SLVSF02D March   2019  – May 2020 TPS23881


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Simplified Schematic
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
    1.     Pin Functions
    2. 6.1 Detailed Pin Description
  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
    6. 7.6 Typical Characteristics
  8. Parameter Measurement Information
    1. 8.1 Timing Diagrams
  9. Detailed Description
    1. 9.1 Overview
      1. 9.1.1 Operating Modes
        1. Auto
        2. Semiauto
        3. Manual/Diagnostic
        4. Power Off
      2. 9.1.2 PoE Compliance Terminology
      3. 9.1.3 Channel versus Port Terminology
      4. 9.1.4 Requested Class versus Assigned Class
      5. 9.1.5 Power Allocation and Power Demotion
      6. 9.1.6 Programmable SRAM
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Port Remapping
      2. 9.3.2 Port Power Priority
      3. 9.3.3 Analog-to-Digital Converters (ADC)
      4. 9.3.4 I2C Watchdog
      5. 9.3.5 Current Foldback Protection
    4. 9.4 Device Functional Modes
      1. 9.4.1 Detection
      2. 9.4.2 Connection Check
      3. 9.4.3 Classification
      4. 9.4.4 DC Disconnect
    5. 9.5 I2C Programming
      1. 9.5.1 I2C Serial Interface
    6. 9.6 Register Maps
      1. 9.6.1 Complete Register Set
      2. 9.6.2 Detailed Register Descriptions
        1.  INTERRUPT Register
          1. Table 6. INTERRUPT Register Field Descriptions
        2.  INTERRUPT MASK Register
          1. Table 7. INTERRUPT MASK Register Field Descriptions
        3.  POWER EVENT Register
          1. Table 8. POWER EVENT Register Field Descriptions
        4.  DETECTION EVENT Register
          1. Table 9. DETECTION EVENT Register Field Descriptions
        5.  FAULT EVENT Register
          1. Table 10. FAULT EVENT Register Field Descriptions
        6.  START/ILIM EVENT Register
          1. Table 11. START/ILIM EVENT Register Field Descriptions
        7.  SUPPLY and FAULT EVENT Register
          1. Table 12. SUPPLY and FAULT EVENT Register Field Descriptions
          2. Detected SRAM Faults and "Safe Mode"
            1. ULA (Ultra Low Alpha) Package Option: TPS23881A
        8.  CHANNEL 1 DISCOVERY Register
        9.  CHANNEL 2 DISCOVERY Register
        10. CHANNEL 3 DISCOVERY Register
        11. CHANNEL 4 DISCOVERY Register
          1. Table 13. CHANNEL n DISCOVERY Register Field Descriptions
        12. POWER STATUS Register
          1. Table 14. POWER STATUS Register Field Descriptions
        13. PIN STATUS Register
          1. Table 15. PIN STATUS Register Field Descriptions
        14. OPERATING MODE Register
          1. Table 16. OPERATING MODE Register Field Descriptions
        15. DISCONNECT ENABLE Register
          1. Table 20. DISCONNECT ENABLE Register Field Descriptions
        16. DETECT/CLASS ENABLE Register
          1. Table 21. DETECT/CLASS ENABLE Register Field Descriptions
        17. Power Priority / 2Pair PCUT Disable Register Name
          1. Table 22. Power Priority / 2P-PCUT Disable Register Field Descriptions
        18. TIMING CONFIGURATION Register
          1. Table 24. TIMING CONFIGURATION Register Field Descriptions
        19. GENERAL MASK Register
          1. Table 25. GENERAL MASK Register Field Descriptions
        20. DETECT/CLASS RESTART Register
          1. Table 27. DETECT/CLASS RESTART Register Field Descriptions
        21. POWER ENABLE Register
          1. Table 28. POWER ENABLE Register Field Descriptions
        22. RESET Register
          1. Table 32. RESET Register Field Descriptions
        23. ID Register
          1. Table 34. ID Register Field Descriptions
        24. Connection Check and Auto Class Status Register
          1. Table 35. Connection Check and Auto Class Field Descriptions
        25. 2-Pair Police Ch-1 Configuration Register
        26. 2-Pair Police Ch-2 Configuration Register
        27. 2-Pair Police Ch-3 Configuration Register
        28. 2-Pair Police Ch-4 Configuration Register
          1. Table 36. 2-Pair Policing Register Fields Descriptions
        29. Capacitance (Legacy PD) Detection
          1. Table 39. Capacitance Detection Register Field Descriptions
