8

SLA7022MU/SLA7029M/SMA7022MU/SMA7029M

SLA7022MU/SLA7029M/SMA7022MU/SMA7029M

2-Phase Stepper Motor Unipolar Driver ICs (2-Phase Excitation)

sDetermining the Output Current

Fig. 1 shows the waveform of the output current (motor coil cur-

rent). The method of determining the peak value of the output

(1) Normal rotation mode

level during motor rotation. (See Fig.2.)

(2) Power down mode

The circuit in Fig.3 (rx and Tr) is added in order to decrease the

Equation (2) can be modified to obtain equation to determine rx.

Fig. 4 and 5 show the graphs of equations (1) and (2) respec-

tively.

(NOTE)

the MOSFET is switched ON and OFF by chopping. This noise

fore cause the comparator to malfunction. To prevent chopping

7,(9)

3,(13)

Fig. 2 Normal mode

0

Phase A

Phase A

Fig. 1 Waveform of coil current (Phase A excitation ON)

7,(9)

3,(13)

Power down

signal

Fig. 3 Power down mode

4

3

2

1

0

01234

Ω)

Ω

Ω

∞

·

2.0

1.5

1.0

0.5

00

200

400

600

800

Ω)

1000

1200

Ω

Ω

Ω

1+

Ω

Ω

1

·

Application Notes

However, when the values of these constants are increased,

calculated value.

1

1

−1

−

1

................................................................ (1)

≅

•

......................................................... (2)

≅

•

1

1+