Hi all.
I'm using L298's to drive my stepper motors. I'm not using the 297 chip; just sending the 4 individual line values from my I/O card in my computer directly to the 298.
I'm driving the steppers with 24V (theoretically; it's actually more like ~21V) that i get from 2 daisychained 12V car battery chargers. The 5V logic signal comes from the I/O card.
I have 4 circuits on a single board. During testing, things were fine for a while, then all of a sudden all 4 L298 chips went snap, crackle and pop, burst into flames, and blew chunks off the chip face right above the 24V pin. The sound and light show would have been quite enjoyable had it not been my own time and energy going up in flames.
All 4 chips were enabled. Only 3 were hooked to motors, and only 2 of the motors were in use. The other motor and the unconnected circuits had all the lines set to zero.
All 4 chips have big-ass heat sinks that hardly even got warm before the blow up occurred.
After a little investigating, i found that while the the wall plug I'm using has 3 pins, the ground pin is not attacked to anything. (damn my old house and various incompetent renovators!) This means that not only are the battery chargers and my computer not grounded, but the 24 volt driving voltage and the 5 V logic are probably not relative to the same ground.
Is this likely the problem? Or is it probably that the voltage I'm getting from the battery chargers is too rough or something? Is the 100nF capacitor in the circuit insufficient?
I really have no idea what's going on here. I might be able to figure it out via trial and error, but I'd really rather not blow up any more cards, ya know?
Any thoughts on this would be appreciated. Thanks in advance.