JAJSFY4C August   2018  – October 2019 LMR36015-Q1

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
    1.     Device Images
      1.      概略回路図
  4. 4 改訂履歴
  5. 5 概要（続き）
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
    1.     Pin Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Timing Requirements
    7. 8.7 System Characteristics
    8. 8.8 Typical Characteristics
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Power-Good Flag Output
      2. 9.3.2 Enable and Start-up
      3. 9.3.3 Current Limit and Short Circuit
      4. 9.3.4 Undervoltage Lockout and Thermal Shutdown
    4. 9.4 Device Functional Modes
      1. 9.4.1 Auto Mode
      2. 9.4.2 Forced PWM Operation
      3. 9.4.3 Dropout
      4. 9.4.4 Minimum Switch On-Time
      5. 9.4.5 Spread Spectrum Operation
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design 1: Low Power 24-V, 1.5-A PFM Converter
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
          1. 10.2.1.2.1  Custom Design With WEBENCH Tools
          2. 10.2.1.2.2  Choosing the Switching Frequency
          3. 10.2.1.2.3  Setting the Output Voltage
            1. 10.2.1.2.3.1 FB for Adjustable Output
          4. 10.2.1.2.4  Inductor Selection
          5. 10.2.1.2.5  Output Capacitor Selection
          6. 10.2.1.2.6  Input Capacitor Selection
          7. 10.2.1.2.7  CBOOT
          8. 10.2.1.2.8  VCC
          9. 10.2.1.2.9  CFF Selection
            1. 10.2.1.2.9.1 External UVLO
          10. 10.2.1.2.10 Maximum Ambient Temperature
      2. 10.2.2 Application Curves
      3. 10.2.3 Design 2: High Density 12-V, 1.5-A FPWM Converter
        1. 10.2.3.1 Design Requirements
        2. 10.2.3.2 Detailed Design Procedure
        3. 10.2.3.3 Application Curves
    3. 10.3 What to Do and What Not to Do
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Ground and Thermal Considerations
    2. 12.2 Layout Example
  13. 13デバイスおよびドキュメントのサポート
    1. 13.1 デバイス・サポート
      1. 13.1.1 開発サポート
        1. 13.1.1.1 WEBENCH®ツールによるカスタム設計
    2. 13.2 ドキュメントのサポート
      1. 13.2.1 関連資料
    3. 13.3 ドキュメントの更新通知を受け取る方法
    4. 13.4 サポート・リソース
    5. 13.5 商標
    6. 13.6 静電気放電に関する注意事項
    7. 13.7 Glossary
  14. 14メカニカル、パッケージ、および注文情報

9.4.4 Minimum Switch On-Time

Every switching regulator has a minimum controllable on-time dictated by the inherent delays and blanking times associated with the control circuits. This imposes a minimum switch duty cycle and therefore a minimum conversion ratio. The constraint is encountered at high input voltages and low output voltages. To help extend the minimum controllable duty cycle, the LMR36015-Q1 automatically reduces the switching frequency when the minimum on-time limit is reached. In this way the converter can regulate the lowest programmable output voltage at the maximum input voltage. An estimate for the approximate input voltage, for a given output voltage, before frequency foldback occurs is found in Equation 2. As the input voltage is increased, the switch on-time (duty cycle) reduces to regulate the output voltage. When the on-time reaches the limit, the switching frequency drops, while the on-time remains fixed.

Equation 2. LMR36015-Q1 Ton_eq2.gif
LMR36015-Q1 Frequenc-Foldback.gifFigure 17. Switching Frequency vs Input Voltage
VOUT = 5 V