Sujet : Re: spread-spectrum model
De : jjSNIPlarkin (at) *nospam* highNONOlandtechnology.com (John Larkin)
Groupes : sci.electronics.designDate : 18. Apr 2024, 21:14:04
Autres entêtes
Organisation : Highland Tech
Message-ID : <o5r22jdevbnlk2bpd4tuph13nbkltarv77@4ax.com>
References : 1 2
User-Agent : Forte Agent 3.1/32.783
On Thu, 18 Apr 2024 13:16:04 -0400, Joe Gwinn <
joegwinn@comcast.net>
wrote:
On Thu, 18 Apr 2024 08:26:56 -0700, John Larkin
<jjSNIPlarkin@highNONOlandtechnology.com> wrote:
>
I'm designing a switching power supply module and could reduce EMI by
going spread-spectrum on the switching frequency. The simple one below
reduces things by 20 dB. Probe the SS node and FFT.
>
The ss inside switching reg chips is no doubt more sophisticated. In
an FPGA, we could do some sort of pseudo-random thing.
>
On a multi-channel power supply, there may be some small advantage to
have a separate spread per channel. That would be easy.
>
I'd check for cross-correlation as well, so no ganging up in systems
using multiple channels in some signal path.
When my engineers get too fussy about stuff like that, I remind them
"it's just a power supply."
>
Depending on details, the problem could manifest itself as peaks or
ripples in the time domain, your beloved homeland.
>
Joe Gwinn
>
TI has a couple of intersting appnotes
https://www.ti.com/lit/pdf/slyt809https://www.ti.com/lit/SLVAF18Their little TPS54302 type parts have radical looking PWM, but the
final DC is super clean. Nice trick.
https://www.dropbox.com/scl/fi/8rytjiwp4hmt2ypgk9bk4/DSC06826.JPG?rlkey=4qipduct0ptrhei07ijdxpsca&raw=1https://www.dropbox.com/scl/fi/kf2kxbxih6xjbx8uv2o0d/TPS54302_spectrum.JPG?rlkey=rd3diu5nvhasfn7228m8yk665&raw=1We may get some EMI from switching rise/fall ringing too, in the
hundred-MHz ballpark. It would help to de-phase that too.