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response to Bob Leonowich's presentation, page 17, Sept 2000

Title: response to Bob Leonowich's presentation, page 17, Sept 2000

I'm sorry that I was not at the meeting to answer these questions.
Here are my responses to the item numbers on your presentation, page 17

1.) Transformer doesn't necessarily provide AC/ESD impulse isolation so this needs to be

ESD was tested informally, but not reported.
Recall that the logic side of the transformer has a 100 ohm and a 3300 pf cap to ground.
This shunts the ESD energy that gets through the transformer.
This is much easier than on the data lines, since the pulse bandwidth is so much lower.

2.) Strategy implies PHY redesign and consequential re-qualification on new generation
devices with higher pincount to support the needed I/O

My method can be implemented in the PHY, or in the power supply, whichever is more cost effective.
My prototype shows a PHY configuration.

3.) Logic side power plane residence of detection implies EMI can leak from noisy logic to wire

The exact same thing is true of the 10/100/1000 data paths.
EMI problems will be dominated by the switching power supply

4.) Approximately 1MHz bandwidth signature pulse signaling precludes aggressive filtering to
limit noise emissions

If you look at page 27 of my presentation, the common mode discovery pulse energy is about 40 dB down
at 1 MHz, the 3 dB point is more like 30 KHz.

5.) Conveyance of current use from supply to upper levels (to facilitate network power
management) requires crossing the isolation barrier and additional monitoring circuits in
the supply

This is not tied to the discovery method.

6.) Longitudinal voltage characterization in terms of <1 volt sensitivity has not been done

What exact tests are you asking for?

7.) Parallel devices may get destroyed at application of higher power

Can you be more specific about which parallel devices you are talking about?

8.) Use of constant signaling and reliance on transformer saturation to detect undercurrent is
very coarse. >10mA signature pulses imply a >0.5W maintenance consumption

The prototype we built uses the power supply to detect a minimum load. It could use transformer saturation, if
that is practical, I'm hearing that the magnetics vendors are against it.
Again, this is a separate issue from the discovery method.
Also, what does the amplitude of the signature pulse have to do with power?
When the DTE power is on, and the undercurrent value matters, and the discovery pulses are off.

9.) 25 pair bundle interference with asynchronous units?

This is on my list of things to test.

10.) Pulse shaping implies expensive immediate implementation

This is true if you use my discrete approach, but why would anybody do that?
An integrated IC solution would use multiple current sources, as the PHY's do now.

11.) 1uF >54V signature cap in PE is big and expensive

The cost needs to be considered. Also, the cap value can probably be lowered.
Even so a 1206 part is not that big.

12.) Extra two diode drops Required in PE lowers maximum power delivered to PE load

We could use a FET switch instead. All discovery methods, except the large cap, face this problem of removing
the effect of the 100 to 500 uF cap on the input of the power supply on discovery.

any comments?

- Rick