JAJSK02 October   2020 TPS23731

PRODUCTION DATA  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and 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: DC-DC Controller Section
    6. 7.6 Electrical Characteristics PoE
    7.     14
    8. 7.7 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  CLS Classification
      2. 8.3.2  DEN Detection and Enable
      3. 8.3.3  APD Auxiliary Power Detect
      4. 8.3.4  Internal Pass MOSFET
      5. 8.3.5  T2P and APDO Indicators
      6. 8.3.6  DC-DC Controller Features
        1. 8.3.6.1 VCC, VB, VBG and Advanced PWM Startup
        2.       27
        3. 8.3.6.2 CS, Current Slope Compensation and blanking
        4. 8.3.6.3 COMP, FB, EA_DIS, CP, PSRS and Opto-less Feedback
        5. 8.3.6.4 FRS Frequency Setting and Synchronization
        6. 8.3.6.5 DTHR and Frequency Dithering for Spread Spectrum Applications
        7. 8.3.6.6 SST and Soft-Start of the Switcher
        8. 8.3.6.7 SST, I_STP, LINEUV and Soft-Stop of the Switcher
      7. 8.3.7  Switching FET Driver - GATE
      8. 8.3.8  EMPS and Automatic MPS
      9. 8.3.9  VDD Supply Voltage
      10. 8.3.10 RTN, AGND, GND
      11. 8.3.11 VSS
      12. 8.3.12 Exposed Thermal pads - PAD_G and PAD_S
    4. 8.4 Device Functional Modes
      1. 8.4.1  PoE Overview
      2. 8.4.2  Threshold Voltages
      3. 8.4.3  PoE Start-Up Sequence
      4. 8.4.4  Detection
      5. 8.4.5  Hardware Classification
      6. 8.4.6  Maintain Power Signature (MPS)
      7. 8.4.7  Advanced Start-Up and Converter Operation
      8. 8.4.8  Line Undervoltage Protection and Converter Operation
      9. 8.4.9  PD Self-Protection
      10. 8.4.10 Thermal Shutdown - DC-DC Controller
      11. 8.4.11 Adapter ORing
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
        1. 9.2.1.1 Detailed Design Procedure
          1. 9.2.1.1.1  Input Bridges and Schottky Diodes
          2. 9.2.1.1.2  Input TVS Protection
          3. 9.2.1.1.3  Input Bypass Capacitor
          4. 9.2.1.1.4  Detection Resistor, RDEN
          5. 9.2.1.1.5  Classification Resistor, RCLS.
          6. 9.2.1.1.6  APD Pin Divider Network, RAPD1, RAPD2
          7. 9.2.1.1.7  Setting Frequency (RFRS) and Synchronization
          8. 9.2.1.1.8  Bias Supply Requirements and CVCC
          9. 9.2.1.1.9  APDO, T2P Interface
          10. 9.2.1.1.10 Output Voltage Feedback Divider, RAUX, R1,R2
          11. 9.2.1.1.11 Frequency Dithering for Conducted Emissions Control
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 EMI Containment
    4. 11.4 Thermal Considerations and OTSD
    5. 11.5 ESD
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 サポート・リソース
    3. 12.3 Trademarks
    4. 12.4 静電気放電に関する注意事項
    5. 12.5 用語集
  13. 13Mechanical, Packaging, and Orderable Information

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

8.3.6.6 SST and Soft-Start of the Switcher

Converters require a soft-start to prevent output overshoot on startup. In PoE applications, the PD also needs soft-start to limit its input current at turn on below the limit allocated by the power source equipment (PSE).

For flyback applications using primary-side control, the TPS23731 provides closed loop controlled soft-start, which applies a slowly rising ramp voltage to a second control input of the error amplifier. The lower of the reference input and soft-start ramp controls the error amplifier, allowing the output voltage to rise in a smooth monotonic fashion.

In all other applications where secondary-side regulation is used, the TPS23731 provides a current-loop soft-start, which controls the switching MOSFET peak current by applying a slowly rising ramp voltage to a second PWM control input. The lower of COMP-derived current demand and soft-start ramp controls the PWM comparator. Note that in this case there is usually a (slower) secondary-side soft-start implemented with the typical TL431 or TLV431 error amplifier to complement the action of the primary-side soft-start.

The soft-start period of the TPS23731 is adjustable with a capacitor between SST and RTN. During soft-start, CSST (Figure 9-1) is being charged from less than 0.2 V to 2.45 V by a ~10µA current source. Once VSST has exceeded approximately 2.1 V (VSTUOF), the VCC startup is also turned off.

The actual control range of the primary-side closed-loop soft-start capacitor voltage is between 0.25V and 2V nominally. Therefore, the soft-start capacitor value must be based on this control range and the required soft-start period (tSS) according to:

Equation 5. GUID-C7F20DA4-007E-48EB-9D18-CF956EDBE0D0-low.gif

The actual control range of the current-loop soft-start capacitor voltage is between 0.6V and 1.2V nominally. Therefore, the soft-start capacitor value must be based on this control range and the required soft-start period (tSS) according to:

Equation 6. GUID-E9F65530-CB12-4EF3-807A-2417AB66D5EC-low.gif

Note that the VCC startup turns off only when 2.1 V is reached, allowing additional time for the secondary-side soft-start to complete. For more details regarding the secondary-side soft start, refer to Application Information.