ZHCSJY0B June   2012  – June 2019 LMR12015 , LMR12020

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      典型应用电路
  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 Recommended Operating Ratings
    3. 6.3 Electrical Characteristics
    4. 6.4 Typical Performance Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Boost Function
      2. 7.3.2  Low Input Voltage Considerations
      3. 7.3.3  High Output Voltage Considerations
      4. 7.3.4  Frequency Synchronization
      5. 7.3.5  Current Limit
      6. 7.3.6  Frequency Foldback
      7. 7.3.7  Soft Start
      8. 7.3.8  Output Overvoltage Protection
      9. 7.3.9  Undervoltage Lockout
      10. 7.3.10 Thermal Shutdown
    4. 7.4 Device Operation Modes
      1. 7.4.1 Enable Pin / Shutdown Mode
  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  Inductor Selection
          1. 8.2.1.2.1 Inductor Calculation Example
          2. 8.2.1.2.2 Inductor Material Selection
        3. 8.2.1.3  Input Capacitor
        4. 8.2.1.4  Output Capacitor
        5. 8.2.1.5  Catch Diode
        6. 8.2.1.6  Boost Diode (Optional)
        7. 8.2.1.7  Boost Capacitor
        8. 8.2.1.8  Output Voltage
        9. 8.2.1.9  Feedforward Capacitor (Optional)
        10. 8.2.1.10 Calculating Efficiency and Junction Temperature
          1. 8.2.1.10.1 Schottky Diode Conduction Losses
          2. 8.2.1.10.2 Inductor Conduction Losses
          3. 8.2.1.10.3 MOSFET Conduction Losses
          4. 8.2.1.10.4 MOSFET Switching Losses
          5. 8.2.1.10.5 IC Quiescent Losses
          6. 8.2.1.10.6 MOSFET Driver Losses
          7. 8.2.1.10.7 Total Power Losses
          8. 8.2.1.10.8 Efficiency Calculation Example
          9. 8.2.1.10.9 Calculating the LMR2015/20 Junction Temperature
      2. 8.2.2 Application Curves
      3. 8.2.3 LMR12015/20 Circuit Examples
  9. 9 Layout
    1. 9.1 Layout Considerations
      1. 9.1.1 Compact Layout
      2. 9.1.2 Ground Plane and Shape Routing
      3. 9.1.3 FB Loop
      4. 9.1.4 PCB Summary
  10. 10器件和文档支持
    1. 10.1 器件支持
      1. 10.1.1 第三方米6体育平台手机版_好二三四免责声明
      2. 10.1.2 开发支持
        1. 10.1.2.1 使用 WEBENCH® 工具创建定制设计
    2. 10.2 相关链接
    3. 10.3 接收文档更新通知
    4. 10.4 社区资源
    5. 10.5 商标
    6. 10.6 静电放电警告
    7. 10.7 Glossary
  11. 11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

7.3.1 Boost Function

Capacitor C2 in , commonly referred to as CBOOST, is used to store a voltage VBOOST. When the LMR12015/20 starts up, an internal LDO charges CBOOST, using an internal diode, to a voltage sufficient to turn the internal NMOS switch on. The gate drive voltage supplied to the internal NMOS switch is VBOOST – VSW.

During a normal switching cycle, when the internal NMOS control switch is off (tOFF) (refer to Figure 22), VBOOST equals VLDO minus the forward voltage of the internal diode (VD2). At the same time the inductor current (iL) forward biases the catch diode D1 forcing the SW pin to swing below ground by the forward voltage drop of the catch diode (VD1). Therefore, the voltage stored across CBOOST is

Equation 1. VBOOST – VSW = VLDO – VD2 + VD1

Thus,

Equation 2. VBOOST = VSW + VLDO – VD2 + VD1

When the NMOS switch turns on (tON), the switch pin rises to

Equation 3. VSW = VIN – (RDSON × IL),

reverse biasing D1, and forcing VBOOST to rise. The voltage at VBOOST is then

Equation 4. VBOOST = VIN – (RDSON × IL) + VLDO – VD2 + VD1

which is approximately

Equation 5. VIN + VLDO – 0.4V

VBOOST has pulled itself up by its "bootstraps", or boosted to a higher voltage.

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