ECP5 and ECP5-5G High-Speed I/O Interface
Technical Note
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FPGA-TN-02035-1.3
The additional guidelines below are not as effective as the ones listed above. However, following them is still
recommended to improve the SSN immunity further:
Assign the DM (data mask) pad in a data DQS group close to the other side of DQS pads where a pseudo powerm
pad is located. If the data DQS group includes VREF1, locate DM to the other side of VREF with respect to DQS. It
can be used as an isolator due to its almost static nature in most applications.
Other DQS groups (neither data nor spacer group) can be used for accommodating DDR memory interface’s
address, command, control, and clock pads.
You can assign more unused I/O pads to pseudo power if you want to increase the SSN immunity. Note that the
SSN immunity does not get increased at the same rate as the increased number of pseudo power pads. The first
few pseudo power pad placements described above are more crucial. Keep the total pseudo power pad ratio
(VCCIO versus GND) between 2:1 to 3:1.
It is a good idea to shield the VREF pad by locating pseudo power pads around it if extra pins are available in the
bank where the VREF1 pad is not located.