ZHCSH82 December   2017 LM25574-Q1

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      简化应用电路原理图
  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 High Voltage Start-Up Regulator
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown and Stand-by Mode
      2. 7.4.2 Oscillator and Sync Capability
      3. 7.4.3 Error Amplifier and PWM Comparator
      4. 7.4.4 Ramp Generator
      5. 7.4.5 Maximum Duty Cycle and Input Drop-out Voltage
      6. 7.4.6 Current Limit
      7. 7.4.7 Soft-Start
      8. 7.4.8 Boost Pin
      9. 7.4.9 Thermal Protection
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1  External Components
      2. 8.1.2  R3 (RT)
      3. 8.1.3  L1
      4. 8.1.4  C3 (CRAMP)
      5. 8.1.5  C9
      6. 8.1.6  C1
      7. 8.1.7  C8
      8. 8.1.8  C7
      9. 8.1.9  C4
      10. 8.1.10 R5, R6
      11. 8.1.11 R1, R2, C2
      12. 8.1.12 R4, C5, C6
      13. 8.1.13 Bias Power Dissipation Reduction
    2. 8.2 Typical Application
      1. 8.2.1 Typical Schematic for High Frequency (1 MHz) Application
  9. 9 Layout
    1. 9.1 Layout Guidelines
      1. 9.1.1 PCB Layout and Thermal Considerations
    2. 9.2 Layout Example
  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
  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

8.1.13 Bias Power Dissipation Reduction

Buck regulators operating with high input voltage can dissipate an appreciable amount of power for the bias of the IC. The VCC regulator must step-down the input voltage VIN to a nominal VCC level of 7 V. The large voltage drop across the VCC regulator translates into a large power dissipation within the VCC regulator. There are several techniques that can significantly reduce this bias regulator power dissipation. Figure 18 and Figure 19 depict two methods to bias the IC from the output voltage. In each case the internal VCC regulator is used to initially bias the VCC pin. After the output voltage is established, the VCC pin potential is raised above the nominal 7 V regulation level, which effectively disables the internal VCC regulator. The voltage applied to the VCC pin should never exceed 14 V. The VCC voltage should never be larger than the VIN voltage.

LM25574-Q1 2256012.gifFigure 18. VCC Bias from VOUT for 8 V < VOUT < 14 V
LM25574-Q1 3130551.gifFigure 19. VCC Bias with Additional Winding on the Output Inductor