Author Topic: stepper motor IC faulting  (Read 81 times)

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Offline snarkysparky

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stepper motor IC faulting
« on: September 20, 2020, 09:25:00 pm »
STK672-640

This well designed stepper driver IC  |O  has only power grounds pinned out and also has a analog input to set the PWM current for the motor windings with a max val of 1.31V.

I am trying to drive this vref with a D/A converter so software can set the drive current.  But the IC frequently looses its mind at the beginning of drive with an overcurrent condition caused by it driving both windings of a unipolar stepper motor simultaneously.

It wont work at all at low levels of vref.

I really believe the issue is the ground lead voltage bump up when the FET turns on being seen be the vref circuitry as a sudden drop in vref.   The app note only mentions setting vref by a pair or resistors with the low resistor connected directly to power ground.  This would give a bootstrap effect to vref during the drop induced by high current flow.

The power grounds go directly into the boards unbroken ground plane. 
The D/A output is some distance away and cannot compensate for the ground bounce when driving the motor.

I came up with a scheme to add a summing op amp amplifier to the board which will add the local ground pin voltage to the D/A signal and help a bunch with keeping vref constant with respect to the die ground of the IC.

But is there an easier way?
 


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