KW24D512 USB Impedance

[atillametetured]

Greetings Kinetis experts,

I have a quick question. Is there a special reason why USB stick of KW24D512 has single ended impedance of 70 ohm and not 50 ohm for all lines?

Regards,

Mete

[jc_pacheco]

Hello Mete, 

I mean the instructions provided in the .brd file (see NOTES section).

Where did you get the 8.000 of width?

You can also ask your manufacturer to get the 50 Ohm single ended requirement.

[atillametetured]

Greetings Juan, 

Please find attached pictures, All are from LAY-28057;

Width = 8.000 tracks, combined with the stack-up supplied are 70 ohm single ended impedance for the board.

Regards,

Mete

[jc_pacheco]

It appears that this table is not accurate, please follow the specifications provided in the .brd file. 

[atillametetured]

Hello Juan,

And which specifications are those please?

Regards

[miduo]

Hi,

Sorry I did not aware the USB impedance changed fr this part. From what I know what we always using is the 1:1 (50/50) which was found to provide the best performance for our FRDM, TWR and USB designs. Please let me know where indicate the impedance changed and I will help to confirm.

[atillametetured]

Hello Fang,

Thanks for your reply. When the below stack up is used for the board (from the open source .brd file)

Signle ended impedance of 8 mil lines become as follows (you need to zoom in sorry)

Am I missing anything? Different dielectric perhaps?

Regards,

Mete