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Lost USB connection with the eZdsp

Hello all,

I have been having trouble keeping the eZdsp (320f28335) connected to code composer studio. I have read several other similar posts and tried the suggestions to no avail. To diagnose the problem, I have set up a very simple circuit where I connect the epwm1a output to a digital isolator, the other side of the isolator to a gate driver and an IGBT. The gate driver and IGBT share a seperate ground while  the eZdsp only shares a ground with the isolator. I put a scope on the 5V input to the eZdsp and get a very smooth, flat line at 5.1V. I then run the code, which pwms at 20kHz (50% duty) and I see a ton of ripple in the supply to the chip (+/- half a volt!). This is causing enough of a ripple to kill the usb, but not enough to reset the chip so my code keeps running. Has anyone else had this problem? Any ideas for solutions?  Thanks

 

 

Gideon