What should be the length of the path to be drawn for SDRAM AND FLASH?

Freedom_Neo · ‎2022-04-21

I am using below commponet

MCU: STM32H7B3IIT6

SDRAM: IS45S16800F-7CTLA1-TR

FLASH: MX25LM51245GMI00

I am revising the card design according to high speed signals. But how do I calculate the length of the paths to be drawn for SDRAM and FLASH?

How many mm and how much impedance should it have?

Piranha · ‎2022-04-23

The shorter the better, but it's more important for all related signal lines to be of the same length. And for all high-speed signal lines the best is to optimize the impedance to 50 ohms. That's why you have those 33 ohm series resistors - in series with IC output pin's impedance of approximately 17 ohms it adds up to 50 ohms. Search for a term "transmission line".

For PCB routes target approximately the 50 ohm common impedance with this:

https://www.eeweb.com/tools/edge-coupled-microstrip-impedance/

View solution in original post

Piranha · ‎2022-04-23

The shorter the better, but it's more important for all related signal lines to be of the same length. And for all high-speed signal lines the best is to optimize the impedance to 50 ohms. That's why you have those 33 ohm series resistors - in series with IC output pin's impedance of approximately 17 ohms it adds up to 50 ohms. Search for a term "transmission line".

For PCB routes target approximately the 50 ohm common impedance with this:

https://www.eeweb.com/tools/edge-coupled-microstrip-impedance/