DP83848J: Trace length matching.

Sam Kuo

Prodigy 10 points

Part Number: DP83848J

This is our application, we use a cable connection thru RMII bus between two boards.

It is a RMII layout routing, please help confirm the following question:

The 50MHz external oscillator is synchronized outputted to both DP83848JSQ and DPU, since the lengths of the two don't match, They should be synchronized in terms of clock. Should we make their lengths equal?

OSC - DP83848J : 2" (board 1) + Lsync??

OSC - DPU : 2" (board 1) + 8" (cable) + 10" (board 2) = 20"

If we should do synchronized, we may do fine tune Lsync to 18". correct?

Extending from the previous question, For Data bus and clock is there any rule for the trace length matching? with in 2"?

Due to the regulation that the length of signal can’t over 6 inches, but we broke the rule and total length is 10 inches, Is it possible to increase the re-timer or re-driver (model/part number) to solve this problem. Any solution TI suggest?

Due to we have cable connection, how to tranfer data loss from 6" on board to cable?

over 1 year ago

0 Alvaro (Al-vuh-roe) Reyes over 1 year ago

TI__Genius 16626 points

Hi Sam,

I didn't check this till the end of day, I will take a look and respond again on Monday.

Regards,

Alvaro

0 Alvaro (Al-vuh-roe) Reyes over 1 year ago in reply to Alvaro (Al-vuh-roe) Reyes

TI__Genius 16626 points

Hi Sam,

Is this design already made? Are you concerned with potential problems or did you already make the board

Like you said, the lengths are long. We have an IBIS model available for the DP83848. Running a simulation can help understand the risk.

For Re-driver suggestions, I'd need to have a different department help with that. Would you be okay if I reassigned this post to them?

Regards,

Alvaro

0 Sam Kuo over 1 year ago in reply to Alvaro (Al-vuh-roe) Reyes

Prodigy 10 points

Hi Alvaro,

We are working on design, not get really board.

We think TI can provide model first, but may I how to judge pass or fail or risk?

For redriver, please help to assign to right person, thank.

0 Alvaro (Al-vuh-roe) Reyes over 1 year ago in reply to Sam Kuo

TI__Genius 16626 points

Hi Sam,

On the DP83848J Product Page , the IBIS Model can be used to test signal integrity.

You want to keep on eye on VIH, VIL, VOH, VOL, and the Timing specs. Make sure that these values match the required specs of the MAC that you plan on using in your system.

I am now going to reassign this thread to someone who can help you with re-drivers.

Best of luck!

Alvaro

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DP83848J: Trace length matching.