ZHCSOB0A july   2021  – august 2023 LM5157

PRODUCTION DATA  

  1.   1
  2. 1 特性
  3. 2 应用
  4. 3 说明
  5. 4 Revision History
  6. 5 Device Comparison Table
  7. 6 Pin Configuration and Functions
  8. 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
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Line Undervoltage Lockout (UVLO/SYNC/EN Pin)
      2. 8.3.2  High Voltage VCC Regulator (BIAS, VCC Pin)
      3. 8.3.3  Soft Start (SS Pin)
      4. 8.3.4  Switching Frequency (RT Pin)
      5. 8.3.5  Dual Random Spread Spectrum – DRSS (MODE Pin)
      6. 8.3.6  Clock Synchronization (UVLO/SYNC/EN Pin)
      7. 8.3.7  Current Sense and Slope Compensation
      8. 8.3.8  Current Limit and Minimum On Time
      9. 8.3.9  Feedback and Error Amplifier (FB, COMP Pin)
      10. 8.3.10 Power-Good Indicator (PGOOD Pin)
      11. 8.3.11 Hiccup Mode Overload Protection (MODE Pin)
      12. 8.3.12 Maximum Duty Cycle Limit and Minimum Input Supply Voltage
      13. 8.3.13 Internal MOSFET (SW Pin)
      14. 8.3.14 Overvoltage Protection (OVP)
      15. 8.3.15 Thermal Shutdown (TSD)
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Standby Mode
      3. 8.4.3 Run Mode
        1. 8.4.3.1 Spread Spectrum Enabled
        2. 8.4.3.2 Hiccup Mode Protection Enabled
  10. 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 Custom Design With WEBENCH® Tools
        2. 9.2.2.2 Recommended Components
        3. 9.2.2.3 Inductor Selection (LM)
        4. 9.2.2.4 Output Capacitor (COUT)
        5. 9.2.2.5 Input Capacitor
        6. 9.2.2.6 Diode Selection
      3. 9.2.3 Application Curve
    3. 9.3 System Examples
  11. 10Power Supply Recommendations
  12. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Examples
  13. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 第三方产品免责声明
      2. 12.1.2 Development Support
        1. 12.1.2.1 Custom Design With WEBENCH® Tools
      3. 12.1.3 Export Control Notice
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 接收文档更新通知
    4. 12.4 支持资源
    5. 12.5 Trademarks
    6. 12.6 静电放电警告
    7. 12.7 术语表
  14. 13Mechanical, Packaging, and Orderable Information

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9.2.2.3 Inductor Selection (LM)

When selecting the inductor, consider three key parameters: inductor current ripple ratio (RR), falling slope of the inductor current, and RHP zero frequency (fRHP).

Inductor current ripple ratio is selected to have a balance between core loss and copper loss. The falling slope of the inductor current must be low enough to prevent subharmonic oscillation at high duty cycle (additional RSL resistor is required if not). Higher fRHP (lower inductance) allows a higher crossover frequency and is always preferred when using a small value output capacitor.

The inductance value can be selected to set the inductor current ripple between 30% and 70% of the average inductor current as a good compromise between RR, FRHP, and inductor falling slope.