JAJSHG3 May   2018 LM3102-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.      代表的なアプリケーションの回路図
      2.      効率と負荷電流との関係(VOUT＝3.3V)
  4. 4 改訂履歴
  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 Switching Characteristics
    7. 6.7 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  COT Control Circuit Overview
      2. 7.3.2  Start-Up Regulator (VCC)
      3. 7.3.3  Regulation Comparator
      4. 7.3.4  Zero Coil Current Detect
      5. 7.3.5  Overvoltage Comparator
      6. 7.3.6  Current Limit
      7. 7.3.7  N-Channel MOSFET and Driver
      8. 7.3.8  Soft Start
      9. 7.3.9  Thermal Protection
      10. 7.3.10 Thermal Derating
    4. 7.4 Device Functional Modes
      1. 7.4.1 ON-Time Timer, Shutdown
  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 Custom Design With WEBENCH® Tools
        2. 8.2.2.2 Design Steps for the LM3102-Q1 Application
        3. 8.2.2.3 External Components
      3. 8.2.3 Application Curve
    3. 8.3 System Examples
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11デバイスおよびドキュメントのサポート
    1. 11.1 デバイス・サポート
      1. 11.1.1 開発サポート
        1. 11.1.1.1 WEBENCH®ツールによるカスタム設計
    2. 11.2 ドキュメントの更新通知を受け取る方法
    3. 11.3 コミュニティ・リソース
    4. 11.4 商標
    5. 11.5 静電気放電に関する注意事項
    6. 11.6 Glossary
  12. 12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

7.3.6 Current Limit

Current limit detection is carried out during the OFF-time by monitoring the re-circulating current through the synchronous MOSFET. Referring to the Functional Block Diagram, when the main MOSFET is turned off, the inductor current flows through the load, the PGND pin and the internal synchronous MOSFET. If this current exceeds 2.7 A, the current limit comparator toggles, and as a result disabling the start of the next ON-time period. The next switching cycle starts when the re-circulating current falls back below 2.7 A (and the voltage at the FB pin is below 0.8 V). The inductor current is monitored during the ON-time of the synchronous MOSFET. As long as the inductor current exceeds 2.7 A, the main MOSFET will remain inhibited to achieve current limit. The operating frequency is lower during current limit due to a longer OFF-time.

Figure 19 illustrates an inductor current waveform. On average, the output current IOUT is the same as the inductor current IL, which is the average of the rippled inductor current. In case of current limit (the current limit portion of Figure 19), the next ON-time will not initiate until that the current drops below 2.7 A (assume the voltage at the FB pin is lower than 0.8 V). During each ON-time the current ramps up an amount equal to:

Equation 4. LM3102-Q1 30021338.gif

During current limit, the LM3102-Q1 operates in a constant current mode with an average output current IOUT(CL) equal to 2.7 A + ILR / 2.

LM3102-Q1 30021326.pngFigure 19. Inductor Current - Current Limit Operation