LMD18245 datasheet(13/21 Pages) NSC

13 / 21 page

The Typical Application

Figure 7 shows the typical application, the power stage of a

chopper drive for bipolar stepper motors. The 20 k

Ω resistor

and 2.2 nF capacitor connected between RC and ground set

the off-time at about 48 µs, and the 20 k

Ω resistor connected

between CS OUT and ground sets the gain at about 200 mA

per volt of the threshold for chopping. Digital signals control

the thresholds for chopping, the directions of the winding

currents, and, by extension, the drive type (full step, half

step, etc.). A µprocessor or µcontroller usually provides the

digital control signals.

ONE-PHASE-ON FULL STEP DRIVE (WAVE DRIVE)

To make the motor take full steps, windings A and B can be

energized in the sequence

→B→A*→B*→A→ …,

where A represents winding A energized with current in one

direction and A* represents winding A energized with current

in the opposite direction. The motor takes one full step each

time one winding is de-energized and the other is energized.

To make the motor step in the opposite direction, the order of

the above sequence must be reversed. Figure 8 shows the

winding currents and digital control signals for a wave drive

application of the typical application circuit.

TWO-PHASE-ON FULL STEP DRIVE

To make the motor take full steps, windings A and B can also

be energized in the sequence

→A*B→A*B*→AB*→AB→ …,

and because both windings are energized at all times, this

sequence produces more torque than that produced with

01187816

FIGURE 7. Typical Application Circuit for Driving Bipolar Stepper Motors

LMD18245 Datasheet(PDF) 13 Page - National Semiconductor (TI)