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

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      High-Efficiency Converter Using TPS23754
  4. 4 Revision History
  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 Electrical Characteristics: PoE and Control
    7. 6.7 Switching Characteristics
    8. 6.8 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  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. 7.4.1.1  Threshold Voltages
        2. 7.4.1.2  PoE Start-Up Sequence
        3. 7.4.1.3  Detection
        4. 7.4.1.4  Hardware Classification
        5. 7.4.1.5  Inrush and Start-Up
        6. 7.4.1.6  Maintain Power Signature
        7. 7.4.1.7  Start-Up and Converter Operation
        8. 7.4.1.8  PD Hotswap Operation
        9. 7.4.1.9  Converter Controller Features
        10. 7.4.1.10 Bootstrap Topology
        11. 7.4.1.11 Current Slope Compensation and Current Limit
        12. 7.4.1.12 Blanking – RBLNK
        13. 7.4.1.13 Dead Time
        14. 7.4.1.14 FRS and Synchronization
        15. 7.4.1.15 T2P, Start-Up, and Power Management
        16. 7.4.1.16 Thermal Shutdown
        17. 7.4.1.17 Adapter ORing
        18. 7.4.1.18 PPD ORing Features
        19. 7.4.1.19 Using DEN to Disable PoE
        20. 7.4.1.20 ORing Challenges
  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  Input Bridges and Schottky Diodes
        2. 8.2.2.2  Protection, D1
        3. 8.2.2.3  Capacitor, C1
        4. 8.2.2.4  Detection Resistor, RDEN
        5. 8.2.2.5  Classification Resistor, RCLS
        6. 8.2.2.6  Dead Time Resistor, RDT
        7. 8.2.2.7  Switching Transformer Considerations and RVC
        8. 8.2.2.8  Special Switching MOSFET Considerations
        9. 8.2.2.9  Thermal Considerations and OTSD
        10. 8.2.2.10 APD Pin Divider Network, RAPD1, RAPD2
        11. 8.2.2.11 PPD Pin Divider Network, RPPD1, RPPD2
        12. 8.2.2.12 Setting Frequency (RFRS) and Synchronization
        13. 8.2.2.13 Current Slope Compensation
        14. 8.2.2.14 Blanking Period, RBLNK
        15. 8.2.2.15 Estimating Bias Supply Requirements and CVC
        16. 8.2.2.16 T2P Pin Interface
        17. 8.2.2.17 Advanced ORing Techniques
        18. 8.2.2.18 Soft Start
        19. 8.2.2.19 Frequency Dithering for Conducted Emissions Control
      3. 8.2.3 Application Curves
  9. 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

7.4.1.8 PD Hotswap Operation

IEEE 802.3at has taken a new approach to PSE output limiting. A type 2 PSE must meet an output current versus time template with specified minimum and maximum sourcing boundaries. The peak output current may be as high as 50 A for 10 μs or 1.75 A for 75 ms. This makes robust protection of the PD device even more important than it was in IEEE 802.3-2008.

The internal hotswap MOSFET is protected against output faults and input voltage steps with a current limit and deglitched (time-delay filtered) foldback. An overload on the pass MOSFET engages the current limit, with VRTN-VVSS rising as a result. If VRTN rises above about 12 V for longer than about 400 μs, the current limit reverts to the inrush value, and turns the converter off. The 400 μs deglitch feature prevents momentary transients from causing a PD reset, provided that recovery lies within the bounds of the hotswap and PSE protection. Figure 25 shows an example of recovery from a 16 V PSE rising voltage step. The hotswap MOSFET goes into current limit, overshooting to a relatively low current, recovers to about 950-mA full current limit, and charges the input capacitor while the converter continues to run. The MOSFET did not go into foldback because VRTN-VVSS was less than 12 V after the 400 μs deglitch.

TPS23754 TPS23754-1 TPS23756 pse_v_lvs885.gifFigure 25. Response to PSE Step Voltage

The PD control has a thermal sensor that protects the internal hotswap MOSFET. Conditions like start-up or operation into a VDD to RTN short cause high power dissipation in the MOSFET. An overtemperature shutdown (OTSD) turns off the hotswap MOSFET and class regulator, which are restarted after the device cools. The hotswap MOSFET will be re-enabled with the inrush current limit when exiting from an overtemperature event.

Pulling DEN to VSS during powered operation causes the internal hotswap MOSFET to turn off. This feature allows a PD with Option three ORing per Figure 26 to achieve adapter priority. Take care with synchronous converter topologies that can deliver power in both directions.

The hotswap switch will be forced off under the following conditions:

  1. VAPD above VAPDEN (about 1.5 V)
  2. VDEN < VPD-DIS when VVDD– VVSS is in the operational range
  3. PD over-temperature
  4. (VVDD– VVSS) < PoE UVLO (about 30.5 V)