User’s Guide
LM5157 SEPIC Evaluation Module
ABSTRACT
The LM5157EVM-SEPIC Evaluation Module (EVM) is designed to showcase the LM5157 wide input voltage
converter, implementing a SEPIC converter with a coupled inductor. The EVM operates at 2.1 MHz, and it
produces a regulated output of 12 V, 12 W from an input of 4 V to 32 V. When the input voltage is between
4 V to 6 V, the output power is derated down to 6 W. The factory-installed converter is the LM5157-Q1.
However, by replacing the IC, the EVM can also be used to demonstrate the performance of the LM51571-Q1,
LM5157, LM51571, LM51581-Q1, LM5158-Q1, LM51581, and LM5158. The difference between the LM5157-Q1
and LM51571-Q1, or between the LM5157 and LM51571, is that the latter has a lower switch current limit for
applications with less output current need.
Table of Contents
1 Features and Electrical Performance................................................................................................................................... 2
1.1 Electrical Parameters......................................................................................................................................................... 2
1.2 EVM Power Derating Curve............................................................................................................................................... 3
1.3 Terminals and Signal Test Points....................................................................................................................................... 4
2 Application Schematic........................................................................................................................................................... 5
3 EVM Picture.............................................................................................................................................................................5
4 Test Setup and Procedure......................................................................................................................................................6
4.1 Bench Setup.......................................................................................................................................................................6
4.2 Test Equipment.................................................................................................................................................................. 6
4.3 Precautions........................................................................................................................................................................ 6
5 Test Data..................................................................................................................................................................................7
5.1 Efficiency............................................................................................................................................................................7
5.2 Output Regulation.............................................................................................................................................................. 7
5.3 Thermal Performance........................................................................................................................................................ 8
5.4 Typical Power Up............................................................................................................................................................... 8
5.5 Output Ripple Voltage........................................................................................................................................................ 9
5.6 Step Load Response........................................................................................................................................................11
5.7 Bode Plots........................................................................................................................................................................14
6 Schematics............................................................................................................................................................................15
7 Bill of Materials..................................................................................................................................................................... 16
8 Board Layout.........................................................................................................................................................................18
List of Figures
Figure 1-1. Power Derating vs. Input Voltage.............................................................................................................................. 3
Figure 2-1. Typical SEPIC Schematic Employing the LM5157/LM51571 and Coupled Inductor................................................ 5
Figure 3-1. LM5157EVM-SEPIC 3D-Rendered Picture...............................................................................................................5
Figure 4-1. Test Setup................................................................................................................................................................. 6
Figure 5-1. Efficiency vs. Load under Normal VIN, FSW = 2.1 MHz..............................................................................................7
Figure 5-2. Efficiency vs. Load under Low VIN, FSW = 2.1 MHz...................................................................................................7
Figure 5-3. Output Regulation vs Input Voltage, IOUT = 1 A.........................................................................................................7
Figure 5-4. Output Regulation vs Load, vIN = 12 V......................................................................................................................7
Figure 5-5. Thermal Image: VIN = 6 V, IOUT = 1 A, VBIAS = 6 V, No Forced Air Cooling...............................................................8
Figure 5-6. EVM Power Up under IOUT = 1 A.............................................................................................................................. 8
Figure 5-7. Output Ripple Voltage under VIN = 6 V and IOUT = 1 A............................................................................................. 9
Figure 5-8. Output Ripple Voltage under VIN = 18 V and IOUT = 1 A......................................................................................... 10
Figure 5-9. Step Load Response under VIN = 6 V, IOUT = 0.5 to 1 A Step................................................................................. 11
Figure 5-10. Step Load Response under VIN = 12 V, IOUT = 0.5 to 1 A Step.............................................................................12
Figure 5-11. Step Load Response under VIN = 30 V, IOUT = 0.5 to 1 A Step............................................................................. 13
Figure 5-12. EVM Bode Plots, Vin = 12 V, Vout = 12V, Iout = 1 A............................................................................................. 14
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SNVU738 – MARCH 2022
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