OK, I got one of your DRC8825 (Sales order #949957). Vref is now stable but can not get above 18mV and I need 675mV for a 1.5Amp motor ([1.5 / 2]*90%). Vref climbs from 0mV to 18mV then goes back down to 0mV.
Yes, I made sure the heat sink is not shorting out any board components.
Do I need to hook up the Raspberry PI before doing the Vref?
Here are some pictures of my setup. I am using a 12VDC power supply, will be using 24VDC for the final design.
Hello.
To set VREF, you do not need the connections for STEP and DIR, and you do not need the motor connected, but you do need to enable the driver by driving nRESET and nSLEEP high. Your pictures do not show the rest of your system; can you verify what those pins are connected to and if you are driving them high? Additionally, could you post some pictures that show your full setup as well as some showing how you are measuring VREF?
By the way, the DRV8825 carrier should be able to handle 1.5A per phase without additional cooling, so since you are only setting it to 1.35A, you should not need the heat sink.
Brandon
A big thanks for the great support. 
Connecting the “nRESET and nSLEEP” to GPIO 3.3V pin did the trick. I have been able to set Vref to 675mV and it is very stable.
As for the heat sink, I agree with you it is not really needed, I am going to use the heat sink and a small fan (30mm) just to ensure the chip is nicely cool and happy. I also know the chip can be hot enough to burn your fingers but the chip is fine and working perfectly.
I also plan to use a TL Smoother just attempt to smooth the motor steps.
Agan thanks for the info and support.
