Electronic – AD9850 just works for a few minutes

damagedds

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:

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

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Best Answer

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

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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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