A4402 ALLEGRO [Allegro MicroSystems], A4402 Datasheet - Page 13

• Manufacturer Part Number: A4402
• Description: Constant On-Time Buck Converter with Integrated Linear Regulator
• Manufacturer: ALLEGRO [Allegro MicroSystems]

A4402
The ground from each of the components should be very close to
each other and be connected on the same surface as the com-
ponents. Internal ground planes should not be used for the star
ground connection, as vias add impedance to the current path.
In order to further reduce noise effects on the PCB, noise sensi-
tive traces should not be connected to internal ground planes.
The feedback network from the switcher output should have an
independent ground trace that goes directly to the exposed pad
underneath the device. The exposed pad should be connected to
internal ground planes and to any exposed copper used for heat
dissipation. If the grounds from the device are also connected
V
V
SW
LIN
R7
C5
R4
C6
R6
VLIN
VSW
TON
GND
FB2
VIN2
VO2
WDI
TSET
NPOR
VIN2
C5
R7
A4402
PAD
R5
R6
R4
BOOT
ISEN
VIN1
GND
POR
ENB
FB1
LX
U1
C6
C3
R3
GND
R2
GND
D1
PCB Layout Diagram
R5
C4
C2
R3
L1
C1
R1
GND
C8
Constant On-Time Buck Converter
C7
directly to the exposed pad the ground reference from the feed-
back network will be less susceptible to noise injection or ground
bounce.
To reduce radiated emissions from the high frequency switching
nodes it is important to have an internal ground plane directly
under the LX node. The plane should not be broken directly
under the node as the lowest impedance path back to the star
ground would be directly under the signal trace. If another trace
does break the return path, the energy will have to find another
path, which is through radiated emissions.
R2
V
with Integrated Linear Regulator
IN1
GND
GND
C4
C2
C1
C3
Thermal Vias
D1
PCB
C8
R1
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
A4402
GND
L1
C7
VIN1
Solder
Trace (2 oz.)
Signal (1 oz.)
Ground (1 oz.)
Thermal (2 oz.)
Star Ground
13