SLVS933D July   2009  – December 2020 TPS23753A

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Product Information
  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: Controller Section Only
    6. 7.6 Electrical Characteristics: PoE and Control
    7. 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 Pin Description
        1. 8.3.1.1  APD
        2. 8.3.1.2  BLNK
        3. 8.3.1.3  CLS
        4. 8.3.1.4  CS
        5. 8.3.1.5  CTL
        6. 8.3.1.6  DEN
        7. 8.3.1.7  FRS
        8. 8.3.1.8  GATE
        9. 8.3.1.9  RTN
        10. 8.3.1.10 VB
        11. 8.3.1.11 VC
        12. 8.3.1.12 VDD
        13. 8.3.1.13 VDD1
        14. 8.3.1.14 VSS
    4. 8.4 Device Functional Modes
      1. 8.4.1  Threshold Voltages
      2. 8.4.2  PoE Start-Up Sequence
      3. 8.4.3  Detection
      4. 8.4.4  Hardware Classification
      5. 8.4.5  Maintain Power Signature (MPS)
      6. 8.4.6  TPS23753A Operation
        1. 8.4.6.1 Start-Up and Converter Operation
        2. 8.4.6.2 PD Self-Protection
        3. 8.4.6.3 Converter Controller Features
      7. 8.4.7  Special Switching MOSFET Considerations
      8. 8.4.8  Thermal Considerations
      9. 8.4.9  FRS and Synchronization
      10. 8.4.10 Blanking – RBLNK
      11. 8.4.11 Current Slope Compensation
      12. 8.4.12 Adapter ORing
      13. 8.4.13 Protection
      14. 8.4.14 Frequency Dithering for Conducted Emissions Control
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Support Resources
    3. 12.3 Electrostatic Discharge Caution
    4. 12.4 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.4.14 Frequency Dithering for Conducted Emissions Control

The international standard CISPR 22 (and adopted versions) is often used as a requirement for conducted emissions. Ethernet cables are covered as a telecommunication port under section 5.2 for conducted emissions. Meeting EMI requirements is often a challenge, with the lower limits of Class B being especially hard. Circuit board layout, filtering, and snubbing various nodes in the power circuit are the first layer of control techniques. A more detailed discussion of EMI control is presented in Practical Guidelines to Designing an EMI Compliant PoE Powered Device With Isolated Flyback, SLUA469. Additionally, IEEE 802.3at sections 33.3 and 33.4 have requirements for noise injected onto the Ethernet cable based on compatibility with data transmission.

Occasionally, a technique referred to as frequency dithering is used to provide additional EMI measurement reduction. The switching frequency is modulated to spread the narrowband individual harmonics across a wider bandwidth, thus lowering peak measurements. The circuit of Figure 8-11 modulates the switching frequency by feeding a small AC signal into the FRS pin. These values may be adapted to suit individual needs.

GUID-088C8FBC-330A-4284-9440-83A3A6D0A453-low.gifFigure 8-11 Frequency Dithering