JAJSA67I April   2004  – February 2019 LM2743

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
    1.     Device Images
      1.      代表的なアプリケーションの図
  4. 4 改訂履歴
  5. 5 概要（続き）
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Start Up and Soft-Start
      2. 8.3.2  Normal Operation
      3. 8.3.3  Tracking a Voltage Level
      4. 8.3.4  Tracking Voltage Slew Rate
      5. 8.3.5  Sequencing
      6. 8.3.6  SD Pin Impedance
      7. 8.3.7  MOSFET Gate Drivers
      8. 8.3.8  Power Good Signal
      9. 8.3.9  UVLO
      10. 8.3.10 Current Limit
      11. 8.3.11 Foldback Current Limit
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Synchronous Buck Converter Typical Application using LM2743
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Custom Design With WEBENCH® Tools
          2. 9.2.1.2.2 Duty Cycle Calculation
          3. 9.2.1.2.3 Input Capacitor
          4. 9.2.1.2.4 Output Inductor
          5. 9.2.1.2.5 Output Capacitor
          6. 9.2.1.2.6 MOSFETs
          7. 9.2.1.2.7 Support Components
          8. 9.2.1.2.8 Control Loop Compensation
          9. 9.2.1.2.9 Efficiency Calculations
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Example Circuit 1
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
        3. 9.2.2.3 Bill of Materials
      3. 9.2.3 Example Circuit 2
        1. 9.2.3.1 Design Requirements
        2. 9.2.3.2 Detailed Design Procedure
        3. 9.2.3.3 Bill of Materials
      4. 9.2.4 Example Circuit 3
        1. 9.2.4.1 Design Requirements
        2. 9.2.4.2 Detailed Design Procedure
        3. 9.2.4.3 Bill of Materials
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12デバイスおよびドキュメントのサポート
    1. 12.1 デバイス・サポート
      1. 12.1.1 開発サポート
        1. 12.1.1.1 WEBENCH®ツールによるカスタム設計
    2. 12.2 ドキュメントの更新通知を受け取る方法
    3. 12.3 コミュニティ・リソース
    4. 12.4 商標
    5. 12.5 静電気放電に関する注意事項
    6. 12.6 Glossary
  13. 13メカニカル、パッケージ、および注文情報

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

9.2.1.2.4 Output Inductor

The output inductor forms the first half of the power stage in a Buck converter. It is responsible for smoothing the square wave created by the switching action and for controlling the output current ripple (ΔIOUT). The inductance is chosen by selecting between tradeoffs in efficiency and response time. The smaller the output inductor, the more quickly the converter can respond to transients in the load current. However, as shown in the efficiency calculations, a smaller inductor requires a higher switching frequency to maintain the same level of output current ripple. An increase in frequency can mean increasing loss in the MOSFETs due to the charging and discharging of the gates. Generally the switching frequency is chosen so that conduction loss outweighs switching loss. The equation for output inductor selection is:

Equation 21. LM2743 20095223.gif
Equation 22. LM2743 20095224.gif
Equation 23. L = 1.6 µH

 

Here we have plugged in the values for output current ripple, input voltage, output voltage, switching frequency, and assumed a 40% peak-to-peak output current ripple. This yields an inductance of 1.6 µH. The output inductor must be rated to handle the peak current (also equal to the peak switch current), which is (IOUT + (0.5 x ΔIOUT)) = 4.8 A, for a 4 A design. The Coilcraft DO3316P-222P is 2.2 µH, is rated to 7.4-A peak, and has a direct current resistance (DCR) of 12 mΩ.

After selecting an output inductor, inductor current ripple should be re-calculated with the new inductance value, as this information is needed to select the output capacitor. Re-arranging the equation used to select inductance yields the following:

Equation 24. LM2743 20095262.gif

VIN(MAX) is assumed to be 10% above the steady state input voltage, or 3.6V. The actual current ripple will then be 1.2A. Peak inductor/switch current will be 4.6A.