SparkFun Forums

[messi]

Hi everybody,

I would like to know if I have to check the impedance of the LPC2148 USB routing on my 6layer board?
Or is it just enough to route it differentially?

Has anyone a hint or tip about this topic.

Best regards

Messi

Stack-Up:
------------
L1: Top (SMT)
L2: Gnd
L3: Vertical (USB)
L4: Horizontal
L5: 3.3V
L5: Bottom (SMT)

[leon_heller]

Full-speed USB should be OK without impedance matching. Why do you need a 6-layer board? You stackup looks a bit weird, BTW.

Leon

[messi]

Full-speed USB should be OK without impedance matching. Why do you need a 6-layer board? You stackup looks a bit weird, BTW.

Leon

I don't think so.
This stackup is the most common one.
I use a 6Layer stackup because I use various components on a small board (45x88mm or 1.7x3.4") on both sides. One reason is also EMC the other is also to get a better feeling for multi layer boards.

Why do you think that the stackup is weird?

Cheers, J

[leon_heller]

Gnd and power planes are usually on the two innermost layers as they need to be close together.

Leon

[messi]

This depends on the philosophy. Do you know this link:
http://www.hottconsultants.com/techtips ... -up-3.html

My goal was to be sure that I have a good EMC design.
Pwr and Gnd together is good to create additional Capacitors. But then you are more exposed to EMI especially when you will have a plastic case.

So it is always a question of compromises. I think that I will have less problems with this stackup then with your suggestion. Especially since I also use ground areas on the top/bottom layer.

I know my company is also doing your stackup but they are also using metal cases.
I hope that I will be right if not I will try your stackup the next time.

Cheers

J

[leon_heller]

With proper design techniques a four-layer board will meet EMC requirements and be a lot cheaper, and be able to use a plastic enclosure. I once designed a system like that and we didn't have any problems conforming to CE.

Leon