LM3481EVAL

User's Guide SNVA304A – April 2008 – Revised May 2013 AN-1756 LM3481 Evaluation Board 1 Introduction The LM3481 is a current mode, low side N channel FET controller. It can be utilized in numerous configurations including a Boost, Flyback or SEPIC (Single Ended Primary Inductor Converter). This evaluation board demonstrates the flexibility of the LM3481 in a boost topology. The operating conditions for the evaluation board are listed below: 3V ≤ VIN ≤ 11V VOUT = 12V 0A ≤ IOUT ≤ 1.5A The circuit and bill of materials for this design are given below: R7 121 kÖ VIN J1 R8 121 kÖ C8 390 pF VIN ISEN VC UVLO C COMP R3 1.37 kÖ C6 0.12 éF LM3481 FB R2 20 kÖ L1 7.8 éH C3 0.47 éF 1 éF VOUT C9 Q1 DR PGND + C1, C2 100 éF D1 + C4, C5 100 éF R4 100Ö FA/SYNC/SD AGND R6 61.9 kÖ R1 169 kÖ C7 2.2 nF R5 20 mÖ Figure 1. Circuit Diagram All trademarks are the property of their respective owners. SNVA304A – April 2008 – Revised May 2013 Submit Documentation Feedback AN-1756 LM3481 Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 1 Bill of Materials 2 www.ti.com Bill of Materials Table 1. Bill of Materials 300 kHz, Vin = 5V, Vo = 12V, IO = 1.5A 2 Designat or Function Description Part Number Vendor U1 Controller LM3481 VSSOP-10 LM3481 Texas Instruments C1 Input Filter Cap 100 µF, 20V, D case, OxiCap TPSV107M020R0060 AVX C2 Input Filter Cap 100 µF, 20V, D case, OxiCap TPSV107M020R0060 AVX C3 Decoupling Cap .47 µF, 16V, X7R, 1206 ECJ-3VB1C474K Panasonic C4 Output Filter Cap 100 µF, 16V, Y case, Ta TPSD107M016R0100 AVX C5 Output Filter Cap 100 µF, 16V, Y case, Ta TPSD107M016R0100 AVX C6 Comp Cap 0.12 µF, 25V, 0805 ECJ-2YB1E124K Panasonic C7 Current Limit Sense Cap 2200 pF, 50V, 0805 ECJ-2VB1H222K Panasonic C8 Comp Cap 390 pF, 50V, 0805 08055C391KAT2A AVX C9 VCC Cap 1 µF, 25V, 1206 12063C105KAT AVX C11 Analog Input By. Cap 1 µF, 10V, 0805 0805ZC105KAT AVX R1 Resistor Divider (Upper) 169 kΩ, 1%, 0805 CRCW0805169KFK Vishay R2 Resistor Divider (Lower) 20k, 1%, 0805 CRCW080520K0FK Vishay R3 Comp Resistor 1.37k, 1%, 0805 CRCW08051K37FK Vishay R4 Filter Resistor 100Ω, 1%, 0805 CRCW0805100RFK Vishay R5 Sense Resistor 20 mΩ, 1% WSL2512R0200FE Vishay R6 Freq. Adj. Resistor 61.9 kΩ, 1%, 0805 CRCW08056192F Vishay R7 UVLO Res. Div. 121 kΩ, 1%, 0805 CRCW08051213F Vishay R8 UVLO Res. Div. 121 kΩ, 1%, 0805 CRCW08051213F Vishay L1 Input Filter 7.8µ , 8A, DCR = 10 mΩ RLF12560-7R8N8R2 TDK D1 Schottky Diode 4A,30V, Vf = 0.4V SL-43 Vishay Q1 FET SO-8, Rdson = 2.9 mΩ@VDS = 30V SI4368DY Vishay J1 Jumper Shunt LM with handle, 2 positions 881545-2 Tyco Electronics VIN VIN Post Turret 90mil mounting diameter 97H6305 Newark Catalog GND VIN GND Post Turret 90mil mounting diameter 97H6305 Newark Catalog GND VOUT Post Turret 90mil mounting diameter 97H6305 Newark Catalog VOUT VOUT GND Post Turret 90mil mounting diameter 97H6305 Newark Catalog AN-1756 LM3481 Evaluation Board SNVA304A – April 2008 – Revised May 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Performance www.ti.com 3 Performance Benchmark data has been taken from the evaluation board using the LM3481. Figure 2 shows an efficiency measurement taken at the maximum load of 1.5A with Vin at 5V. Figure 2. Efficiency vs Load The advantage of the evaluation board is the ability to examine performance tradeoffs through substitution of parts. By careful selection of the components used, it is possible to optimize the application circuit for a given parameter. For instance, the FET footprint has been designed to accommodate either one SO-8 or two parallel SO-8 packages. The selection of the FET would then be determined by the design constraints. An example would be that a lower system cost could be obtained by selection of a FET with a higher RDS(ON), although performance would be sacrificed through reduced efficiency. 4 Current Limit The purpose of the R4 (RSL) resistor is to provide flexibility in the selection of the slope compensation needed for the required application. The amount of slope compensation directly determines the minimum inductance required for stability. (Please see the LM3481/LM3481Q High Efficiency Low-Side N-Channel Control for Switching Regulators (SNVS346) data sheet for adjustment of slope compensation and for a complete discussion on how to calculate the R4 value needed). This evaluation board uses R4 and C7 to filter the Isen signal with negligible affect on the slope compensation. 5 Layout Fundamentals Good layout for DC-DC converters can be implemented by following a few simple design guidelines: 1. Place the power components (catch diode, inductor, and filter capacitors) close together. Make the traces between them as short and wide as possible. 2. Use wide traces between the power components and for power connections to the DC-DC converter circuit. 3. Connect the ground pins of the input and output filter capacitors and catch diode as close as possible using generous component-side copper fill as a pseudo-ground plane. Then, connect this to the ground plane through several vias. 4. Arrange the power components so that the switching loops curl in the same direction. 5. Separate noise sensitive traces, such as the voltage feedback path, from noisy traces associated with the power components. 6. Ensure a good low-impedance ground for the converter IC. 7. Place the supporting components for the converter IC, such as compensation and frequency selection components as close to the converter IC as possible, but away from noisy traces and the power components. Make their connections to the converter IC and its pseudo-ground plane as short as SNVA304A – April 2008 – Revised May 2013 Submit Documentation Feedback AN-1756 LM3481 Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 3 Layout Fundamentals www.ti.com possible. 8. Place noise sensitive circuitry such as radio or modem blocks away from the DC-DC converter. Figure 3. Top Layer Figure 4. Bottom Layer 4 AN-1756 LM3481 Evaluation Board SNVA304A – April 2008 – Revised May 2013 Submit Documentation Feedback Copyright © 2008–2013, 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. 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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