IS31LT3948 General DEMO Board Guide Description 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. Features 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. Recommended Input and Output Ratings Note: The input voltage must be lower than the output voltage(total Vf). Absolute Maximum Ratings Procedure The IS31LT3948 DEMO Board is fully assembled and tested. Follow the steps listed below to verify board operation. Caution: Do not turn on the power supply until all connections are completed. 1) 2) 3) Package Type IS31LT3948-GRLS2-EBAC SOP-8 Input voltage ≤ 15VAC voltage ≤ 45VDC Caution: Do not exceed the conditions listed above, otherwise the board will be damaged or output current will be limited. Evaluation Board Order information Part Number Input: 12VAC Output: 12LEDs in series/333mA 4) Connect the terminals of the power supply to the VIN1 and VIN2 pin(If the board don’t have the rectifier(D1,D3-D5), Connect the positive terminal of the power supply to the VIN1 of the board and the negative terminal of power supply to the VIN2 of the board) . 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. Table1: Ordering Information Quick Start Recommended Equipment 30VDC Power supply LED panel (1W LED, 12 LEDs in series) Multi-meter Figure 1: Photo of IS31LT3948 Evaluation Board For pricing, delivery, and ordering information, please contacts ISSI’s analog marketing team at [email protected] or (408) 969-6600. Integrated Silicon Solution, Inc. – www.issi.com Rev B, 08/26/2013 1 IS31LT3948 General DEMO Board Guide Bill of Materials No. 1 2 3 4 5 6 7 8 9 10 11 12 Name AL Capacitor AL Capacitor AL Capacitor SMD Capacitor SMD Resistor SMD Resistor SMD Resistor SMD Resistor SMD Resistor SMD Resistor SMD Resistor SMD Resistor Description 220uF±10%,35V NC 220uF±10%,63V,Low ESR 10uF±20%,25V 2.4KΩ±5%,1206 NC 430KΩ±1%,0805 24KΩ±1%,0805 0.22Ω±1%,1206 10KΩ±1%,0805 1.8Ω±1%,1206 0Ω,0805 Ref Des. C1,C2 C5 C3 C4 R1 R2 R3 R4 R5,R6 R7 R8,R9 R10 Qty. 2 1 1 1 1 1 1 1 2 1 2 1 13 14 15 16 17 18 19 SMD Resistor Schottky Diode Diode SMD Inductor MOS MOS IC NC SS36,3A,60V,SMA 1N4007,1A,1000V,SMA 100uH,Isat≥3A 11A,100V,13N10L,NMOS,TO-252 NC IS31LT3948,SOP8 R11 D1-D6 Ds L1 Q1 Q2 U1 1 6 1 1 1 1 1 Note Figure 2 IS31LT3948 General DEMO Board Schematic Integrated Silicon Solution, Inc. – www.issi.com Rev B, 08/26/2013 2 IS31LT3948 General DEMO Board Guide 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 the Rcs and Rfb ground to IS31LT3948 ground connection should be as short Integrated Silicon Solution, Inc. – www.issi.com Rev B, 08/26/2013 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. 3 IS31LT3948 General DEMO Board Guide PCB Layout Figure 3 Board PCB Layout- Top Layer Figure 4 Board PCB Layout-Bottom Layer Figure 5 Component Placement Guide -Top Layer Figure 6 Component Placement Guide -Bottom Layer Copyright © 2013 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. does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless Integrated Silicon Solution, Inc. receives written assurance to its satisfaction, that: a.) the risk of injury or damage has been minimized; b.) the user assume all such risks; and c.) potential liability of Integrated Silicon Solution, Inc is adequately protected under the circumstance Integrated Silicon Solution, Inc. – www.issi.com Rev B, 08/26/2013 4