ZHCS576I January   2011  – August 2021 LMZ14201H

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 描述
  4. 4 Revision History
  5. 5 Pin Configuration and 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
      1. 7.1.1 COT Control Circuit Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Output Overvoltage Comparator
      2. 7.3.2 Current Limit
      3. 7.3.3 Thermal Protection
      4. 7.3.4 Zero Coil Current Detection
      5. 7.3.5 Prebiased Start-Up
    4. 7.4 Device Functional Modes
      1. 7.4.1 Discontinuous Conduction and Continuous Conduction Modes
  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 Design Steps for the LMZ14201H Application
          1. 8.2.2.1.1 Enable Divider, RENT and RENB Selection
          2. 8.2.2.1.2 Output Voltage Selection
          3. 8.2.2.1.3 Soft-Start Capacitor, CSS, Selection
          4. 8.2.2.1.4 Output Capacitor, CO, Selection
            1. 8.2.2.1.4.1 Capacitance
            2. 8.2.2.1.4.2 ESR
          5. 8.2.2.1.5 Input Capacitor, CIN, Selection
          6. 8.2.2.1.6 ON-Time, RON, Resistor Selection
            1. 8.2.2.1.6.1 Discontinuous Conduction and Continuous Conduction Mode Selection
      3. 8.2.3 Application Curve
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Power Module SMT Guidelines
    2. 10.2 Layout Example
      1. 10.2.1 Power Dissipation and Board Thermal Requirements
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 接收文档更新通知
    3. 11.3 支持资源
    4. 11.4 Trademarks
    5. 11.5 静电放电警告
    6. 11.6 术语表
  12. 12Mechanical, Packaging, and Orderable Information

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
8.2.2.1.3 Soft-Start Capacitor, CSS, Selection

Programmable soft-start permits the regulator to slowly ramp to its steady-state operating point after being enabled, thereby reducing current inrush from the input supply and slowing the output voltage rise-time to prevent overshoot.

Upon turnon, after all UVLO conditions have been passed, an internal 8uA current source begins charging the external soft-start capacitor. The soft-start time duration to reach steady-state operation is given by the formula:

Equation 4. tSS = VREF × CSS / Iss = 0.8 V × CSS / 8 uA

This equation can be rearranged as follows:

Equation 5. CSS = tSS × 8 μA / 0.8 V

Use of a 4700-pF capacitor results in 0.5-ms soft-start duration. This is a recommended value. Note that high values of CSS capacitance will cause more output voltage droop when a load transient goes across the DCM-CCM boundary. Use Equation 18 below to find the DCM-CCM boundary load current for the specific operating condition. If a fast load transient response is desired for steps between DCM and CCM mode the soft-start capacitor value should be less than 0.018 µF.

Note that the following conditions will reset the soft-start capacitor by discharging the SS input to ground with an internal 200-μA current sink:

  • The enable input being “pulled low”
  • Thermal shutdown condition
  • Overcurrent fault
  • Internal VIN UVLO
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