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TPS2375 / maintain power signature resistor

Ryuji
Guru 20090 points
Other Parts Discussed in Thread: TPS2375
Hello,
 
There is the resistor of R11 in the TPS2375 EVM user's guide P.22( red circle of attached picture).
Is this resistor necessary for PoE ?
If yes , please let me know the calculation for deciding the value.
 
 
Best Regards,
Ryuji Asaka
  • 0
    TI__Mastermind 42795 points

    This resistor is only used on the EVM to achieve a 10mA MPS load with a 48V supply. In the normal application, your output load can do this (so R11 is not required).

  • 0 in reply to Eric Wright
    Guru 20090 points
    Hello Eric san,
     
    Thank you for the reply.
    I understood.
     
    I have one more questions.
    There are bridge diode of D4 and D5 in the same schematics of EVM
    Are these diode nesessary ?
     
     
    I found same diode on other PoE reference design.
    Thus, I think that these diode nesessary for PoE.
     
    Best Regards,
    Ryuji Asaka
  • 0 in reply to Ryuji
    TI__Mastermind 42795 points

    Hello,

    D4 and D5 are required so that the PD can accept either polarity of DC input (D4 is for one pair set and D5 is for the other).

  • 0 in reply to Eric Wright
    Prodigy 10 points

    Hi Eric-


    Does the presence of a 10mA constant load for MPE affect the detection or classification sequence?  Is the output of the TPS2375 disconnected during this phase of the process so that the PSE doesn't see the load on the other side of the TPS2375 during detection and classification?

    Thanks,

    Brian

  • 0 in reply to Brian Gery
    TI__Mastermind 42795 points

    Hello Brian,

    Detection and classification signatures are applied between VDD and VSS and the internal MOSFET between VSS and RTN is OFF during this phase. So, any loading between VDD and RTN is essentially isolated from the VDD-VSS side during detection (between ~3V and ~10V) and classification (between ~15V and ~20V) and will not affect this phase.