A3989_V データシートの表示（PDF） - Allegro MicroSystems

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A3989_V

Bipolar Stepper and High Current DC Motor Driver

Allegro MicroSystems 

A3989

Bipolar Stepper and High Current DC Motor Driver

Applications Information

Motor Configurations For applications that require either dual

DC or dual stepper motors, Allegro offers the A3988 and A3995.

Both devices are offered in a 36 pin QFN package. Please refer to

the Allegro website for further information and datasheets for the

devices.

Layout The printed circuit board should use a heavy ground-

plane. For optimum electrical and thermal performance, the

A3989 must be soldered directly onto the board. On the under-

side of the A3989 package is an exposed pad, which provides a

path for enhanced thermal dissipation. The thermal pad should be

soldered directly to an exposed surface on the PCB. Thermal vias

are used to transfer heat to other layers of the PCB.

Grounding In order to minimize the effects of ground bounce

and offset issues, it is important to have a low impedance single-

point ground, known as a star ground, located very close to the

device. By making the connection between the exposed thermal

pad and the groundplane directly under the A3989, that area

becomes an ideal location for a star ground point.

A low impedance ground will prevent ground bounce during

high current operation and ensure that the supply voltage remains

stable at the input terminal. The recommended PCB layout shown

in the diagram below, illustrates how to create a star ground

under the device, to serve both as low impedance ground point

and thermal path.

The two input capacitors should be placed in parallel, and as

close to the device supply pins as possible. The ceramic capaci-

tor should be closer to the pins than the bulk capacitor. This is

necessary because the ceramic capacitor will be responsible for

delivering the high frequency current components.

Sense Pins The sense resistors, RSx, should have a very

low impedance path to ground, because they must carry a large

current while supporting very accurate voltage measurements

by the current sense comparators. Long ground traces will cause

additional voltage drops, adversely affecting the ability of the

comparators to accurately measure the current in the windings.

As shown in the layout below, the SENSEx pins have very short

traces to the RSx resistors and very thick, low impedance traces

directly to the star ground underneath the device. If possible,

there should be no other components on the sense circuits.

Note: When selecting a value for the sense resistors, be sure not to

exceed the maximum voltage on the SENSEx pins of ±500 mV.

VBB

VBB

OUT1A

OUT1B

GND

CCP

RS1

U1

OUT2B

OUT2A

CIN1

RS2

CVCP

GND

RS3

CIN3

OUT3B

CIN2

OUT3A

CVCP

CIN3

CCP

RS1

CIN1

RS2

1

NC

OUT1A

SENSE1

OUT1B

VBB

OUT2B

SENSE2

OUT2A

NC

A3989

PAD

MODE

OUT3A

SENSE3

OUT3B

VBB

OUT3B

SENSE3

OUT3A

NC

RS3

CIN2

CVDD1

VDD

CVDD2

GND

CVDD1

CVDD2

Figure 5. Printed circuit board layout with typical application circuit, shown at right. The copper area directly under the

A3989 (U1) is soldered to the exposed thermal pad on the underside of the device. The thermal vias serve also as electrical

vias, connecting it to the ground plane on the other side of the PCB , so the two copper areas together form the star ground.

Allegro MicroSystems, LLC

10

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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