This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS23753A can't work normally,can't get 5V output

Other Parts Discussed in Thread: TPS23753A, TLV431, TL431

Hi,

We have a custom design using TPS23753A to implement 5V/1.6A poe output. Attachment is the schematic. The schematic refers to TPS23753A-EVM .

when external power into a PD as Adapter Option 2, 5V output is fine. 

TP-LINK TL-SF1005P as a PSE,when plugging in the network cable, the output of PD can't get 5V .

Waveform of  VDD-VSS is showed as below picture,the TPS23753A can't work normally.

Please advise how to debug this issue, thanks!

  • Hi Hugh,

    Have you tried configuring the PD as a class 3 instead of class 0? From the plot above, it looks like detection is successful but classification is failing. I am not sure which PSE inside the TP-Link TL-SF1005P, but maybe it does not support class 0.

    Let me know.
  • hi John,

    I have tested ,configuring the PD as a class 3 instead of class 0. But the result and waveform as before, the problem has not solved still.

    I doubt that,is there any wrong in Selection of components or schematic?

    Thank you.
  • Hi Hugh,

    Can you also send schematic of the your PD's front end (RJ45 connector to PoE PD)? Also, have you tried connecting this PSE to an EVM to make sure the PSE is operating correctly? Is it possible to measure the input current as well? I'm curious to know how it goes during classification.
  • hi Darwin,

    Attachment is the PD's front end schematic, there isn't an EVM around me now. I can show the waveforms of V_CLS, I_PI. but i can't sure that the

    Test Methods of  input current is correct, can U teach me how to get the current if mine is error.

    Additionally, when external power into a PD as Adapter Option 2, 5V output is fine, but i add a 6 ohm resistance as the load output, the 5V output Voltage will drop to 2V. 

    Will TLV431 or TL431A  affect the circuit performance?

    RJ45 connector.pdf

    Thank you.

  • Hi Darwin,
    The problem confused me for a long time now, I can't find the real reason where the error occurred.
    Please advise how to debug this issue, thanks!
  • HI Hugh,

    In comparing your schematic and our EVM, I am not seeing any obvious errors. I am sorry if this sounds silly, but is their any chance D204 is installed backwards? If this were the case, the classification pulse could be fooling the TPS23753A to believe the adapter is present.

    Just an idea until Darwin comes up with something better.
  • Hugh,

    I looked at the PD front end schematic you sent. Is C105 really a 33uF capacitor? The maximum PoE PD port capacitance is 0.12uF. I suspect this large capacitor is causing the PSE current limited class voltage regulator to hit current limit. Try removing C105.

    Also, on the DC/DC side you mentioned TLV431 or TL431. You should use TLV431 instead and adjust R220, R221, R222 to match the EVM values for proper operation. I also noticed that U201 has a CTR of 80 - 600%. Use an opti-isolator with a more controlled CTR (80% to 160% is OK).

    If you need to adjust values for any reason, please follow the guidance in TI application report: http://www.ti.com/lit/pdf/slva305

  • hi,all.

     I am sorry i did not reply timely, thank you for your help and enthusiasm  sincerely.

    I have solved the problem  by learning slva305.pdf carefully, Found  the PD front end schematic , selection of components D102 is fatal error. I will be more serious  in the future work.