ZHCSIX0H March   2009  – October 2018 LM5008A

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      典型应用，基本降压稳压器
  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 Switching Characteristics
    7. 6.7 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 Control Circuit Overview
      2. 7.3.2 Start-Up Regulator (VCC)
      3. 7.3.3 Regulation Comparator
      4. 7.3.4 Overvoltage Comparator
      5. 7.3.5 On-Time Generator and Shutdown
      6. 7.3.6 Current Limit
      7. 7.3.7 N-Channel Buck Switch and Driver
      8. 7.3.8 Thermal Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
  8. 8 Application 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 Selection Of External Components
        3. 8.2.2.3 Low-Output Ripple Configurations
      3. 8.2.3 Application Curves
  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 第三方产品免责声明
      2. 11.1.2 使用 WEBENCH® 工具创建定制设计
      3. 11.1.3 开发支持
    2. 11.2 文档支持
      1. 11.2.1 相关文档
        1. 11.2.1.1 PCB 布局资源
        2. 11.2.1.2 热设计资源
    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

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

7.3.6 Current Limit

The LM5008A contains an intelligent current limit OFF timer. If the current in the Buck switch exceeds 0.51 A the present cycle is immediately terminated and a non-resetable OFF timer is initiated. The length of off-time is controlled by an external resistor (RCL) and the FB voltage (see Figure 4). When FB = 0 V, a maximum off-time is required, and the time is preset to 35 µs. This condition occurs when the output is shorted and during the initial part of start-up. This amount of time ensures safe short-circuit operation up to the maximum input voltage of 95 V. In cases of overload where the FB voltage is above zero volts (not a short circuit), the current limit off-time is less than 35 µs. Reducing the off-time during less severe overloads reduces the amount of foldback, recovery time, and the start-up time. The off-time is calculated from Equation 5.

Equation 5. LM5008A 30074929.gif

The current limit-sensing circuit is blanked for the first 50 ns to 70 ns of each on-time, so it is not falsely tripped by the current surge which occurs at turnon. The current surge is required by the re-circulating diode (D1) for its turnoff recovery.