AM6442: DDR Design and Layout Questions

Mari Tsunoda

Expert 5726 points

Part Number: AM6442
Other Parts Discussed in Thread: TMDS64EVM

Tool/software:

Hi Team,

My customer is designing the DDR4 pattern and has a couple question regarding this document.

On p.19, Table 2-6, it says that 1ps = 5mils. Does the requirements in table 2-6 and 2-7 take into consideration the DDR4 internal trace length?
For example, on table 2-7 it says DRS31(BYTE0 length) is MAX500ps(≒2500mil=63.5mm), is it ok to think of this as the longest length possible from AM6442 BGA pin to DDR4 BGA pin?
Can you provide the trace length list for the TMDS64EVM (including signals other than DDR)

Best regards,

Mari Tsunoda

over 1 year ago

0 JJD over 1 year ago

TI__Guru* 96681 points

Hi Mari,

1. The requirements are from pin to pin. You do not need to consider the package pin delays, as the training algorithm will compensate for any further mismatch caused by the package

2. The EVM design files are on ti.com: https://www.ti.com/tool/TMDS64EVM which includes layout board files. You can get trace length info there.

Regards,

James

0 Mari Tsunoda over 1 year ago in reply to JJD

TI__Expert 5726 points

Hi James,

Thanks for the quick reply.

Had a follow-up question from the customer regarding the DDR4 MAX trace length.

From table 2-6, 2-7, DRS31(BYTE0 length)=500ps(≒2500mil=63.5mm).

It seems like MAX trace length for DDR4 = 100mm would be more common. Is there a reason why the DDR4 trace length requirement is quite strict (63.5mm)?

Best regards,

Mari Tsunoda

0 JJD over 1 year ago in reply to Mari Tsunoda

TI__Guru* 96681 points

I don't think 63mm is strict. That's 2.5 inches! Because of the high speed bus associated with DDR4, it is necessary to limit the distance between the two devices. What restrictions do the have on the board that require the DDR4 to be more than 2.5in from the processor?

Regards,

James

0 Mari Tsunoda over 1 year ago in reply to JJD

TI__Expert 5726 points

Hi James,

Thanks for the response.

JJD said:
2. The EVM design files are on ti.com: https://www.ti.com/tool/TMDS64EVM which includes layout board files. You can get trace length info there.

Is it possible to give the trace lengths in a table or excel sheet?

My customer cannot open CAD files made in Allegro or similar tool.

Best regards,

Mari

+1 JJD over 1 year ago in reply to Mari Tsunoda

TI__Guru* 96681 points

Hi Mari,

sorry, this is not something we typically provide. There is a free Allegro viewer on the web which can be used to view the board files: https://www.cadence.com/en_US/home/tools/pcb-design-and-analysis/allegro-downloads-start.html

REgards,

James

0 Mari Tsunoda over 1 year ago in reply to JJD

TI__Expert 5726 points

Thanks. Let me mark this as resolved and open a new thread if they have more questions.

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AM6442: DDR Design and Layout Questions