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

7.2.2.7 D1 - Async Diode

A Schottky type re-circulating diode is required for all LM5574-Q1 applications. Ultra-fast diodes are not recommended and can result in damage to the IC due to reverse recovery current transients. The near excellent choice reverse recovery characteristics and low forward voltage drop are particularly important diode characteristics for high input voltage and low output voltage applications common to the LM5574-Q1. The reverse recovery characteristic determines how long the current surge lasts each cycle when the buck switch is turned on. The reverse recovery characteristics of Schottky diodes minimize the peak instantaneous power in the buck switch occurring during turn-on each cycle. The resulting switching losses of the buck switch are significantly reduced when using a Schottky diode. The reverse breakdown rating must be selected for the maximum VIN, plus some safety margin.

The forward voltage drop has a significant impact on the conversion efficiency, especially for applications with a low output voltage. Rated current for diodes vary widely from various manufacturers. The worst case is to assume a short-circuit load condition. In this case the diode carries the output current almost continuously. For the LM5574-Q1, this current can be as high as 0.7A. Assuming a worst case, 1V drop across the diode, the maximum diode power dissipation can be as high as 0.7W. For the reference design, a 100V Schottky in a SMA package was selected.