JAJS383E September   2009  – April 2018 TPS54418

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
    1.     Device Images
      1.      概略回路図
      2.      効率と出力電流との関係
  4. 4 改訂履歴
  5. 5 概要（続き）
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Fixed Frequency PWM Control
      2. 8.3.2  Slope Compensation and Output Current
      3. 8.3.3  Bootstrap Voltage (Boot) and Low Dropout Operation
      4. 8.3.4  Error Amplifier
      5. 8.3.5  Voltage Reference
      6. 8.3.6  Adjusting the Output Voltage
      7. 8.3.7  Enable and Adjusting Undervoltage Lockout
      8. 8.3.8  Soft-Start Pin
      9. 8.3.9  Sequencing
      10. 8.3.10 Constant Switching Frequency and Timing Resistor (RT/CLK Pin)
      11. 8.3.11 Overcurrent Protection
      12. 8.3.12 Frequency Shift
      13. 8.3.13 Reverse Overcurrent Protection
      14. 8.3.14 Synchronize Using the RT/CLK Pin
      15. 8.3.15 Power Good (PWRGD Pin)
      16. 8.3.16 Overvoltage Transient Protection
      17. 8.3.17 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Small Signal Model for Loop Response
      2. 8.4.2 Simple Small Signal Model for Peak Current Mode Control
      3. 8.4.3 Small Signal Model for Frequency Compensation
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1  Step One: Select the Switching Frequency
        2. 9.2.2.2  Step Two: Select the Output Inductor
        3. 9.2.2.3  Step Three: Choose the Output Capacitor
        4. 9.2.2.4  Step Four: Select the Input Capacitor
        5. 9.2.2.5  Step Five: Minimum Load DC COMP Voltage
        6. 9.2.2.6  Step Six: Choose the Soft-Start Capacitor
        7. 9.2.2.7  Step Seven: Select the Bootstrap Capacitor
        8. 9.2.2.8  Step Eight: Undervoltage Lockout Threshold
        9. 9.2.2.9  Step Nine: Select Output Voltage and Feedback Resistors
          1. 9.2.2.9.1 Output Voltage Limitations
        10. 9.2.2.10 Step 10: Select Loop Compensation Components
        11. 9.2.2.11 Power Dissipation Estimate
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12デバイスおよびドキュメントのサポート
    1. 12.1 デバイス・サポート
      1. 12.1.1 WEBENCH®ツールによるカスタム設計
      2. 12.1.2 開発サポート
    2. 12.2 商標
    3. 12.3 静電気放電に関する注意事項
    4. 12.4 Glossary
  13. 13メカニカル、パッケージ、および注文情報

8.3.12 Frequency Shift

To operate at high switching frequencies and provide protection during overcurrent conditions, the TPS54418 device implements a frequency shift. If frequency shift was not implemented, during an overcurrent condition the low-side MOSFET may not be turned off long enough to reduce the current in the inductor, causing a current runaway. With frequency shift, during an overcurrent condition the switching frequency is reduced from 100%, then 75%, then 50%, then 25% as the voltage decreases from 0.8 to 0 volts on VSENSE pin to allow the low-side MOSFET to be off long enough to decrease the current in the inductor. During start-up, the switching frequency increases as the voltage on VSENSE increases from 0 to 0.8 volts. See Figure 7 for details.