Introduction
For some time I have been planning to build a number of devices that make use of stepper motors. Since I have no experience in using stepper motors I had no idea what parts, what driver and controller circuits I would need to get them running.
After extensive research on the internet I decided to make a bipolar stepper motor driver based on Texas Instruments’ LMD18245, which is a 3A, 55V DMOS Full-Bridge Motor Driver. It incorporates all the circuit blocks required to drive and control current in a bipolar stepper motor.
This integrated circuit is a bit more involved to program (although surprisingly simple compared to what it delivers) but comes with many extra features (for free), such as overcurrent protection and thermal shutdown.
Creating a test board for the LMD18245
The only drawback of the LMD18245 is that it comes in a 15-pin TO-220 package which is not breadboard-friendly. To overcome this problem I designed a small breakout board for the chip:
It has footprint for all the parts needed for normal operation or experimenting with the LMD18245. It also has a 15 pin header to allow easy access to each pin of the chip.
I designed the circuit and PCB in Eagle. Eagle doesn’t come with the part for the LMD18245, but a quick search on Eagle’s web site made me happy with a part someone had made available as a free download. As usual, after downloading it I double checked the footprint used against the datasheet and found it correct, so I started designing the circuit with it. I even printed the PCB artwork on paper (as usual) to check it against the actual parts I would use to populate the PCB with. Everything checked out, so I sent the Gerber files for production.
After a few weeks I was happy to receive the ready boards and I started assembling two of them (two LMD18245s are required to drive one bipolar stepper motor). Soon I realized that, although the footprint of the LMD18245 were correct, the holes for the LMD18245 were too small. That means all the holes had to be enlarged. Luckily, I have a small drill and drill bits as small as 0.3mm diameter, so I picked a 0.8mm one and widened the holes as can be seen in the images below.