FUNCTIONAL DESCRIPTION

The circuit is intended to drive both windings of a

bipolar stepper motor.

The peak current control is generated through

switch mode regulation.

There is a choice of three different current levels

The current can also be switched off completely

The current level in the motor winding is selected

with these inputs. (See fig. 2)

If any of the logic inputs is left open, the circuit will

treat it has a high level input.

Current Level

H

H

No Current

L

H

H

L

L

L

Phase

This input determines the direction of current flow

in the windings, depending on the motor connec-

tions. The signal is fed through a Schmidt-trigger

for noise immunity, and through a time delay in

order to guarantee that no short-circuit occurs in

the output stage during phase-shift.

High level on the PHASE input causes the motor

current flow from Out A through the winding to

Out B

Current Sensor

Only one comparator is active at a time. It is acti-

vated by the input logic according to the current

The motor current flows through the sensing re-

When the current has increased so that the volt-

ence voltage on the other comparator input, the

comparator goes high, which triggers the pulse

generator.

=

Single-pulse Generator

The pulse generator is a monostable triggered on

the positive going edge of the comparator output.

The monostable output is high during the pulse

The single pulse switches off the power feed to

the motor winding, causing the winding current to

ignored.

Output Stage

The output stage contains four Darlington transis-

tors (source drivers) four saturated transistors

(sink drivers) and eight diodes, connected in two

H bridge.

Figure 1

ELECTRICAL CHARACTERISTICS (Continued)

Symbol

Parameter

Test Condition

Min.

Typ.

Max.

Unit

PROTECTION

Thermal Shutdown Temperature

-

170

-

°C

L6219

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