Skip to main content
Freedom_Neo
Freedom_Neo
Senior
April 21, 2022
Solved

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

  • April 21, 2022
  • 1 reply
  • 1928 views

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?

0693W00000LydJfQAJ.png0693W00000LydK9QAJ.png

This topic has been closed for replies.
Best answer by Piranha

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/

1 reply

Piranha
PiranhaBest answer
Principal III
April 23, 2022

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/

Terms & ConditionsAccessibility statement