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SSTL-2 Class I outputs with 8mA drive strength?

Mark13
Beginner
182 Views

Ì am using a NIOS-processor in a Cyclone IV EP4CE55F23I7N. Connected to the FPGA is a DDR-SDRAM with differential clock input. The clock is outputted from FPGA via SSTL-2 Class I outputs. If no external series resistors are used for those in the Cyclone IV hand book the use of 50 Ohms OCT is recommended together with 50ohms parallet against VTT. Is there a reason against using 8mA output drive strength instead of 50 Ohms OCT? The clock seems to be better with that setting. On some boards I get sporadic PLL-lock losses that do not appear with 8mA drive strength.
Best regards
M.B.

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2 Replies
EngWei_O_Intel
Employee
167 Views

Hi there

Table 6–2 of https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/cyclone-iv/cyiv-51006.pd... shows the available current strength setting for different IO standard. It also stated that when you use programmable current strength, on-chip series termination (RS OCT) is not available. Those are the optimum setting done by the characteristic team.

We can refer to below link for more information:

https://www.intel.com/content/www/us/en/programmable/support/support-resources/knowledge-base/soluti...

 

Thanks.

Eng Wei

EngWei_O_Intel
Employee
136 Views

Hi there

We do not receive any response from you to the previous reply that have been provided. This thread will be transitioned to community support. If you have a new question, feel free to open a new thread to get the support from Intel experts. Otherwise, the community users will continue to help you on this thread. Thank you.

 

Eng Wei

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