Electronics > Beginners

how would you connect these power planes

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hsn93:
hello,

how would you connect these planes which are close to each other

VDDIO - 3v3
VDDCORE 1v2



having 4 layers pcb .. (should i consider 6?)
is it ok to have the 3v3 plane on layer 2 , and 1v2 on layer 3 ? or i should put a ground plane in between them ??
like this:

i try my best to put all component in the top layer as well.

suggestions?

hsn93:
hello, i though this is to generic question and thats why nobody answered.

for me i asked because i dont know what is good way to approach this,


so i will put another picture with a specific question:


shown in the picture 3 planes in (top plane red = gnd) - 2nd layer brown (3v3) - 3rd layer cyan (1v2)
not shown (bottom layer blue = gnd)

there is highlighted net which i can route in any layer. i remember that i watch videos of dave "or fedevel academy" saying its good practice to route in one layer as much as possible .. the thing is that this will cut the ground
"long trace = cut the plane"

now what would be the best practice

to route in top layer and place vias between top and bottom ground planes like this?


or to change the layers of the net like this:

hsn93:
hello, there was no reply on this post so i thought its so stupid question or to general. hence i went through the design and i want to ask more specific question,


here is a video showing RF injection to crystal oscillator.

so a question about the planes:

is it good idea to not put a power plane under the crystal ? so only bottom layer (ground plane)?

here is a picture of what i mean:


would it have better accuracy?
i know that a oscillation tracks should not pass over tracks so would power plane consider as track ? (because current takes shortest path and the shortest path could be under the crystal at some point? so is it wise to make what i did in this picture ? refereing to XC2

Karlo_Moharic:
put a ground plane between each power plane

dmills:
If you are forced to use 4 layer for a two power plane design then that is about as good as you can do, but depending on what you need to fan that qfp out (And hence what happens to the ground pour) I would tend to be more concerned by the nets crossing reference plane edges then the polygons themselves.

For this reason I tend to favour a solid ground on L2 rather then the bottom layer even if it makes the power a rather complex pair of interlocking polygons on L3 & 4, then do most of the fanout on L1. This keeps the fanout above a solid ground, which is very much what you want.

It does of course compromise the reference plane for the back of the board, but 4 layers, what can you do?
Do watch the copper distribution, the layers should be reasonably symmetric to avoid the board warping.

6 layers of course is nice, but it adds reasonably significant cost.

Regards, Dan.

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