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Application Report

SNVA212B–January 2007–Revised April 2013

AN-1572 Quick Start Guide for a 3 Amp Buck Regulator

Using the LM5576 and LM25576

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

ABSTRACT

This application note provides an easy to use process to design a 3 Amp buck regulator using the LM5576

and LM25576 switching regulators.

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

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SNVA212B–January 2007–Revised April 2013 AN-1572 Quick Start Guide for a 3 Amp Buck Regulator Using the LM5576

and LM25576

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Summary of content (6 pages)

PAGE 1
Application Report SNVA212B – January 2007 – Revised April 2013 AN-1572 Quick Start Guide for a 3 Amp Buck Regulator Using the LM5576 and LM25576 ..................................................................................................................................................... ABSTRACT This application note provides an easy to use process to design a 3 Amp buck regulator using the LM5576 and LM25576 switching regulators. 1 2 Contents Introduction ........................................
PAGE 2
Introduction 1 www.ti.com Introduction The LM5576 and LM25576 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 (LM25576) or a 75V (LM5576) N-Channel buck switch with an output current capability of 3 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 3 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 LM25576. If the Input Voltage Max Spec [3] is greater than 42V but less than 75V use the LM5576. 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 10-5 (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: Rcomp = 6 x 104 x Rfb1[9] x Cout[13] + Selected value of Rcomp: Rfb1[9] Vout[1] (9) Ohms [14] Calculate the value of Ccomp Ccomp = 1 8 x 103 x Rcomp[14] Selected value of Ccomp: (10) Farads [15] Step 12.
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