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[OMAPL138] DDR_ZP pin with a capacitor allowed ?

Naoki Kawada
Guru 19890 points

Hi,

It looks like that DDR_ZP pin is generating some noise.
Datasheet says DDR_ZP pin should be connected to ground with 5Ω. 
If we apply a capacitor to this pin, can DDR_ZP can work correctly ?

Any suggestion would be appreciated.
Kawada

  • 0
    TI__Mastermind 43660 points

    Hello Naoki Kawada,

    Thanks for your post.

    The DDR_ZP pin is configured as DDR2 reference output for drive strength calibration of N and P channel outputs. The impedance of the output IO is selected by the value of a reference resistor connected to pin DDR_ZP. The recommendation is tie this pin to ground via 50 ohm resistor @ 5% tolerance. 

    The noise on DDR_ZP is not a device issue. The device is in market for long time and we don't see any noise issue on DDR_ZP pin. It seems to be a system issue. Please ensure the following things in your system design.

    1. Check the DDR supply voltage and its noise level. Ensure enough decoupling capacitors are provided on this rail as per TI recommendation.

    2. Ensure the DDR routing guidelines are followed. 

    http://processors.wiki.ti.com/index.php/DDR_Routing_Checklist#DDR2.2FmDDR.2FDDR3_Routing_Checklist

    3. Make sure all the TI guidelines are followed in your board design.

    Adding capacitor to this pin is not recommended by TI as it lead to more issues on DDR interface.

    Regards,

    Senthil

  • 0 in reply to Senthilkumar Srinivasan
    Guru 19890 points

    Hi Senthil,

    Thanks for your reply.
    I understood your comments, but you looks non-TIer. Your id indicates "Community member". 
    Can I understand your comments are "formal answers" from TI ?

    Best Regards,
    Kawada

  • 0 in reply to Naoki Kawada
    TI__Mastermind 35645 points

    Hi Kawada,

    We apologise for your misinterpretation and we authorise senthil as a TI employee which he is yet to finish his TI process formalities and he would be displayed as "TI employee" status on TI E2E forums in near future.

    Hereby, we declare that, in moving forward, you could take senthil's comments on the E2E forums posts would be formal answers from TI.

    Thanks & regards,
    Sivaraj K

  • 0 in reply to Sivaraj Kuppuraj
    Guru 19890 points

    Hi Sivaraj,

    Ok, thanks for your notification.

    Best Regards,
    Kawada