SLUSCV2A June   2017  – April 2021 TPS54308

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Fixed-Frequency PWM Control
      2. 7.3.2  Force Continuous Conduction Mode (FCCM)
      3. 7.3.3  Error Amplifier
      4. 7.3.4  Slope Compensation and Output Current
      5. 7.3.5  Enable and Adjusting Undervoltage Lockout
      6. 7.3.6  Safe Start-Up into Pre-Biased Outputs
      7. 7.3.7  Voltage Reference
      8. 7.3.8  Adjusting Output Voltage
      9. 7.3.9  Internal Soft Start
      10. 7.3.10 Bootstrap Voltage (BOOT)
      11. 7.3.11 Overcurrent Protection
        1. 7.3.11.1 High-Side MOSFET Overcurrent Protection
        2. 7.3.11.2 Low-Side MOSFET Overcurrent Protection
      12. 7.3.12 Output Overvoltage Protection (OVP)
      13. 7.3.13 Thermal Shutdown
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 TPS54308 8-V to 28-V Input, 5-V Output Converter
      2. 8.2.2 Design Requirements
      3. 8.2.3 Detailed Design Procedure
        1. 8.2.3.1 Custom Design With WEBENCH® Tools
        2. 8.2.3.2 Input Capacitor Selection
        3. 8.2.3.3 Bootstrap Capacitor Selection
        4. 8.2.3.4 Output Voltage Set Point
        5. 8.2.3.5 Undervoltage Lockout Set Point
        6. 8.2.3.6 Output Filter Components
          1. 8.2.3.6.1 Inductor Selection
          2. 8.2.3.6.2 Output Capacitor Selection
          3. 8.2.3.6.3 Feedforward Capacitor
      4. 8.2.4 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Development Support
        1. 11.1.2.1 Custom Design With WEBENCH® Tools
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information
8.2.3.6.1 Inductor Selection

Use Equation 8 to calculate the minimum value of the output inductor (LMIN).

Equation 8. GUID-5B6E998D-4A73-4723-894D-B80D34FA5CAE-low.gif

Where:

  • KIND is a coefficient that represents the amount of inductor ripple current relative to the maximum output current

In general, the value of KIND is at the discretion of the designer, however, the following guidelines can be used. For designs using low-ESR output capacitors, such as ceramics, a higher KIND can be used. When using higher-ESR output capacitors, KIND = 0.2 yields better results.

For this design example, use KIND = 0.3. The minimum inductor value is calculated as 9.24 μH. For this design, a close standard value of 10 μH was selected for LMIN.

For the output filter inductor, the RMS current and saturation current ratings must not be exceeded. Use Equation 9 to calculate the RMS inductor current (IL(RMS)).

Equation 9. GUID-3ED70464-EB59-4910-BE59-48407D5BC771-low.gif

Use Equation 10 to calculate the peak inductor current (IL(PK)).

Equation 10. GUID-7B5E8115-2E46-4E9C-AFA6-CCACD3E76188-low.gif

Smaller or larger inductor values can be used, depending on the amount of ripple current the designer wants to allow as long as the other design requirements are met. Larger value inductors have lower AC current and result in lower output voltage ripple. Smaller inductor values increase AC current and output voltage ripple.