IS31LT3948 General DEMO Board Guide Description Input: 10-25VDC Output: 4-12LEDs in series/333mA Note: The input voltage must be lower than the output voltage(total Vf). IS31LT3948 is a PFM step-up DC-DC converter designed for driving the white LED arrays for large size LCD panel backlighting applications. With internal OVP circuit, the chip and the system can be safe even if the load is not connected. The device features external PWM dimming or DC dimming, which allows the flexible control of the backlighting luminance. IS31LT3948 incorporates a unique FB scheme which automatically adjusts the integrated DC/DC converter to the optimum output voltage for the system, maximizing the efficiency. IS31LT3948 general DEMO board is used in general lamp. The IS31LT3948 DEMO Board is fully assembled and tested. Follow the steps listed below to verify board operation. Features Caution: Do not turn on the power supply until all connections are completed. Wide input voltage range: 5V-100V Constant Current Output limited only by external component selection (Note) No loop compensation required Internal over-voltage protection Internal over-temperature protection Note: The maximum output current is determined by Vout/Vin ratio as well as the external components. If output current and Vout/Vin ratio is high, high current components of inductor and NMOS are needed. Absolute Maximum Ratings Input voltage ≤ 30VDC voltage ≤ 44VDC Caution: Do not exceed the conditions listed above, otherwise the board will be damaged or output current will be limited. Procedure 1) 2) 3) 4) Connect the negative terminal of the power supply to the VIN1 pin and the positive terminal to the VIN2 pin. Connect the negative of the LED panel (LED arrays) to the LED- terminal. Connect the positive of the LED panel (LED arrays) to the LED+ terminal. Turn on the power supply and the LED panel (LED arrays) will be light. Order information Part Number Package Type IS31LT3948-GRLS2-EBAC SOP-8 Quick Start Recommended Equipment 30VDC Power supply LED panel (1W LED, 12 LEDs in series) Multi-meter Recommended Input and Output Ratings Bill of Materials No. 1 2 3 4 Name AL Capacitor AL Capacitor SMD Capacitor SMD Resistor Description 220uF±10%,35V 220uF±10%,50V,Low ESR 10uF±20%,25V 2.4KΩ±5%,1206 Ref Des. C1 C3 C4 R1 Qty. 1 1 1 1 5 6 7 8 9 10 11 SMD Resistor SMD Resistor SMD Resistor SMD Resistor SMD Resistor Schottky Diode Diode 24KΩ±1%,0805 430KΩ±1%,0805 10KΩ±1%,0805 0.135Ω±1%,0805 0.9Ω±1%,0805 SS36,3A,60V,SMA 1N4007,1A,1000V,SMA R4 R3 R7 R5 R8 D2 Ds 1 1 1 1 1 1 1 Integrated Silicon Solution, Inc. – www.issi.com R1.0, 18/12/2012 Mfr 1 IS31LT3948 General DEMO Board Guide 12 13 14 100uH,Isat≥3A 11A,100V,13N10L,NMOS,TO-252 IS31LT3948,SOP8 SMD Inductor MOS IC L1 T1 U1 1 1 1 L1 VCC+ R1 C4 VIN GATE R3 T1 C1 TOFF CS ADJ FB GND OVP R4 LED+ D2 U1 IS31LT3948 C3 R5 R7 Ds R8 GND LED- Figure 1 IS31LT3948 General DEMO Board Schematic Detailed Description Component Selection The component selection is very important. They have a significant effect on the operating state of the demo board. The output capacitor must be a low ESR capacitor so as to minimize it’s affect on the line regulation and load regulation. Please read the datasheet carefully to get more information about the component selection. PCB layout consideration As for all switching power supplies, especially those providing high current and using high switching frequencies, layout is an important design step. If layout is not carefully done, the regulator could show instability as well as EMI problems. • Wide traces should be used for connection of the high current loop to minimize the EMI and unnecessary loss. • The external components ground should be connected to IS31LT3948 ground as short as possible. Especially theRcs and Rfb ground to Integrated Silicon Solution, Inc. – www.issi.com R1.0, 18/12/2012 IS31LT3948 ground connection should be as short and wide as possible to have an accurate LED current. • The capacitor C1, C2, C3 should be placed as close as possible to IS31LT3948 for good filtering. Especially the output capacitor C3 connection should be as short and wide as possible. • NMOS drain is a fast switching node. The inductor and Schottky diode should be placed as close as possible to the drain and the connection should be kept as short and wide as possible. Avoid other traces crossing and routing too long in parallel with this node to minimize the noise coupling into these traces. The feedback pin (e.g. CS, FB, OVP) should be as short as possible and routed away from the inductor, the schottky diode and NMOS. The feedback pin and feedback network should be shielded with a ground plane or trace to minimize noise coupling into this circuit. The thermal pad on the back of NMOS package must be soldered to the large ground plane for ideal power dissipation. 2 IS31LT3948 General DEMO Board Guide PCB Layout Figure 2 Board PCB Layout- Top Layer Figure 3 Board PCB Layout-Bottom Layer Figure 4 Component Placement Guide -Top Layer Figure 5 Component Placement Guide -Bottom Layer Revision history Date Revision 2012.03.06 R1.0 Initial release R1.1 1. 2. 3. 4. 5. 2012.04.19 Changes Recommend output 1-12LEDs change to 4-12LEDs BOM: Add tolerance to cap and resistor. BOM: R1 3KΩ change to 2.4KΩ. BOM: L1 Isat>2.5A change to Isat>3A. BOM: MOS 13N06L change to 13N10L. Add package TO-252. 6. Add order information. 7. Change PCB layout to ISSI logo. 8. Change EVB photo. Integrated Silicon Solution, Inc. – www.issi.com R1.0, 18/12/2012 3 IS31LT3948 General DEMO Board Guide Copyright © 2006 integrated Silicon Solution, Inc. All rights reserved. ISSI reserves the right to make changes to this specification and its products at any time without notice. ISSI assumes no liability arising out of the application or use of any information, products or services described herein. Customers are advised to obtain the latest version of this device specification before relying on any published information and before placing orders for products. Integrated Silicon Solution, Inc. – www.issi.com R1.0, 18/12/2012 4