LM3430_07 NSC [National Semiconductor], LM3430_07 Datasheet

LM3430_07

Manufacturer Part Number

LM3430_07

Description

LED Backlighting Solution with LM3430 and LM3432

Manufacturer

NSC [National Semiconductor]

Datasheet

1.LM3430_07.pdf (16 pages)

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LED Backlighting Solution

with LM3430 and LM3432

Introduction

Since the release of high brightness White LED (HB-WLED)

in the middle of 1990's, tremendous research efforts have

been undergoing to improve the emission efficiency, reliability

and thermal packaging technologies in order to expand its

range of applications. In the last few years, improvements in

HB-WLED performance and price structure attracts more po-

tential applications considering this new lighting source tech-

nology as an alternative to conventional one. One area of

applications, LCD display backlighting, consider this new

backlighting method as the ultimate solution to replace the

existing Cold Cathode Fluorescent Lamps (CCFL). Backlight

LED-driver solutions need to exhibit following characteristics:

•

The LM3432 is a 6-channel high voltage current regulator

which provides a simple solution for LED backlighting appli-

cations and the LM3430 is a companion device to supply high

voltage required to drive serially connected LED strings. The

LM3430 and the LM3432 provide a complete solution to most

HB-WLED backlighting applications for notebook and PC

Instead of voltage control, LED-driver need direct LED

current control to ensure consistent color and brightness;

High conversion efficiency under various conditions;

Support PWM dimming;

Limit LED's rail voltage while LEDs open circuited;

Ability to shutdown individual channel(s) when short or

open circuited LED(s) detected;

Device over temperature detect and shutdown;

Low profile, small size and ease to use.

300289

National Semiconductor

Application Note 1679

TK Man

September 2007

monitor. In this application note, a typical example for a solu-

tion to drive six strings of twelve LEDs in series running at

20mA per string is described in details.

The Demonstration Board

The LM3432 is used to drive 6-channel LED strings with 12

LEDs in series per string running at 20mA. This example pro-

vides a simple solution for HB-WLED backlight applications

in notebooks and monitors. The LM3432 is powered with its

companion device, LM3430, the Dynamic Headroom Control

(DHC) feature helps to provide the optimal system efficiency.

The design specification for this demonstration board is

shown in below:

Design Specifications:

•

PWM Dimming Function:

•

Supply Voltage, VIN

Boost Converter Switching Frequency, F

Boost Converter Output Voltage, V

Number of LED String

Number of LED per String

LED Current per String, I

Analog Dimming Mode

Digital Dimming Mode

(With load disconnected)

Control Voltage Input, V

Dimming Frequency, F

External PWM Signal

LED

PWM

20 kHz to 25 kHz, 2.5V

1V to 3V (0% to 100%)

LED

≊

23 kHz

www.national.com

6V to 21V

1 MHz

20 mA

peak

50V

Related parts for LM3430_07

LM3430_07 Summary of contents

Page 1

LED Backlighting Solution with LM3430 and LM3432 Introduction Since the release of high brightness White LED (HB-WLED) in the middle of 1990's, tremendous research efforts have been undergoing to improve the emission efficiency, reliability and thermal packaging technologies in order ...

Page 2

Demonstration Board Schematic www.national.com 2 30028901 ...

Page 3

Connecting the Demonstration Board to LED Panel LM3430+LM3432 Demonstration Board Connecting the demonstration board outputs to the LED pan simple; just use a flat cable connecting the output header, CN1 to the respective input points of the LED ...

Page 4

Configuration of the Demonstration Board for Evaluation Analog PWM Dimming Mode • Leave jumper JP3 open to enable the Analog Dimming Mode; • Short pins 1-2 of jumper JP5 to select the Analog control input; • The VR1 is used ...

Page 5

Connect Power Supply to the Demonstration Board Input supply voltage connected to the V IN solder pads of the demonstration board 21V. Once the power is applied, all LEDs on the LED panel will be lighted ...

Page 6

Demonstration Board in Operation (Powered by a Notebook Adapter) www.national.com 6 30028905 ...

Page 7

Typical Operating Waveforms In below some operating waveforms are presented for refer- ence. The demonstration board is powered by a note-book adaptor with nominal output voltage of 16VDC. Power-Up PWM Dimming Characteristic Rising Edge (Channel 1 Waveform) Analog PWM Dimming ...

Page 8

PCB Layout LM3430+LM3432 Demonstration PC Board Top Overlay www.national.com 30028910 8 ...

Page 9

LM3430+LM3432 Demonstration PC Board Top Layout 9 30028911 www.national.com ...

Page 10

LM3430+LM3432 Demonstration PC Board Bottom Layout www.national.com 30028912 10 ...

Page 11

Bill of Materials for the Demonstration Board Designation Type Boost Converter Section (LM3430 Controller IC M1 N-MOSFET D1 Schottky Diode L1 Power Inductor C20 Ceramic Capacitor "C22 - C25 Ceramic Capacitor GRM55DR61H106KA88L C28 - C31" C0, C1, C21 ...

Page 12

Designation Type Current Control Section (LM3432 LED Current Regulator IC C34 Ceramic Capacitor C35 Ceramic Capacitor C36, C38 Ceramic Capacitor C37 Ceramic Capacitor R7 Resistor R25 Resistor R27, R28 Resistor R38 Resistor R39 Resistor VR1 Variable Resistor FAULTb ...

Page 13

... Some hints on selection of the key parameters and com- ponents will be described in below. For full details of the design equations and theories, please refer to the LM3430 and LM3432 datasheets. BOOST CONVERTER DESIGN WITH LM3430 The function of the boost converter is to step up the input voltage to a higher LED rail voltage to drive strings of twelve LEDs connected in series ...

Page 14

Selecting the Current Sensing Resistor The current sensing resistor, R SNS regulation of the inductor current and to provide cycle by cycle current limit function. The resistance selected must be low enough to keep the power dissipation to a minimum ...

Page 15

Selection of Gain Setting Resistor for Dynamic Headroom Control By connecting the VDHC pin of LM3432 through a gain setting resistor to the VDHC pin of the LM3430, the LM3432's DHC function will regulate the LED rail voltage from the ...

Page 16

THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE ...

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