DMOS Microstepping Driver with Translator

A3983

7

Allegro MicroSystems, LLC

115 Northeast Cutoff, Box 15036

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

www.allegromicro.com

Application Layout

Layout

. The printed circuit board should use a heavy ground-

plane. For optimum electrical and thermal performance, the

A3983 must be soldered directly onto the board. On the under-

side of the A3983 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 A3983, 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 star ground can

be created using the exposed thermal pad under the device, to

serve both as a 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 (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.

C2

ROSC

PAD

A3983

C5

C6

C3

C4

R4

R5

C1

OUT2B

OUT1B

OUT2A

OUT1A

VBB2

VBB1

DIR

SENSE2

SENSE1

CP1

GND

ENABLE

GND

CP2

VCP

VREG

ROSC

VDD

MS1

MS2

STEP

REF

RESET

SLEEP

GND

GND

GND

GND

GND

GND

GND

R4

U1

OUT2B

GND

R5

OUT2A

OUT1A

OUT1B

C3

C4

C5

ROSC

C2

C6

C1

VBB

VDD

CAPACITANCE

BULK

PCB

Thermal Vias

Trace (2 oz.)

Signal (1 oz.)

Ground (1 oz.)

Thermal (2 oz.)

Solder

A3983