JAJSEG0 December   2017 LM25576-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.      簡略化されたアプリケーション回路図
  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 Electrical Characteristics
    5. 6.5 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 High Voltage Start-Up Regulator
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown and Stand-by Mode
      2. 7.4.2 Oscillator and Sync Capability
      3. 7.4.3 Error Amplifier and PWM Comparator
      4. 7.4.4 RAMP Generator
      5. 7.4.5 Maximum Duty Cycle and Input Drop-Out Voltage
      6. 7.4.6 Current Limit
      7. 7.4.7 Soft-Start
      8. 7.4.8 Boost Pin
      9. 7.4.9 Thermal Protection
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1  External Components
      2. 8.1.2  R3 (RT)
      3. 8.1.3  L1
      4. 8.1.4  C3 (CRAMP)
      5. 8.1.5  C9, C10
      6. 8.1.6  D1
      7. 8.1.7  C1, C2
      8. 8.1.8  C8
      9. 8.1.9  C7
      10. 8.1.10 C4
      11. 8.1.11 R5, R6
      12. 8.1.12 R1, R2, C12
      13. 8.1.13 R7, C11
      14. 8.1.14 R4, C5, C6
      15. 8.1.15 Bias Power Dissipation Reduction
    2. 8.2 Typical Application
      1. 8.2.1 Typical Schematic for High Frequency (1 MHz) Application
      2. 8.2.2 Typical Schematic for Buck and Boost (Inverting) Application
  9. 9 Layout
    1. 9.1 Layout Guidelines
      1. 9.1.1 PCB Layout and Thermal Considerations
    2. 9.2 Layout Example
  10. 10デバイスおよびドキュメントのサポート
    1. 10.1 デバイス・サポート
      1. 10.1.1 開発サポート
        1. 10.1.1.1 WEBENCH®ツールによるカスタム設計
    2. 10.2 ドキュメントの更新通知を受け取る方法
    3. 10.3 コミュニティ・リソース
    4. 10.4 商標
    5. 10.5 静電気放電に関する注意事項
    6. 10.6 Glossary
  11. 11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

7.3.1 High Voltage Start-Up Regulator

The LM25576-Q1 contains a dual-mode internal high voltage startup regulator that provides the VCC bias supply for the PWM controller and boot-strap MOSFET gate driver. The input pin (VIN) can be connected directly to the input voltage, as high as 42 Volts. For input voltages below 9 V, a low dropout switch connects VCC directly to VIN. In this supply range, VCC is approximately equal to VIN. For VIN voltage greater than 9 V, the low dropout switch is disabled and the VCC regulator is enabled to maintain VCC at approximately 7 V. The wide operating range of 6 V to 42 V is achieved through the use of this dual mode regulator.

The output of the VCC regulator is current limited to 25 mA. Upon power up, the regulator sources current into the capacitor connected to the VCC pin. When the voltage at the VCC pin exceeds the VCC UVLO threshold of 5.35 V and the SD pin is greater than 1.225 V, the output switch is enabled and a soft-start sequence begins. The output switch remains enabled until VCC falls below 5 V or the SD pin falls below 1.125 V.

An auxiliary supply voltage can be applied to the VCC pin to reduce the IC power dissipation. If the auxiliary voltage is greater than 7.3 V, the internal regulator will essentially shut off, reducing the IC power dissipation. The VCC regulator series pass transistor includes a diode between VCC and VIN that should not be forward biased in normal operation. Therefore the auxiliary VCC voltage should never exceed the VIN voltage.

In high voltage applications extra care should be taken to ensure the VIN pin does not exceed the absolute maximum voltage rating of 45 V. During line or load transients, voltage ringing on the VIN line that exceeds the Absolute Maximum Ratings can damage the IC. Both careful PC board layout and the use of quality bypass capacitors located close to the VIN and GND pins are essential.

LM25576-Q1 20208704.gifFigure 8. VIN and VCC Sequencing