STM32MP157DAC EVB: DDR3L Length Matching
Hi,
I am referring to the STM32MP157D-DK1 EVB (STM32MP157DAC1), specifically the "mb1272-bdp" design file, and would like to clarify the correct method for measuring DDR3L to Microprocessor (MP) trace lengths on the PCB.
My question is regarding the Clock P/N signals:
Should the PCB trace length be measured from the MP pin to the DDR3L chip clock pin (CK_P/N), or from the MP pin to the 100 Ω termination resistor? The reason for the question is that the termination is placed after the DDR3L chip, which adds additional trace length.
After reviewing the EVB design (mb1272-bdp design file) and analyzing the trace lengths using the ST-provided length equalization Excel file, I have the following observations:
When measuring trace length from the MP pin to the DDR3L chip pin:
The address group signals are mostly within acceptable limits, except for A16, RAS, and A0.
However, the data strobe signals (DQS P/N) are outside the required −15 mm to 0 mm range with respect to the clock signal.
Address Group:
The Data groups (DSQ P/N):
2. When measuring trace length from the MP pin to the clock termination resistor:
The address group signals show multiple mismatches.
The data strobe signals (DQS P/N) fall within the acceptable range.
Address group:
The Data groups (DSQ P/N) are okay:
We have followed the trace length guidelines of the EVB for our custom board design. Therefore, we would greatly appreciate your guidance on which method of trace length measurement should be followed to validate the DDR3L layout correctly.
Could you please confirm if using the same trace lengths as the STM32MP157D-DK1 EVB (MB1272-BDP) is acceptable for a custom design? We would prefer not to deviate from the EVB implementation, since it is known to work reliably, unless a deviation is absolutely necessary.
Thank you!