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TPS23861: Channel Configuration and Output Power Limit

Aditya Singh
Intellectual 280 points
Part Number: TPS23861
Other Parts Discussed in Thread: TPS23882

Hi Team,

We hare using TPS23861 PSE controller in our design. Below are our queries-

  • We are doing the PSE design for Type 1 POE only (15.4W). We will be using TPS23861 in manual mode. Is it  possible to configure all channels of PSE controller to Type 1 only? I don't want to provide more than 15.4W of output power from each channel.
  • As per my understanding if ICUT is set to 374mA then port will be turned off if PD draws current more than 374mA. Is my understanding correct?
  • When our port is set to Type 1 POE and type 2 PD gets connected, will it perform the classification and supply the power as per Type 2 POE (25.5W)?
  • What is the recommended voltage that should be set for DC-DC regulator in case of Type 1 POE.

Best Regards,

Aditya Kumar Singh

  • 0
    Intellectual 280 points

    Hi Team,

    Please let me know if any other detail is required from my end for the above queries.

    I look forward to hearing from you as soon as possible.

    Best Regards,

    Aditya Kumar Singh

  • 0 in reply to Aditya Singh
    TI__Mastermind 41760 points

    Hi Aditya, sorry for delay as we're currently heavy on apps support at this time. Please give us up to early next week to answer this post. sorry for the inconvenience and thank you!

  • 0 in reply to Darwin Fernandez
    TI__Mastermind 41760 points

    Hi Aditya, I don't believe you need to set it manual mode for how you want to operate the PSE. Semi auto should be okay (and manual mode is usually only for debugging). You just need to set the current to Class 3 current for all ports. In addition, you need to make sure PoEP (PoE Plus Register) is not enabled.

    This will force Type 1 power; even if a Class 4 PD is connected to the PSE. PSE will demote any PD to Type 1 power only.

    I recommend ordering the EVM and testing this out with the TPS23861 GUI. Thanks!

  • 0 in reply to Darwin Fernandez
    Intellectual 280 points

    Hi Darwin,

    Thanks for your response-

    As suggested we will use TPS83861 in semi-automatic mode and disable the PoEP resistor. We will also set the current limit to 374mA. Please share your thoughts on below queries-

    • As per my understanding if ICUT is set to 374mA then port will be turned off if PD draws current more than 374mA. Is my understanding correct?
    • What is the recommended voltage that should be set for DC-DC regulator in case of Type 1 POE.
  • 0 in reply to Aditya Singh
    TI__Mastermind 41760 points

    Hi Aditya,

    The TPS23861 will foldback that current during an overload, if that port stays in foldback during a certain amount of time (Tovld), then the port will remove power.

    Typical output voltage for PSE 50-54V. This is what we recommend to minimize the amount of voltage loss through the cable. Thanks!

  • 0 in reply to Darwin Fernandez
    Intellectual 280 points

    Hi Darwin,

    Ok, in this case with the 54V output voltage and considering Ilim as 374mA the total output power will be 20.2W while using TPS23861. But according to the standard min power required from PSE is 15.6W. We need to support 4 ports and for that we need to design at least 80.8W of isolated power which is approximately 18W more than the required power. It will be burden on our system and create a lot of issues like heating, bulky design etc.

    So, we are thinking that rather than supply 20.2W can't we supply max. 17W which will reduce the power supply design. To do we need to set Ilim at 315mA. Is there a way to do it in TPS23861. If not, then is there any other PSE controller which have similar Ilim?

    Thanks,

    Aditya Kumar Singh

  • 0 in reply to Aditya Singh
    TI__Mastermind 41760 points

    Hi Aditya,

    Yes TPS23882 would be your next best option. This IC actually looks at power versus the TPS23861 that looks at current. So the power at Type 1 would be set to 15.4W. Then if you wanted to fine tune the power, this IC allows flexibility to adjust the power by increments of 0.5W. I recommend looking at the product page below and its EVM to evaluate below. Thanks!

    https://www.ti.com/product/TPS23882

    https://www.ti.com/tool/TPS23882EVM-008

    https://www.ti.com/tool/BOOST-PSEMTHR8-097

    https://www.ti.com/tool/USB2ANY