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TMS320C6747: Noise on DVDD pins around EMIFB can affect to McASP data lines ?

Naoki Kawada
Guru 19890 points
Part Number: TMS320C6747
Other Parts Discussed in Thread: DA8XX

Hello,

My customer is saying that some spike noise was seen on DVDD pins, especially on E12,F12,G12 and F11 with their target board. In fact, these pins are present beside EMIFB pins so they are wondering if the noise might come from EMIFB.  And they are also saying the noise can be routed to McASP data lines. I saw some captures on the McASP data line with the spike noise and found the similar noise appeared in both pins . Please take a look :

  

Now If they apply 1000pF and 0.1uF bypass capacitors, the noise seems to be reduced considerably.
So they questions are 

1. Can you suggest which DVDD pin is related to each peripheral ? It seems they want to know the exact power network inside the device and apply their workaround for exact pins. Is it possible for you to share such information ? 
2. Do you have any guide line for noise immunity ? I think we can suggest the following wiki for bypass capacitors, but do you have any other references for robust design for the noise ?

Best Regards,
Naoki

===

PS :The device is actually not C6747, but DA8xx.

  • 0
    TI__Guru 65405 points
    Hi Naoki,

    I've forwarded this to the design experts. Their feedback should be posted here.

    BR
    Tsvetolin Shulev
  • 0
    TI__Mastermind 42545 points
    Hi Naoki,
    We cannot provide any detail on which DVDD pin supplies individual peripherals. The part is designed to have all the DVDD pins powered by one power supply and there are noise limits that are defined on this supply inputs. I cannot speculate concerning where the noise is originating based on the information provided. The noise could be present on the DVDD supply pin which then couples to the McASP lines or it could be the opposite.
    It sounds like the Power Delivery Network for the DVDD supply isn't sufficient to filter the noise shown. There are entire books written on the subject of analyzing this problem. Another app note on the TI site can be found here.
    www.ti.com/.../swpa222a.pdf
    Regards,
    Bill
  • 0 in reply to Bill Taboada
    Guru 19890 points

    Hello, Bill

    Thank you for your quick reply. I have an additional question about PDN document you provided. It seems it introduces fundamentals of PDN with some flow charts for deciding some PDN parameters. For example, in case of extracting DC resistance, it suggests users have to judge that the extracted DC resistance meets TI's recommendations, which it is described in device data manual. This app note is dedicated for OMAP4, and I'm guessing some PDN requirement numbers are actually present in its data manual. 
    When getting back to Primus device, do you have any numbers for PDN requirements ? If the answer is no (That's my current understanding), does this app note still help the customer ?

    Best Regards,
    Naoki