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TPS23730: TPS23730

J
Expert 1065 points
Part Number: TPS23730

I am reading the TI POE IC([TPS23730's datasheet]), and I have some questions I would like to ask you, if you can help me I will very much appreciate it.

1.) What's the internal hot-swap MOSFET, I have no idea what's this use for?
2.) What's Oring?
3.) What's APD function and PPD function, I cannot understand clearly in the datasheet.
4.) Why need to use RTN pin, GND pin, and RTN pin, all three are ground why cannot just use one.
5.) What's beat frequency

I have read this datasheet but I still cannot understand the above question, hope someone can give some help.

  • 0
    TI__Mastermind 21320 points

    Hello Jack,

    1. The internal hot swap MOSFET connects VSS to RTN after power is successfully negotiated with a PoE handshake. This keeps the DCDC off during the PoE handshake. For example, the classification voltage is up to 20V, which could precharge the input bulk cap OR startup the DCDC. This could interfere with the PoE handshake. 

    2. OR - ing is combining a DC power source, also known as auxiliary or adapter, with PoE. Either PoE OR the adapter will power the load. We have an application note on how to achieve this for our IC's : https://www.ti.com/lit/an/slva306a/slva306a.pdf?ts=1626107842170&ref_url=https%253A%252F%252Fwww.google.com%252F 

    3.APD stands for Auxilary Power Detect. This pin is a voltage threshold to detect if auxiliary power is connected. It turns off the internal hotswap MOSFET to disable the PoE from powering the DCDC, therefore giving the adapter priority to power. 

    PPD stands for Passive Power Detect. Passive power is the nomenclature for lower voltage PoE power that is not a part of the IEEE802.3 standard. It is typically 18V-32V (24V average). This is not an adapter used in the paper above, but a different type of PSE. PPD enables a lower turn on threshold for the PoE input so that this voltage range can turn on the part when detected. 

    4. Grounding an IC is key for critical feedback systems within a power control IC. All these pins connect to the same plane. 

    5. Beat frequency is the frequency created when two or more frequencies combine to creating a super imposed frequency. My suggestion is to research this topic online. The mention of it with respect to the TPS23730 is that the TPS23730 can be synchronized to an external clock that can eliminate such frequencies. 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • 0 in reply to Michael Pahl
    Expert 1065 points

    Hi Pahl,

    Thanks for your response. after your explanation I understand a lot but still have some questions I'd like to ask you.

    1.) It is necessary to enable the APD right? it can prevent the POE handshake from interfering by DC/DC converter.

    2.) About PPD I am still confused, according to your response, we do not need to use PPD? Why we need to use PPD pin, could you give an example?

  • 0 in reply to J
    TI__Mastermind 21320 points

    1. No, the internal hotswap MOSFET prevents PoE handshake from interfering with the DCDC converter. APD is used with an auxiliary power source. APD must be connected to RTN if it is not used. If APD is high, it prevents the PoE from powering the DCDC. 

    2. You use PPD in passive PoE. If your PoE input is IEEE802.3 compliant, meaning the input voltage range is 37V-57V, then you do not need PPD. If you PoE input voltage range is 18V-32V, then you use PPD. If you are not using passive PoE, then you do not use PPD. 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • 0 in reply to Michael Pahl
    Expert 1065 points

    Hi Pahl
    There is a question I am still confused about.
    1.) If I don't have an auxiliary power source, I need to connect to RTN. I am confused about why need to prevent the PoE from powering the DCDC, which means always can't let the DCDC work if the APD pin is high? 

  • +1 in reply to J
    TI__Mastermind 21320 points

    1. Correct, no auxiliary power connect APD to RTN. 

    PoE handshake voltages are high enough to turn on DCDC. That is why we have a hotswap FET. That was your original question.

    once PoE handshake is done, then we DO want PoE to power the DCDC, hence the hotswap FET closes and PoE powers the DCDC. 

    for your application, connect APD to RTN. 

    You can always order an EVM which has jumpers for APD, PPD, and you can test with a PSE. 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • 0 in reply to Michael Pahl
    Expert 1065 points

    Hi Pahl 
    Thank you. I got it. 

    If I have any question about that, can I mail to you or I need to put the same question on that?

  • 0 in reply to J
    TI__Mastermind 21320 points

    Hey Jack, 

    Please create a new E2E thread for new questions. Thanks!

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments