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TPS2372: INRUSHDL_EN and AUTCLS Timming of use.

Kami Huang60
Genius 3830 points
Part Number: TPS2372

Dear Sir/Ms.

My customer asked questions about the application scenario, and I was not so clear. I want to ask you some advice.


Regarding Pin16 / IRSHDL_EN: Enable the PSE influx delay (about 81.5 milliseconds). May I ask Disable&Enable. Will this delay be considered in some cases?
(Is there a practical example for this requirement? Or can it replace the description, thank you)

a). Is the "surge limiting function" of the IC a mechanism to avoid excessive Inrush current when the internal MOSFET is turned on?
b). May I ask if the Inrush current of the product is too large and the time is too long to exceed the basic specifications and cause Inrush to detect Fail, can the inrush delay mechanism be activated to try to improve the problem?

If the current class settings of TPS2372-4 are as follows, what is the difference between turning off Autoclass and turning on Autoclass when connecting to the three specifications of PSE (PoE / PoE + / PoE ++)?

Best Regards,

Kami Huang

  • 0
    Prodigy 200 points

    Dear Sir/Ms.

    Additional question setting picture as below.

    If the current class settings of TPS2372-4 are as follows, what is the difference between turning off Autoclass and turning on Autoclass when connecting to the three specifications of PSE (PoE / PoE + / PoE ++)?

    Best Regards,

    Tom Chang

  • 0
    TI__Mastermind 21320 points

    Hello Kami,

    Inrush is a phase in the PoE power on sequence. 

    It can be turned off in special cases, but it should not be used without special consideration. 

    The IRSHDL_EN pin delays the PG signal until the inrush phase is over. the TPS2372 also has internal inrush current limiting on the internal hotswap FET between VSS and RTN. So there are different functions here. 

    disabling the IRSHDL_EN pin should not affect the PoE interoperability. Again, it is a delay to the DCDC starting up so that is a designer choice. 

    There is no connection between the Class of the PD and the Autoclass function. The class of the PD sets what the power level the PD requests from the PSE. Autoclass is part of the IEEE802.3.bt standard which states that if both PSE and PD support Autoclass, then for a specific interval after startup, the PD must draw its maximum power level, and the PSE will make that power draw the maximum power instead of the Class power level. For example, if a PD drew 68W in the interval, that would be the new maximum power the PSE would allocate to the PD, instead of 71W. 

    I do not recommend using it. 

    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
    Prodigy 200 points

    Dear Michael,

    Do you mean that automatic classification function is not recommended?

    Thanks & Best Regards,

    Tom Chang

  • 0 in reply to Tom Chang
    TI__Mastermind 21320 points

    Yes.

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

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments