Re: [802.3_4PPOE] 4P-PoE End to End System Imbalance (Channel Pair To Pair Resistance Imbalance) Ad-Hoc
My comment was that there are two aspects to balance: the channel leading to the PD (including the PSE), and the PD itself. If the PD has a single power channel, it's reasonable to expect that balance will be maintained all the way to the point that the two pair sets are joined. If the PD has two power channels, it may be unbalanced by design and the balance need only be specified up to the PD PI.
For this reason, it may be appropriate to spec balance from PI to PI (channel unbalance), and then specify the PD inputs separately. A manufacturer can then design a PD knowing the behavior of the channel right to the PI. Interestingly, there are only two cases I can think of that a PD would want to maintain good balance between the pairs: operating at maximum power (to avoid current limit in either pair) and operating in "green" mode (where matched currents give maximum cable efficiency).
On Apr 22, 2014, at 7:46 AM, Darshan, Yair <YDarshan@xxxxxxxxxxxxx> wrote:
> Hi all,
> 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.
> • How to address temperature effect on P2PCRUNB?
> • 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)?.
> Yair response:
> • All parameters in the standard are tested for compliance at room temperature.
> System and component vendors are responsible to design the parts/system to meet their spec over their spec of operating temperature range.
> • We can study and supply the guidelines/equations in informative annex to help decide what to do in temperatures below room temperature but it can’t be part of the standard. (not high priority)
> 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.
> • We need to define the PD load current on Mode A and Mode B in which below that current, P2P requirements can be ignored.
> • Example: if Mode A requires 350mA and Mode B require 113mA than P2P discussion is not relevant to this case.
> • We agree that we need to investigate it and address it.
> • Dave Dwelley made a comment about this issue which I didn't record.
> • Dave please send us your comment about this topic to be recorded and addressed.
> 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.
> • (1) What is the minimum resistance in the channel that above it, we don’t care? In other words, what is the minimum resistance in the PD that makes the diodes, connectors, transformers less important in the total channel P2PRUNB?
> • (2) Do we need to specify minimum length?.
> Yair Response: we will know the answer based on (1) and running simulations/calculations per Wayne proposal for 4 channel length options.
> • What will be minimum Ω/m for patch cords?
> • Yair: I suggest to use the 9.38Ω/100m (93.8mΩ/m as max value and 5% less as the minimum value since patch cords normally need to be flexible than the horizontal cable so their wire diameter is smaller that horizontal cables such as CAT6A.
> • Yair: I remember that Wayne said that the 0.15m channel length option is with 14 Ω/100m.
> -Wayne to confirm.
> -Wayne: What is your opinion to the above proposal?
> • In IEEE802.3 March 2014 meeting , Jeff Heat had a comment for the PD model. Jeff to send the details of it to the ad-hoc if you want us to discuss it.
> Darshan Yair
> Power over HDBaseT Subcommittee
> HDBaseT Alliance
> Chief R&D Engineer
> Analog Mixed Signal Group
> Microsemi Corporation
> 1 Hanagar St., P.O. Box 7220
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