Trying to build my own RaspBerry clone

[sidereal]

Hi

I am starting my hand on building my own Raspberry Clone. I have built Arduino clones, before Arduino was a thing, and you had to use DIP package ATMEL controllers.
Now I want to try my hand at ARM based CPUs in contrast to MCUs such as the typical ATMEL products (e.g. ATMEGA xxxx).
 

This is my first time with ARM, so please bear with  me.

I have chosen the Sitara family of processors, AM437x series. I am using the open source BeagleBoan project as my start point.

I as seeing in the Datasheet for AM 335x (the one used by BeagleBones) as well as for AM 437x, that the decoupling capacitor can be 10.08 µF . See here, page 93.

But the BeagleBone schematic uses > 20.13 µF capacitor. See page 5. How is the correct value of the capacitor determined?

Thank you.

[Terry Bites]

Cash to burn??

[thinkfat]

Read the datasheet more thoroughly. Don't omit the footnotes. Good luck.

[tmadness]

So a few things:
I admire your moxie and wish you the best of luck. But you should probably clarify to your self what you are doing, I don't see a clear goal and there's a bit of confusion in your post.
Second, decoupling is a interesting topic, there are objective Measures of effective implementation. But few projects require that kind of analysis. Rules of thumb:
spread your decoupling into two types bulk and local decoupling. Bulk decoupling is what you are probably asking about, the large 10/20 uf cap. Size/price matters if you are going to manufacture at volume, hence why the beaglebone has 10 uF caps. Err on the side of larger caps when you are doing something where pennies extra don't matter. The other kind of decoupling, local decoupling, take from the reference design, I think I saw 10nf and .1 uf caps on the beaglebone. Get these as close to your pins as possible. Don't skimp on local decoupling, 1 per pin or 1 per group of 2-4 pins minimum.
Arguably, placement and layout of decoupling matters more in most cases than absolute value. Place the caps close to the pins. Always. Keep a high quality ground and power pour accessable to your caps. Bad designs have meandering power rails and ground loops. If you can afford it put a power and gnd plane underneath. If you can't then wide traces, that are the closest to a straight line from your power supply. Go for the widest via that your design can fit, ideally every pin gets its own via or direct power connection. At the power supply side go for multiple parallel vias, like go Overkill.
And finally, choose quality ceramic caps. Don't use electrolytic, tantalums only for bulk, ideally bulk should be ceramic as well.

[sidereal]

Thanks guys