        30. Power-on Fault Register
          1. Table 40. Power-on Fault Register Field Descriptions
        31. PORT RE-MAPPING Register
          1. Table 41. PORT RE-MAPPING Register Field Descriptions
        32. Channels 1 and 2 Multi Bit Priority Register
        33. Channels 3 and 4 Multi Bit Priority Register
          1. Table 42. Channels n MBP Register Field Descriptions
        34. 4-Pair Wired and Port Power Allocation Register
          1. Table 44. 4-Pair Wired and Power Allocation Register Field Descriptions
        35. 4-Pair Police Ch-1 and 2 Configuration Register
        36. 4-Pair Police Ch-3 and 4 Configuration Register
          1. Table 46. 4-Pair Police Register Field Descriptions
        37. TEMPERATURE Register
          1. Table 48. TEMPERATURE Register Field Descriptions
        38. 4-Pair Fault Configuration Register
          1. Table 49. 4-Pair Fault Register Field Descriptions
        39. INPUT VOLTAGE Register
          1. Table 50. INPUT VOLTAGE Register Field Descriptions
        40. CHANNEL 1 CURRENT Register
        41. CHANNEL 2 CURRENT Register
        42. CHANNEL 3 CURRENT Register
        43. CHANNEL 4 CURRENT Register
          1. Table 51. CHANNEL n CURRENT Register Field Descriptions
        44. CHANNEL 1 VOLTAGE Register
        45. CHANNEL 2 VOLTAGE Register
        46. CHANNEL 3 VOLTAGE Register
        47. CHANNEL 4 VOLTAGE Register
          1. Table 52. CHANNEL n VOLTAGE Register Field Descriptions
        48. 2x FOLDBACK SELECTION Register
          1. Table 53. 2x FOLDBACK SELECTION Register Field Descriptions
        49. FIRMWARE REVISION Register
          1. Table 54. FIRMWARE REVISION Register Field Descriptions
        50. I2C WATCHDOG Register
          1. Table 55. I2C WATCHDOG Register Field Descriptions
        51. DEVICE ID Register
          1. Table 57. DEVICE ID Register Field Descriptions
        52. CHANNEL 1 DETECT RESISTANCE Register
        53. CHANNEL 2 DETECT RESISTANCE Register
        54. CHANNEL 3 DETECT RESISTANCE Register
        55. CHANNEL 4 DETECT RESISTANCE Register
          1. Table 58. DETECT RESISTANCE Register Fields Descriptions
          1. Table 59. DETECT CAPACITANCE Register Fields Descriptions
        60. CHANNEL 1 ASSIGNED CLASS Register
        61. CHANNEL 2 ASSIGNED CLASS Register
        62. CHANNEL 3 ASSIGNED CLASS Register
        63. CHANNEL 4 ASSIGNED CLASS Register
          1. Table 60. CHANNEL n ASSIGNED CLASS Register Field Descriptions
        64. AUTO CLASS CONTROL Register
          1. Table 63. AUTO CLASS CONTROL Register Field Descriptions
        65. CHANNEL 1 AUTO CLASS POWER Register
        66. CHANNEL 2 AUTO CLASS POWER Register
        67. CHANNEL 3 AUTO CLASS POWER Register
        68. CHANNEL 4 AUTO CLASS POWER Register
          1. Table 65. AUTO CLASS POWER Register Fields Descriptions
        69. ALTERNATIVE FOLDBACK Register
          1. Table 66. ALTERNATIVE FOLDBACK Register Field Descriptions
        70. SRAM CONTROL Register
          1. Table 67.  SRAM CONTROL Register Field Descriptions
          2. SRAM START ADDRESS (LSB) Register
          3. SRAM START ADDRESS (MSB) Register
            1. Table 68. SRAM START ADDRESS Register Field Descriptions
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Introduction to PoE
        1. 2-Pair Versus 4-Pair Power and the New IEEE802.3bt Standard
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. Connections on Unused Channels
        2. Power Pin Bypass Capacitors
        3. Per Port Components
        4. System Level Components (not shown in the schematic diagrams)
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
    1. 11.1 VDD
    2. 11.2 VPWR
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Kelvin Current Sensing Resistors
    2. 12.2 Layout Example
      1. 12.2.1 Component Placement and Routing Guidelines
        1. Power Pin Bypass Capacitors
        2. Per-Port Components
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Receiving Notification of Documentation Updates
    3. 13.3 Support Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

