Datasheet

LTC3544
13
3544fa
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3544. These items are also illustrated graphically
in Figures 3 and 4. Check the following in your layout:
1. The power traces, consisting of the PGND trace, the
GNDA trace, the SW traces, the PV
IN
trace and the V
CC
trace should be kept short, direct and wide.
2. Does each of the V
FBx
pins connect directly to the
respective feedback resistors? The resistive dividers
must be connected between the (+) plate of the corre-
sponding output fi lter capacitor (e.g., C13) and GNDA.
If the circuit being powered is at such a distance from
the part where voltage drops along circuit traces are
large, consider a Kelvin connection from the powered
circuit back to the resistive dividers.
APPLICATIONS INFORMATION
3. Keep C8 and C9 as close to the part as possible.
4. Keep the switching nodes (SWx) away from the sensi-
tive V
FBx
nodes.
5. Keep the ground connected plates of the input and
output capacitors as close as possible.
6. Care should be taken to provide enough space between
unshielded inductors in order to minimize any trans-
former coupling.
Design Example
As a design example, consider using the LTC3544 as a
portable application with a Li-Ion battery. The battery
provides V
IN
ranging from 2.8V to 4.2V. The demand at
2.5V is 250mA necessitating the use of the 300mA output
for this requirement.
C6R5
R6
L2
C4
V
OUT3
C12R8
R11
L3
C10
V
OUT2
C3
C1
R2
V
OUT4
3544 F03
R3
SW200B
SW200B
SW300
SW300
PGND PV
IN
SW1000
RUN100
GNDA
C15R15
R16
RUN100
V
FB100
V
FB100
RUN200ARUN200A
SW200A
SW200A
V
FB200B
V
FB200A
V
FB200B
V
FB300
V
FB300
RUN300 RUN300
RUN200B RUN200B
V
FB200A
V
CC
GNDA
PGND
V
CC
2.25V TO 5.5V
PV
IN
2.25V TO 5.5V
C8
L4
L1
LTC3544
C9
C13
V
OUT1
Figure 3. LTC3544 Layout Diagram
Figure 4. LTC3544 Suggested Layout
C1
C9
C10
GND
L1 L4
L2 L3
PGND
3544 F04
V
CC
C4
C3
C2