Stepping motor controller - is this chip suitable?

Why do you find that staggering? The chip uses switch mode current control and there should be no other losses than the switching and RdsON losses. There are SOT23 FETs rated at 5A.

Start off by reading the classic stepper tutorial:

Steppers usually win on grunt, servos on speed. That stepper is

-- Cheers, James Arthur

snipped-for-privacy@yahoo.com wrote

Actually, on a closer look, the stepper does about 10mNm and the brushless is similar. I was looking at the stall torque on the brushless one.

Stef wrote

Yes, I have seen them, but would *you* design a product which had to be highly reliable, over a wide temperature range, which used SOT23 FETs carrying 5A?

With a stepper motor driver one might need to adjust things like the current and various pulse timings, and if anything goes slightly out of perfection, a device like that will go up in a puff of smoke in about 1 second.

The one thing I have sussed out when looking at these stepper controllers is that most new ones work in "current mode" and one chooses a stepper motor which is specced at a small fraction of the supply voltage e.g. a 3V motor with a 30V supply. The resulting performance is much better, over simply switching a constant voltage onto the motor coils which is what all the older stepper chips do.

That was not the point, I just mentioned them because of your amazement by the rated current of a certain size chip. Just compare the rated currents.

But to answer your question: Probably not. I'd feel more comforable if there was at least a 2:1 safety margin. But I would have to know all operating conditions and read the entire datasheet for a definitive answer.

But you seem to be on the virge of dicarding a 10:1 overrated chip just because of it's physical size, that does not make sense to me.

Study the specs, and make sure it is overrated by a marging you are comfortable with under all expected conditions. And if the chip still fits the application, just be happy with the small size. :-)

In chips like these (IIRC you were considering the A3987), current is set by a resistor, switch timing is not adjustable and it has built in protections. Adding external components increases the possible points of failure and you must make sure your upper and lower switch times don't cause overlap. And if you use standard mosfets for your external switches, you lose the benefit of thermal shutdown.

These current mode drivers have been around for a while now, so I would not call them 'new'. ;-) But you can still drive your 12V stepper from 12V with one of these. Have you read the Jones tutorial? I think it has a section on the pro's and cons of current drivers (it has been a while since I read it myself).