Datasheet

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GND

LM3508

COUT

CIN

DIM

PGND

OUT

ILED

SET

OPEN

2 3 4 LEDs

RSET

VIN

ISET

IOUT

VOUT

DIM

PGND

User's Guide

SNVA223–June 2007

AN-1593 LM3508 Evaluation Board

1 Introduction

The LM3508 is a synchronous step-up DC/DC converter designed for white LED applications. The

evaluation board is set up to drive four standard V

white LEDs from a 2.7 V to 5.5 V input supply. A fifth

LED can be placed across the R1 pad for testing up to five low VF LEDs. The LED current is set using the

RSET resistor via the equation I

LED

= 0.2V/RSET. The evaluation board comes with RSET = 10 Ω for

approximately 20 mA LED current. LED dimming is achieved by applying a PWM waveform of up to 100

kHz to the DIM pin.

2 Schematic

3 Bill of Materials

Designator Component Part Number Manufacturer

U1 LM3508TL, µSMD 9-bump LM3508 National Semiconductor

L 22 µH, ISAT = 330 mA VLF3010AT-220MR33 TDK

CIN 1 µF, 10V Ceramic C1608JB1A105M TDK

COUT 1 µF, 25V Ceramic C1608JB1E105M TDK

C3216X7R1E105K

D1–D3 White LED LW M67C Osram

R1 0 Ω Resistor CRCW0603 Vishay

R1 10 Ω Resistor CRCW060310R0F Vishay

All trademarks are the property of their respective owners.

SNVA223–June 2007 AN-1593 LM3508 Evaluation Board

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Summary of content (5 pages)

PAGE 1
User's Guide SNVA223 – June 2007 AN-1593 LM3508 Evaluation Board 1 Introduction The LM3508 is a synchronous step-up DC/DC converter designed for white LED applications. The evaluation board is set up to drive four standard VF white LEDs from a 2.7 V to 5.5 V input supply. A fifth LED can be placed across the R1 pad for testing up to five low VF LEDs. The LED current is set using the RSET resistor via the equation ILED = 0.2V/RSET.
PAGE 2
Bill of Materials www.ti.com Figure 1. LM3508 Evaluation Board Layout Topside Figure 2.
PAGE 3
Bill of Materials www.ti.com Figure 3. LM3508 Evaluation Board Layout Mid Layer 2 Figure 4.
PAGE 4
Board Operation 4 www.ti.com Board Operation To operate the LM3508 evaluation board, connect a 2.7 V to 5.5 V supply between the VIN header and PGND. 5 Jumper Connections • • • • EN is a 3-position jumper (see the bottom right jumper in Figure 2). The middle pin connects to EN of the device. The top pin of the EN header connects to PGND (device disabled) and the bottom pin connects to the VIN (device enabled). DIM is a 3-position header (see Figure 2). The middle pin connects to DIM of the LM3508.
PAGE 5
IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete.