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TPS23881: some parameters does not meet the requirements of sifos AT test

jingjing liu
Prodigy 50 points
Part Number: TPS23881
Other Parts Discussed in Thread: TPS23882, TPS23882B, TPS2388

HI all,

      Several chips of  TPS2881 is used for POE at  interfaces in the AC5X  switchboard.When it  has a sifos at test,the parameter of Tlim_1 in theTest: pwron_maxi  doesn't meet the requirements.

      The minimum and the maximum requirement  of Tlim_1 is 50 ms and 75 ms.Our test result is 9999ms.It may be over the measure range of the instrument.The parameter of Tlim_1 shown in the Datasheet is typical 60ms.According our test result,the port  maybe is not disable when the current is over the limited.

          

     Do you have the  sifos af/at  test on your demo board?Also, can you check whether the software have the function?it can  diasble the port when the current over the limited.

      The design is showed as the picture。Can you give me some recommends, thank you.

  • 0
    TI__Intellectual 1480 points

    Hi Jingjing, 

    I recommend to only use the Sifos .bt tester for TPS23881 compliance testing. Report is available here https://www.ti.com/lit/ug/slvt186/slvt186.pdf . 

    Regarding "Do you have the  sifos af/at  test on your demo board?"

    No, running the Sifos .at/.af tester on this device can show failures because the TPS23881 can only operate as a IEEE 802.3bt PSE and it's not possible to operate in "af only" mode or "at only" mode. However, the .bt standard ensures that .at and .af PDs can work with this device. 

    Regarding "Also, can you check whether the software have the function?it can  diasble the port when the current over the limited."

    Yes, this feature is enabled in the TPS23881 firmware. The default TLIM setting is 60ms. 

    Regards,

    Sai Gunda

  • 0 in reply to Sai Gunda
    Prodigy 50 points

    Hi Sai,

            Our swicth have 40 at ports and 8 bt ports.And also we have another switch board,there are 24 at ports.We all use the TPS23881 for  the PSE controller.

            According the test requirement,we should pass the sifos af/at test of all the at/bt ports.We also run the af/at tester on the bt ports.

            As the BT port is compatible with af/at.Why  can't  the TPS23881 operate in "af only" mode or "at only" mode? Can we modify the software to pass the sifos af/at test?

            Also Do you have some the customers using the TPS23881 for  the at/af PSE controller?Do they run the the sifos at/af tester？

  • 0 in reply to jingjing liu
    TI__Intellectual 1480 points

    Hi Jingjing, 

    The AT Type-1 and Type-2 Sifos tests will check for specific values which the TPS23881 may fail. One for example is the Min_Valid_I_hold (part of Test: mps_dc_pwrdn) which uses pass range of 5-10 mA for 802.3at PSEs. The TPS23881 can produce 4mA during this test and fail. This is because TPS23881 is a Type-4 PSE and therefore was designed to pass 4-9 mA criteria which is in the .bt specification. 

    Regarding "Can we modify the software to pass the sifos af/at test?" 

    No, sorry. 

    Regarding "Also Do you have some the customers using the TPS23881 for  the at/af PSE controller?Do they run the the sifos at/af tester" 

    Typically the TPS23882 is used as for Type-3 / 2 Pair applications. I will reach out to Sifos regarding what options are available for conformance tests in this situation since their software seems to only offer Type-4 PSE Testing in 4 Pair configuration. 

    Regards,

    Sai Gunda

  • 0 in reply to Sai Gunda
    Prodigy 50 points

    Hi sai,

           We look at the datasheets of 23881/23882/23882B.The three chips all can be used for the PSE bt controller.They can apply to  IEEE 802.3bt PSE solution for PoE 2 Type-3 2-Pair power over ethernet application.So,I have some questions to ask:

         (1)The TPS23882 can apply to  IEEE 802.3bt PSE solution for PoE 2 Type-3 2-Pair power over ethernet application.If I use it for PSE at ports ,can the PSE board pass the sifos af/at test?

        (2)What the difference between the TPS23882 and TPS23882B?Can we use the TPS23882B for PSE AT ports？

    （3）We should pass the sifos af/at test for the PSE AT ports.Can we use the TPS2388?

  • 0 in reply to jingjing liu
    TI__Intellectual 1480 points

    Hi Jingjing, 

    Regarding the original question. Please use the BT Type-3 (make sure to select one of the pairs Alt A or Alt B) to run the Sifos test in 2-Pair mode. 

    During this test, Sifos will emulate Type 1 and Type 2 PDs only. IEEE802.3bt standard ensures that a .bt compliant PSE device, will work with .af and .at PDs. So this will allow you test TPS23881 for .at conformance. 

    Regarding the TLIM results, I was able to see the expected 60ms result for TLIM when I ran the test on our EVM board. I will email you the full report since we don't have an .at conformance report for this device formally published on ti.com.   

    Regarding "(1)The TPS23882 can apply to  IEEE 802.3bt PSE solution for PoE 2 Type-3 2-Pair power over ethernet application.If I use it for PSE at ports ,can the PSE board pass the sifos af/at test?"

    Yes, TPS23882 is .at compliant. We used the same settings shown above to run the Sifos test on this device and the published report is https://www.ti.com/lit/ug/slvt185/slvt185.pdf . 

    Regarding "(2)What the difference between the TPS23882 and TPS23882B?Can we use the TPS23882B for PSE AT ports"

    TPS23882B features autonomous mode whereas the TPS23882 does not. Autonomous mode means you can use the PSE controller to power PDs without host configuration. TPS23882B is also shown to be .at compliant but we do not have a published report yet. 

    Regarding "(3）We should pass the sifos af/at test for the PSE AT ports.Can we use the TPS2388?"

    TPS2388 is also .at compliant but I don't recommend this. You can test the TPS23881 for .at compliance using the steps above. 

  • 0 in reply to Sai Gunda
    Prodigy 50 points

    Hi sai,

           We use the BT Type-3 to run the sifos test for the at/af ports which use the TPS23881.But there is also the paremeter of Tlim_Max_2 which cannot pass.

    My colleague used the TPS23881 as the AF/AT PSE controller.The switch board could pass the at/af sifos test using the BT Type-3.

           So I think it can solve this problem modifying the software.Can you give some advice to our software engineers.

  • 0 in reply to jingjing liu
    TI__Intellectual 1480 points

    Jingjing, 

    During the pwron_maxi test, a short circuit stimulus is applied and the PSE is triggered into foldback mechanism. It seems the foldback is triggering but after the TLIM = 60ms expires, the port is not shut off. I would like to verify this behavior by looking at the port waveforms. 

    Can you run the pwron_maxi tests and enable the Show traces and provide the generated waveform? Also can you tell me what version of SRAM the TPS23881 are using? 

    Regards,

    Sai Gunda