JAJSAY1E March   2008  – October 2017 LM2854

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回路
  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 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  Switching Frequency
      2. 7.3.2  Enable
      3. 7.3.3  Soft-Start
      4. 7.3.4  Tracking
      5. 7.3.5  Pre-Biased Start-up Capability
      6. 7.3.6  Feedback Voltage Accuracy
      7. 7.3.7  Positive Current Limit
      8. 7.3.8  Negative Current Limit
      9. 7.3.9  Overtemperature Protection
      10. 7.3.10 Loop Compensation
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Soft-Start and Track Mode
      3. 7.4.3 Normal Operating Mode
  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 Input Filter Capacitor
        2. 8.2.2.2 AVIN Filtering Components
        3. 8.2.2.3 Soft-Start Capacitor
        4. 8.2.2.4 Tracking - Equal Soft-Start Time
        5. 8.2.2.5 Tracking - Equal Slew Rates
        6. 8.2.2.6 Enable and UVLO
        7. 8.2.2.7 Output Voltage Setting
        8. 8.2.2.8 Compensation Component Selection
        9. 8.2.2.9 Filter Inductor and Output Capacitor Selection
      3. 8.2.3 Application Curves
      4. 8.2.4 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 ドキュメントのサポート
      1. 11.1.1 関連資料
    2. 11.2 商標
    3. 11.3 静電気放電に関する注意事項
    4. 11.4 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

7.3.3 Soft-Start

The LM2854 begins to operate when both the AVIN and EN voltages exceed the rising UVLO and enable thresholds, respectively. A controlled soft-start eliminates inrush currents during start-up and allows the user more control and flexibility when sequencing the LM2854 with other power supplies. An external soft-start capacitor is used to control the LM2854 start-up time. During soft-start, the voltage on the feedback pin is connected internally to the non-inverting input of the error amplifier. The soft-start period lasts until the voltage on the soft-start pin exceeds the LM2854 reference voltage of 0.8 V. At this point, the reference voltage takes over at the non-inverting amplifier input.

In the event of either AVIN or EN decreasing below the falling UVLO or enable threshold respectively, the voltage on the soft-start pin is collapsed by discharging the soft-start capacitor through a 5-kΩ transistor to ground.