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RE: DRV8825: Irregularities in output waveform

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Hi Luis,

First, answers to your questions:

  1. The nFault pin never goes low, nor does the device get very warm.
  2. I'm not sure what you mean by "error with stencil".  Could you elaborate?
  3. The devices are all new on this board.  So I had three devices with this behavior on the Rev B board and now three more with this behavior on the Rev C board.
  4. Assembly was done with a paste stencil and a reflow oven this time all joints look good under magnification.

Now, my questions:

  1. You mentioned fixing the ground thermal relief connections.  Which ones are you referring to?  I am looking at the gerbers for the EVM-DRV8825 and I see all of the ground connections have thermal relief except for the ones in the thermal pad under the device.  The only other one that might be considered a complete connection is pin 14 of the DRV8825 device, and even that is only connected on one end.  On my Rev C board the thermal pad under the device has the required plated through holes with complete connection around the entire circumference of the plated through hole.
  2. I see what you mean on the long return path of the sense resistors.  I assume I want to minimize the length of the path between those resistors and the GND pins of the device.  Please let me know if this is correct.
  3. I should be able to solder a jumper to the bottom ground plane to drastically shorten that path for testing.  Do you think this would be a valid test?

I would very much like to get this working with mods to the Rev C board so that I fully understand the issues prior to embarking on a new layout.

Thanks again for your help,

John


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