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L6470 High Speed Issue

Question asked by gregmar on Sep 18, 2014
Latest reply on Oct 3, 2014 by Enrico Poli
Dear Motor IC Forum:

I am using an L6470 to drive a stepper motor attached to a gearbox and am not able to achieve step rates greater than roughly 700 steps/sec with any microstepping setting. The motor gets loud and stalls as speeds increase. At speeds below 500 steps/sec the motor works perfectly. The Rm of the motor is 4.5 ohms. The Lm is 3.6mh (spec sheet). The Ke is 0.143 v/hz (approximately). I have played with all setting except pmt and have not been able to get more speed. I need roughly 2000 steps/sec.

I also tried the L6472 on the same setup and had no issues reaching the required speeds. The problem is I also need to run at very low step rates of 5-10 steps/second at 1/16th steps. With the L6472 the motor is not smooth enough and vibrates quite a bit.

What I need is the high speed range of the L6472 and the low speed smoothness of the L6470.  So my questions are:

1) Am I doing something radically wrong with the L6470 that is preventing me from reaching higher speeds or is this normal for this chip?

2) Can I connect the motor to both chips and activate one or the other depending on the speed requirements? I do not want to put in a switching system to switch between chips but simply connect them both to the motor and put one chip in the high impedance state while I am using the other i.e 6470-1A to 6472 1A to Motor A etc.

Thanks for your help,