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TPS23730: A Poe PD can still be IEEE 802.3xx compliant when is working with a PSE passive (24V) without changing the PCB ?

Said Djedid
Prodigy 30 points
Part Number: TPS23730

My main doubt is :

I need to develop an IP camera which is :

  • IEEE 802.3xx compliant,
  • Work with an active PoE PSE @ 37V-60V,
  • Work with a passive PoE (without PSE) @ 24V
  • There is only one way to supply the IP camera : RJ45 cable. 

 

In the datasheet (TPS23730), it can be read that there is APD and PPD pin .

As I explained before, in my case, there is only one power source, and it comes from the Ethernet cable.

So, the APD pin is not used.

 

However, there is the PPD pin.

So, if I put the PPD pin to VSS through a pull-down resistor

  • the TPS23730 will be turn on @ 24V and the DC/DC too ?
  • Will the UVLO protection disabled ? Even when the PSE is an active one ?
  • Would we compliant with IEEE standard or the PPD pin need to be left open in order to be compliant ?

 

If you confirm the last question, if I can turn on the TPS @ 24V , will this mean that we are no longer compliant with IEEE 802.3 ?

(maybe because of voltage level input => not in the range of  37V – 60V ? )

For an IP camera wich is only supply with the Ethernet cable, is it possible to used only a buck instead of a flyback ? 

What about the Handshaking Protocol ?

As we can see, the voltage levels for the handshaking protocol are under 20.5V.

What if we supply the TPS23730 with for example 16V ? for example 24V ?

 

If PPD pin is tie to VSS , what is going on with the inrush phase ?

  • Will it be disabled ?
  • Even when a PSE active who is compliant IEEE 802.3xx ?

 

Can be we IEEE 802.3xx compliant when an active PSE is used and at the same time, working with a voltage (typically 24V) of a PSE passive without changing the PCB ?

If PPD pin is tied to VSS, the compliance with IEEE standard is lost ?

 

Thank you.

  • 0
    TI__Mastermind 30621 points

    Hi Said,

    Thanks for reaching out!

    1. If you only have one RJ-45 port and you want this port be able to support standard PSE and 24V passive PoE injector. Yes, you will fail the standard test due to UVLO. If Passive injector is 48V input it will pass and no need to use PPD pin. 

    2. If you have two RJ-45 ports, you can configure one port for standard PSE and another port dedicated for the 24V passive PoE injector.

    3. If PoE injector is lower than 20.5 V, you may have to use two RJ-45 ports as you mentioned the classification could be influenced. 

    4. PDD ties to VSS will disable the PPD function. No influence for standard PSE or passive Injector voltage > PD's UVLO. To use PPD normally a voltage divider is needed. You can check https://www.ti.com/tool/TPS23730EVM-093 for more details of TPS23730 reference design. 

    Best regards,

    Diang

  • 0 in reply to Diang Xing
    Prodigy 30 points

    Hi Diang,

    Thank you for your answers.

    So, if I wanted to realise an IP camera over IEEE 802.3xx compliant and also "not compliant", I must to use two connectors and one of them need to be connected to PPD or APD in order to bypass the UVLO ?

    Can the TPS23730 power on if there is no handshake protocol?

    If there is no handshake protocol,

    - what about TPS23730 soft start ? Is it always done ?

    - what about the delay of 80ms before to startup ? Is it always done ?

    If I used a hotswap controller for the passive PSE in order to control the inrush current, what could be the impact if the PD want also regulate the start up current?

    Thank you.

    Best regards,

    Said   

  • 0 in reply to Said Djedid
    TI__Mastermind 30621 points

    Hi Said,

    Thanks for your reply. 

    I will take a look and get back to you later.

    Best regards,

    Diang

  • 0 in reply to Diang Xing
    TI__Mastermind 30621 points

    Hi Said,

    Thanks for your waiting.

    - The TPS23730 can be turned on as well as the VDD-VSS is higher than 39.5 V or the PPD-VSS is higher than 2.66 V.

    - TPS23730 will still have the ~80ms inrush delay and DC/DC soft start without handshake.

    The handshake is mainly the communication between PSE-PD for power allocation, power protection ...

    Best regards,

    Diang

  • 0 in reply to Diang Xing
    TI__Mastermind 30621 points

    Hi Said,

    Since we have not received your reply for a relative long time. I will close this thread for now. Please reply or open a new thread if you have further questions.

    Best regards,

    Diang