2-Phase Stepper Motor Unipolar Driver IC (2-Phase/1-2 Phase Excitation)

SLA7032M/SLA7033M

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

current (I

O

) based on this waveform is shown below.

(Parameters for determining the output current I

O

)

V

b

: Reference supply voltage

r

1

,r

2

: Voltage-divider resistors for the reference supply voltage

R

S

: Current sense resistor

(1) Normal rotation mode

I

O

is determined as follows when current flows at the maximum

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

I

O

≅

r

2

r

1

+r

2

•

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

I

O

Phase A

0

Phase A

V

b

................................................................

(1)

R

S

Fig. 2 Normal mode

V

b

(5

V

)

r

1

3,(14)

r

2

9,(10)

R

S

(2) Power down mode

The circuit in Fig.3 (r

x

and T

r

) is added in order to decrease the

coil current. I

O

is then determined as follows.

I

OPD

≅

1+

1

r

1

(r

2

+r

X

)

r

2

•

r

X

1

1

r

1

V

b

R

s

•

I

OPD

−1

−

1

r

2

•

V

b

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

R

S

Equation (2) can be modified to obtain equation to determine r

x

.

r

X

=

Fig. 3 Power down mode

V

b

(5

V

)

r

1

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

tively.

3,(14)

9,(10)

r

X

Power down

signal

T

r

r

2

Fig. 4 Output current I

O

vs. Current sense resistor R

S

Fig. 5 Output current I

OPD

vs. Variable current sense resistor r

x

4

2.0

2

r

2

· V

b

I

O

=

r

1

+r

2

R

S

r

1

=510Ω

r

2

=100Ω

r

x

=∞

V

b

=5V

Output current I

OPD

(A)

Output current I

O

(A)

3

1.5

R

S

=0.5Ω

1

· V

b

r

1

(r

2+

r

X

)

R

S

1+

r

2 ·

r

X

r

1

=510Ω

r

2

=100Ω

V

b

=5V

I

OPD

=

1.0

R

S

=0.8Ω

R

S

=1Ω

1

0.5

0

0

1

2

3

4

00

200

400

600

800

1000 1200

Current sense resistor R

S

(Ω)

Variable current sense resistor r

X

(Ω)

32

SLA7032M/SLA7033M