ZHCSL47A April   2020  – January 2021 LM5181

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and 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  Integrated Power MOSFET
      2. 8.3.2  PSR Flyback Modes of Operation
      3. 8.3.3  Setting the Output Voltage
        1. 8.3.3.1 Diode Thermal Compensation
      4. 8.3.4  Control Loop Error Amplifier
      5. 8.3.5  Precision Enable
      6. 8.3.6  Configurable Soft Start
      7. 8.3.7  External Bias Supply
      8. 8.3.8  Minimum On-Time and Off-Time
      9. 8.3.9  Overcurrent Protection
      10. 8.3.10 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Standby Mode
      3. 8.4.3 Active Mode
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Design 1: Wide VIN, Low IQ PSR Flyback Converter Rated at 5 V, 0.5 A
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1  Custom Design With WEBENCH® Tools
          2. 9.2.1.2.2  Custom Design With Excel Quickstart Tool
          3. 9.2.1.2.3  Flyback Transformer – T1
          4. 9.2.1.2.4  Flyback Diode – DFLY
          5. 9.2.1.2.5  Zener Clamp Circuit – DF, DCLAMP
          6. 9.2.1.2.6  Output Capacitor – COUT
          7. 9.2.1.2.7  Input Capacitor – CIN
          8. 9.2.1.2.8  Feedback Resistor – RFB
          9. 9.2.1.2.9  Thermal Compensation Resistor – RTC
          10. 9.2.1.2.10 UVLO Resistors – RUV1, RUV2
          11. 9.2.1.2.11 Soft-Start Capacitor – CSS
      2. 9.2.2 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Examples
  12. 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
    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
  13. 13Mechanical, Packaging, and Orderable Information

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机械数据 (封装 | 引脚)
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8.3.9 Overcurrent Protection

In case of an overcurrent condition on the isolated output or outputs, the output voltage drops lower than the regulation level since the maximum power delivered is limited by the peak current capability on the primary side. The peak primary current is maintained at 0.75 A (plus an amount related to the 100-ns propagation delay of the current limit comparator) until the output decreases to the secondary diode voltage drop to impact the reflected signal on the primary side. At this point, the LM5181 assumes the output cannot be recovered and re-calibrates its switching frequency to 9 kHz until the overload condition is removed. The LM5181 responds with similar behavior to an output short circuit condition.

For a given input voltage, Equation 13 gives the maximum output current prior to the engagement of overcurrent protection, where η is the efficiency. The typical threshold value for ISW-PEAK from Section 7 is 0.75 A.

Equation 13. GUID-1EA01C0B-57DF-499B-A249-18198371D988-low.gif

A failsafe current limit set at 1.2 A, or 1.6 times the nominal peak current limit, provides redundant fault protection in case of transformer short circuit or saturation effects. This initiates a 7.5-ms hiccup interval after eight overcurrent events.