EZ-USB FX3 CyUSB3014 series termination resistors 22 ohm

[lucac]

Hi, I'm designing a PCB with CyUSB3014 and an FPGA; the application note AN170707 (hardware design guidelines and schematic checklist) says that I have to put a 22 ohm series termination resistor on each line of GPIF interface in order to avoid reflection, but most of GPIF lines are bidirectional, so where should I put the resistors? Should I put that closer to the FX3 or to the FPGA? 
Can I use the DCI (Digitally Controlled Impedance) technology of Xilinx FPGA instead of putting resistors on the PCB?
Why should I put 22 ohm if my traces on PCB are 50 ohm? Isn't it better to put 50 ohm?

[JayakrishnaT_76 · Accepted solution]

Hello,

You can place the 22 ohm series resistors close to FX3 as done in the Superspeed explorer kit. You can refer to the schematics and layout of Superspeed explorer kit by downloading the hardware files from the following link:

https://www.cypress.com/documentation/development-kitsboards/cyusb3kit-003-ez-usb-fx3-superspeed-exp...

"Can I use the DCI (Digitally Controlled Impedance) technology of Xilinx FPGA instead of putting resistors on the PCB?"

>> As mentioned in AN170707, we recommend to use series resistors itself on GPIF II lines.

"Why should I put 22 ohm if my traces on PCB are 50 ohm? Isn't it better to put 50 ohm?"

>> As mentioned in AN170707, If the GPIF lines are to be routed for more than 5 inches or routed through a medium that can cause impedance mismatch, we recommend doing signal integrity simulation using the EZ-USB™ FX3 IBIS model, and come up with a termination. The IBIS model for FX3 can be found in the following link:

https://www.cypress.com/documentation/models/cyusb3014-fx3-ibis-model

So, as mentioned in the Application note, you can do signal integrity simulation and decide the required terminations.