How to select correct DDR chip

[V3rn3r]

Hi folks!
The small story before my question. I'm going to use NXP's LS1043A (1Ghz, 1.2Ghz, 1.4Ghz, 1.6Ghz versions) processor in my industrial router project. After surfing through the datasheet I figured out that it is possible to use a DDR3L OR DD4 IC's and in reference design was used DDR4(512Mx8). Searchings in Reference design's BOM figured out that this is an MT40A512M8HX-093E:A. And as I understood on Digikey this is an obsolete part. And even not an industrial version of the chip. Digikey says that chip is using 1066Mhz speed.

My question is how can I figure out what DDR4 (DDR3L) speed might be used with this kind of processors and how can I figure out the compatible speed of DDR IC's to my processor IC?

PS: Google provides more information about Fly-By topology for DDR4 layout. Are there any strict rules about the layout? (or I was unlucky and didn't found T-branch designs)

[robertferanec]

I have not checked the part, but what very often happen with Micron chips is, that they have new silicon revision, so they change one letter in part name and the old one becomes obsolete. But the chips are essentially the same. Double check your chip if this is not the case - just a new silicon revision.

DDR4: yes there are some rules what you ened to follow. Maybe this can give you some info: https://www.fedevel.com/welldoneblog...useful-things/

[V3rn3r]

Yeah, I found in the list of the PCN Obsolence EOL new part that is recommended as a replacement. But it has a different clock speed. If previous it was 1067Mhz now it is 1200Mhz.
Will it affect PLL configuration or something else?

[Paul van Avesaath]

most chips will clock down, so its upto 1200Mhz, but will work on the lower clock too.. when they reccommend the part you can be sure that it will work ..

[V3rn3r]

Great! That makes me feel much better!))
Many thanks! Going on with the design then!)

[robertferanec]

Yes, Paul van Avesaath is correct. We also use memories rated for higher speed.

[anovickis]

You can also use DDR3L memory chips when you have a design for DDR3 in 1.5V (but not other way)
And yes lower speed is OK

[robertferanec]

anovickis, very good point! V3rn3r, if you decide to go for DDR3L chips, double check datasheet - it should say something like Compatible with 1.5V.

[V3rn3r]

Very useful thread!! Thank you, folks!!!