LTC3544_15 Datasheet, PDF (13/16 Pages) Linear Technology – Quad Synchronous Step-Down Regulator

LTC3544
APPLICATIONS INFORMATION
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 filter 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.
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.
V_OUT1
C13
V_OUT3
C4
V_OUT2
C10
V_CC
L4 ^{2.25V TO 5.5V}
C8
GNDA
R15
C15
R16 _RUN100
SW1000 V_CC GNDA V_FB200A
RUN100
V_FB200B
V_FB100
V_FB100
LTC3544
V_FB300
V_FB300
RUN200A RUN200A
RUN300
RUN300
L2 _SW200A
SW200A
RUN200B
RUN200B
R5
C6
SW200B PGND PV_IN SW300
R6
V_FB200A
SW200B
C9
SW300 ^L1
L3
R8
C12
V_FB200B
PGND
PV_IN
2.25V TO 5.5V
R11
Figure 3. LTC3544 Layout Diagram
R2
C1
R3
V_OUT4
C3
3544 F03
C1
C4
GND
L1
L4
V_CC
C9
L2
C10
L3
C2 C3
PGND
3544 F04
Figure 4. LTC3544 Suggested Layout
3544fa
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