F429 + SDRAM PCB Design

sk-st · ‎2014-09-27

Posted on September 27, 2014 at 19:57

Hello,

i am currently working on my first PCB with a STM32. The F429 and the SDRAM have LQFP/TSOP packages. Unfortunately the FMC Pins needed for SDRAM are distributed over all sides of the LQFP. I have looked on the gerber files of the F429 DISCO Board and not seen any measures to get all (data/address) lines to the same length. Well, the F429 can clock the SDRAM at max. of 90 MHz. How critical are different wire lengths under such conditions?

Is there a (non religious!, just practical) design guide?

megahercas6 · ‎2014-09-28

Posted on September 28, 2014 at 09:19

just keep it short. ideally put sdram below stm32f429.

Note that if you are going to use it in software access (not dma) it will run only to 22MTps (while sram will do 36MTps) so at this speed, any pcb will work

Mark Edwards · ‎2014-09-28

Posted on September 29, 2014 at 00:13

I have attached a pic of my solution to the problem and as you can see I haven?t managed to get the track lengths even either and I haven?t had any problems yet.

Putting it underneath would be a good idea but in my case that space is filled by a FPGA.