Hi Luis,
First, answers to your questions:
- The nFault pin never goes low, nor does the device get very warm.
- I'm not sure what you mean by "error with stencil". Could you elaborate?
- 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.
- Assembly was done with a paste stencil and a reflow oven this time all joints look good under magnification.
Now, my questions:
- 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.
- 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.
- 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