PCIe AC coupling capacitors values

cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 

PCIe AC coupling capacitors values

Jump to solution
13,761 Views
xabiven
Contributor II

Hello all,

I have a question on the value of the required AC coupling capacitor for PCIe links.

Indeed, the QorIQ data-sheets (Txxx and LSxxx) specify the AC coupling capacitors depending on the targeted protocol. So, it recommends:

 * PCIe GEN2 (2.5 GT/s): CTX =   75 to 200 nF

 * PCIe GEN2 (5.0 GT/s): CTX =   75 to 200 nF

 * PCIe GEN3 (8.0 GT/s): CTX = 176 to 265 nF

I observed that the reference boards always have 100 nF capacitor, like on traditional GEN2 designs.

=> Does GEN3 is implemented on demo-boards ?

=> Should I use capacitor in the range 176-200 nF if I design an interface which can run wether at GEN2 or GEN3 rates ?

=> Or, should I use a classic 220nF capacitor for a PCIe GEN3 capable interface, considering it will be able to negotiate the link down to GEN2 speed ? Will it provide a reliable GEN 2 link ?

Best regards,

Labels (1)
Tags (1)
0 Kudos
Reply
1 Solution
9,227 Views
ufedor
NXP Employee
NXP Employee

New designs have to have 220 nF AC coupling capacitors which are fine for PCIe Gen 3 as well as Gen 2/Gen 1.

View solution in original post

0 Kudos
Reply
2 Replies
9,227 Views
xabiven
Contributor II

Hi Ufedor,

It's noted, thanks a lot for you quick feedback

Regards,

0 Kudos
Reply
9,228 Views
ufedor
NXP Employee
NXP Employee

New designs have to have 220 nF AC coupling capacitors which are fine for PCIe Gen 3 as well as Gen 2/Gen 1.

0 Kudos
Reply