[SI-LIST] Re: si-list Digest V5 #275
- From: "Anders Frederiksen" <af@xxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 13 Jul 2005 10:58:20 +0200 (CEST)
[Dimiter]
> I am routing a board with an MPC5200 (freescale/mot) which has a
> DDR interface (133 MHz clock). What sort of termination resistors =
> (resistor arrays?) do I put?
[David]
> Overshoots are the biggest problem I have seen when running without any =
> termination. [...]
Now I'm scared again. I'm having a design layed out right now with no series
resistors. Short (<5cm, probably typically 2-3cm for most banks) transmission
lines
- but interface towards a Xilinx FPGA that typically is not happy with
over/undershoots. Luckily the DDR is only 2.5V - so I think it'll be ok.
> Simulating a DDR design at the conditions above sounds like a waste of =
> time to me, and please don't go into suggesting more simulation,
I'd like to simulate - but have no tools and little time to learn/find cheap
tools/models and learn to use them :-(
> I am only looking for the right package/vendor/distributor of the resistors I
> have to use, I know the rest of the story.
I use 0804 quad packs in bulk. You can't go much smaller (31mW) if you can risk
a
steady bus. Bussed packages will save you som space but are typically more
expensive, harder to get and worse SI wise.
However, for this current design we use 0201 (50mW) - they'll fit nicely
between the
vias of the BGAs. Hence, the PCB designer and I loves them - but probably
production
is a bit more worried...
Cheers,
Anders
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