For given values of R

output current as a function of current-sensing resistance (R

Reduced/Holding Current Mode

Additional circuitry (Figure 4) enables reducing motor current. The

external transistor changes the voltage-divider ratio, V

output current. I

I

R

•

V

b

(3)

R

R

S

or

I

R

•

V

b

(4)

R

R

S

where R

FIGURE 4. HOLD CURRENT MODE

FIGURE 3. CURRENT-SENSING RESISTANCE

3.0

2.0

1.0

0

1.5

2.5

3.5

0.5

CURRENT-SENSING RESISTANCE in OHMS

Dwg. GK-014

1.5

2.5

0

0.5

1.0

2.0

3.0

4.0

Ω

Ω

∞

SLA7024M & SMA7029M MAX.

SLA7026M MAX.

Dwg. EK-010

RS

V

REF

SENSE

R 1

R 2

HOLD

R 5

C 3

R X

V b

HIGH-CURRENT PWM,

UNIPOLAR STEPPER MOTOR

CONTROLLER/DRIVERS