DP83867IS: Requited PCB trace length for RGMII internal delay compensation

Takashi Onawa

Part Number: DP83867IS

Hi Team,

I found the note below in DP83867IS datasheet. I think almost 2.25m additional trace is needed to introduce 1.5ns delay to FR-4 PCB though...

Which way does TI eventually recommend for the internal delay compensation, using Skew control register or trace compensation?

When operating without RGMII internal delay, the PCB design requires clocks to be routed such that an additional trace delay of greater than 1.5 ns is added to the associated clock signal.

Regards,

Takashi Onawa

over 7 years ago

0 Ross Pimentel over 7 years ago

TI__Mastermind 23675 points

Hi Takashi-san,

Trace compensation is not possible due to trace parasitic.
You must use either internal delay within the PHY or the MAC.
The DP83867IS has a register for controlling the internal delay on both TX and RX path.

0 Takashi Onawa over 7 years ago in reply to Ross Pimentel

TI__Genius 13200 points

Hi Ross-san,

Thanks for your quick response on this.
OK, I understood.

By the way, I made a mistake in my calculation for the trace length estimation... needed trace length for 1.5ns should be around 0.225m.

Regards,
Takashi Onawa

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DP83867IS: Requited PCB trace length for RGMII internal delay compensation