RE: Maximum Power for add in card more than 25W

["Ingraham, Andrew" <Andrew.Ingraham@compaq.com>]

> I'm designing a PCI add in card, from the PCI Spec
> (page 146), there are two pins that are used to
> indicate the power comsumption for an add in card. 
> 
> My question is, how if an add in card consume more
> power than the maximum power that is shown by the
> PRST1# and PRST2# pin (i.e 25W)?
 
It isn't only the table on page 146.  Page 150 also states: "The maximum
power allowed for any PCI board is 25 watts..."

If you exceed it, you are not PCI compliant, you run the risk of damaging
the computer it's plugged into, or making it not come up properly, and you
create a hot spot in the box.  The 25 watt limit is both electrical and
thermal.

> what are the workaround so that my add in board which
> consume more than 25W can works. Thanks.
 
One workaround, which I have seen, is to design a 2-card adapter with a flex
cable between them.  You consume two adjacent slots.  Both cards have all
power and ground pins.  The combination can draw up to 50 watts total.

There's no guarantee that the system you plug it into will give you all 50
watts, but some will, and at least you won't violate that particular PCI
spec.

Regards,
Andy