PBL 3770A

7

Figure 8. Typical stepper motor driver application with PBL 3770A.

Figure 9. Typical source saturation vs.

output current.

In order to minimize electromagnetic

interference, it is recommended to route

M

printed circuit board directly to the

terminal connector. The motor wires

should be twisted in pairs, each phase

separately, when installing the motor

system.

Unused inputs

Unused inputs should be connected to

proper voltage levels in order to obtain

the highest possible noise immunity.

Ramping

A stepper motor is a synchronous motor

and does not change its speed due to

load variations. This means that the

torque of the motor must be large

enough to match the combined inertia of

the motor and load for all operation

modes. At speed changes, the requires

torque increases by the square, and the

required power by the cube of the speed

change. Ramping, i.e., controlled

acceleration or deceleration must then

be considered to avoid motor pull-out.

V

The supply voltages, V

be turned on or off in any order. Normal

dv/dt values are assumed.

Before a driver circuit board is

removed from its system, all supply

voltages must be turned off to avoid

destructive transients being generated

by the motor.

Switching frequency

The motor inductance, together with the

pulse time, t

frequency of the current regulator. The

choice of motor may then require other

values on the R

those recommended in figure 6, to

obtain a switching frequency above the

audible range. Switching frequencies

above 40 kHz are not recommended

because the current regulation can be

affected.

Analog control

As the current levels can be continu-

ously controlled by modulating the V

R

input, limited microstepping can be

achieved.

1.8

1.6

1.4

1.2

1.0

.8

.6

.4

.2

0

0

.40

.80

1.2

j

T = 25

°C

1.6

1.8

1.6

1.4

1.2

1.0

.8

.6

.4

.2

0

0

.40

.80

1.2

j

T = 25

°C

1.6

Figure 10. Typical sink saturation vs.

output current.

1.8

1.6

1.4

1.2

1.0

.8

.6

.4

.2

0

0

.40

.80

1.2

j

T = 125

°C

1.6

Figure 11. Typical lower diode voltage

drop vs. recirculating current.

Interference

As the circuit operates with switched-

mode current regulation, interference-

generation problems can arise in some

applications. A good measure is then to

decouple the circuit with a 0.1

µF

ceramic capacitor, located near the

package across the power line V

ground.

Also make sure that the V

sufficiently decoupled. An electrolytic

capacitor should be used in the +5 V rail,

close to the circuit.

The ground leads between R

circuit GND should be kept as short as

possible. This applies also to the leads

connecting R

10 respectively.

Phas

e

I

1

I

0

TC

E

M

A

M

B

V

M

M

V

C

C

V

R

GN

D

Phase

B

I

1

B

I

0

B

PBL 3770A

1

1

6

3,

14

8

7

9

2

1

0

1

6

4, 5

12, 13

1

1

5

Phase

A

I

1

A

I

0

A

1

1

5

Diodes are

UF 4001 or

BYV27

t

r

r

100

ns

Phas

e

I

1

I

0

TC

E

V

M

M

V

C

C

V

R

GN

D

M

A

M

B

PBL 3770A

1

1

6

3,

14

8

7

9

2

1

0

1

6

4, 5

12, 13

STEPPER

MOTOR

820

pF

820

pF

1

k

56

k

0.5

820

pF

820

pF

1

k

56

k

0.5

V

(+5

V)

C

C

V

(+5

V)

C

C

V

M

M

V

M

M