A4402 Datasheet, PDF (13/15 Pages) Allegro MicroSystems – Constant On-Time Buck Converter with Integrated Linear Regulator

A4402
Constant On-Time Buck Converter
with Integrated Linear Regulator
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
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.
PCB Layout Diagram
C5
GND
R5
R7
U1
R6
VIN2
GND
VLIN
VSW
C6
C1
C8
C2
C3
R1
C4
VIN1
GND
C7
L1
Star Ground
R4
GND
GND
R2
D1
R3
C5
R7 R6
V_LIN
C6
R4
V_SW
R5
V_IN1
TON
GND
FB2
VIN2
VO2
WDI
TSET
NPOR
C1 C8
ENB
C2
A4402 ^VIN1
GND
R1 C7
PAD
LX
C3
L1
BOOT
D1
ISEN
POR
R2
C4
FB1
R3
A4402
PCB
Thermal Vias
Solder
Trace (2 oz.)
Signal (1 oz.)
Ground (1 oz.)
Thermal (2 oz.)
Allegro MicroSystems, Inc.
13
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com