NJM3717

Figure 3. Definition of terms

50 %

V

CH

t

on

t

off

V

E

| V

– V

|

MA

MB

f =

s

ton toff

+

D =

t

off

+

1

t

t

s FUNCTIONAL DESCRIPTION

The NJM3717 is intended to drive a bipolar constant current through one motor winding of a 2-phase stepper

motor.

Current control is achieved through switched-mode regulation, see figure 4 and 5.

Three different current levels and zero current can be selected by the input logic.

The circuit contains the following functional blocks:

• Input logic

• Current sense

• Single-pulse generator

• Output stage

Input logic

Phase input. The phase input determines the direction of the current in the motor winding. High input forces the

current from terminal M

a delay circuit eliminates the risk of cross conduction in the output stage during a phase shift.

Half- and full-step operation is possible.

Current level selection. The status of I

current levels can be selected according to the table below.

Motor current

I

0

I

1

High level

100% L

L

Medium level

60% H

L

Low level

20% L

H

Zero current

0%

H

H

The specific values of the different current levels are determined by the reference voltage V

of the sensing resistor R

The peak motor current can be calculated as follows:

i

at 100% level

i

at 60% level

i

at 20% level

The motor current can also be continuously varied by modulating the voltage reference input.