input Voltage Max Spec [3] is less than 42V use the LM25574. If the Input Voltage Max Spec [3] is greater than 42V but less than 75V use the LM5574. Both devices require the Input Voltage Min Spec [2] to be greater than 6V. Selected Regulator: [4] Step 3.
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Quick Guide Design Worksheet www.ti.com Step 6. Calculate the value of CRAMP: CRAMP = L1[7] x 5 x 10-6 (5) Selected value of CRAMP: Farads [8] Step 7. Set Rfb2 to 5kOhms if Vout[1] is less than or equal to 5 Volts. If Vout[1] is greater than 5V set Rfb2 to 10K Ohms. Selected value of Rfb2: Ohms [9] Calculate the value of Rfb1: Rfb1 = 1.225 x Rfb2[9] (Vout[1] ± 1.225) (6) Selected value of Rfb1: Ohms [10] Step 8. Select the re-circulating diode, D1.
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Quick Guide Design Worksheet www.ti.com Step 11. Ccomp and Rcomp configure the error amplifier gain characteristics to accomplish a stable overall loop gain. One advantage of current mode control is the ability to close the loop with only two feedback components. Calculate the value of Rcomp: Rfb1[9] 5 Rcomp = 2.
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