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AM57xx DDR3L layout

g.f.
Guru 15510 points
Other Parts Discussed in Thread: AM5728

Hi,

I have a question about AM5728 DDR3L layout routing.

In AM572x datasheet, there are DDR3L layout guideline and I'm reading it.
Also I'm refering to AM572x IDK schematcis, and there was difference between
guide and schematics.

In IDK schematics, Address Line are connected to VTT via termination resistor and
also connected to VDD_DDR and GND via capacitor. Please see the attached IDK schematics.
But in guidline, its only connected to VTT via termination registor.

Why Address Line are connected to VDD_DDR and GND via capacitor?
Which layout should I use in customer board?

AM57xx IDK DDR3.pdf

best regards,
g.f.

  • 0
    Guru 15510 points
    I have additonal question about DDR3L layout.
    In AM57xx GP EVM(TI_AM572XEVM_REV_A3) schematics page.19 and page20,
    DDR1_CKE and DDR2_CKE was pulldowned via 4.7kohm.
    But in Layout Guidline, there are no information about CKE pulldown.

    Why its pulling down the CKE signal?
    Should I pulldown DDR1_CKE and DDR2_CKE at customer board?

    best regards,
    g.f.
  • 0
    TI__Genius 9575 points
    It is not required to AC couple the DDR Addr/Ctrl lines to the supply as in the IDK design. Please follow the data sheet recommendations. I don't know the background of why the IDK has it done differently. I'll check and let you know if I find anything different

    Regards, Siva
  • 0 in reply to g.f.
    TI__Genius 9575 points
    There is no requirement to have extra pull-down resistors on the CKE signals. These are typically required for supporting system use-modes where SoC no longer drives the CKE signal to the DDR memory which are not supported on AM57x.
  • 0 in reply to sivak
    Guru 15510 points
    Hi Sivak,

    Thank you for the reply.
    I will remove the AC couple of DDR Addr/Ctrl line and follow the datasheet.

    I found information about external pulldown resistor on CKE signal.
    From AM572x Technical Reference Manual(spruhz6g.pdf) page.3374 "15.3.4.17 Forcing CKE to tri-state",
    external pulldown was used. It seem that I should keep external pulldown resistor on CKE signal.

    best regards,
    g.f.
  • 0 in reply to sivak
    Guru 19845 points

    Hi Siva-san,

    sivak said:
    It is not required to AC couple the DDR Addr/Ctrl lines to the supply as in the IDK design. Please follow the data sheet recommendations. I don't know the background of why the IDK has it done differently. I'll check and let you know if I find anything different

    You mention the capacitors which are used to AC couple the DDR Addr/Ctrl lines to the supply, but do not mention the bypass capacitors put between the terminator resistors and the supply on the DDR Addr/Ctrl lines.

    Is it required to use the bypass capacitors near the terminator resistors?

    I asked the similar question for AM335x here: http://e2e.ti.com/support/arm/sitara_arm/f/791/t/537684

    Best regards,

    Daisuke