Decoupling capacitors

[zexx86]

Posted on March 15, 2011 at 20:54

Decoupling capacitors

[Tesla DeLorean]

Posted on May 17, 2011 at 14:28

Noise spikes in your supplies at the CMOS switching frequencies within the part. Do you have to pass/certify any RF/EMI standards? Do you have any radio, or noise sensitive circuits.

The bulk capacitors are there to provide immediate surges of current. What's the motivation not to use them, they can't represent that large a cost? They would be especially useful in 2-layer PCB's because the power distribution is usually pretty crappy. I think ST recommends about 7 external caps if I remember there last powerpoints.

[Tesla DeLorean]

Posted on May 17, 2011 at 14:28

[zexx86]

Posted on May 17, 2011 at 14:28

Thank you for explanation

My problem is, that I can put smd parts only from one side of the pcb, so there is not so space to add it as close as needed.

I can include them, but few mm-cm far from stm32 - I am not sure about result.

I dont need to pass any standard (for now) but there is a radio receiver connected via cables to this board (mostly 2.4Ghz).

[zexx86]

Posted on May 17, 2011 at 14:28

Do you think decoupling capacitors far from pins are usefull too ?

http://4d.zexos.org/images/stm32board2.png

is the board image

[kasper]

Posted on May 17, 2011 at 14:28

Hello,

For burst immunity my experience is every mm of traces counts to reach a high level of immunity. 

I know our demands are quite high, but for the supply we like to get 4kv immunity in surge, even than the standard only states 1kv.

To reach that level the decoupling must be made very well.

Kasper