TPS23754: IEEE802.3at PoE ethernet cable loss

YC Chen

Prodigy 10 points

Other Parts Discussed in Thread: TPS23754

We would like to know how where the 4.5W gap comes between 802.3 at PSE 30W and PD 25.5W.

From IEEE calculated formula, type 2 Rchan is DC pair loop resistance 12.5ohm

What is the difference between Rchan and DCR of ethernet cable?

Ex：DCR of Cat5e 24AWG is 8.29 ohm, what the Rchan is?

Our purpose is to calculate the cable loss between different ethernet cable(Cat5e、Cat6...)

Thanks

over 1 year ago

0 LeonardEllis over 1 year ago

TI__Guru 71526 points

Hello YC,

Please indicate the device you are using in this design.

Thank you,

~Leonard

0 YC Chen over 1 year ago in reply to LeonardEllis

Prodigy 10 points

Hello Leonard,

thanks for reply

The question raised is to do research on the IEEE 802.3at specification

The main purpose is to understand what is the parameter (Rchan) in the cable loss 4.5W gap is obtained and how to use the DCR of various ethernet cable to calculate cable loss

+1 YC Chen over 1 year ago in reply to LeonardEllis

Prodigy 10 points

Hello Leonard,

We use TPS23754.

Thanks

0 Raymond Lin over 1 year ago in reply to YC Chen

TI__Mastermind 29096 points

Hi YC,

The 4.5W comes from cable loss after a 100m Cat5 cable with cable DC resistance of 12.5Ohm. The power on PD side represents the minimum power allowed at PD side:

Refer to this thread for some additional information: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1230232/tps23754-power-gap-between-pse-output-and-pd-input

If you need further clarification, please let us know!

Thanks and Regards,

Raymond Lin

Power management

Power management forum

TPS23754: IEEE802.3at PoE ethernet cable loss