TIDUEX8 September   2020

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Highlighted Products
      1. 2.2.1 TPS23730
      2. 2.2.2 TLV431
    3. 2.3 System Design Theory
      1. 2.3.1 IEEE802.3bt Introduction
  8. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Required Hardware
      1. 3.1.1 Hardware
    2. 3.2 Testing and Results
      1. 3.2.1 Test Setup
      2. 3.2.2 Test Results
        1. 3.2.2.1 Efficiency
        2. 3.2.2.2 Control Loop Gain/Stability
        3. 3.2.2.3 Load Transient
        4. 3.2.2.4 Input and Output Ripple
        5. 3.2.2.5 Switching Waveforms
        6. 3.2.2.6 Start Up Response
        7. 3.2.2.7 Soft-Stop Response
        8. 3.2.2.8 Output Short Circuit Response
        9. 3.2.2.9 Thermal Performance
  9. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 PCB Layout Recommendations
      1. 4.3.1 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
  10. 5Related Documentation
    1. 5.1 Trademarks
  11. 6Terminology
  12. 7About the Author

2.2.1 TPS23730

The TPS23730 is an IEEE802.3bt compliant powered device (PD) interface that supports Type-3 PoE. All basic functionality such as detection, classification, inrush current limit (200 mA) and automatic maintain power signature (MPS) are integrated into a small form factor. A 0.3-Ω internal switch supports Type-3 up to 60 W of continuous power from the PSE which allows beyond 1.2 A through the PD during normal operation.

A critical TPS23730 feature to the design of this application is the soft-stop function. The soft-stop feature minimizes stress on switching power FETs, allowing FET BOM cost reduction. Soft-stop action consists in discharging in a controlled way the output capacitor of the converter, sending back the energy to the input bulk capacitor.

Another feature of the TPS23730 is the advanced startup function. This function allows for a smaller VCC capacitor, bootstrap circuitry is not needed, and it accounts for PSE inrush timing requirements.

The TPS23730 also features an auxiliary power detect (APD) input that allows an auxiliary supply to power the load. In scenarios where both PoE and the auxiliary supply are present, the TPS23730 allows the auxiliary supply to take priority over PoE.

The TPS23730 also contains several protection features such as thermal shutdown, current limit foldback and a robust 100-V internal switch.