Path: Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Fri, 19 Apr 2024 14:30:46 +0000 From: Joe Gwinn Newsgroups: sci.electronics.design Subject: Re: spread-spectrum model Date: Fri, 19 Apr 2024 10:30:45 -0400 Message-ID: References: <7qk22jlrrc9949ccrkdk058b4dinnnt75f@4ax.com> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 62 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-hbXFDtliKGR306Wk3jagKaCHoQ9F6BbAT9Ube5NLwqoQg3CPdlgY/mhywXT1JgQWnuOFQcnfJrxVvAm!jI48qO3zG2hVgYMTk7p1nU2tclrgTOhqSNarQ3GBI6s/JHPYqkd7ohrQ+sor21FK6xwbajU= X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/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: 3448 On Thu, 18 Apr 2024 12:14:04 -0700, John Larkin wrote: >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." In my world, we have multiple parallel components (like array sections) in the signal path powered by independent power supplies that are required to have independent noise, to prevent correlated gain when these parallel paths are summed, say in a radar beamformer. Telling the power-supply folk that it's just a power supply is a good way to get buried in details. >>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 interesting appnotes > > > > > > >Their little TPS54302 type parts have radical looking PWM, but the >final DC is super clean. Nice trick. > > > > > >We may get some EMI from switching rise/fall ringing too, in the >hundred-MHz ballpark. It would help to de-phase that too. TI stuff is widely used in radar, but in the most capable radars the dithering is provided by bespoke radar firmware, and not left to the converter chip. But those chips do work well. Joe Gwinn