SAM5808B datasheet(80/83 Pages) ETC1

80 / 83 page

SAM5808B

SAM5808B.pdf

– Rev 14/05/2018

12.4. SDR SDRAM

For SDRAM following layout rules should be applied:

 4 layer PCB is needed for SDR SDRAM. Layer 1 = Signal + Ground plane, Layer 2 =

Ground plane, Layer 3 = Signal + Power Supply Plane, Layer 4 = Signal + Ground plane

 If 4 SDRAM memory devices, it is recommended to implement 2 devices on each side of

the PCB.

 All DRDQ15-DRDQ0, DRDS0-DRDS1, DRDM0-DRDM1 should be routed together and

should have same length, considering all the SDRAM devices. It means that each DRDQx

signal should have the same length from its SAM5808B DRDQx pin to each of the DRDQx

pin of each SDRAM device. It also means that all the DRDQx and DRDMx signals should

have the same length.

 All DRDA13-DRDA0, DRDBA1-DRDBA0 should be routed together and should have the

same length, considering one SDRAM device. It means that all the DRDAx/DRDBAx

signals should have a same length L1 from SAM5808B to the first SDRAM device and a

same length L2 from SAM5808B to the second SDRAM device... Tolerance should be

lower than +/-2mm.

 DRRAS/, DRCAS/, DRWE/, DRCKE should be routed together and should have the same

length.

 SDRAM systems have only a single-ended clock (DRCK), so the important trace-matching

relationship is not to a second differential clock trace but instead to the other groups. Match

clock traces to data group traces within ±12mm. If multiple clocks are transmitted from the

controller to components, all clock traces should be equivalent to within ±0.5mm. Matching

trace lengths to this level of accuracy helps minimize skew.

It is also needed to match clock traces to each signal trace in the address and command

groups to within ±10mm. If clock traces cannot be matched to the trace lengths of these

groups within 10mm, then all clock trace lengths must be increased as a group. The

longest-to-shortest trace-

length difference must be ≤20mm, so both longest and shortest

traces determine how much length must be added to all clock lines.

SAM5808B Datasheet(PDF) 80 Page - List of Unclassifed Manufacturers