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User's Guide

SNVA461A–September 2011–Revised April 2013

AN-2094 LM3481 SEPIC Evaluation Board

1 Introduction

The LM3481 SEPIC evaluation board is designed to provide the design engineer with a fully functional

power converter solution with two output voltage options. It produces a selectable output voltage of 12 V

at 1.25A or 5V at 3A. The switching frequency for the converter is set to 500 kHz. The printed circuit board

consists of 2 layers of FR4 material with 2 ounce copper on both layers. This document contains the

evaluation board schematics, bill-of-materials (BOM) and a quick setup procedure. For complete circuit

design information, see the LM3481/LM3481Q High Efficiency Low-Side N-Channel Controller for

Switching Regulators Data Sheet (SNVS346).

The performance of the evaluation board is as follows:

5V Output Voltage Option:

Input Voltage Range : 4.5V to 25V

Output Voltage : 5V ± 2%

Output Current : 0A to 3A

Switching Frequency : 500 kHz

Load Regulation : 0.1%

Board Size : 2.4 x 1.8 inches

12V Output Voltage Option:

Input Voltage Range : 4.5V to 18V

Output Voltage : 12V ± 2%

Output Current : 0A to 1.25A

Switching Frequency : 500 kHz

Load Regulation : 0.1%

Board Size : 2.4 x 1.8 inches

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SNVA461A–September 2011–Revised April 2013 AN-2094 LM3481 SEPIC Evaluation Board

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Summary of content (11 pages)

PAGE 1
User's Guide SNVA461A – September 2011 – Revised April 2013 AN-2094 LM3481 SEPIC Evaluation Board 1 Introduction The LM3481 SEPIC evaluation board is designed to provide the design engineer with a fully functional power converter solution with two output voltage options. It produces a selectable output voltage of 12 V at 1.25A or 5V at 3A. The switching frequency for the converter is set to 500 kHz. The printed circuit board consists of 2 layers of FR4 material with 2 ounce copper on both layers.
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Powering and Loading Considerations 2 www.ti.com Powering and Loading Considerations Read this entire page prior to attempting to power the evaluation board. 2.1 Qucik Setup Procedure 1. Use an input power supply with at least 5A current capability. Connect the positive output of the power supply to the VIN terminal P1. Connect the negative output of the power supply to the input GND terminal P2. 2. Connect a load with 3A capability to the VOUT terminal P3 and GND terminal P4. 3.
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Board Configuration www.ti.com 4 Board Configuration 4.1 Output Voltage Option A jumper has been provided on the evaluation board in order to select the output voltage option of 12V or 5V. Shorting the jumper ses the output voltage to 12V. Leaving the jumper open will set the output voltage to 5V. 4.2 Under-Voltage Lock-Out (UVLO) The LM3481 evaluation board has a resistor divider connected to the UVLO pin to set the on and off thresholds to 4.25V and 4.05V, respectively.
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Board Configuration 4.7 www.ti.com Momentary Overload or Short Circuit Protection In case of an overload or a short circuit event, the voltage across the sense resistor would increase beyond 220 mV. This would then activate the short circuit current limit and limit the switching frequency by a factor of 8 while the event exists.
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Typical Performance Characteristics www.ti.com 5 Typical Performance Characteristics Efficiency at VOUT = 12V 100 80 90 70 80 EFFICIENCY (%) EFFICIENCY (%) Efficiency at VOUT = 5V 90 60 50 40 30 Vin = 4.5V Vin = 6V Vin = 12V Vin = 18V Vin = 25V 20 10 0 0.0 0.5 1.0 70 60 50 40 30 Vin = 4.5V Vin = 6V Vin = 12V Vin = 18V 20 10 0 1.5 2.0 ILOAD(A) 2.5 3.0 0.0 Startup at VOUT = 5V and VIN = 4.5V 0.5 1.0 1.5 2.0 ILOAD(A) 2.5 3.
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Typical Performance Characteristics www.ti.com Load Transient at VIN = 5V VIN= 5V VOUT 5.2 Load Transient at VIN = 12V 6 13.0 5 12.5 6 VIN= 12V 5 ILOAD 4.0 3.6 3.2 0.0 0.5 1.0 TIME (ms) 1.5 1 10.5 1 0 10.0 0 5.5 21 5.0 20 4.5 19 4.0 VIN 20 3.5 3.0 16 12 8 4 0 1 2 3 4 5 6 7 TIME (ms) 8 Input Transient at Iload = 3A and VOUT = 12V 22 13.0 12.5 12.0 11.5 VOUT 18 11.0 17 10.5 VIN 16 10.0 15 9.5 2.0 14 9.0 1.5 13 8.5 1.0 12 9 10 8.
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Evaluation Board Schematic www.ti.com 6 Evaluation Board Schematic Figure 3.
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Evaluation Board Schematic www.ti.com Table 1. LM3481 Bill of Materials (BOM) 8 Qty Designator Value 1 C1 100 µF 2 C2, C3 4.7 µF 1 C4 0.
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PCB Layout www.ti.com 7 PCB Layout Figure 4. Top Layer Components and Overlay Figure 5.
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PCB Layout www.ti.com Figure 6. Bottom Overlay Figure 7.
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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.