ZHCSIJ1E June   1999  – July 2018 LM2574 , LM2574HV

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      典型应用（固定输出电压版本）
  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 for All Output Voltage Versions
    6. 6.6  Electrical Characteristics – 3.3-V Version
    7. 6.7  Electrical Characteristics – 5-V Version
    8. 6.8  Electrical Characteristics – 12-V Version
    9. 6.9  Electrical Characteristics – 15-V Version
    10. 6.10 Electrical Characteristics – Adjustable Version
    11. 6.11 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 Current Limit
      2. 7.3.2 Undervoltage Lockout
      3. 7.3.3 Delayed Start-Up
      4. 7.3.4 Adjustable Output, Low-Ripple Power Supply
    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
      1. 8.1.1 Input Capacitor (CIN)
      2. 8.1.2 Inductor Selection
      3. 8.1.3 Inductor Ripple Current
      4. 8.1.4 Output Capacitor
      5. 8.1.5 Catch Diode
      6. 8.1.6 Output Voltage Ripple and Transients
      7. 8.1.7 Feedback Connection
      8. 8.1.8 ON/OFF Input
      9. 8.1.9 Additional Applications
        1. 8.1.9.1 Inverting Regulator
        2. 8.1.9.2 Negative Boost Regulator
    2. 8.2 Typical Applications
      1. 8.2.1 Fixed Output Voltage Applications
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Custom Design With WEBENCH® Tools
          2. 8.2.1.2.2 Inductor Selection (L1)
          3. 8.2.1.2.3 Output Capacitor Selection (COUT)
          4. 8.2.1.2.4 Catch Diode Selection (D1)
          5. 8.2.1.2.5 Input Capacitor (CIN)
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Adjustable Output Voltage Applications
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Programming Output Voltage
          2. 8.2.2.2.2 Inductor Selection (L1)
          3. 8.2.2.2.3 Output Capacitor Selection (COUT)
          4. 8.2.2.2.4 Catch Diode Selection (D1)
          5. 8.2.2.2.5 Input Capacitor (CIN)
        3. 8.2.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Grounding
    4. 10.4 Thermal Considerations
  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 器件命名规则
        1. 11.1.3.1  降压稳压器
        2. 11.1.3.2  降压/升压稳压器
        3. 11.1.3.3  占空比 (D)
        4. 11.1.3.4  环流二极管或导流二极管
        5. 11.1.3.5  电容器等效串联电阻 (ESR)
        6. 11.1.3.6  等效串联电感 (ESL)
        7. 11.1.3.7  输出纹波电压
        8. 11.1.3.8  电容器纹波电流
        9. 11.1.3.9  待机静态电流 (ISTBY)
        10. 11.1.3.10 电感器纹波电流 (ΔiIND)
        11. 11.1.3.11 连续与非连续模式运行
        12. 11.1.3.12 电感器饱和
        13. 11.1.3.13 运算伏特微秒常数 (E × Top)
    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

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

8.1.4 Output Capacitor

An output capacitor is required to filter the output voltage and is needed for loop stability. The capacitor must be located near the LM2574 using short PCB traces. Standard aluminum electrolytics are usually adequate, but low ESR types are recommended for low output ripple voltage and good stability. The ESR of a capacitor depends on many factors, some which are: the value, the voltage rating, physical size, and the type of construction. In general, low-value or low-voltage (less than 12 V) electrolytic capacitors usually have higher ESR numbers.

The amount of output ripple voltage is primarily a function of the equivalent series resistance (ESR ) of the output capacitor and the amplitude of the inductor ripple current, ΔIIND (see 电感器纹波电流 (ΔiIND)).

The lower capacitor values (100 μF to 330 μF) allows typically 50 mV to 150 mV of output ripple voltage, while larger-value capacitors reduce the ripple to approximately 20 mV to 50 mV (as seen in Equation 5).

Equation 5. Output Ripple Voltage = (ΔIIND) (ESR of COUT)

To further reduce the output ripple voltage, several standard electrolytic capacitors may be paralleled, or a higher-grade capacitor may be used. Such capacitors are often called high-frequency, low-inductance, or low-ESR. These reduce the output ripple to 10 mV or 20 mV. However, when operating in the continuous mode, reducing the ESR below 0.03 Ω can cause instability in the regulator.

Tantalum capacitors can have a very low ESR, and must be carefully evaluated if it is the only output capacitor. Because of their good low temperature characteristics, a tantalum can be used in parallel with aluminum electrolytics, with the tantalum making up 10% or 20% of the total capacitance.

The ripple current rating of the capacitor at 52 kHz must be at least 50% higher than the peak-to-peak inductor ripple current.