FEDEVEL
Platform forum

nick38 , 03-10-2021, 12:04 PM

Hi,

I'm looking at the iMX6 Rex board and I noticed that there are a lot of 220n decoupling capacitors in parallel.
How do you know how many you need to place and also how do you know what value to use?
For example the VDDARM_IN pins have 6 220n capacitors in parallel and capacitors in parallel adds the capacitance.
So why not just place a single 1.2uF capacitor? that way you have more space to do the fanout and also routing.
Please be patience with me as I'm just stating to learn advance routing.

Thanks!

robertferanec , 03-11-2021, 05:31 AM

These are recommendations from design guide and reference schematic.

PS: You can't simply use 1x 1.2uF, that is not how decoupling works. I would recommend to watch my videos on this topic: https://www.youtube.com/playlist?lis...uvkR_TjpnF1Z7f

nick38 , 03-11-2021, 07:25 AM

Hi Robert, thanks for your reply. One more question. Why did you use 0402 capacitors instead of 0201? it seems to me that by using 0201 you could have save more space in the board.

robertferanec , 03-12-2021, 05:14 AM

Simple answer: because 0201 was not so common when we were designing the board and we didn't want to have problems with manufacturing. Now, I would use 0201.