Texas Instruments AN-2255 Manuale utente

AN-2255 LM3463 Evaluation Board

User's Guide

Literature Number: SNVA642

May 2012

Contents

1 Introduction ........................................................................................................................ 5

2 Standard Settings of the LM3463 Evaluation Board ................................................................. 5

3 LM3463 Evaluation Board Schematic ..................................................................................... 6

4 Bill Of Materials .................................................................................................................. 6

5 Board Layout ...................................................................................................................... 8

6 Connection Diagram ............................................................................................................ 9

7 Primary Power Supply ......................................................................................................... 9

8 Response of the DHC Loop ................................................................................................ 12

9 Reducing the System Startup Time ...................................................................................... 12

10 MOSFET Power Dissipation Limit ........................................................................................ 13

11 Analog Dimming Control .................................................................................................... 13

12 PWM Dimming Control ....................................................................................................... 13

13 Disabling Output Channel(s) ............................................................................................... 17

14 Cascading the LM3463 evaluation board .............................................................................. 17

15 PCB Design ...................................................................................................................... 18

16 Typical Waveforms ............................................................................................................ 20

2Table of Contents SNVA642–May 2012

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List of Figures

1 Circuit diagram of the LM3463 evaluation board ....................................................................... 6

2 Top Layer .................................................................................................................... 8

3 Bottom Layer ................................................................................................................ 8

4 Connecting the LM3463 evaluation board to a primary power supply............................................... 9

5 Different voltage levels of the VRAIL at system startup................................................................. 10

6 Procedures of setting the rail voltage levels. .......................................................................... 11

7 Procedure of selecting a primary power supply ....................................................................... 12

8 Adjusting the tST with different value of RISR......................................................................... 13

9 Typical waveforms of a complete data frame in the serial interface mode ........................................ 15

10 PWM dimming duty vs code value of a data byte..................................................................... 15

11 Conversion characteristic of the analog voltage to PWM dimming control circuit ................................ 17

12 A 12 channel lighting system using serial interface mode for dimming control ................................... 18

13 A 12 channel lighting system using DC interface mode for dimming control...................................... 19

14 A 12 channel lighting system using Direct PWM mode for dimming control ...................................... 19

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SNVA642–May 2012 List of Figures

User's Guide

SNVA642–May 2012

AN-2255 LM3463 Evaluation Board

The LM3463 is a 6-channel linear LED driver with Dynamic Headroom Control (DHC) designed to drive six

strings of high brightness LEDs at maximum supply voltage up to 95V. Each output channel of the

LM3463 evaluation board is designed to deliver 200 mA of LED driving current. The LED turn on voltage

is set to 48V by default, thus the board is able to deliver up to 57.6W total output power. The six output

channels are divided into 4 individual groups to facilitate average LED current control by means of PWM

dimming. The PWM dimming control interface of the LM3463 can accept standard TTL level PWM signals,

analog voltage or serial data to control the dimming duty of the four LED groups individually. The analog

dimming control interface accepts an analog control voltage in the range from 0V to 2.5V to adjust the

reference voltage of the linear current regulators, which enables true LED current adjustment. This

evaluation board is designed to be connected to an external primary power supply. Using three connection

wires, the VIN, GND and VFB, the dynamic Headroom Control (DHC) circuit of the LM3463 adjusts the

output voltage of the primary power supply to maximize system efficiency.

4AN-2255 LM3463 Evaluation Board SNVA642–May 2012

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Introduction

1 Introduction