RE: PSE vs. PD power dissipation again
Rick, I agree with you.
This is part of important data that we need in order to help us deciding
which option is best.
Our info from marketing says that 5-12watts is the big market, what others
think?
Yair.
> -----Original Message-----
> From: Rick Brooks [SMTP:ribrooks@xxxxxxxxxxxxxxxxxx]
> Sent: ו, מרץ 23, 2001 5:31 PM
> To: Dave Dwelley; stds-802-3-pwrviamdi@xxxxxxxx
> Subject: RE: PSE vs. PD power dissipation again
>
> Dave,
> that is a concise summary alright.
>
> One more thing that we should try to consider is the overall market.
> We should try to give the best tradeoffs to the center of mass of that
> market.
> Let's try to make the center of mass better.
>
> Otherwise, it is easy for each of us to try to make the spec favor our
> part of the market (PSE or PD).
> Since I would do PSE's, say, I would favor lower PSE cost and higher port
> density, so option 1.
>
> In a way, I hate to ask for marketing input here, but that might be the
> best way to help
> to choose the best of the 2 options.
>
>
> For example:
> If we all think that the largest part of the market will be rather large
> PD's (maybe 8 to 12 watts)
> that need a big input capacitors, then Option 2 might be the best.
>
> If we all think that the PD designs will be all over the map in terms of
> power
> and required DC/DC capacitance, then option 1 might be the best.
> I'm talking here about numbers of units shipped, not just the fact that
> there will be 1W PD's and 12W PD's.
>
> We should lower overall (relative) cost of the system:
> # of PSE ports shipped
> cost per PSE port
> # of PD ports shipped
> cost per PD port
>
>
> thoughts?
> - Rick
>
>
>
>
>
>
>
> -----Original Message-----
> From: Dave Dwelley [SMTP:ddwelley@xxxxxxxxxx]
> Sent: Thursday, March 22, 2001 5:46 PM
> To: stds-802-3-pwrviamdi@xxxxxxxx
> Subject: RE: PSE vs. PD power dissipation again
>
>
> At the risk of repeating some of this discussion, let me summarize the
> PSE-PD dissipation issue as I see it. If I've made a mistake in any of the
>
> following points, please correct me!
>
> We seem to be split into two camps:
>
> Inrush limit by PD:
> - No dissipation in PSE, which means we can integrate multiple switches
> - Requires inrush circuit in PD = more $$ in PD (amount of $ subject to
> debate)
> - Puts power dissipation in PD FET always = bigger PD FET
> - Requires rapid overcurrent disconnect in PSE
> - A PSE with this design cannot power up a PD with no inrush limit
>
> Inrush limit by PSE:
> - Requires big FETs in the PSE to survive 500mA/100ms wire short
> - Can power any PD - with or without inrush protection
> - Dissipation can be in PSE, PD, or shared
> - Must allow extended over-current faults before turn-off - adds to PSE
> dissipation
> - Can power big PD cap faster (500mA vs 350) if the PSE is sized to
> dissipate the additional power
>
> We need to endorse only one of these two, since they have mutually
> exclusive features.
>
> Option 1 really only has one compelling feature, which is low watts in the
>
> PSE. We can integrate multiple option 1s in one chip. Multiple option 2s
> can't be integrated without some accommodation - sequential turn on,
> dynamically controlled current limit - something. There are secondary
> benefits to option 1 - it won't power up non-inrush-controlled PDs, which
> almost gets us the "second check" that Roger has been asking for, and it
> won't put a heavy load on a power-managed PSE for long durations during a
> wire short.
>
> Option 2 has some nice features, most notably the ability to power up
> nearly any PD. It can also ride out a brief short on the wire without
> disconnecting the PD. A minor downside is that the PSE power supply must
> absorb a fair-sized overload if a PD classified as a low power device
> (with
> power allocated thusly) suffers a wire short. If we chose option 2, we
> encompass a wider range of PD designs, including some very low cost
> options. But it limits the ability to integrate multiple channels down the
>
> road.
>
> As an IC designer, I naturally favor option 1 - I'd like to sell PSE chips
>
> with many integrated channels. As an engineer, I'm willing to weigh the
> pros and cons of each (including ones I haven't thought of yet) and vote
> for the best solution. Let's continue to air out the pros and cons until
> Don's vote - coming soon, right, Don?
>
> Dave
>
>
>
>