A4950ELJTR-T View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
Manufacturer
A4950ELJTR-T Datasheet PDF : 9 Pages
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A4950
Full-Bridge DMOS PWM Motor Driver
Application Information
Sense Pin (LSS)
In order to use PWM current control, a low-value resistor is
placed between the LSS 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 LSS 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 A4950 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 A4950 must be soldered
directly onto the board. On the underside of the A4950 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 μF) in parallel with a lower valued
ceramic capacitor placed as close as practicable to the device.
GND
GND
RS
C1
C2
BULK
CAPACITANCE
OUT2
OUT1
VBB
GND
GND
A4950
PCB
Thermal Vias
Solder
Trace (2 oz.)
Signal (1 oz.)
Ground (1 oz.)
Thermal (2 oz.)
1 GND
IN2
IN1
VREF
A4950
PAD
OUT2
LSS
RS
OUT1
VBB
C1
VBB
C2
Bill of Materials
Item
Reference
1
RS
2
C1
3
C2
Value
0.25
(for VREF = 5 V, IOUT = 2 A)
0.22
100
Units
Ω
μF
μF
Description
2512, 1 W, 1% or better,
carbon film chip resistor
X5R minimum, 50 V or greater
Electrolytic, 50 V or greater
Allegro MicroSystems, Inc.
7
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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