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TPS2373: Using for cable longer than 100m condition

Part Number: TPS2373

Hi Sir,

What if I use TPS2373 in 500m cable condition? Is there any setting or component needs to be noticed?

Thank you.

C.T.

  • Hello Chentsu,

    I would not recommend going beyond the 100m officially supported by the 803.2 standard, but if you do decide to, your biggest enemy will be the considerable transmission losses across the Cat5e cable.

    No additional components will be needed on the PD side, but you will need to supply more power on the PSE side. You will need to configure the class resistors on the PD so it will be 1 or 2 classes above your desired power level. Again, I would not recommend this.

    I'll loop in a PSE expert who can give more advice about the PSE side.

    Thanks,
    Thomas A.

  • Hi Thomas,

    Thanks for your explanation, so except of the power level, is it also affect the result of DETECTION and CLASSIFICATION?

    for example, I have to reduce the value of Rclass(Rdet) due to the increased cable resistor to keep the same classification(detection) current, am I right?

    Thank you.
    C.T.
  • Chentsu,

    What I meant was the PD needs to request more power from the PSE (through classification) to make up for the power losses due to the longer cable length. Now that you mention it, the added resistance of the long ethernet cable may cause you to fail class & detection, so slightly lower class/detection resistors would be necessary.

    Going beyond 100m is a bad idea. It is better to use PoE repeaters every 100 meters.

    Best,
    Thomas A.
  • Hi Thomas,

    Thank you for your great soppurt, I understand it, but I'm not going to add resistor for it, for example:

    The Rdet is typ. 24.9KOhm for 100m condition, because 24.9K+cable resistor is in the range of detection current, so I mean I should use the lower Rdet(<24.9K) for the highier cable resistor condition to keep the Idet constant, am I right?
  • Hi Chentsu,

    Yes, use lower resistors for detection & classification to accommodate for the higher resistance due to cable length.
  • Hi Thomas,

    Got it, thanks for your great support.