• Menu
  • Product
  • Email
  • PDF
  • Order now

  • Automotive SEPIC Reference Design Using an Integrated FET

    • TIDT316 December   2022

       

  • CONTENTS
  • SEARCH
  • Automotive SEPIC Reference Design Using an Integrated FET
  1.   Description
  2.   Features
  3.   Applications
  4. 1Test Prerequisites
    1. 1.1 Voltage and Current Requirements
    2. 1.2 Considerations
    3. 1.3 Dimensions
  5. 2Testing and Results
    1. 2.1 Efficiency Graph
    2. 2.2 Loss Graph
    3. 2.3 Load Regulation
    4. 2.4 Line Regulation
    5. 2.5 Thermal Images
      1. 2.5.1 8-V Input Voltage
      2. 2.5.2 12-V Input Voltage
      3. 2.5.3 18-V Input Voltage
      4. 2.5.4 Conclusion
    6. 2.6 Bode Plots
      1. 2.6.1 5.2-V Input Voltage (Board Input, 5.0 V at Power Stage)
      2. 2.6.2 12-V Input Voltage
      3. 2.6.3 18-V Input Voltage
  6. 3Waveforms
    1. 3.1 Switching
      1. 3.1.1 Switchnode (SW) to GND
        1. 3.1.1.1 8-V Input Voltage
        2. 3.1.1.2 12-V Input Voltage
        3. 3.1.1.3 18-V Input Voltage
      2. 3.1.2 Diode D1 (Referenced to VOUT)
        1. 3.1.2.1 8-V Input Voltage
        2. 3.1.2.2 12-V Input Voltage
        3. 3.1.2.3 18-V Input Voltage
    2. 3.2 Output Voltage Ripple
    3. 3.3 Input Voltage Ripple (AC-Coupled)
      1. 3.3.1 Board Input
      2. 3.3.2 Power Stage Input
    4. 3.4 Load Transients
      1. 3.4.1 8-V Input Voltage
      2. 3.4.2 12-V Input Voltage
      3. 3.4.3 18-V Input Voltage
    5. 3.5 Start-Up Sequence
      1. 3.5.1 8-V Input Voltage
      2. 3.5.2 12-V Input Voltage
      3. 3.5.3 18-V Input Voltage
    6. 3.6 Shutdown Sequence
      1. 3.6.1 8-V Input Voltage
      2. 3.6.2 12-V Input Voltage
      3. 3.6.3 18-V Input Voltage
  7.   A Output Ripple Reduction, Output Current Capability, and Dithering Option
    1.     A.1 Output Ripple Reduction by Adding Ceramic Output Capacitors (MLCCs)
      1.      A.1.1 Initial Design
      2.      A.1.2 Adding one 47-µF X7R Ceramic Capacitor, MLCC, 10 V, X7R, 1210
      3.      A.1.3 Adding a Second 47-µF Capacitor (Final Design)
    2.     A.2 Maximum Output Current Capability at Ultra-Low Cold Cranking Using LM5157
    3.     A.3 Dithering Option via Resistor R10
      1.      A.3.1 Enabled
      2.      A.3.2 Disabled
  8. IMPORTANT NOTICE
search No matches found.
  • Full reading width
    • Full reading width
    • Comfortable reading width
    • Expanded reading width
  • Card for each section
  • Card with all content

 

TEST REPORT

Automotive SEPIC Reference Design Using an Integrated FET

Description

This reference design is a small SEPIC auxiliary power supply using the LM5157-Q1 device with integrated FET. A highlight of this design is the small board space by achieving a reasonable efficiency, so switching frequency has been set to a tradeoff of 440 kHz. Output voltage can be set from 5 V to 7 V, depending on the load requirements.

Though the design has been tested up to 2-A peak current the continuous current is around 1 A, resulting in a reasonable temperature rise +30 K at the SMA rectifier (hottest spot). The maximum output current depends on the minimum input voltage due to peak current limitation.

Optional ORing diodes at the BIAS pin to supply the controller with output voltage are allowing cold cranking as low as 2 V after start up VIN > 3 V. The undervoltage lockout UVLO allows a flexible set up.

An optional tiny LC input filter attenuates reflected ripple. The inductor was selected for high self-resonance frequency to act beyond the FM band.

Features

  • 6-V bias supply for automotive applications and general purposes, steps up and steps down
  • Cost-effective with a single driver, single FET, and single rectifier
  • High integration due to powerful internal FET
  • Provides input filter to prevent FM band noise
  • Supports ultra-low cold-cranking as low as 1.5-V input voltage by ORing diodes
  • This reference design is completely built and has completed testing in a lab

Applications

  • Steering wheel control
GUID-20221111-SS0I-WQS8-JJX6-FH9GTH540JS0-low.jpg Top Board Photo

1 Test Prerequisites

1.1 Voltage and Current Requirements

Table 1-1 Voltage and Current Requirements
ParameterSpecifications
Input Voltage Range8 V to 18 V
Output Voltage6 V
Output Current 1 ACONT, up to 2 APK
Estimated Switching Frequency 440 kHz
TopologySEPIC
IC LM5157-Q1

 
Texas Instruments

© Copyright 1995-2025 Texas Instruments Incorporated. All rights reserved.
Submit documentation feedback | IMPORTANT NOTICE | Trademarks | Privacy policy | Cookie policy | Terms of use | Terms of sale