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TPS23751: Ethernet Phy IC damage when connect POE

irfan memon
Prodigy 170 points
Part Number: TPS23751
Other Parts Discussed in Thread: PMP11254,

Hi,

Phy IC (LAN8740) damage when connect with POE.Working fine with 12V adapter power and NON POE Lan.

Please help us to resolve the issue. attached schematic of POE,Ethernet PHY and 12V adapter supply circuit.

  • 0
    TI__Expert 3700 points

    Hi,

    Thank you for your question. The PoE team is currently out of the office celebrating the U.S. Holiday of Thanksgiving and will respond by Tuesday, December 3rd.

    Thank you for considering Texas Instruments PoE devices.

    Best Regards,

    Brett Colteaux

  • 0 in reply to Brett Colteaux
    Prodigy 170 points
    A Message from the TI E2E™ support forums
    Texas Instruments

     

    Benjamin Bawkon replied to TPS23751: Ethernet Phy IC damage when connect POE.

    I only took a brief look.

    It looks to me like a ground problem.  The 'ground' coming out of your bridges (D42, D44) is "GND-VSS", whereas the ground connected to your transformer via Q101 (T2, Pin 3) is not.  The grounding scheme on this design is really difficult to follow, especially on low-resolution pictures.

    Have you verified the operation of your POE-PD circuit by itself?  Do you get ~12V out of it?

    I suspect they PHY chip failing is just a symptom of bad power - Double check your POE-PD circuit.

    Good Luck!

    Ben

     
     

    You received this notification because you subscribed to the forum.  To unsubscribe from only this thread, go here.

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    refid:baf8e273-1d69-4ee3-bec2-68ccfa37a50c

    Hi,

    Thanks for the reply,

    Actually POE is working fine and also get the 12V output but PHY IC damaged when frequently on/off (connect/disconnect) POE by using J4

    or simultaneously present the POE power as well as Adapter power and connect disconnect POE power by using J4.

    D42,D44  GND-VSS and Q101 GND are different.actually we have follow PMP11254 application note.

     

  • 0 in reply to irfan memon
    TI__Mastermind 21320 points

    Hello,

    If I am understanding correctly, the PoE input is on J4. The ground of J4 is VSS, when it should be Earth Ground. Please refer to the the Input Section 1.4 of the following application note for more information: 

    Regards,

    Michael Pahl

  • 0 in reply to Michael Pahl
    Prodigy 170 points

    Hi,

    We had done as per Slua469 before couple of day.but still damaged PHY.

    We have note that No any single phy damage on POE switch part no DES-1210-08P whenever 40-50 PHY IC damaged on ES-5104PH V2 / ES-1008PH V2.

    we dont understand why PHY IC damage on ES-5104PH V2 and ES-1008PH V2.

    We have allready communicate with EDIMAX support .

  • 0 in reply to irfan memon
    TI__Mastermind 21320 points

    Hello,

    I would like to point out that the ground for J4 is VSS, so I am unsure how this was changed for a couple of days. The ground should be earth ground, and connected to an earth ground plane that is isolated from VSS. 

    The capacitors on the Bob Smith connections are the incorrect values as well. 

    I would also encourage you to look at the data transformer datasheet to ensure the data lines are connected properly. 

    Additionally, you could grab an EVM to connect to the PSE to eliminate the multiple PSE's as a source of the problem. 

    Regards,

    Michael Pahl

  • 0 in reply to Michael Pahl
    Prodigy 170 points

    Hi,

    Actually we have tried with your per your suggested before couple of day by refer different app notes but that time also PHY damaged.

    The capacitor on the bob smith also we have changed 10nf/100V  but still PHY damaged.

    We are the Manufacturer of Security product from 20 years and Same PHY circuit we are using last 10 years (we are not connect BOb smith components in our all products)

    Now Only POE circuit is new for us.

    Please note that PHY damaged in within 5 minutes as Only connect POE or connect Adapter +POE and On/Off it.

    Regards,

    Irfan

  • 0 in reply to irfan memon
    TI__Mastermind 21320 points

    Hello Irfan,

    Please try using a TPS23751 EVM to power your phy to see if it is damaged. Power the EVM and then connnect the data-out to the phy and check to see if it damaged. Thank you.


    Regards,

    Michael Pahl

  • 0 in reply to Michael Pahl
    Prodigy 170 points

    Hi,

    Right now we have no TPS23751 EVM. meanwhile can you tell me that how can create/generate power delay/soft start in TPS23751 for 5 second ?

    actually we have a POE splitter and it is connect with our PHY section and test as per above same.that is working ok. no found damaged in PHY.

    that POE splitter has power delay of 5-7 second. thats why we want create delay in power.

    Regards,

    Irfan

  • 0 in reply to irfan memon
    TI__Mastermind 21320 points

    Hello Irfan,

    For a 5-7 second delay, I would suggest an external control such as a timer or microcontroller. You would need to delay the power being applied to VDD1 which controls the DC-DC. 

    However, please note that the IEEE802.3 standard is for the PSE to shut off power after 60ms if the MPS current is not met. You will need a dummy load that is less than inrush but more than MPS. 

    Regards,

    Michael Pahl

  • 0 in reply to Michael Pahl
    Prodigy 170 points

    Hi,

    Phy damaged issue is resolved by putting Bidirection TVS on Differential line and Unidirectional TVS on Each line Tx+/- and Rx+/- at phy side.

    Above is test at POE switch (PSE) adapter (48V/2A) with earth connection but without earth  up to 40V for 0.5us-2us are comes when plug /unplug event of POE connector (J4). that is the new issue for us.

    so now without earth why up to 40v are comes on differential pair at the time of plug/unplug of POE connector (J4).

    Please note that up to 40v are comes without any protection diode connected on differential pair it is reduce up to 15-20v when connected TVS diode.

    Attached waveform is differential line RXP-RXN with tvs protection and with Earth connected in POE switch

    Note- without earth means no earth connected in POE switch (PSE) adapter.and earth means earth connected in POE switch adapter.

  • 0 in reply to irfan memon
    TI__Mastermind 21320 points

    Hello,

    So to understand, there is a 40V spike on the PD on J4 VDD-VSS when you plug it in when there is no earth ground. But if the PSE is connected to earth ground, there is no spike? And if you add the TVS diode the spike is reduced to 15-20V. Is that causing any damage? 

    Am I understanding, if you connect earth ground to the PSE and the diodes there is no problem, is that correct?

    For new issues, please create new threads. Thank you. 

    Regards,

    Michael Pahl