SLVS885I October   2008  – December 2017 TPS23754 , TPS23754-1 , TPS23756


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      High-Efficiency Converter Using TPS23754
  4. Revision History
  5. Pin Configuration and Functions
    1.     Pin Functions
  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 Electrical Characteristics: PoE and Control
    7. 6.7 Switching Characteristics
    8. 6.8 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  APD
      2. 7.3.2  BLNK
      3. 7.3.3  CLS
      4. 7.3.4  Current Sense (CS)
      5. 7.3.5  Control (CTL)
      6. 7.3.6  Detection and Enable (DEN)
      7. 7.3.7  DT
      8. 7.3.8  Frequency and Synchronization (FRS)
      9. 7.3.9  GATE
      10. 7.3.10 GAT2
      11. 7.3.11 PPD
      12. 7.3.12 RTN, ARTN, COM
      13. 7.3.13 T2P
      14. 7.3.14 VB
      15. 7.3.15 VC
      16. 7.3.16 VDD
      17. 7.3.17 VDD1
      18. 7.3.18 VSS
      19. 7.3.19 PowerPAD
    4. 7.4 Device Functional Modes
      1. 7.4.1 PoE Overview
        1.  Threshold Voltages
        2.  PoE Start-Up Sequence
        3.  Detection
        4.  Hardware Classification
        5.  Inrush and Start-Up
        6.  Maintain Power Signature
        7.  Start-Up and Converter Operation
        8.  PD Hotswap Operation
        9.  Converter Controller Features
        10. Bootstrap Topology
        11. Current Slope Compensation and Current Limit
        12. Blanking – RBLNK
        13. Dead Time
        14. FRS and Synchronization
        15. T2P, Start-Up, and Power Management
        16. Thermal Shutdown
        17. Adapter ORing
        18. PPD ORing Features
        19. Using DEN to Disable PoE
        20. ORing Challenges
  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.  Input Bridges and Schottky Diodes
        2.  Protection, D1
        3.  Capacitor, C1
        4.  Detection Resistor, RDEN
        5.  Classification Resistor, RCLS
        6.  Dead Time Resistor, RDT
        7.  Switching Transformer Considerations and RVC
        8.  Special Switching MOSFET Considerations
        9.  Thermal Considerations and OTSD
        10. APD Pin Divider Network, RAPD1, RAPD2
        11. PPD Pin Divider Network, RPPD1, RPPD2
        12. Setting Frequency (RFRS) and Synchronization
        13. Current Slope Compensation
        14. Blanking Period, RBLNK
        15. Estimating Bias Supply Requirements and CVC
        16. T2P Pin Interface
        17. Advanced ORing Techniques
        18. Soft Start
        19. Frequency Dithering for Conducted Emissions Control
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 ESD
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • PWP|20
Thermal pad, mechanical data (Package|Pins)
Orderable Information

Hardware Classification

Hardware classification allows a PSE to determine a PD’s power requirements before powering, and helps with power management once power is applied. Type 2 hardware classification permits high power PSEs and PDs to determine whether the connected device can support high-power operation. A type 2 PD presents class 4 in hardware to indicate it is a high-power device. A type 1 PSE will treat a class 4 device like a class 0 device, allotting 13 W if it chooses to power the PD. A PD that receives a 2 event class understands that it is powered from a high-power PSE and it may draw up to 25.5 W immediately after the 80-ms start-up period completes. A type 2 PD that does not receive a 2-event hardware classification may choose to not start, or must start in a 13 W condition and request more power through the DLL after start-up. The standard requires a type 2 PD to indicate that it is underpowered if this occurs. Start-up of a high-power PD under 13 W implicitly requires some form of powering down sections of the application circuits.

The maximum power entries in Table 1 determine the class the PD must advertise. The PSE may disconnect a PD if it draws more than its stated class power, which may be the hardware class or a lower DLL-derived power level. The standard permits the PD to draw limited current peaks that increase the instantaneous power above the Table 1 limit; however, the average power requirement always applies.

The TPS23754 implements two-event classification. Selecting an RCLS of 63.4 Ω provides a valid type 2 signature. TPS23754 may be used as a compatible type 1 device simply by programming class 0–3 per Table 1. DLL communication is implemented by the ethernet communication system in the PD and is not implemented by the TPS23754.

The TPS23754 disables classification above VCU_OFF to avoid excessive power dissipation. CLS voltage is turned off during PD thermal limit or when APD or DEN are active. The CLS output is inherently current limited, but should not be shorted to VSS for long periods of time.

Figure 23 shows how classification works for the TPS23754. Transition from state-to-state occurs when comparator thresholds are crossed (see Figure 20 and Figure 21). These comparators have hysteresis, which adds inherent memory to the machine. Operation begins at idle (unpowered by PSE) and proceeds with increasing voltage from left to right. A 2-event classification follows the (heavy-lined) path towards the bottom, ending up with a latched type 2 decode along the lower branch that is highlighted. This state results in a low T2P during normal operation. Once the valid path to type 2 PSE detection is broken, the input voltage must transition below the mark reset threshold to start anew.

TPS23754 TPS23754-1 TPS23756 events_sts_lvs885.gifFigure 23. Two-Event Class Internal States