LM1771EVAL

User's Guide SNVA163B – July 2006 – Revised April 2013 AN-1477 LM1771 Evaluation Board 1 Introduction The LM1771 is an efficient buck switching controller capable of converting an input voltage between 2.8 V to 5.5 V into a regulated output voltage as low as 0.8 V. The LM1771 utilizes a constant on-time control scheme that eliminates the need for external compensation components. The LM1771 features a precision enable pin to allow for easy sequencing and flexibility in setting the operating range of the power supply. Three timing options are available, which translates to three possible frequency options for any given output voltage. Available in the small-sized LLP-6 package, the LM1771 allows for a complete power supply design to occupy very little board space without sacrificing efficiency. The LM1771 evaluation board was designed with space critical applications in mind. The entire power supply occupies less than .86” X .76” on a two layer PCB, but is capable of delivering a maximum continuous load current of 2A. The output voltage is set at 2.5 V, but can be easily varied by replacing one of the feedback resistors. The 2000 ns timing option (LM1771U) is used to attain a 378 kHz switching frequency. The input voltage is nominally 5 V, but can varied over the entire operating range of the LM1771 (2.8 V to 5.5 V) for testing purposes. At the full 2A load, the efficiency of the power supply is greater than 92%. VIN CIN VIN Enable EN Q1 HG L LM1771 VOUT LG COUT Q2 CFF RFB1 FB GND RFB2 Figure 1. Schematic All trademarks are the property of their respective owners. SNVA163B – July 2006 – Revised April 2013 Submit Documentation Feedback AN-1477 LM1771 Evaluation Board Copyright © 2006–2013, Texas Instruments Incorporated 1 Bill of Materials (BOM) (5 V to 2.5 V Conversion) 2 www.ti.com Bill of Materials (BOM) (5 V to 2.5 V Conversion) Table 1. Bill of Materials (BOM) 3 Designator Description Part Number Quantity Manufacturer U1 LM1771, 2000ns LM1771 1 Texas Instruments Q1 PMOS Si3867DV 1 Siliconix Q2 NMOS Si3460DV 1 Siliconix Cin 22 µF Capacitor, 0805 GRM21BR60J226ME39 1 Murata Cout 68µF Capacitor, 6 V, 55 mΩ, C-Case 6TPC68M 1 Sanyo Rfb1 21 kΩ Resistor, 0603 CRCW06032102F 1 Vishay Rfb2 10 kΩ Resistor, 0603 CRCW06031002F 1 Vishay Coilcraft L 5.0 µH Inductor MSS7341-502NLB 1 Cff 1 nF Capacitor, 0603 VJ0603102KXXA 1 Vishay Test Points Individual Test Points 160-1026-02-05-00 4 Wearnes Performance Figure 2. Efficiency vs IOUT (VIN = 5V) 2 AN-1477 LM1771 Evaluation Board SNVA163B – July 2006 – Revised April 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated PCB Layout www.ti.com 4 PCB Layout Figure 3. Top Layer Figure 4. Bottom Layer SNVA163B – July 2006 – Revised April 2013 Submit Documentation Feedback AN-1477 LM1771 Evaluation Board Copyright © 2006–2013, Texas Instruments Incorporated 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. 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. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. 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