Re: [SI-LIST] : multiple power planes

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From: DORIN OPREA ([email protected])
Date: Thu Oct 05 2000 - 06:08:22 PDT

Hi Jeff,

I would start with device placement and mark the area for each required
power supply; thus I can see the possible islands within the same
reference plane throughout the stack up. I would chose the reference
plane for the lowest voltage supply the closest to the corresponding
devices. Depending on the placement, I will try to have only wide traces
for 5V and 12V distribution if possible. You have also to consider
strong coupling between power and ground planes, probably Hadco ZBC.

Have fun,

Jeff Reeve wrote:

> I apologize in advance if this issue has been beat to death
> already…but here it goes….
> I have a board with multiple power rails 12V, 5V, 3.3V, 2.5V and 1.8V.
> It seems like overkill to make separate power/gnd planes for each of
> the voltages…sheesh 10 planes to handle power! So what are you guys
> out there doing to limit the number of planes and yet still maintain
> low EMI? I would like to implement in the least planes possible and
> maintain 50-55 ohm impedance. Signal rates will be up to 100MHz. 1.8V
> will carry up to 8A, 2.5V will carry up to 6A, 3.3V will carry up to
> 4A, 5V will carry up to 8A and 12V will be less than 1.5A. Typical
> devices on this board are FPGAs, SDRAM, RiscProcessor, Multi-media
> Processors, 10/100 Ethernet chip sets, SCSI chip sets, IDE chipsets,
> USB chipsets, etc. Anybody willing to share recommended stack up?
> Any advice and other pearls would be most appreciated!
> Jeff

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