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Hi Wayne and all,
Yes, in very short channel the equipment MDI, and other elements of the equipment circuit, will dominate i.e. it will be almost similar to the PSE PI and PD PI P2PRUNB that we agree that we need to define anyway.
I will simulate results with 0.15m cable with 0.14 Ω/m when simulation only PSE and PD PIs.
The following are the main topics that I plane to discuss in the ad-hoc meeting on Thursday this week.
I'll appreciate if you will review it prior the meeting and send your thoughts so we can convergence to consensus as fast as possible.
During the meeting, the objective is to close these questions and move forward.
• We agree that we don’t care of high temperature since it works for us (high temperature higher resistance lower P2PCRUNB)
• So the question is narrowed to below room temperature (20-24°C)?.
System and component vendors are responsible to design the parts/system to meet their spec over their spec of operating temperature range.
Please see what IEEE802.3-2012 says about this topic:
33.7.7 Temperature and humidity
The PD and PSE powered cabling link segment is expected to operate over a reasonable range of
environmental conditions related to temperature, humidity, and physical handling. Specific requirements and
values for these parameters are beyond the scope of this standard.
Proposed Recommendation: To focus on results at room temperature for the baseline.
Anything else could be informative or per 33.7.7 or both or not addressed pending our time.
• Example: if Mode A requires 350mA and Mode B require 113mA than P2P discussion is not relevant to this case.
Proposed Recommendation: During normal operation, If total PD load current is at a value that the current over the pair is less than 600mA/TBD, the P2PCRUNB requirements may be ignored.
Yair Response: we will know the answer based on (1) and running simulations/calculations per Wayne proposal for 4 channel length options.
-Wayne to confirm.
-Wayne: What is your opinion to the above proposal?
Thinking about possible use cases, it seems to me it is possible, someone may provide PSE equipment in a rack and PD equipment in the rack unit below it in the same rack. If we agree this is a possible use case, it could be connected by a patch cord 0.15 m long. Patch cords have a de-rated DC resistance requirement of 14, as Yair states. In finding the absolute minimum, someone could also use un-de-rated patch cord material.
In any case, for this use case, I think the DC resistance, and the DC resistance unbalance, of the cabling system, is low enough that the equipment MDI, and other elements of the equipment circuit, will dominate.
Power over HDBaseT Subcommittee
Chief R&D Engineer
Analog Mixed Signal Group
1 Hanagar St., P.O. Box 7220