115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

™

HIGH-CURRENT PWM,

UNIPOLAR STEPPER MOTOR

CONTROLLER/DRIVERS

For given values of R

illustrate output holding current as a function of R

sensing resistance (R

1.0

0.6

0

0

300

500

HOLDING-CURRENT RESISTANCE in OHMS

Dwg. GK-015

100

200

400

600

Ω

Ω

Ω

Ω

0.8

0.4

0.2

FIGURE 5A. HOLD-CURRENT RESISTANCE

(SLA7024M and SMA7029M)

NOTE: Holding current determines holding torque, which is normally

greater than running torque. Consult motor manufacturer for recommended

safe holding current and motor winding temperature limits in “standstill” or

“detent” mode.

FIGURE 5B. HOLD-CURRENT RESISTANCE (SLA7026M)

The MOSFET outputs create ringing noise with PWM, but the RC filter

precludes malfunctions. The comparator operation is affected by R

and, thus, current overshoot is influenced by component values. Empirical

adjustment to “fine-tune” the current limit is likely.

3.0

2.0

1.0

0

300

500

700

0.5

HOLDING-CURRENT RESISTANCE in OHMS

Dwg. GK-015-1

1.5

2.5

0

100

200

400

600

800

Ω

Ω

Ω

Ω