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Hi Fred, It is obvious that PD can draw ICUT for
TCUT and TCUT is 50ms minimum. See my presentation from last Wednesday meeting.
This is our starting point since we are discussing only ILIM region (short
circuit behavior) and not Overload (ICUT, TCUT). So as I showed, TLIM_MIN is the crossing
point of the current with ICUT_MAX = ILIM_MIN. (PD always draws ICUT_MIN as
maximum average value) The assumption that when using constant
current limit we get longer TLIM_MIN should be correct and the question is how
to derive this number. You didn’t supply the info how you
calculate those numbers. Yair From:
owner-stds-802-3-poep@ieee.org [mailto:owner-stds-802-3-poep@ieee.org] On Behalf Of Hello, An updated ILIM slide is attached. The calculations
performed assume that a PD can draw ICUT for TCUT and that TCUT is longer than
or equal to TLIM. Therefore, a PD could legally draw ICUT constantly even
if the PD voltage is increased. If we do not want to allow this we need
to put the appropriate language in the specification. The PSE can only source ILIM_MIN when enough voltage
difference exists between the PSE and the PD. When a smaller difference
exists, less than ILIM_MIN is sourced by the PSE and the PSE is no longer
monitoring TLIM. The PD voltage ramps to it final value exponentially
from this point forward. The values obtained match IEEE 802.3 needs and provide a
shorter TLIM for IEEE 802.3at (because of the higher ILIM and the smaller
voltage change). Please provide comments before the next meeting on Wed. May
9. Thanks for helping this specification move forward, Technical Leader CISCO Systems M/S SJ-19-3 Tel. (408) 525-9859 PS I would also like to thank |