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What values do I use for tRCD, tRC and tRAS in the IMX6UL DDR3 script aid?

Question asked by Andrew Parlane on Feb 1, 2018
Latest reply on Apr 19, 2018 by sachin shetty

We are building a board with the IMX6UL and a MT41K128M16JT-125 DDR3L chip.


The datasheet for the DDR3L chip states that for speed grade 125 the data rate is 1600 MT/s. However the max speed of the DDR bus on the IMX6UL is stated as "up to 400MHz (800 MT/s)" (table 33-1 in the TRM).


In table 1 of the DDR3L chip it states that tRCD is 13.75ns for speed grade 125 at 1600 MT/s. There is not an entry for 800 MT/s. In table 29 it has entries for DDR3L-800 which are speed grades 25 / 25E, and it lists tRCD values for that in terms of clock ticks, giving 5 ticks for grade 25E and 6 ticks for grade 25, where 1 tick is 2.5ns, so 12.5ns for grade 25E or 15ns for grade 25.


That's three options I have to use for tRCD. The same applies for tRC and tRAS. I'm guessing I want to use one of the values for the DDR3L-800 but not sure if to use the grade 25 or grade 25E. I could try both, but I'd prefer to understand how this works and not just go with the faster one because it works on one board.


Thanks for any advice.