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DDR3 Termination on Beaglebone Black

Matthias Fuchs
Prodigy 170 points


Hi,

we are just investigating if we could get rid of the DDR3 termination resistors and VTT ref source in our current AM335x design.

Former boards like the Starter Kit plattform and the Silica Pengwyn board come with DDR3 termination while the new Beaglebone Black

comes without. Of course PCB routing and stackup has an impact, but the traces between CPU and the single DRAM chip on all of these boards are very short

So is the BB Black design some kind of unserious? Or under what circumstances could we save the parts for termination?

Matthias

  • 0
    TI__Guru**** 393215 points
    Hi Matthias,
     
    BB Black is an absolutely serious design. DDR3 without VTT termination is possible for a point-to-point design (1x16-bit DDR3 memory chip). This is explained in the AM335X Datasheet, Rev.F. Look in section 5.6.2.3, particularly subsection 5.6.2.3.3.9.
  • 0 in reply to Biser Gatchev-XID
    Expert 2300 points

    I've also been thinking about removing the VTT terminations as it eats board space and complicates routing a bit.

    As Biser mentions from the datasheet, Figure 5-48 example without  VTT termination (like BBB) is shown but it doesn't really state pros/cons of with vs without.

    Just that "it may provide acceptable signal integrity without VTT termination". Would be great to understand the tolerance-factors here of board-fab / impedance and best practices for simulating the layout. For instance on the Beaglebone Black, is there any documentaion written on this subject. Also curious if any data from simulation is fed back to trim the DDR-config of the CPU.

    /David