DP83867IS: Buffer device for RGMII lines

Takashi Onawa

Part Number: DP83867IS
Other Parts Discussed in Thread: SN74AHC245,

Hi Team,

My customer wants to insert a buffer device such as SN74AHC245 between MAC and PHY because the interval is a little bit long(almost 5 inchs).
In their system, They haven't gotten good result with large packets due to poor signal integrity on RGMII lines. So they expect to improve by adding the Buffer,

1. At first, Do you think there are any concerns and notes about adding buffer device between Mac and Phy? If there are, please let me know.

2. Do you think they can get any improvement by adding the buffer?

I can send the schematic and waveform captures off-line to you after someone assigned for this thread.

MAC : Xillinx Zinq
Phy : DP83867IS

Regards,

Takashi Onawa

over 5 years ago

0 Ross Pimentel over 5 years ago

TI__Mastermind 23675 points

Hi Takashi-san,

I think a buffer will certainly improve their stripline reach.
This might not be the correct part for the PHY though.
Looking at Voh of the DP83867IS, it has a min of 2.0V. The buffer you are looking at has a Vih min of 2.1V.
Do you mind reaching out to the owners of the buffer and check this high Vih.

I am also concerned about the propagation delay through the buffer. From the datasheet, it looks like it could be from 5.8 up to 8.4ns.
RGMII is very sensitive the the offsets between the data pins and clock. You have a very narrow margin to meet timing because it is DDR.
Can you verify the channel to channel max variation?

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DP83867IS: Buffer device for RGMII lines