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TPS2372: PoE .bt finger3~5

Roy Chou
Prodigy 120 points
Part Number: TPS2372

Hi all,

I have a confusing point in PoE.bt with PoE_CustomerPPT_Full_hyperlinked_for_ESP.pptx.

Look at the figure below.

Figuer1(4) Finger2(4) Finger3(4) could classify that PD is connected by 4 pair and PSE provide 30W power.

Figuer1(4) Finger2(4) Finger3(0) Finger4(0) could classify that PD is connected by 4 pair and PSE provide 45W power.

Figuer1(4) Finger2(4) Finger3(1) Finger4(1) could classify that PD is connected by 4 pair and PSE provide 60W power.

Figuer1(4) Finger2(4) Finger3(2) Finger4(2) Finger5(2) could classify that PD is connected by 4 pair and PSE provide 75W power.

Figuer1(4) Finger2(4) Finger3(3) Finger4(3) Finger5(3) could classify that PD is connected by 4 pair and PSE provide 90W power.

 

But Finger3 can classify all the power that PD need, why still having finger4 and finger5?

Thanks.

 

Roy

  • 0 in reply to Roy Chou
    TI__Genius 9230 points

    Hi Roy,

    The 3rd finger is used by the PD to request power levels above 25.5W.

    The 4th finger is used by the PSE to confirm power levels up to 51W.

    The 5th finger is used by the PSE to confirm power levels up to 71.3W.

    For example, if the PD requests class 5 on the 3rd finger, the 4th finger will only confirm up to the class 5 level (40W at PD, 45W at PSE)

    Special thanks to David Abramson for the clarification.

    Good luck,
    Tom

  • 0 in reply to Thomas Amlee
    Prodigy 120 points

    Hi Tom,

    Thank you for your replying.

    PSE Type3 is having 4-fingers and Type4 is having 5fingers. In the figure as attached, finger3 can classify all the power that PD need. Why still have four and five finger?

    Or the reason is that would like to difine PSE type and PSE type couldn't define only by class level? Must be dinfed by finger amounts? Thanks.

    Regards,

    Roy

  • 0 in reply to Roy Chou
    TI__Genius 9230 points

    Hi Roy,

    The PD notices the existence of the 4th or 5th finger as verification that the PSE is of the appropriate type (3 or 4). Remember, the PSE initiates the classification finger by sending ~18V to the PD, which then sends a regulated 2.5V through the selected class resistor.

    - Tom