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DDC264 Maximum Distance to controller

Ryan Callaway
Prodigy 70 points

Other Parts Discussed in Thread: DDC264

Hi Team!

I've been looking around and haven't been able to find an answer, hoping ya'll can help here!

Customer is using our DDC264 chips..

What is the maximum distance acceptable from the DDC to the controller? Not sure if we need to plop in some Line Drivers or something here.

 

Any insight would be greatly appreciated!

 

Thanks :)

  • 0
    TI__Guru 66550 points
    Ryan,

    There's no exact answer here since there are many factors at play. Are you talking about the digital control signals like CONV, CLK, and DIN/DOUT?

    Regards,

    -Adam
  • 0
    TI__Expert 4680 points

    We have seen in the past in our EVM what looked like a small noise increase due to digital output switching. This was more visible when we were using socket vs using solder down parts. But still, if the trace length is similar or longer to that on the EVM (maybe apps can provide that number), I would probably recommend the use of a line driver at the output. At the same time, place a resistor footprint (not populated) that can short input to output of the driver, so that it can be used if finally the line driver is not needed. 

    Best regards

  • 0 in reply to Adam Sidelsky
    TI__Prodigy 70 points

    Yes, the digital control signals is what we're trying to figure out. I'll also look into the EVM for this part and see what I can dig up there on the length.

    Please let me know if you need more information :)

  • 0 in reply to Ryan Callaway
    TI__Guru 66550 points
    Ryan,

    The EVM signals are maximum 6 inches or so. I agree with Edu's suggestion. In the past I've seen reflection issues with very long (more than a few feet) cables on control lines. My quick and dirty way of fixing this was to add resistance in series to correct the termination slightly. The bypass paths Edu mentioned can also be used to add the series resistance I'm mentioning.

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    TI__Prodigy 70 points
    Thanks for all the insight everyone.

    What about the distance between DDC and the low-current device being measured (in this case photodiodes)?
  • 0 in reply to Ryan Callaway
    TI__Guru 66550 points

    Ryan,

    We keep these signals short and relatively consistent channel-to-channel on our EVM since the trace capacitance affects the DDC input noise. They are at most 1.5 inches on the DDC264 EVM for example. Longer lengths are fine but I cannot comment on what others are using. Edu might now that information. 

    Regards,

    -Adam