A4987 Datasheet, PDF (9/16 Pages) Allegro MicroSystems – DMOS Dual Full-Bridge PWM Motor Driver with Overcurrent Protection

A4987
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
A4987 must be soldered directly onto the board. On the under-
side of the A4987 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 A4987, 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, R_Sx , 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 R_Sx 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.
OUT2B
OUT2A OUT1A
OUT1B
GND
R4
R5
GND
A4987
PCB
Thermal Vias
Solder
Trace (2 oz.)
Signal (1 oz.)
Ground (1 oz.)
Thermal (2 oz.)
OUT2B
OUT2A
R4
C7
OUT1A
R5
OUT1B
C7
U1
C1
C3
C4
C6
ROSC
GND
GND
BULK
C2
VDD
CAPACITANCE
VBB
OUT2B
PH2
GND
C3
CP1
CP2
C4
VCP
C6
ES package configuration shown
PAD
A4987
ROSC
OUT1B
PH1
GND
REF
IN01
VDD
C1
C2
VDD
VBB
Allegro MicroSystems, Inc.
9
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com