I received my driver this week. I ordered it on ebay from Rattm Motor. First thing I checked is the contact of the driver chip with heat sink. There was a gap of 2mm! between them. They put some silicon pad in between. I shortened the spacers to make contact between heatsink and driver chip. Then I added a heat conducting paste an mica in between.
Next I added a base resistor of 330 Ohm to the transistor. Then I changed the 10k resistor in the RC time constant circuit for 20k. This way I gained a bit more delay before driver goes to 30% of current set by trimmer.
Measurements are done on the capacitor of RC time constant circuit. Settings on oscilloscope were 2ms/div horizontally and 0.1V/div vertical. The fed frequency was 1ms.
I also checked the output voltage on the VREG pin and measured 4.67V. This is probably because driver can not supply current for all things that require 5V on board.
Then I changed the resistor for alert (pin1) from 510 Ohm to 3k9.
As last thing a looked to the output current. I took the measurement across the resistors on the RNFA pin. There were no spikes or artifacts seen.
It's quite hard to take a good picture of this because the oscillogram is not steady. The settings on vertical were 0.2V/div so 1 division is 1A. I set it to 1.5A because I don't have larger motor at my hand. The feed frequency was 1ms. For a brief moment I set it to 4A just to see the output, but the motor went fast to hot. But the heat sink was at the end only a bit warm to the touch. Supply voltage to the board was 20V.
For now I can say that driver board is working good. Tomorrow I'll do some more tests at higher step frequencies.