TMS320C6678: DDR3 impedance requirement

Koichiro Tashiro

Part Number: TMS320C6678

Tool/software:

Hi,

According to "DDR3 Design Requirements for Keystone Devices" (sprabi1d.pdf), 50ohm +/-5% impedance is required for single-ended impedance.

My customer is asking it is OK to relax the value to 50ohm +/-10%.
What is the reason to require +/-5%?

Thanks and regards,
Koichiro Tashiro

9 months ago

0 Robert Eschler 9 months ago

TI__Guru 51845 points

I do not have the background on the 5% recommendation, but yes typical PCB manufacturing impedance tolerances are 10%. In the design the impedance should target 50-ohms with no variation (as this would create larger impedance variation once combined with manufacturing tolerances).

0 Koichiro Tashiro 9 months ago in reply to Robert Eschler

TI__Mastermind 22935 points

Hi Robert,

Thanks for your reply.
I am not sure I understood your answer clearly.
Do you mean it is OK to relax +/-10%?

Thanks and regards,
Koichiro Tashiro

+1 Robert Eschler 9 months ago in reply to Koichiro Tashiro

TI__Guru 51845 points

I would expected maximum of +/- 10% impedance variation to be OK.

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TMS320C6678: DDR3 impedance requirement