LM3431EVAL National Semiconductor, LM3431EVAL Datasheet

LM3431EVAL

Manufacturer Part Number

LM3431EVAL

Description

BOARD EVAL FOR LM3431 LED DRIVER

Manufacturer

National Semiconductor

Series

PowerWise®r

Datasheets

1.LM3431MHNOPB.pdf (24 pages)

2.LM3431EVAL.pdf (8 pages)

Specifications of LM3431EVAL

Current - Output / Channel

140mA

Outputs And Type

4, Non-Isolated

Features

Dimmable

Voltage - Input

8 ~ 18V

Utilized Ic / Part

LM3431

Kit Contents

Board, Datasheet

Svhc

No SVHC (15-Dec-2010)

Kit Features

Designed To Drive 4 Parallel Strings Of 8 Series LEDs At 140mA Per String From An Input 8V To 18V

Mcu Supported Families

LM3431

Rohs Compliant

Lead Free Status / RoHS Status

Contains lead / RoHS non-compliant

Voltage - Output

Lead Free Status / Rohs Status

Supplier Unconfirmed

Current page: 1 of 8
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LM3431 Evaluation Board

Introduction

The LM3431 is a combination switching boost voltage regu-

lator and multi-channel LED current controller. The LM3431

Evaluation Board is designed to drive 4 parallel strings of 8

series LEDs at 140mA per string from an input voltage range

of 8V to 18V. The boost switcher regulates LED cathode volt-

age for optimum efficiency, while allowing the output voltage

to vary according to the LED forward voltage. The LM3431

incorporates complete fault protection features including LED

short and open protection, over-current protection, over-volt-

age and under-voltage protection, and thermal shutdown.

The error detection flag can be monitored at the DLY post,

which has a programmable delay time.

The board includes a DIM input terminal for a selectable dig-

ital or analog dimming control signal. PWM dimming frequen-

cies up to 1kHz at 100:1 contrast ratio and contrast ratios up

to 500:1 at 200Hz are possible.

The evaluation board is designed to operate at ambient tem-

peratures up to 70°C.

The complete evaluation board schematic is shown in Figure

2. Typical waveforms and performance curves are shown in

Figures 3-8.

Although a wide variety of LED combinations and currents

can be driven with the LM3431, the schematic must be mod-

ified to achieve optimum performance with any given array.

However, for initial evaluation and demonstration, some mod-

ifications from the default settings are possible. A few of the

possible variations are described below and listed in Tables

2 and 3.

LED current can be set as low as 100mA per string without

significantly degrading performance; the number of strings

can be reduced from 4 to 3 or 2; and the number of series

LEDs can be set between 6 and 9.

To design for LED arrays other than the default, and for com-

plete device and design information, refer to the LM3431

datasheet.

Before Powering Up

Before powering up the LM3431 evaluation board, a few op-

tions must be selected.

First, verify that the default LED current setting of 140mA is

appropriate to drive the LEDs. To drive LEDs at other cur-

rents, refer to Table 2. If the required LED current is not listed,

refer to the LM3431 datasheet, as more extensive modifica-

tions will be required.

300468

National Semiconductor

Application Note 1764

Allan Fisher

January 10, 2008

By default, the LM3431 evaluation board has channels 1-4

enabled. To drive fewer channels, first remove the sense re-

sistor or NPN on the channel to be disabled (R10-R13 or Q2-

Q5). Then refer to Table 3 and make any other required

changes. Table 3 also gives options for driving fewer LEDs

per string.

Finally, select the type of dimming control signal to be used.

By default, R-MODE is installed, which enables digital dim-

ming control mode. To use this mode, connect a digital PWM

signal to the DIM post. The dimming signal must have a min-

imum high logic level of 2.3V.

To enable analog dimming, remove the MODE resistor and

connect an analog voltage level to the DIM post. In analog

mode, the dimming duty cycle is varied by the voltage at the

DIM post within a range of 0.37V to 2.5V. The default analog

dimming frequency is 1kHz. To modify this frequency, change

C5 as described in the datasheet.

Any dimming frequency between 180Hz and 20kHz can be

used in either digital or analog dimming control mode. How-

ever the default schematic is not designed for dimming fre-

quencies above 1kHz. Once the evaluation board has been

configured, connect the LED strings as shown in Figure 2. The

first anode of each string connects to the VA post and the last

cathode of each string connects to VC1 through VC4. LEDs

can be connected either via the 8-pin header or to the terminal

posts. Figure 1 shows the pinout of the header.

Connect the input voltage supply to the VIN and GND posts.

When all connections and polarities have been verified, pow-

er can be applied. When the input voltage rises above 7.7V

typically, the EN pin will cross the UVLO threshold and the

LM3431 will startup. EN can be pulled low (via the EN post)

to shutdown the evaluation board.

FIGURE 1. LED Connection, Top View Header Pinout

www.national.com

30046801

Related parts for LM3431EVAL

LM3431EVAL Summary of contents

Page 1

... LEDs. To drive LEDs at other cur- rents, refer to Table 2. If the required LED current is not listed, refer to the LM3431 datasheet, as more extensive modifica- tions will be required. © 2008 National Semiconductor Corporation National Semiconductor Application Note 1764 Allan Fisher January 10, 2008 By default, the LM3431 evaluation board has channels 1-4 enabled ...

Page 2

www.national.com 2 ...

Page 3

Ref # Function IC1 Boost controller and LED driver C1 Cin C2 Cin C3 VCC C4 Comp C5 MODE DLY C10 VA C11 REFIN bypass C12 REF bypass C13 Comp2 C14 THM C15 ...

Page 4

Ref # Function R18 AFB R19 AFB R20 HG R21 - R23 NDRV R24 ch.4 R25 THM hys Rmode MODE/F Rrestart restart select RVCC Optional Components Several of the components shown in the schematic are not installed and are optional. ...

Page 5

Typical Evaluation Board Performance Unless otherwise specified, the following conditions apply: Vin = 12V 25°C, LED array = 4 parallel strings of 8 LEDs at 140mA per string. LED part number: Nichia NFSW036BT. FIGURE 3. Maximum Contrast Ratio ...

Page 6

PCB Layout www.national.com FIGURE 9. Top Side PCB Layout FIGURE 10. Bottom Side PCB Layout 6 30046809 30046810 ...

Page 7

Notes 7 www.national.com ...

Page 8

... For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Amplifiers www.national.com/amplifiers Audio www.national.com/audio Clock Conditioners www.national.com/timing Data Converters www.national.com/adc Displays www.national.com/displays Ethernet www.national.com/ethernet Interface www.national.com/interface LVDS www.national.com/lvds Power Management www.national.com/power Switching Regulators www.national.com/switchers LDOs www ...

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