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Advanced Layout course - capacitors count

Alex Shuklin , 07-24-2020, 11:23 PM
Hi, Robert!
Thanks for great courses, I've just started advanced Layout course, and that's my first one. Can you please explain, why do we have such decoupling capacitors count in our lessons?
In VDDARM_CAP net there are 8 pins, and 4 0.22u capacitors with 1 bulk.
In VDDSOC_CAP - 7 pins with 6 small capacitors and 1 bulk.
If I do my own design, what is the way to the choose number of capacitors? Try to do 1 piece for every pin and sometimes group them by 2, if there not enough space?
Or is there's some topic to read which explains that?
robertferanec , 07-25-2020, 03:14 AM
iMX6 Design guide recommends values and number of decoupling capacitors. Similar for other boards - I follow reference designs or design guides.

If you are not sure, usually I use 100nF per pin for decoupling (but it depends on the chip). For bulk ... it depends ... any values from 1uF, 4.7uF, 10uF, 22uF, up .... sometimes I use similar components what are already used on the board.

PS: I am currently working on a video to determine optimal decoupling and it is ..... complicated. It is much easier just to follow existing designs.

Example from Hardware Development Guide for the i.MX 6ULL Applications Processor:

Alex Shuklin , 07-25-2020, 05:52 AM
Oh, I missed that. Thanks a lot!
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