Dual Full-Bridge PWM Motor Driver

L6219DS

5

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Applications Information

PWM Current Control

The L6219DS dual bridge is designed to drive both windings of

a bipolar stepper motor. Output current is sensed and controlled

internal comparator, and monostable multivibrator.

When the bridge is turned on, current increases in the motor

winding and it is sensed by the external sense resistor until

comparator’s input:

The comparator then triggers the monostable which turns off

the source driver of the bridge. The actual load current peak

will be slightly higher than the trip point (especially for low-

inductance loads) because of the internal logic and switching

motor current decays, circulating through the ground-clamp

diode and sink transistor. The source driver’s off time (and

therefore the magnitude of the current decrease) is determined

by the monostable’s external RC timing components, where

1000 pF.

The fixed-off time should be short enough to keep the current

chopping above the audible range (< 46 μs) and long enough to

properly regulate the current. Because only slow-decay current

control is available, short off times (< 10 μs) require additional

efforts to ensure proper current regulation. Factors that can

negatively affect the ability to properly regulate the current

when using short off times include: higher motor-supply

voltage, light load, and longer than necessary blank time.

When the source driver is re-enabled, the winding current (the

sense voltage) is again allowed to rise to the comparator’s

threshold. This cycle repeats itself, maintaining the average

motor winding current at the desired level.

Loads with high distributed capacitances may result in high

attempt to trip the comparator, resulting in erroneous current

time delay should be used to further delay the action of the

comparator. Depending on load type, many applications will

not require these external components (SENSE connected to

COMP IN).

+

–

0

Dwg. W M-003-1A

I

OUT

Dwg. E P -006-1

R S

BB

V

BR IDG E ON

SOUR C E OF F

ALL OF F

PWM Output Current Wave Form

Load Current Paths