ZHCSHY7A April   2018  – May 2018 UCC28742

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      简化原理图
      2.      10W、5V 交流/直流转换器的典型效率
  4. 4 修订历史记录
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Detailed Pin Description
        1. 7.3.1.1 VDD (Device Bias Voltage Supply)
        2. 7.3.1.2 GND (Ground)
        3. 7.3.1.3 VS (Voltage-Sense)
        4. 7.3.1.4 DRV (Gate Drive)
        5. 7.3.1.5 CS (Current Sense)
        6. 7.3.1.6 FB (Feedback)
      2. 7.3.2 Secondary-Side Optically Coupled Constant-Voltage (CV) Regulation
      3. 7.3.3 Control Law
      4. 7.3.4 Constant Current Limit and Delayed Shutdown
      5. 7.3.5 Valley-Switching and Valley-Skipping
      6. 7.3.6 Start-Up Operation
      7. 7.3.7 Fault Protection
    4. 7.4 Device Functional Modes
  8. 8 Applications and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Custom Design With WEBENCH® Tools
        2. 8.2.2.2  VDD Capacitance, CDD
        3. 8.2.2.3  VDD Start-Up Resistance, RSTR
        4. 8.2.2.4  Input Bulk Capacitance and Minimum Bulk Voltage
        5. 8.2.2.5  Transformer Turns Ratio, Inductance, Primary-Peak Current
        6. 8.2.2.6  Transformer Parameter Verification
        7. 8.2.2.7  VS Resistor Divider and Line Compensation
        8. 8.2.2.8  Standby Power Estimate
        9. 8.2.2.9  Output Capacitance
        10. 8.2.2.10 Feedback Loop Design Consideration
      3. 8.2.3 Application Curves
    3. 8.3 Do's and Don'ts
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11器件和文档支持
    1. 11.1 器件支持
      1. 11.1.1 开发支持
        1. 11.1.1.1 使用 WEBENCH® 工具创建定制设计
      2. 11.1.2 器件命名规则
        1. 11.1.2.1  电容术语（以法拉为单位）
        2. 11.1.2.2  占空比术语
        3. 11.1.2.3  频率术语（以赫兹为单位）
        4. 11.1.2.4  电流术语（以安培为单位）
        5. 11.1.2.5  电流和电压调节术语
        6. 11.1.2.6  变压器术语
        7. 11.1.2.7  功率术语（以瓦特为单位）
        8. 11.1.2.8  电阻术语（以 Ω 为单位）
        9. 11.1.2.9  时序术语（以秒为单位）
        10. 11.1.2.10 电压术语（以伏特为单位）
        11. 11.1.2.11 交流电压术语（以 VRMS 为单位）
        12. 11.1.2.12 效率术语
    2. 11.2 文档支持
      1. 11.2.1 相关文档
    3. 11.3 接收文档更新通知
    4. 11.4 社区资源
    5. 11.5 商标
    6. 11.6 静电放电警告
    7. 11.7 术语表
  12. 12机械、封装和可订购信息

8.2.2.7 VS Resistor Divider and Line Compensation

The VS divider resistors determine the output voltage regulation point of the flyback converter, also the high-side divider resistor (RS1) determines the line voltage at which the controller enables continuous DRV operation. RS1 is initially determined based on the transformer auxiliary to primary turns-ratio and the desired input voltage operating threshold.

Equation 20. UCC28742 qu20_from_qu19_lusca8.gif

IVSL(run) is VS pin run current with a typical value 210 µA for a design. The low-side VS pin resistor is selected based on desired output over voltage VOV.

Equation 21. UCC28742 qu21_same_as_qu02_slusd71.gif

The UCC28742 can maintain tight output current limit over input line by utilizing the line compensation feature. The line compensation resistor (RLC) value is determined by current flowing in RS1 and expected gate drive and MOSFET turn-off delay. Assume a 50-ns internal delay in the UCC28742.

Equation 22. UCC28742 qu22_from_qu21_lusca8.gif
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