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A4986

DMOS Dual Full-Bridge PWM Motor Driver

Allegro MicroSystems 

A4986

DMOS Dual Full-Bridge PWM Motor Driver

with Overcurrent Protection

Application Layout

Layout. The printed circuit board should use a heavy ground-

plane. For optimum electrical and thermal performance, the

A4986 must be soldered directly onto the board. On the under-

side of the A4986 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.

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 pad and the ground plane

directly under the A4986, 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 two input capacitors should be placed in parallel, and as

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

tor (CIN1) should be closer to the pins than the bulk capacitor

(CIN2). This is necessary because the ceramic capacitor will be

responsible for delivering the high frequency current components.

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. 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.

A4986

PCB

Thermal Vias

Solder

Trace (2 oz.)

Signal (1 oz.)

Ground (1 oz.)

Thermal (2 oz.)

C3

C4

GND

C5

ROSC

C1

GND

GND

VDD

C6

GND

U1

OUT2B

GND

OUT2A

R4

R5

OUT1A

GND

GND

VBB

BULK

OUT1B

CAPACITANCE

C2

GND

C3

C4

C5

ROSC

C1

VDD

CP1

A4986

GND

CP2

VCP

PH2

OUT2B

VBB2

VREG

INO2

IN12

IN11

ROSC

SLEEP

VDD

IN01

PAD SENSE2

OUT2A R4

OUT1A

SENSE1

R5

VBB1

OUT1B

PH1

REF

GND

C6

C2

VBB

Allegro MicroSystems, Inc.

9

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

www.allegromicro.com

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