ZHCSA01H October   2011  – June 2019 LMR24210

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      典型应用
  4. 4 修订历史记录
  5. 5 Pin Configuration and Functions
    1.     Pin Descriptions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Ratings
    4. 6.4 Electrical Characteristics
    5. 6.5 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  COT Control Circuit Overview
      2. 7.3.2  Start-up Regulator (VCC)
      3. 7.3.3  Regulation Comparator
      4. 7.3.4  Zero Coil Current Detect
      5. 7.3.5  Overvoltage Comparator
      6. 7.3.6  On-Time Timer, Shutdown
      7. 7.3.7  Current Limit
      8. 7.3.8  N-Channel Mosfet and Driver
      9. 7.3.9  Soft Start
      10. 7.3.10 Thermal Protection
      11. 7.3.11 Thermal Derating
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Detailed Design Procedure
        1. 8.2.1.1 Custom Design With WEBENCH® Tools
        2. 8.2.1.2 External Components
      2. 8.2.2 Application Curve
  9. 9 Layout
    1. 9.1 Layout Considerations
    2. 9.2 Layout Examples
    3. 9.3 Package Considerations
  10. 10器件和文档支持
    1. 10.1 器件支持
      1. 10.1.1 开发支持
        1. 10.1.1.1 使用 WEBENCH® 工具创建定制设计
    2. 10.2 接收文档更新通知
    3. 10.3 社区资源
    4. 10.4 商标
    5. 10.5 静电放电警告
    6. 10.6 Glossary

封装选项

机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息

7.3.7 Current Limit

Current limit detection is carried out during the off-time by monitoring the re-circulating current through the synchronous MOSFET. Referring to the Functional Block Diagram, when the main MOSFET is turned off, the inductor current flows through the load, the PGND pin and the internal synchronous MOSFET. If this current exceeds 1.8 A, the current limit comparator toggles, and as a result disabling the start of the next on-time period. The next switching cycle starts when the re-circulating current falls back below 1.8 A (and the voltage at the FB pin is below 0.8 V). The inductor current is monitored during the on-time of the synchronous MOSFET. As long as the inductor current exceeds 1.8 A, the main MOSFET remains inhibited to achieve current limit. The operating frequency is lower during current limit due to a longer off-time.

Figure 18 illustrates an inductor current waveform. On average, the output current IOUT is the same as the inductor current IL, which is the average of the rippled inductor current. In case of current limit (the current limit portion of Figure 18), the next on-time will not initiate until the current drops below 1.8A (assume the voltage at the FB pin is lower than 0.8 V). During each on-time the current ramps up an amount equal to:

Equation 6. LMR24210 30173838.gif

During current limit, the LMR24210 operates in a constant current mode with an average output current IOUT(CL) equal to 1.8 A + ILR / 2.

LMR24210 30173826.pngFigure 18. Inductor Current - Current Limit Operation