Datasheet

LMD18245

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SNVS110E –APRIL 1998–REVISED APRIL 2013

HALF STEP DRIVE WITH TORQUE COMPENSATION

To make the motor take half steps, the windings can also be energized with sinusoidal currents (Figure 19).

Controlling the winding currents in the fashion shown doubles the step resolution without the significant torque

ripple of the prior drive technique. The motor takes one half step each time the level of either winding current

changes. Half step drive with torque compensation is microstepping drive. Along with the obvious advantage of

increased step resolution, micro-stepping reduces both full step oscillations and resonances that occur as the

motor and load combination is driven at its natural resonant frequency or subharmonics thereof. Both of these

advantages are obtained by replacing full steps with bursts of microsteps. When compared to full step drive, the

motor runs smoother and quieter.

Table 2 shows the lookup table for this application of the typical application circuit. Dividing 90°electrical per full

step by two microsteps per full step yields 45° electrical per microstep. α, therefore, increases from 0 to 315° in

increments of 45°. Each full 360° cycle comprises eight half steps. Rounding |cosα| to four bits gives D A, the

decimal equivalent of the binary number applied at M4 A through M1 A. DIRECTION A controls the polarity of the

current in winding A. Figure 19 shows the sinusoidal winding currents.

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