Detailed Pin Description

The following descriptions refer to the pinout and the functional block diagram.

DRAIN1-DRAIN8: Channels 1-8 output voltage monitor and detect sense. Used to measure the port output voltage, for port voltage monitoring, port power good detection and foldback action. Detection probe currents also flow into this pin.

The TPS23881 uses an innovative 4-point technique to provide reliable PD detection and avoids powering an invalid load. The discovery is performed by sinking two different current levels via the DRAINn pin, while the PD voltage is measured from VPWR to DRAINn. If prior to starting a new detection cycle the port voltage is >2.5 V, an internal 100-kΩ resistor is connected in parallel with the port and a 400-ms detect backoff period is applied to allow the port capacitor to be discharged before the detection cycle starts.

There is an internal resistor between each DRAINn pin and VPWR in any operating mode except during detection or while the port is ON. If the port n is not used, DRAINn can be left floating or tied to GND.

GAT1-GAT8: Channels 1-8 gate drive outputs are used for external N-channel MOSFET gate control. At port turn on, it is driven positive by a low current source to turn the MOSFET on. GATn is pulled low whenever any of the input supplies are low or if an overcurrent timeout has occurred. GATn is also pulled low if the port is turned off by use of manual shutdown inputs. Leave floating if unused.

For improved design robustness, the current foldback functions limit the power dissipation of the MOSFET during low resistance load or short-circuit events and during the inrush period at port turn on. There is also fast overload protection comparator for major faults like a direct short that forces the MOSFET to turn off in less than a microsecond.

The circuit leakage paths between the GATn pin and any nearby DRAINn pin, GND or Kelvin point connection must be minimized (< 250 nA), to ensure correct MOSFET control.

INT: This interrupt output pin asserts low when a bit in the interrupt register is asserted. This output is open-drain.

KSENSA, KSENSB, KSENSC, KSENSD: Kelvin point connection used to perform a differential voltage measurement across the associated current sense resistors.

Each KSENS is shared between two neighbor SEN pins as following: KSENSA with SEN1 and SEN2, KSENSB with SEN3 and SEN4, KSENSC with SEN5 and SEN6, KSENSD with SEN7 and SEN8. To optimize the measurement accuracy, ensure proper PCB layout practices are followed.

OSS: Fast shutdown, active high. This pin is internally pulled down to DGND, with an internal 1-µs to 5-µs deglitch filter.

The turn off procedure is similar to a port reset using Reset command (1Ah register). The 3-bit OSS function allows for a series of pulses on the OSS pin to turn off individual or multiple ports with up to 8 levels of priority.

RESET: Reset input, active low. When asserted, the TPS23881 resets, turning off all ports and forcing the registers to their power-up state. This pin is internally pulled up to VDD, with internal 1-µs to 5-µs deglitch filter. The designer can use an external RC network to delay the turn-on. There is also an internal power-on-reset which is independent of the RESET input.

SCL: Serial clock input for I2C bus.

SDAI: Serial data input for I2C bus. This pin can be connected to SDAO for non-isolated systems.

SDAO: Open-drain I2C bus output data line. Requires an external resistive pull-up. The TPS23881 uses separate SDAO and SDAI lines to allow optoisolated I2C interface. SDAO can be connected to SDAI for non-isolated systems.

A4-A1: I2C bus address inputs. These pins are internally pulled up to VDD. See PIN STATUS Register for more details.

SEN1-8: Channel current sense input relative to KSENSn (see KSENSn description). A differential measurement is performed using KSENSA-D Kelvin point connection. Monitors the external MOSFET current by use of a 0.200-Ω current sense resistor connected to GND. Used by current foldback engine and also during classification. Can be used to perform load current monitoring via ADC conversion.

When the TPS23881 performs the classification measurements, the current flows through the external MOSFETs. This avoids heat concentration in the device and makes it possible for the TPS23881 to perform classification measurements on multiple ports at the same time. For the current limit with foldback function, there is an internal 2-µS analog filter on the SEN1-8 pins to provide glitch filtering. For measurements through an ADC, an anti-aliasing filter is present on the SEN1-8 pins. This includes the port-powered current monitoring, port policing, and DC disconnect.

If the port is not used, tie SENn to GND.

VDD: 3.3-V logic power supply input.

VPWR: High voltage power supply input. Nominally 54 V.

AGND and DGND: Ground references for internal analog and digital circuitry respectively. Not connected together internally. Both pins require a low resistance path to the system GND plane. If a robust GND plane is used to extract heat from the device's thermal pad, these pins may be connected together through the thermal pad connection on the pcb.