LM3508TLEV

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. 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 SW L1 VIN VOUT D1 COUT CIN D2 D3 2 3 4 LEDs SW OUT IN D4 EN LM3508 EN DIM DIM R1 OPEN ILED SET GND PGND RSET PGND ISET 3 IOUT 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 C3216X7R1E105K C1608JB1E105M TDK 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 Submit Documentation Feedback AN-1593 LM3508 Evaluation Board Copyright © 2007, Texas Instruments Incorporated 1 Bill of Materials www.ti.com Figure 1. LM3508 Evaluation Board Layout Topside Figure 2. LM3508 Evaluation Board Layout Mid Layer 1 2 AN-1593 LM3508 Evaluation Board SNVA223 – June 2007 Submit Documentation Feedback Copyright © 2007, Texas Instruments Incorporated Bill of Materials www.ti.com Figure 3. LM3508 Evaluation Board Layout Mid Layer 2 Figure 4. LM3508 Evaluation Board Layout Bottom Side SNVA223 – June 2007 Submit Documentation Feedback AN-1593 LM3508 Evaluation Board Copyright © 2007, Texas Instruments Incorporated 3 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. The left pin of the DIM header connects to PGND (current source off). The right pin connects to VIN (current source on with max LED current of 20 mA). Drive DIM with aPWM waveform (VH > 1.1V, VL < 0.5 V) at up to 100 kHz to adjust the LED brightness. 2 3 4 LEDs is a 3-position header (see Figure 2). Leave open to configure the board for four series LEDs. Place a jumper across the top and middle pin to short D3 and D4 (2 LED solution). Place a jumper across the bottom and middle pin to short only D4 (3 LED solution). The OPEN header opens the current path from the cathode of D4 and the input to the current source. Normally this is shorted. This is for demonstrating OVP and/or disconnecting the LEDs. R1 is a short (0 Ω), which can be replaced with a sense resistor for measuring the LED current or replaced with a fifth LED for evaluation of low VF LEDs. EN has an internal 383 kΩ pull-down resistor which places the part in shutdown by default. DIM also has an internal 383 kΩ pull-down resistor that turns off the current source by default. For more information regarding the operation of the LM3508, see the LM3508 data sheet. 4 AN-1593 LM3508 Evaluation Board SNVA223 – June 2007 Submit Documentation Feedback Copyright © 2007, Texas Instruments Incorporated 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. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. 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