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AM335x DDR I/F unused case treatment

RY9983
Guru 10570 points
Other Parts Discussed in Thread: AM3874

Hello.

My customer would like to NOT use the DDR I/F
There is no description about unused case of DDR I/F in the datasheet and TRM.

I looked at the AM3874 datasheet.
Its DDR I/F is almost same as AM335x DDR I/F, and unused case is described in the datasheet.

- Can I apply this guideline to the AM335x DDR I/F?
Or,
- Could you tell me how can I treat DDR pins as unused case?

 

AM3874 datasheet (sprs695b, P269):

Best regards, RY

 

  • 0
    Guru 15520 points

    Hi RY9983-san,

    Did you get an answer for AM335x unused DDR pins(include DDR power supply pins)?
    I had an answer that all DDR pins can be unconnected.
    But solutions is different by the device, so I'm confused.

    I think I heard from you before but let me ask you again to make sure.
    Is it okay to leave all the DDR pins unconnected
    including DDR power supply pins(VDDS_DDR/VDDS_PLL_DDR)?

    best regards,
    g.f.

  • 0 in reply to g.f.
    Guru 10570 points

    g.f.-san,
    Hello.  I had local TI's support about this.
    Yes.
    You can unconnect all the DDR pins including DDR power supply pins.
    But, I did not confirm treatment of VDDS_PLL_DDR pin. (Sorry, this is my mistake.)

    I think there is no problem.
    But, you should confirm about it if you need exacting confirmation.

    Best regards, RY

  • 0 in reply to RY9983
    Guru 15520 points

    Hi RY-san

    Thank you for the reply.
    You helped me so much.

    I think that there is no problem too.
    Because DDR PLL is independent from other.

    best regards,
    g.f.

  • 0 in reply to g.f.
    TI__Genius 9655 points

    Hello

    This is the recommendation configuration for the DDR pins in case the interface is not used for the AM335x processor. It is not recommended to leave any of the power pins floating unless otherwise noted.

    - Power the VDDS_DDR rail with any available 1.8V supply in the system.

    - Power the VDDS_PLL_DDR with any available 1.8V supply in the system.

    - Connect a weak pull-up to VDDS_DDR (or pull-down to GND) on the DDR_DQS0/1 pins. A value of 10K should suffice.

    - Connect a weak pull-down to GND(or pull-up to VDDS_DDR) on the DDR_DQSn0/1 pins. Make sure these are opposite of the non-inverted DQS. A value of 10K should suffice.

    - Connect a 50 ohm resistor on the DDR_VTP pin.

    - Leave rest of the DDR pins floating.

    Regards, Siva

  • 0 in reply to sivak
    Guru 10570 points

    Siva-san,
    Great thanks for your comment !!
    Although our customer has been already designed, I would like to inform if they have plan for pcb change.

    BTW, your comment is different from local support I had.
    Your answer is from AM335x design team. Right?

    Best regards, RY

  • 0 in reply to RY9983
    TI__Guru 62855 points

    Hello RY,

    The answer Siva provided is from the design team.

    Was the local support you referenced in your previous post someone from TI?  If so, please ask that person to contact Siva directly to discuss this topic with them.

    Regards,
    Paul

  • 0 in reply to peaves
    Guru 10570 points

    Paul-san,

    Thank you so much.
    The local support is PIC(Product Information Center) in TI Japan.
    I appreciate for their very kindness support.
    Please contact them.

    Best regards, RY

  • 0 in reply to peaves
    Guru 15520 points

    Hi peaves,

    Let me ask about unused DDR_DQS0/1 and DDR_DQSn0/1 pins to make me sure.

    Do we must pull-up or pull-down these pins externally?
    Or is it fine to leave floating with enabling internal weak pull-up/pull-down?

    In AM335x datasheet(sprs717f) page.149
    "Figure 5-33. 16-bit LPDDR Interface Using One 16-Bit LPDDR Device",
    DDR_DQSn0/1 pins are NC and noted as follow:
    /////////////////////////////////////////////////////
    A. Enable internal weak pulldown on these pins.
    /////////////////////////////////////////////////////

    best regards,
    g.f.

  • 0 in reply to g.f.
    TI__Guru 62855 points

    The prefered way is to pull-up DQS and pull-down DQSn.  You can also pull-down DQS and pull-up DQSn.  However, they should always be pulled to opposite logic levels.

    You can enable the internal pulls with bits 19 and 29 in the ddr_data0_ioctrl and ddr_data1_ioctrl registers.

    You should be able to use the internal weak pull-up/pull-down resistors if you do not have long signals traces connected to these AM335x terminals.  It may be necessary to use external resistors if you have long signal traces connected that may pick up noise.  This is true for any unused input terminal since you do not want noise to couple into the signal traces and  cause the input buffer to see an invalid logic level (voltage between Vil max and Vih min).

    Regards,
    Paul

  • 0 in reply to peaves
    Guru 15520 points

    Hi Paul,

    Thank you for the reply and the details.
    I understood.

    best regards,
    g.f.