JAJSEQ5A August   2017  – February 2018 UCC24612

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
    1.     Device Images
      1.      ハイサイドSRによるフライバック
      2.      ローサイドSRによるフライバック
  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 Timing Requirements
    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 Power Management
      2. 7.3.2 Synchronous Rectifier Control
      3. 7.3.3 Adaptive Blanking Time
        1. 7.3.3.1 Turn-On Blanking Timer (Minimum On Time)
        2. 7.3.3.2 Turn-Off Blanking Timer
        3. 7.3.3.3 SR Turn-on Re-arm
      4. 7.3.4 Gate Voltage Clamping
      5. 7.3.5 Standby Mode
    4. 7.4 Device Functional Modes
      1. 7.4.1 UVLO Mode
      2. 7.4.2 Standby Mode
      3. 7.4.3 Run 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 SR MOSFET Selection
        2. 8.2.2.2 Bypass Capacitor Selection
        3. 8.2.2.3 Snubber design
        4. 8.2.2.4 High-Side Operation
      3. 8.2.3 Application Curves
        1. 8.2.3.1 Steady State Testing Low-Side Configuration
        2. 8.2.3.2 Steady State Testing High-Side Configuration
  9. 9 Power Supply Recommendations
  10. 10PCB Layout
    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 コミュニティ・リソース
    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

8.2.2.1 SR MOSFET Selection

UCC24612 can be paired with an appropriate MOSFET to replace the diode rectifier on existing designs and demonstrate significant conduction loss reduction. The SR MOSFET selection should consider the tradeoff between cost and performance. Lower on-state resistance gives lower conduction loss, while it reduces the efficiency at light load. Due to the unique implementation of proportional gate drive, the benefit of lower on-state resistance is diminished. It is recommended to select the MOSFET on-state resistance so that the proportional gate drive operates for less than 50% of the full load SR conduction time.

According to UCC28740 datasheet, for 3-A output DCM Flyback design, the secondary side peak current should be about 14 A. To allow the proportional gate drive operating less than 50% of the SR conduction time, SR MOSFET Rdson should be more than 7 mΩ , according to .

Equation 1. UCC24612 Rdson_select.gif

The MOSFET breakdown voltage should be higher than the maximum voltage the SR MOSFET sees under maximum input voltage. For this design, the transformer turns ratio is 3.5, the voltage stress on the SR can be calculated as in Equation 2.

Equation 2. UCC24612 SR_voltagerating.gif

In this EVM, a 150-V, 19-mΩ MOSFET is used to get a balance between the cost and performance.