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Hi Fred and all, Here some answers to
your questions: o What open
circuit inductance reduction has a significant impact on realizing PoE plus
magnetics?
Yair: Realizing PoE magnetic is not an issue IF there is
no constrains (size, power dissipation etc.).
You have to specify first if you can accept
magnetic core with a bit higher
size (in one dimension) or not.
The answer will change If you must stay with the magnetic mechanical size as
been used
in 802.3af or if you allow increase in one dimension.
It is possible to generate quantitative expression in which you can get an idea
of how the magnetic core volume is changes as function of Inductance with
and without DC bias. o How
significant to realizing PoE magnetics is adding a PD surge allowance of
Ppd_ave x 400/350? Yair: The surge
is ~14% above Icable. If Icable is 600mA then the additional current is 14%*600mA=~86Ma
If Iunb/Icable is K (currently K=3% but we know it is higher..) then
Iunb=K*86mA and Ibias will be K*86/2=K*43mA.
For 1% imbalance we will get 0.43mA increase in Ibias. If Iunb is 10% (not 3%)
then it will increase Ibias by 4.3mA only..
Not allowing Surge current will create a bigger problems. If we specify
that Ipeak=Icable (No surge allowed) then the PD designer will be forced to
design application that consume power much lower then 25.5W as permitted with
600mA (we had 29.5W with 720mA). The power will be lower by 10-15% which is
typical (low cost) accuracies and tolerances of power circuits so actual power
will be reduced to 20-21Watts which is not worth the efforts we have made in
this project. This fact
affects the magnitude of applications that we can support market size etc. Compare
to the magnetic issue this is a bigger issue. We have spent
on this question significant time in 802.3af and 802.3at and I believe that our
salvation will not come by going this road…
o Are you
aware of PD customers that use the PD surge allowance? If so provide
details. Yair: Yes I am
aware and data was supplied By me and by Thong. The relevant Market is Security
cameras in which requires between 1 to 3 surge current pulses for a duration of
3-15msec each. Alternate
solution of using big capacitors at PD input is not cost effective. We already
discuss it also. o Quantify
how TX operating inductance changes with bias current. Yair: With typical
magnetic core for 802.3af devices the approximate dependence is as described in
the attached file " Inductance vs Idc at 70degC"
I will do this if transformer vendors submit curves for PoE and PoE plus
transformers. Yair : For 802.3at
devices, I need to know the mechanical constrains as explained above. o What
affect will varying TX and RX inductance have on data communication? Yair: At
frequencies above 1MHz: If you reduce the Inductance from 350uH to ~200uH, the effect
will be negligible è0 (Tested data) For lower
inductance few things more need to be checked and verified. At frequencies
below 1MHz down to 100KHz. From analyzing the System Transfer function per the
Midspan adhoc work it looks that we have a lot of margin. Details at the next
Midspan ad hoc meeting. o Is there
an AC and DC component to the affect bias current will have on system data
integrity? Yair: The
question is not clear to me. From PoE point of view the ac component frequency on
the DC current is much lower then the data frequency. As a result the data
transformer response to the PoE current change immediately i.e. DC bias is as
seen by the transformer follows PoE current at "zero" time. - Discuss how PHY
baseline wander correction can be quantified in terms of reduce OCL
requirements for 100BASE-TX. Yair: I don’t
know. We need PHY experts on this matter. The fact is that if we add to the
channel additional inductance i.e. reducing the total equivalent inductance by
50%, it doesn’t affect the BER. Hope it helps. Yair
Analog
Mixed Signal Group Microsemi
Corporation
Cell:
+972-54-4893019 E-mail: <mailto:ydarshan@microsemi.com>. From:
owner-stds-802-3-poep@IEEE.ORG [mailto:owner-stds-802-3-poep@IEEE.ORG] On Behalf Of --------------à>>
Meeting materials are attached. This is a 1 hour meeting that may go to
90 minutes. Hello, The IEEE 802.3at,
"Transformer and Channel" ad hoc will have a conference call Friday
May 2, 9AM PST. Proposed Agenda - Cover Patent policy - Q & A - Q & A o What open
circuit inductance reduction has a significant impact on realizing PoE plus
magnetics? o How
significant to realizing PoE magnetics is adding a PD surge allowance of
Ppd_ave x 400/350? o Are you
aware of PD customers that use the PD surge allowance? If so provide
details. o Quantify
how TX operating inductance changes with bias current. o What
affect will varying TX and RX inductance have on data communication? o Is there
an AC and DC component to the affect bias current will have on system data
integrity? - Discuss how PHY
baseline wander correction can be quantified in terms of reduce OCL
requirements for 100BASE-TX. - Update on progress - Agree on a system model
for current unbalance calculations. - Use IEEE 802.3
requirements and legacy system data to refine the model used. - Use the refined
approach to model IEEE 802.3at current unbalance. Thanks, PS Some of this
discussion will be based on materials previously presented. http://grouper.ieee.org/groups/802/3/at/public/mar08/schindler_2_0308.pdf Please review the IEEE-SA
PatCom slides http://standards.ieee.org/board/pat/pat-slideset.pdf
prior to the start of our meeting. ______________________________________________________________________________ Frederick Schindler has invited you to a Cisco Unified
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Inductance vs Idc at 70degC.xls