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I am trying to drive AD9850 (DDS). First I started with a module , programmed the micro (ATMega128 ) and everything was ok ( It means there may not be a software error). Then I decided to make my own PCB (because the module has inbuilt low pass filter and I wanted to design my own filter) . I designed a schematic according to the datasheet of the IC and Module.

Now it works fine just for a few minutes. As I turn it on, it takes the commands well and makes the output signal correctly but after 4-5 minutes it dies forever! ( I mean after a restart it does not work also ) I thought about overvoltage or something therefore added overvoltage protection circuit ( 3 zener diodes ) and carefully checked all voltages.

I also electrically tested all connections down to IC pins and all are OK. When I put my oscope probe on the output pin of the Crystal oscillator, I can see a 100MHz signal ( the nominal signal of it).

Finally decided to make another PCB. The new device went the same: worked well just for a few minutes.Has anyone experience on this specific device that can help me on this issue? What is the main cause of damage to the device ?

I also should note that I followed ESD protection guidelines ( wearing antistatic gloves and putting wire on my arm and connecting it to the ground. All clothes from pure cotton.) but I dont know what is destroying my devices. Here is the schematic:

enter image description here

and the PCB: (Please note that all DRC errors in the designed corrected later and tested electrically ).

enter image description here

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  • \$\begingroup\$ The oscillator module is quite a long way from pin9 on the DDS and this might cause excessive clock signals to the DDS that might damage it - try a resistor in series like about 100 ohms. Ground plane? Doesn't look like you have one and this will only make the clock problem worse. If you do have ground and power planes we'll need to see them. \$\endgroup\$
    – Andy aka
    Commented Oct 12, 2013 at 10:08
  • \$\begingroup\$ @Andyaka I have a ground plane but omitted in this photo to make it readable ( it masked the design) . This excessive clock has damaged the device and I should send it to trash or can use it yet? \$\endgroup\$
    – Aug
    Commented Oct 12, 2013 at 10:22
  • \$\begingroup\$ It might be broken for good but I really do think you need a relayout. \$\endgroup\$
    – Andy aka
    Commented Oct 12, 2013 at 10:24
  • \$\begingroup\$ Are you sure you don't have a floating pin such as the reset pin? \$\endgroup\$ Commented Oct 21, 2016 at 14:58

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This stuff is very important not only for performance but quite possibly functioning: -

enter image description here

Noted are the distinct lack of decoupling capacitors right up at the relevant pins of the DDS chip. This will be a significant problem and cannot be understated.

You need a solid groundplane and your xtal needs to be up at the DDS chip with minimal distance.

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  • \$\begingroup\$ before you make it post up here if you want a quick 2nd opinion. \$\endgroup\$
    – Andy aka
    Commented Oct 12, 2013 at 11:42

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