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TPS23754: Connect TPS23754 to a PSE that compliant to 802.3 af

chentsu chung
Mastermind 6180 points
Part Number: TPS23754
Other Parts Discussed in Thread: TPS23750

Hi Sir,

I use 137Ohm as Rcls for TPS23754, the result of classification will be CLASS 2 in 802.3 at.

What I'd like to know is If now I connect it to a PSE that compliant to 802.3 af, then the result will be CLASS 1 based on the table below? (calculate by 1.5V/137Ohm=10.9mA)

Or what the performance will be after connecting PD to a PSE compliant to 802.3 af? Thank you.

  • 0
    TI__Genius 9230 points
    Hi Chentsu,


    See page 9 of the datasheet for an older .af part, TPS23750. www.ti.com/.../tps23750.pdf

    The Resistor will need to be larger (953 ohm) to be classified at class 1.

    Thanks,
    Thomas A.
  • 0 in reply to Thomas Amlee
    Mastermind 6180 points
    Hi Thomas,

    I think I got the answer. The PSE care the Iclass only, so I don't need to change the Rclass, for example, the Vclass of TPS23750 is 10V, so the Iclass will be 10/953=10.5mA, and the Vclass of TPS23754 is 2.5V, then I sitll can get CLASS 1 if I use 243 as Rclass(2.5/243=10.3mA), am I right?

    Now my question is, What if a .at PD connect to .af PSE? How .af PSE will work? Is there any different for the start up process? Thank you.
  • 0 in reply to chentsu chung
    TI__Genius 9230 points

    Hi Chentsu,

    Sorry for the delay. A IEEE803.2af PSE should also classify the PD as type 1 since that 243 ohm resistor will allow for the 10mA current condition to be met. The only difference is that .af only looks at the first classification pulse (CLSA). There are no additional class pulses with CLSB.

    Thanks,
    Thomas A.