07-25-2016 06:58 AM
we design a ddr3 board and use Fly-by routing topology, should a 40Ω pull-up to VTT at the far end of the linebe used? we didn't find DDR Termination Regulator and 40Ω pull-up to VTT on some evaluation board, why?
07-25-2016 07:44 AM
Could you show me your circuit diagram, if possible ?
Do you use an external DRAM chip ?
If yes, you don't need 40ohm pull-up to VTT.
Because you don't need to control CS of DRAM...
07-25-2016 01:32 PM
For a fly-by topology, the address, control, and clock signals should all be terminated to Vtt at the end of the route farthest from the FPGA. DQ and DQS signals use on-die termination and don't require board-level termination to Vtt. The only reason a board may not implement board level termination on address or control signals is that the routes are very short (less than 1 inch typically). Do you have a link to the evaluation board you found without Vtt termination?