Hi,
Typically, if no more than 4 memory chips is used and the PCB traces impedance is matched to 50 Ohm for single-ended signals and to 100 Ohm for differential pairs, the VTT termination is not required even when using the fly-by topology. In other case, the only way to fix the possible DDR bus issues is to redesign the PCB layout to add the VTT termination circuit.
Have a great day,
Artur
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Hi Artur,
Thanks for the reply.
I have used 2 x DDR3L - 16 bit (Total system 32 bit) with Fly-by topology. And both are on TOP side only.
Please see attached image for your reference.
It means that my design will work without any issue though I don't kept bus termination resistors.
The fabrication of oard is done and it is in assembly preocess.
Regards,
Mrudang
Most likely, it will work without any issue.
Best Regards,
Artur
Hi Artur,
Thanks for reply.
Parallally I am working on similar board which has iMX6Q with 4 x DDR3L (MT41K512M16HA-125:A) (Total density = 4GB).
Provide me your valuable answer.
Regards,
Mrudang
1. The preferred topology for 4 memory chips with i.MX6 series processors is T-type. Please follow the design of the i.MX6 SABRE SD board.
2. No VTT termination is required in case of 4 memory chips with T topology routing.
Best Regards,
Artur
Hi Artur
I'm designing a board which can contain i.MX6 Quad, i.MX6 duallite and i.MX6 Solo in the same PCB.
When using Quad, we'll put 4 x DDR3L (MT41K512M16HA-125:A) (Total density = 4GB).
When using duallite we'll put 2 x DDR3L (MT41K512M16HA-125:A) (Total density = 2GB). making other 2 DDR3L no mount.
When using Solo we'll put 1 x DDR3L (MT41K512M16HA-125:A) (Total density = 1GB). making other 3 DDR3L no mount.
My doubt is that if I go with balanced T topology, will there be noise due to the stubs which will be there in the absence of 3 DDR3L RAMs (As in i.MX6 Solo configuration, the PCB remains same and only 1 DDR is populated)?
Or should I go with Flyby topology keeping all four RAMs on top layer?
You are right in that populating only one DDR chip on balanced T-topology bus may affect the signal integrity due to signal reflection on unused trace stubs. In this case, actually, the Fly-by topology seems to be more appropriate.
Best Regards,
Artur