SLUSF22 November   2024 TPS54538

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1  Fixed Frequency Peak Current Mode
      2. 6.3.2  Mode Selection
      3. 6.3.3  Voltage Reference
      4. 6.3.4  Output Voltage Setting
      5. 6.3.5  Switching Frequency Selection / Synchronization
      6. 6.3.6  Phase Shift
      7. 6.3.7  Enable and Adjusting Undervoltage Lockout
      8. 6.3.8  External Soft Start and Prebiased Soft Start
      9. 6.3.9  Power Good
      10. 6.3.10 Minimum On Time, Minimum Off Time, and Frequency Foldback
      11. 6.3.11 Frequency Spread Spectrum
      12. 6.3.12 Overvoltage Protection
      13. 6.3.13 Overcurrent and Undervoltage Protection
      14. 6.3.14 Thermal Shutdown
    4. 6.4 Device Functional Modes
      1. 6.4.1 Modes Overview
      2. 6.4.2 Heavy Load Operation
      3. 6.4.3 Pulse Frequency Modulation
      4. 6.4.4 Forced Continuous Conduction Modulation
      5. 6.4.5 Dropout Operation
      6. 6.4.6 Minimum On-Time Operation
      7. 6.4.7 Shutdown Mode
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Custom Design With WEBENCH® Tools
        2. 7.2.2.2 Output Voltage Resistors Selection
        3. 7.2.2.3 Choosing Switching Frequency
        4. 7.2.2.4 Soft-Start Capacitor Selection
        5. 7.2.2.5 Output Inductor Selection
        6. 7.2.2.6 Output Capacitor Selection
        7. 7.2.2.7 Input Capacitor Selection
        8. 7.2.2.8 Feedforward Capacitor CFF Selection
        9. 7.2.2.9 Maximum Ambient Temperature
      3. 7.2.3 Application Curves
    3. 7.3 Best Design Practices
    4. 7.4 Power Supply Recommendations
    5. 7.5 Layout
      1. 7.5.1 Layout Guidelines
      2. 7.5.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Third-Party Products Disclaimer
      2. 8.1.2 Development Support
        1. 8.1.2.1 Custom Design With WEBENCH® Tools
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

7.2.2.9 Maximum Ambient Temperature

As with any power conversion device, the TPS54538 dissipates internal power while operating. The effect of this power dissipation is to raise the internal temperature of the converter above ambient. The internal die temperature (TJ) is a function of the following:

  • Ambient temperature
  • Power loss
  • Effective thermal resistance, RθJA, of the device
  • PCB combination

The maximum internal die temperature must be limited to 150°C. This limit establishes a limit on the maximum device power dissipation and, therefore, the load current. Equation 25 shows the relationships between the important parameters. It is easy to see that larger ambient temperatures (TA) and larger values of RθJA reduce the maximum available output current. The converter efficiency can be estimated by using the curves provided in this data sheet. Note that these curves include the power loss in the inductor. If the desired operating conditions cannot be found in one of the curves, then interpolation can be used to estimate the efficiency. Alternatively, the EVM can be adjusted to match the desired application requirements and the efficiency can be measured directly. The correct value of RθJA is more difficult to estimate. As stated in the Semiconductor and IC Package Thermal Metrics application note, the value of RθJA given in the Thermal Information table is not valid for design purposes and must not be used to estimate the thermal performance of the application. The values reported in that table were measured under a specific set of conditions that are rarely obtained in an actual application. The data given for RθJC(bott) and ΨJT can be useful when determining thermal performance. See the Semiconductor and IC Package Thermal Metrics application note for more information and the resources given at the end of this section.

Equation 25. I O U T _ M A X = ( T J - T A ) R θ J A × η 1 - η × 1 V O U T

where

  • ŋ is efficiency.

The effective RθJA is a critical parameter and depends on many factors such as the following:

  • Power dissipation
  • Air temperature and flow
  • PCB area
  • Copper heat-sink area
  • Number of thermal vias under the package
  • Adjacent component placement