SN65LVPE504: Connection with x4 Lane PCIe interface

Hi,

The SN65LVPE504 is a 4 channel device.  To fully implement a 4-lane PCIe link 2 devices would be required.

Root Complex ->  LVPE504  ->  Endpoint

Root Complex <-  LVPE504  <-  Endpoint

Regards,

Lee

Hi Lee,

PCIe TX (x4) -> LVPE504 (RX pins?) and output of LVPE504 (TX pins) -> My Connector (RX),

PCIe RX (x4) <- LVPE504 (RX pins?) and output of LVPE504 (TX pins) <- My Connector (TX),

I am confused, because LVPE504 input pin name is RX?

Thanks for Helping.

Hi,

The naming convention can get confusing.  For PCIe it is probably best to start with the CEM connector specification which is present in most PCIe links.  For this connector  the following conventions are used.

PETpx and PETnx pins (the Transmitter differential pair of the connector) must be connected to the PCI Express Transmitter differential pair on the system board, and to the PCI  Express Receiver differential pair on the Add-in Card.

PERpx and PERnx pins (the Receiver differential pair of the connector) shall be connected to the PCI Express Receiver differential pair on the system board, and to the PCI ExpressTransmitter differential pair on the Add-in Card.

This is shown in the graphic below which a different 4 channel PCIe redriver is connected to the CEM connector on an Add-in-Card.  The signals highlighted by the green boxes are connected to the CEM gold fingers on the Add-in-Card

Regards,

Lee

Hi Lee,

Thanks for helping. My PCIe channel Gen2 (5Gbps), because I am not use CEM connector, not necessary for me.

My system have x4 Lane PCIe signals this for signals goes to Molex x4 Lane connector and this connector connect x4 PCIe cable, end of this cable connect host board this host board have same Molex connector 

and this connector signal goes to PCIe Card edge connector. I want to connect only my signals and connector side together. 

I understand

PCIe Tx ---> SN65LVPE504 ---> Molex Connector Rx

Molex Connector Tx ---> SN65LVPE504  ---> PCIe Rx 

Right? Other signals (Not inside green boxes) represent my PCIe channel? Add in card part access with x4 cable connector. (https://www.onestopsystems.com/product/pcie-x4-cable)

I have another quuestion for you, I saw the above grapics you did not use ac coupling capacitor and I did not see AC coupling value in the datasheet of SN65LVPE504.

This link suggest 220nF capacitor necessary for design?

https://community.nxp.com/thread/463277

Should I use AC coupling capacitor for my design?

Regards.

Hi,

The signals in the Green boxes are connected to the computer.  The PER and PET signals not in the Green boxes are connected to the system endpoint.  In my case it is a SSD.

The 220nF capacitors are not shown in this small picture, but they are included in the schematic design.  In most PCIe systems you should include AC coupling capacitors on the Tx outputs of your board.  The Rx inputs should already have AC coupling on another board in the system like the motherboard or the SSD.

Regards,

Lee

Hi Lee,

I can understand your reply but my question is not related your reply. On my system I have only x4 Lane PCIe, SN65LVPE504 and PCIe x4 Molex Connector. 

I want to connect this three component. Have left side and right side same connection ? 

I searched the datasheet of SN65LVPE504 maximum AC coupling value as below. Can I use 200nF capacitor?

Hi,

The upstream connector - going to the 4x cable will have Tx pins or signals which should be connected to the redriver inputs. The connector Rx pins or signals should be connected to the redriver Tx pins.  There should be 0.22 uF coupling capacitors on these signals.

Regards,

Lee

Hi Lee,

I completed my design as below.

Is there any error?

And I want to use SN65LVPE504RUAR for x1 lane PCIe. In the datasheet not information about unused pin.

What can I do this unused pin?

Regard.