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.
V
DD
V
BB
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
