Path: Xl.tags.giganews.com!local-2.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Thu, 18 Apr 2024 19:15:48 +0000 From: John Larkin Newsgroups: sci.electronics.design Subject: Re: spread-spectrum model Date: Thu, 18 Apr 2024 12:14:04 -0700 Organization: Highland Tech Reply-To: xx@yy.com Message-ID: References: <7qk22jlrrc9949ccrkdk058b4dinnnt75f@4ax.com> X-Newsreader: Forte Agent 3.1/32.783 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 48 X-Trace: sv3-P1T5nn/QKArR0+5WBkZ+hYDsPqFvnhoy5fLUxsyqYrLiBQi+wWR3UgsX8WjsHylMDy60G3S4eH4Zy5D!iyfZqceUo2YkhjpGLftDL/YxxnbOKtWzRffnWdf/B84eUQRIxaM90HXleTIfmJPSb6+GTdWcjyDH!FRv8Xg== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 2748 On Thu, 18 Apr 2024 13:16:04 -0400, Joe Gwinn wrote: >On Thu, 18 Apr 2024 08:26:56 -0700, John Larkin > 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/slyt809 https://www.ti.com/lit/SLVAF18 Their 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=1 https://www.dropbox.com/scl/fi/kf2kxbxih6xjbx8uv2o0d/TPS54302_spectrum.JPG?rlkey=rd3diu5nvhasfn7228m8yk665&raw=1 We may get some EMI from switching rise/fall ringing too, in the hundred-MHz ballpark. It would help to de-phase that too.