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Electronics for CNC apparates

Last update: 31/07/2015

The A3982 is an Allegro small and cheap SMD stepper driver with internal translator using the traditional step-dir-enable commands. It can drive easily stepper motors upto 2A/phase at 35V. Very probably it not represents the best example of the Allegro production (only full or half step modes) but it is really cheap and can be purchased very easily. 


In this case the schematic has been fixed to the half step version (MS1 connected to vdd) but it can very easily modified if the full step is needed.




The schematic follows the traditional style of the Allegro products.

The IC can manage upto 2A/phase bipolar steppers but, in this case, it needs of a good heatsink.

For this reason all components have been positioned on the bottom side of the pcb while only the A3982 ic has been positioned on the top side.

The current level can be fixed trough the small trimmer. 

The formula to calculate the current/phase is given:


this means that using a 0.1 ohm resistor:

1V = 0.8A

1.6V = 2A (max)

Be careful to the max voltage level. The 5V are obtained, using a 5V regulator, directly from the V+ it means that the real max voltage input level is 20-22V according to the regulator characteristics.

We have to consider that the natural application of this ic is a small robotic environment where voltage levels are usually limited. 


The PCB has been studied to use normal components (no smd) but the A3982.

Tracks have been kept quite wide, therefore it can be easily realized using the milling procedure.

All components must be soldered on the bottom side of the pcb leaving the a3982 alone on the top side. This solution will allow to fix the small pcb directly on the heatsink.


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