3957

FULL-BRIDGE PWM

MICROSTEPPING

MOTOR DRIVER

115 Northeast Cutoff, Box 15036

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

Thermal Considerations. Thermal-protection circuitry turns

off all output transistors when the junction temperature reaches

approximately +165

°C. This is intended only to protect the

device from failures due to excessive junction temperatures and

should not imply that output short circuits are permitted. The

output transistors are re-enabled when the junction temperature

cools to approximately +150

°C.

Stepper Motor Applications. The A3957SB or A3957SLB are

used to optimize performance in microstepping/sinusoidal

Figure 5 — Microstepping/Sinusoidal Drive Current

Dwg. WK-004-5

SLOW DECAY

SLOW DECAY

MIXED DECAY

MIXED DECAY

stepper-motor drive applications (see figures 4 and 5). When

the load current is increasing, the slow current-decay mode is

used to limit the switching losses in the driver and iron losses in

the motor. This also improves the maximum rate at which the

load current can increase (as compared to fast decay) due to the

decreasing, the mixed current-decay mode is used to regulate

the load current to the desired level. This prevents tailing of the

current profile caused by the back-EMF voltage of the stepper

motor (see figure 3A).

Figure 4 — Typical Application

Dwg. EP-047-5

47

µF

REF

V

PFD

V

V

BB

PHASE

+5 V

BRIDGE B

47

µF

+5 V

PHASE

A

11

V

BB

REF

PFD

BRIDGE A

B

V

V

V

CC

LOGIC

1

2

322

23

24

6

7

18

19

4

5

21

20

8

9

10

15

16

17

11

12

14

13

NC

NC

NC

NC

NC

NC

NC

NC

NC

NC

NC

NC

NC

NC

1

2

3

22

23

24

6

7

18

19

4

5

21

20

8

9

10

15

16

17

11

12

14

13

LOGIC