AM6412: Query regarding impedance of PCIe

Pavan Kalyan

Part Number: AM6412

Hi ,
In High-Speed Interface Layout Guidelines (Rev. J) Sheet it's mentioned like for PCIe TX and RX traces we need 95ohm Impedance but by checking the Evaluation Board of AM6412 the Impedance is 100Ohm is being used.
In our case we can follow 100Ohm As per Standards or we need to go with 95 Ohm
Please give Confirmation

Regards
Pavan

over 2 years ago

0 -DK- over 2 years ago

TI__Mastermind 27890 points

Hello Pavan,

100 Ohms of differential impedance for PCIe is permissible. Some care will need to be taken to ensure that manufacturing tolerances are tightly maintained as the PCIe specification maximum is 105 Ohms.

0 Pavan Kalyan over 2 years ago in reply to -DK-

Prodigy 225 points

Thanks For your response.
Also Please confirm the range Of impedance According to your statement mentioned above we need to maintain maximum impedance as 105Ohms and Is it ok If we are maintaining the range from 90 to 105 Impedance?
Please confirm the same from your side...

0 -DK- over 2 years ago in reply to Pavan Kalyan

TI__Mastermind 27890 points

From the SoC perspective, this is unlikely to present an issue as long as the link partner is balanced accordingly. I would be more concerned with how the link partner handles it given that this proposed impedance range is on the high end of what the PCIe spec allows.

The overall goal here is to ensure that there are no large impedance discontinuities in the bus that might introduce reflections.

0 Pavan Kalyan over 2 years ago in reply to -DK-

Prodigy 225 points

The Interface is between AM6412 and a Picocom processer
It is mentioned in am6412 datasheet as follows :

our minimum impedance while checking is :93Ohm

our maximum impedance is :99Ohm

I hope these Impedance ranges works fine for the both IC

Please confirm regarding same at the earliest.

+1 -DK- over 2 years ago in reply to Pavan Kalyan

TI__Mastermind 27890 points

Hi,

TI cannot comment on a 3rd party device implementation. From AM64xx perspective 93/99 Ohm is acceptable.

As always, we recommend that you simulate all high-speed interfaces prior to board fabrication.

0 Pavan Kalyan over 2 years ago in reply to -DK-

Prodigy 225 points

Thanks for your Reply

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AM6412: Query regarding impedance of PCIe