SLA7024 데이터 시트보기 (PDF) - Sanken Electric co.,ltd.

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SLA7024

2-Phase Stepper Motor Unipolar Driver ICs

Sanken Electric co.,ltd. 

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

Application Notes

SLA7027MU/SLA7024M/SLA7026M

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 (IO) based on this waveform is shown below.

(Parameters for determining the output current IO)

Vb: Reference supply voltage

r1,r2: Voltage-divider resistors for the reference supply voltage

RS: Current sense resistor

(1) Normal rotation mode

IO is determined as follows when current flows at the maximum

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

IO ≅ r2 • Vb ................................................................ (1)

r1+r2 RS

(2) Power down mode

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

coil current. IO is then determined as follows.

IOPD ≅

1

r1(r2+rX)

1+ r2 • rX

• .V..b...................................................... (2)

RS

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

rX=

1

r1

1

Vb −1

Rs • IOPD

1

−

r2

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

tively.

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

IO

Phase A

0

Phase A

Fig. 2 Normal mode

Vb(5V)

r1

r2

r6

r5

C3

3,(14)

9,(10)

RS

Fig. 3 Power down mode

Vb(5V)

r1

rX

r2

Power down

signal

Tr

r6

r5

3,(14)

9,(10)

C3

Fig. 4 Output current IO vs. Current sense resistor RS

4

3

IO= r2 · Vb

r1+r2 RS

r1=510Ω

2

r2=100Ω

rx=∞

Vb=5V

1

0

0

1

2

3

4

Current sense resistor RS (Ω)

Fig. 5 Output current IOPD vs. Variable current sense resistor rx

2.0

1.5

RS =0.5Ω

1.0

RS =0.8Ω

IOPD=

1

1+r1r(2r2· +rrXX)

· Vb

RS

r1=510Ω

RS =1Ω

r2=100Ω

Vb=5V

0.5

00 200 400 600 800 1000 1200

Variable current sense resistor rX (Ω)

(NOTE)

Ringing noise is produced in the current sense resistor RS when

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

is also generated in feedback signals from RS which may there-

fore cause the comparator to malfunction. To prevent chopping

malfunctions, r5(r6) and C3(C4) are added to act as a noise filter.

However, when the values of these constants are increased,

the response from RS to the comparator becomes slow. Hence

the value of the output current IO is somewhat higher than the

calculated value.

SLA7027MU/SLA7024M/SLA7026M 23

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