DDR3 Interface Design with STM32MP157FAC1 Using KiCad

Design and Layout
1

Hello everyone,

I recently completed the layout of a DDR3 memory interface for the STM32MP157FAC1 SoC using KiCad, based on guidelines from the DDR3 and STM32 hardware design application notes.

Key design highlights:

  • Impedance control:
    • 55 Ω ±10% for single-ended signals
    • 100 Ω ±10% for differential pairs (DQS and CLK)
  • Length matching:
    All critical signals—including CLK, DQS, DQ, address, and control lines—were matched within a 1.016 mm tolerance.
  • Data lane configuration:
    • Byte 0: DQ[7:0], DQM0, DQS0_P/N
    • Byte 1: DQ[15:8], DQM1, DQS1_P/N
    • DQ signals were length matched with their corresponding DQS strobe signals within each byte lane.
  • Control signals:
    RAS#, CAS#, WE#, CS#, CKE, and ODT are length matched with the differential clock (CLK_P/N).
  • Address lines:
    Grouped and length matched among themselves to ensure timing alignment.

Screenshot 2025-07-02 203111
Screenshot 2025-07-02 203111949×606 221 KB

I would truly appreciate any feedback ,

Thank you so much for your time and support.

2

Without detailed review, I will tend to not go far. That said, Length matching is preferred using time delay (ps) over physical length.

I also personally length match as tight as possible instead of only the minimum allowed. Why you might ask? There are a number of variables related to stackup, materials, and fabrication tolerances that can affect the end result. If matching has a tighter result, that creates more flexibility in those other areas that I have little to no control over and still stay within the overall goals.

2 Likes