ZHCS547K January   2010  – February 2018 LM27402

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 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 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 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  Wide Input Voltage Range
      2. 7.3.2  UVLO
      3. 7.3.3  Precision Enable
      4. 7.3.4  Soft-Start and Voltage Tracking
      5. 7.3.5  Output Voltage Setpoint and Accuracy
      6. 7.3.6  Voltage-Mode Control
      7. 7.3.7  Power Good
      8. 7.3.8  Inductor-DCR-Based Overcurrent Protection
      9. 7.3.9  Current Sensing
      10. 7.3.10 Power MOSFET Gate Drivers
      11. 7.3.11 Pre-Bias Start-up
    4. 7.4 Device Functional Modes
      1. 7.4.1 Fault Conditions
        1. 7.4.1.1 Thermal Protection
        2. 7.4.1.2 Current Limit
        3. 7.4.1.3 Negative Current Limit
        4. 7.4.1.4 Undervoltage Threshold (UVT)
        5. 7.4.1.5 Overvoltage Threshold (OVT)
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1  Converter Design
      2. 8.1.2  Inductor Selection (L)
      3. 8.1.3  Output Capacitor Selection (COUT)
      4. 8.1.4  Input Capacitor Selection (CIN)
      5. 8.1.5  Using Precision Enable
      6. 8.1.6  Setting the Soft-Start Time
      7. 8.1.7  Tracking
      8. 8.1.8  Setting the Switching Frequency
      9. 8.1.9  Setting the Current Limit Threshold
      10. 8.1.10 Control Loop Compensation
      11. 8.1.11 MOSFET Gate Drivers
      12. 8.1.12 Power Loss and Efficiency Calculations
        1. 8.1.12.1 Power MOSFETs
        2. 8.1.12.2 High-Side Power MOSFET
        3. 8.1.12.3 Low-Side Power MOSFET
        4. 8.1.12.4 Gate-Charge Loss
        5. 8.1.12.5 Input and Output Capacitor ESR Losses
        6. 8.1.12.6 Inductor Losses
        7. 8.1.12.7 Controller Losses
        8. 8.1.12.8 Overall Efficiency
    2. 8.2 Typical Applications
      1. 8.2.1 Example Circuit 1
        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
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Example Circuit 2
      3. 8.2.3 Example Circuit 3
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Power Stage Layout
      2. 10.1.2 Gate Drive Layout
      3. 10.1.3 Controller Layout
      4. 10.1.4 Thermal Design and Layout
    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 开发支持
        1. 11.1.2.1 使用 WEBENCH® 工具创建定制设计
    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 Glossary
  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

8.1.3 Output Capacitor Selection (COUT)

The output capacitor, COUT, filters the inductor ripple current and provides a source of charge for transient load events. A wide range of output capacitors may be used with the LM27402 that provide excellent performance, including ceramic, tantalum, or electrolytic type chemistries. Typically, ceramic capacitors provide extremely low ESR to reduce the output ripple voltage and noise spikes, while tantalum and electrolytic capacitors provide a large bulk capacitance in a small size for transient loading events. When selecting the output capacitance, the two performance characteristics to consider are output voltage ripple and transient response. The output voltage ripple is approximated by Equation 3:

Equation 3. LM27402 30092671.gif

where ΔVOUT is the amount of peak-to-peak voltage ripple at the power supply output, RESR is the equivalent series resistance of the output capacitor, fSW is the switching frequency, and COUT is the output capacitance used in the design. The tolerable output ripple amplitude is application specific; however a general recommendation is to keep the output ripple less than 1% of the rated output voltage. Note that ceramic capacitors are sometimes preferred because they have very low ESR; however, depending on package and voltage rating of the capacitor, the effective in-circuit capacitance can drop significantly with applied voltage and operating temperature.

The output capacitor also affects the output voltage deviation during a load current transient. The peak output voltage deviation is dependent on many factors such as output capacitance, output capacitor ESR, filter inductance, control loop bandwidth, powertrain parasitics, and so on. Given sufficient control loop bandwidth, a good approximation of the output voltage deviation is seen in Equation 4:

Equation 4. LM27402 30092683.gif

ΔVTR is the transient output voltage deviation, ΔIOUT is the load current step change and L is the filter inductance. VL is the minimum inductor voltage, which is duty ratio dependent.

VL = VOUT , if D ≤ 0.5,

VL = VIN - VOUT , if D > 0.5

For a desired ΔVTR, a minimum output capacitance is found by Equation 5:

Equation 5. LM27402 30092684.gif