VCC width

[krw@att.bizzzzzzzzzzzz]

On Tue, 18 May 2010 14:45:15 +0200, "aleksa" <aleksazr@gmail.com> wrote:

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message news:b734v55bqgpfdrp97cb011jauogvcqelj9@4ax.com...
It's going to be interesting to try to get an ARM or an FPGA to work
on a 2-layer board. The Vcc and ground current spikes can be horrific
for a fast, many-pin chip, and a wimpy routed (non-plane) ground
structure will cause nasty ground bounce noise.
Make the ground and Vcc as wide as you can, and stitch them with lots
of bypass caps. Lots of luck.

I have a working FPGA board, Spartan II XC2S50 TQFP144.
If I replace the PC with ARM, I could even use VQFP100.
The freq is not much, 40 MHz, and I doubt I'll go higher than that.

The clock frequency isn't (usually) the issue; how fast are your edges?

I've placed vias on every VCC/GND pair and placed caps on the bottom
side. The bottom side is almost free of signals, so there's no problem
connecting the power.

The total distance from the pin to the cap and cap to ground is what matters.

As for the ARM @ 180 MHz... well let's wait and see.
I hear other people made it.

Again, the core frequency doesn't matter, much. The package should be
designed well enough to handle that part. Your problem is managing the
delta-I on the power, ground, and signals.