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TPS23754: tps23754

Namith HL
Intellectual 570 points
Part Number: TPS23754
Other Parts Discussed in Thread: TPS23861,

Hi Darwin,

As per your feedback we have changed the optocoupler (FOD817A) and TL431A ,now we are getting 24V output fine.

But we have given two option type1 and type 2 by giving jumper setting option for classification resistor selection I.e 63.4ohm and 90.9 ohm.

we have TPS23861EVM  PSE ,when we keeping our jumper at the 63.4ohm position it passes signature detection and classification ,but when we keeping at the 90.9ohm position it fails the signature,,Is it because PSE is type 2?

when we use the TYPE1 midspan PSE by keeping jumper at the 90.9 Position it fails to pass the signature detection.

Please tel us the reason for this signature failure?suggest  more about this signature setting ,since both the type1 and Type 2 PD.

Note:our circuit draws about 200mA maximum at the output(24V/0.2mA) about 4.8W.

If it is 4.5W Output power it supposed to pass signature detection for type1 (90.9ohm) right?

Please suggest where we done wrong or how to solve this ?

Other than this signature issue converter is working fine.

Regards,

Namith

  • 0
    TI__Mastermind 41760 points
    Hi Namith,

    Glad to hear the converter is working well. But sorry to hear about the detection failures. This is highly unusual as detection and classification should be independent of each other. Can you re-send the schematic so that I have the latest one? Thanks!

    Regards,
    Darwin
  • 0 in reply to Darwin Fernandez
    Intellectual 570 points

    Hi,

    Please find the attached schematic ,requested to review and give us the feedback on this signatute detection and classification failures as the earliest.

    Note: we need both type 1 and type 2(POE & POE+) option for application.selection can be fixed with jumper setting classification resistor.

    Regards,

    Namith24v output.pdf

  • 0 in reply to Namith HL
    TI__Mastermind 41760 points
    Hi Namith,

    The circuit in the attached does not have issues as we've tested the front end EVM in the past. Do you have your specific schematic so that we can narrow down what might be the issue on your board? If it's exactly the same as the attached, you may want to check the VDD, VSS, and RTN connections/components to make sure the values/connections are correct.
  • 0 in reply to Darwin Fernandez
    Intellectual 570 points

    Hi Darwin,

    Thank you for Continuing support for us,

    I have tested POE output with PSE,following are the results.

    • From Type 1 PSE Adapter input T2P is High (9.79V)
    • From Type 2 PSE ( TPS23861 EVM-612) input T2P is Low(0.475)
    • I have loaded the converter upto 0.875A output voltage is 24.16V (No load O/P V=24.20)
    • As per Power calculation converter giving efficiency upto 86% ,great

    Still i have doubts over this classification resistor adjustment.

    As per the datasheet of TPS23754 ,

    For Class 4 mentioned as the Min 13W and Max 25.5W, does it mean it only allows output power from 13W  and max 25W ?

    For  Class 3 mentioned as the Min 6.49W and Max 13W, does it mean it only allows output power from 6.49W  and max 13W ?If  we load less than 6.4 W this will not support?

    Suppose we load only 5W i.e less than 6.49W (By fixing 90.9ohm resistor) does classification would fail?

    If we kept 63.4 ohm does it will support all power from 0 to 25.5 W?

    If we fix these issue everything will be good ,we have tested with different cable length  upto 100mtr working fine.

    Regards,

    Namith

  • 0 in reply to Namith HL
    TI__Mastermind 41760 points
    Hi Namith,

    I can see how the table might be confusing. The table represents the max power ranges. If the PD’s max power is 7W, then it is Class 3. It does NOT mean that the PD can’t operate below 6.5W. It can operate at 6W too and still be class 3 if the max expected power is within the class 3 range. The “min” means these minimum max power the PD will output for that class range.

    If the PSE passes detection, the PSE should still power up the PD even if it's operating below the min range. As long the load at the PSE is above MPS (10mA), then the PSE should not remove power.

    Since you are using the TPS23861EVM, you can use the GUI to see what the PSE is reading for detection when you change the class resistor jumper. Do you have a schematic of your jumper configuration/connections on your PCB?

    Regards,
    Darwin