PCI card current loads

["Witalka, Jerome J RV" <jjw1@PO9.RV.unisys.com>]

We are in the process of designing support for multiple PCI busses in a   
high end UNIX/NT system.  Our power supply guru has the following   
questions that he was unable to answer from reading the PCI spec. Anyone   
have the answers?


I need to know two things about the PCI cards we will be using in the   
next platform. Ideally, I would like to know worst-case values, but   
realize I may have to settle for typical numbers.

1) What is their dynamic load current characteristic, at the card level?

For example, assume a 5V card drawing an average power of 20W. This could   
occur with a DC current of 4A, which would happen if all logic activity   
was perfectly filtered out by on-card capacitors. More likely, there   
would be some lesser DC current with an AC component riding on top. The   
question is: How big is this dynamic component, and what frequency is it   
at? I do not care about individual gates and signals, but rather the   
combined result of everything on the card.

Is there a different answer for different cards (3.3V only, 5V only,   
Universal)?

2) What is the amount of bus capacitance, at the card level?

This will directly bear on how well the card filters out its dynamic   
switching currents, but I also care about how much capacitance the power   
system must charge during turn-on. Again, is there a different answer for   
different cards (3.3V only, 5V only, Universal)?

 --------

The PCI spec is very vague and states only that "All power planes must be   
decoupled to ground in such a manner as to provide for reasonable   
management of switching currents to which the plane and its supply path   
are subjected." Refer to section 4.3.4.3.

Thanks in advance for any help you can provide.

Kirk Soldner - Power Design
’ˆ	w