SparkFun Forums

[ben11235]

I'm designing an Arduino board that is almost completely digital. The analog paths to the analog pins and the atmega324 are the only analog components. It uses 3 voltage levels, 2.5V, 3.3V and 5V. It's a 4 layer board, and I'm wondering what's the best method for providing power and ground. 2.5V is used by one clock and possibly the atmega. 3.3V powers the digital peripherals and possibly the atmega. 5V powers the 5V pin and possibly the atmega. The atmega uses jumpers to select its operating voltage.

I'm thinking about a 4 layer board with top and bottom being signal layers, and the two internal layers being Vcc and GND. I read in a TI app note on analog digital that it's best to have a continuous ground plane split in to analog zones. I'm not sure I need that for the atmega chip, it's the only analog thing on the board. I'm also thinking of using the Vcc plane to route power on a trace by trace basis(maybe with fills), Is this reasonable? Do I need to worry about signal path like I do for the ground plane? I can use the same ground for multiple voltage levels, right?

Finally, I know vias can run from the top layer through all the layers, blind vias connect two internal layers, and buried vias connect one external layer to a number of internal layers. Is this correct?

[Ross Robotics]

Since your not making a motherboard that will have Ghz speed, you don't need to worry about signal paths etc.. Also you only need one ground plane. Having to split ground planes is if your board will carry analog and digital components. Since you say that yours is mostly digital then don't worry about splitting planes. You could use the 2 inner layers for the 3.3V and the other inner layer for 5V. Leaving the 2.5V routing by traces. That would leave you with a signal layer and the bottom, a ground layer.

And yes, you have the via basics correct.

When you get over 100Mhz (IMO), than you should worrying about signal traces, like the length and how they are run. Same as the analog and digital. I have made a few boards in my day, I have yet to have a defective board because I didn't split the grounds. I know there are several dedicated analog and digital chips that need to have there own ground, but I don't think you have any..

[MichaelN]

... Having to split ground planes is if your board will carry analog and digital components... I have made a few boards in my day, I have yet to have a defective board because I didn't split the grounds. I know there are several dedicated analog and digital chips that need to have there own ground, but I don't think you have any..

The latest thinking seems to be that split planes should rarely (if ever) be used, as they can cause more problems than they solve. You’re better off “partitioning” the board into analog and digital “zones”, and taking care where you run tracks. Keith Armstrong has a good series of articles that covers this (you have to register, but they don’t spam):
http://www.compliance-club.com/KeithArm ... artid=4152
http://www.compliance-club.com/pdf/1284 ... 5(1st).PDF