A3995 Allegro MicroSystems, A3995 Datasheet - Page 7

• Manufacturer Part Number: A3995
• Description: DMOS Dual Full Bridge PWM Motor Driver
• Manufacturer: Allegro MicroSystems

A3995
Motor Configurations
stepper/dc motor driver or dual stepper motor driver, Allegro offers
the A3989 and A3988. These devices are offered in the same QFN
package as the A3995. The A3988 is capable of driving 2 bipolar
stepper motors at output currents up to 1.2 A. The stepper control
logic is industry standard parallel communication. Please refer to
the Allegro website for further information and datasheets about
those devices.
Layout
plane. For optimum electrical and thermal performance, the
A3995 must be soldered directly onto the board. On the under-
side of the A3995 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
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 A3995, that area
becomes an ideal location for a star ground point.
OUT1B
OUT1A
EV package layout shown.
CIN1
The printed circuit board should use a heavy ground-
GND
Figure 5. Printed circuit board layout with typical application circuit, shown at right. The copper area directly under the
A3995 (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.
In order to minimize the effects of ground bounce
RS1
VDD
CCP
U1
For applications that require either a
VBB
CVDD1
CVDD2
CVCP
GND
DMOS Dual Full Bridge PWM Motor Driver
RS2
GND
CIN3
CIN2
OUT2B
OUT2A
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
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.
CIN1
RS1
The sense resistors, RSx, should have a very
1
NC
OUT1A
SENSE1
OUT1B
VBB
OUT1B
SENSE1
OUT1A
NC
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
CCP
A3995
PAD
CVDD1
CVDD2
V
CVCP
BB
SENSE2
SENSE2
MODE2
OUT2A
OUT2B
OUT2B
OUT2A
VBB
NC
CIN3
RS2
CIN2
7