[SI-LIST] Re: Mixed digital/RF board with switching power supplies

  • From: "Mikhail Matusov" <matusov@xxxxxxxxxxxx>
  • To: <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 6 Jul 2007 16:34:00 -0400

----- Original Message ----- 
From: "J.D. Bakker" <jdb@xxxxxxxxxxxx>

> Linear Technology have an interesting appnote:
> http://www.linear.com/pc/downloadDocument.do?id=4159
> In this document, Linear Technology's Application Note 70, a switchmode 
> power supply design is presented with less than 100uV output noise, and 
> little RFI. This is achieved by using a switch controller which has 
> controlled output switch slewing, allowing a trade-off between EMI/RFI and 
> efficiency.

Yes, I am aware of this appnote. IIRC it uses a push-pull topology with a 
transformer. In the board we are discussing it wasn't practical to use 
anything more complicated than a buck regulator...  Also, I don't think my 
problem is in the output voltage not being clean enough as I can observe the 
offending spurs in RF connectors even on the board with only the power 
supplies populated and no other active components!

> An additional measure you could implement is to synchronize the switchers, 
> and shift the switching overtones away from your frequency of interest.

Unfortunately, this is not going to work as my band of interest is roughly 
40-50 MHz wide.

Thanks for your help anyway.


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