[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.
/Mikhail
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