LM1770EVAL

User's Guide SNVA125B – September 2005 – Revised April 2013 AN-1400 LM1770 Evaluation Board 1 Introduction The LM1770 is a synchronous buck switching controller that is capable of accepting an input voltage in the range of 2.8 V to 5.5 V and producing an output voltage as low as 0.8 V. By utilizing a constant on time control scheme it allows a power supply to be designed quickly without the need for external compensation components. The LM1770 is available in three different timing options to allow flexibility on switching frequency and is offered in a small SOT23-5 package. These features enable a power supply to be designed that occupies an extremely small footprint while maintaining high efficiency. The LM1770 demo board was designed to illustrate what is possible when designing in space critical applications. It accepts a 5 V input rail and produces a 2.5 V output. Despite the small size (the board measures 0.7" v 0.68"), it is capable of delivering up to a maximum continuous current of 2A. At this load the efficiency is above 92%. For testing of the board, the input voltage can be varied over the entire operating range of 2.8 V to 5.5 V. The timing option used for this design is the 2000 ns option (LM1770U), which sets the nominal switching frequency to 378 kHz. Modifications can easily be made to the board to adjust the output voltage, by changing one of the feedback resistors. 2 Schematic VIN CIN VIN HG Q1 L1 LM1770 VOUT COUT LG Q2 CFF RFB1 FB GND RFB2 All trademarks are the property of their respective owners. SNVA125B – September 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated AN-1400 LM1770 Evaluation Board 1 Bill of Materials (BOM) 3 Bill of Materials (BOM) Designator Quantity Manufacturer U1 LM1770, 2000ns Option LM1770 1 TI Q2 NMOS SI3460DV 1 Siliconix Q1 PMOS SI3867DV 1 Siliconix Cout 47 µF Cap, 4 V, 70 mΩ, B Case 4TPC47M 1 Sanyo Rfb1 21 kΩ Resistor, 0603 CRCW06032102F 1 Vishay Rfb2 10 kΩ Resistor, 0603 CRCW06031002 1 Vishay 5.0 µH Inductor MSS7341-502NLB 1 Coilcraft Cff 10 nF Capacitor, 0603 VJ0603Y103KXAAT 1 Vishay Cin 22 µF Capacitor, 0805 GRM21BR60J226ME39B 1 muRata Individual test points 160-1026-02-05-00 3 Wearnes L Test Points 4 www.ti.com Description Part No Performance 100 95 EFFICIENCY (%) 90 85 80 75 70 65 60 55 50 .01 .1 1 10 ILOAD (A) Figure 1. Efficiency vs IOUT 2 AN-1400 LM1770 Evaluation Board SNVA125B – September 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated PCB Layout www.ti.com 5 PCB Layout Figure 2. Top Layer Figure 3. Bottom Layer LM1770 Demo Board Information Board Material FR4 Size 0.7" x 0.68" Layers 2 Copper Thickness 1oz Plating HASL Board Thickness 0.062" SNVA125B – September 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated AN-1400 LM1770 Evaluation Board 3 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. 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