ZHCSY68D October   2008  – April 2025 LM5574-Q1

PRODUCTION DATA  

  1.   1
  2. 1 特性
  3. 2 应用
  4. 3 说明
  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 Shutdown and Standby
      2. 6.3.2 Current Limit
      3. 6.3.3 Soft Start
      4. 6.3.4 Thermal Protection
    4. 6.4 Device Functional Modes
      1. 6.4.1 High Voltage Start-Up Regulator
      2. 6.4.2 Oscillator and Sync Capability
      3. 6.4.3 Error Amplifier and PWM Comparator
      4. 6.4.4 Ramp Generator
      5. 6.4.5 Maximum Duty Cycle and Input Dropout Voltage
      6. 6.4.6 Boost Pin
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Bias Power Dissipation Reduction
    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  External Components
        3. 7.2.2.3  R3 (RT)
        4. 7.2.2.4  L1- Inductor
        5. 7.2.2.5  C3- Ramp Capacitor
        6. 7.2.2.6  C9 -Output Capacitor
        7. 7.2.2.7  D1 - Async Diode
        8. 7.2.2.8  C1- Input Capacitor
        9. 7.2.2.9  C8 - Vcc Capacitor
        10. 7.2.2.10 C7 - BST Capacitor
        11. 7.2.2.11 C4 - SS Capacitor
        12. 7.2.2.12 R5, R6 - Feedback Resistor
        13. 7.2.2.13 R1, R2, C2 - SD Pin Components
        14. 7.2.2.14 R4, C5, C6 - Compensation Components
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
      3. 7.4.3 Power Dissipation
      4. 7.4.4 Thermal Considerations
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
        1. 8.1.1.1 Custom Design With WEBENCH® Tools
    2. 8.2 接收文档更新通知
    3. 8.3 支持资源
    4. 8.4 Trademarks
    5. 8.5 静电放电警告
    6. 8.6 术语表
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

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7.4.4 Thermal Considerations

The junction-to-ambient thermal resistance of the LM5574-Q1 varies with the application. The most significant variables are the area of copper in the PCB and the amount of forced air cooling provided. The junction-to-ambient thermal resistance of the LM5574-Q1 mounted in the evaluation board varies from 90°C/W with no airflow to 60°C/W with 900 LFM (Linear Feet per Minute). With a 25°C ambient temperature and no airflow, the predicted junction temperature for the LM5574-Q1 is 25 + ((90 × 0.6) = 79°C. If the evaluation board is operated at 0.5A output current, 70V input voltage and high ambient temperature for a prolonged period of time the thermal shutdown protection within the IC can activate. The IC turns off to allow the junction to cool, followed by restart with the soft-start capacitor reset to zero.