Dual Full-Bridge DMOS
PWM Motor Driver
A4954
7
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Application Information
Sense Pins (LSSx)
In order to use PWM current control, a low-value resistor is
placed between the LSSx pin and ground for current sensing pur-
poses. To minimize ground-trace IR drops in sensing the output
current level, the current sensing resistor should have an indepen-
dent ground return to the star ground point. This trace should be
as short as possible. For low-value sense resistors, the IR drops in
the PCB can be significant, and should be taken into account.
When selecting a value for the sense resistor be sure not to
exceed the maximum voltage on the LSSx pin of ±500 mV at
maximum load. During overcurrent events, this rating may be
exceeded for short durations.
Ground
A star ground should be located as close to the A4954 as possible.
The copper ground plane directly under the exposed thermal pad
of the device makes a good location for the star ground point. The
exposed pad can be connected to ground for this purpose.
Layout
The PCB should have a thick ground plane. For optimum
electrical and thermal performance, the A4954 must be soldered
directly onto the board. On the underside of the A4954 package is
an exposed pad, which provides a path for enhanced thermal dis-
sipation. The thermal pad must be soldered directly to an exposed
surface on the PCB in order to achieve optimal thermal conduc-
tion. Thermal vias are used to transfer heat to other layers of the
PCB.
The load supply pin, VBB, should be decoupled with an electro-
lytic capacitor (typically 100 F) in parallel with a lower valued
ceramic capacitor placed as close as practicable to the device.
OUT3
OUT2
RS12
GND
GND
GND
C1
BULK
C2
CAPACITANCE
VBB
OUT4
OUT1
RS34
GND
V
BB
1
PAD
A4954
R
S12
C1
C2
VBB
OUT4
LSS34
OUT3
OUT2
LSS12
OUT1
VBB
VREF34
IN3
IN4
IN2
IN1
VREF12
GND
GND
R
S34
Bill of Materials
Item Reference Value Units Description
1 RS12, RS34
0.25
(for V
REF
= 5 V, I
OUT
= 2 A)
2512, 1 W, 1% or better,
carbon film chip resistor
2 C1 0.22 F X5R minimum, 50 V or greater
3 C2 100 F Electrolytic, 50 V or greater
