31

SI-7300 and SI-7330A

Application Note

s Determining the output

The output current, lo is fixed by the following circuit ele-

ments:

:

Current detection resistor

Supply voltage

:

Variable current resistor

To operate a motor at maximum current level, set Rx =

infinity (open). Based on the specifications of SI-7300A, its

output current lo can be seen as:

lo (rms value): 535 to 625 mA

To compute lo when different values are used for Rs and

computed as follows:

1

1

RS

The graph of this equation is shown below.

.

.

.

.

s Power down mode

The SI-7300A can be operated in power down mode. The

circuit is shown below. When transistor Tr is switched on,

the reference voltage drops and the output current can be

decreased.

Waveform of output current

Rx

Tr

2

SI-7300A

SI-7300A Pull-out torque

vs. Response frequency

500

1000

5000

0

1

2

3

4

5

Motor

23PM-C108

(Fixed)

2-phase excitation

Response frequency f (pps)

φ

s Example of a Frequency vs.

Torque characteristic

The graph shows the relation-

ship between frequency and

pull-out torque of SI-7300A.

4

3

2

01

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

4

3

2

01

0

1

2

3

Current detection resistor Rs (

Ω)

max

V

min

V

1

Rs

1

Rs

Current detection resistor Rs (

Ω)

4

3

2

01

0

1

2

3

Variable current resistor Rx (k

Ω)

4

3

2

01

0

0.2

1.0

1.6

Variable current resistor Rx (k

Ω)

1.4

1.2

0.8

0.4

0.6

max Rs

= 0.7

Ω

min

max Rs

= 1Ω

min

Rs = 0.3

Ω

Rs = 0.8Ω

Rs

1.131

Rx

1

Rs

1.107

Rx