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Original question:

POE Output Load detection Problem

TPS23753: MPS and Ethernet Link Disconnection issue

kalpesh diyora
Intellectual 265 points
Part Number: TPS23753

HI, We are using diode oring for Adaptor and TPS23753 output voltage(POE). Adaptor priority is there with Setting the POE voltage less compare to Adaptor voltage.

In this case, POE is continuously disconnection to less minimum load. Along with POwer, CISCO switch disables Data and device went offline mode,.

  • 0
    TI__Genius 9230 points
    Hello Kalpesh,

    Is your adapter configuration the same as "option 3 ORing" detailed in the app note, slva306a?

    If so, is your system implementing the circuit described in section 3.6 to keep the PSE connected?

    Regards,
    Thomas A.
    PoE PD Apps Engineer
  • 0 in reply to Thomas Amlee
    Intellectual 265 points

    Yes,We have option 3 oring scheme in our design.

    Priority is to adapter with Vadp>Vpoe.

    We do not implemented circuit of section 3.6 but we have 1kohm resistor load on output side of Poe circuit which is loading equivalent 6~7mA on input of POE. This is with considering efficiency.

    10mA MPS is not found maintained.

    Power loss on Poe line is not disturbing the system performance but along with power loss it also disconnect data and Ethernet link found missed.

    Why this should happen?

    Generally, Data should not get missed if power loss due to MPS.

  • 0 in reply to kalpesh diyora
    TI__Genius 9230 points
    Hi Kalpesh,

    To clarify, did you attach this 1kohm resistor to the output of the PD (VDD-RTN) or on the output of the converter? You will need to reduce the resistor value until 10mA is the input current draw.

    Give the section 3.6 circuit a try. It should satisfy the MPS requirement given a correctly sized resistor.

    Best,
    Tom A.
  • 0 in reply to Thomas Amlee
    Intellectual 265 points

    Hi Tom,

    We have verified with adding resistor to make the minimum load of 10mA. It is working fine. Switch is not droping the power on POE line after this change.

    What is the required minimum current to keep POE power according to 802.3af standard?

    Power drop on POE line is not creating the issue but it should not drop data link. Can you advise on this?

  • 0 in reply to kalpesh diyora
    TI__Genius 9230 points
    HI Kalpesh,

    " A valid MPS consists of a minimum dc current of 10 mA (at a duty cycle of at least 75 ms on every 225 ms)"

    This information can be found on page 15 of the TPS23753 datasheet.

    The DC power on the Ethernet cable is independent of the differential data signal. However, your PSE may be configured to remove the data link if the DC MPS signal is no longer sensed. I would check the PSE end.

    Thanks,
    Tom A.
  • 0 in reply to Thomas Amlee
    Intellectual 265 points

    Thank you.

    Please check on pse if you can suggest.

    We are using Cisco 2960 series switch as PSE.

  • 0 in reply to kalpesh diyora
    TI__Genius 9230 points

    Hi Kalpesh,
     
    At this point, I would suggest for you to make contact with Cisco’s support team.

    Our guess is that there might be something in the switch’s software to disable data when they see DC disconnect but this needs to be verified with Cisco's help.
     
    Thank you,
    Thomas Amlee
    PoE PD Apps Engineer

  • 0 in reply to kalpesh diyora
    TI__Genius 15685 points

    Hi kalpesh,

    I think we have found the root cause of switch's power removal on the PD side. The next step is to find why Cisco switch cut the data link during low load condition. PoE chips only control power and have no ability of data transmission. Technically, from PSE side, if it sees low port current not satisfying MPS spec in IEEE standard, it should remove power and the PSE chip has nothing to do with data. The data control is usually on the CPU/ PHY side which is beyond our knowledge. The best way is to find a Cisco contact to further support you. Thanks. 

    Best regards,

    Penny