LTC3545-1_15 Datasheet, PDF (16/20 Pages) Linear Technology – Triple 800mA Synchronous Step-Down Regulator–2.25MHz

LTC3545/LTC3545-1
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 LTC3545/LTC3545-1. These items are also illustrated
graphically in Figures 3 and 4. Figure 3 shows the power
path components and traces. In this figure the feedback
networks are not shown since they reside on the bottom
side of the board. Check the following in your layout:
1. The power traces consisting of the PGND trace, the SW
trace, the PV_IN trace, the V_IN and GNDA traces, 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 cor-
responding output filter capacitor (e.g. C2) 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 C1 and C5 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.
V_IN
C5
GNDA
SW1
C2
L1
V_OUT3
L3
C4
(VIA TO FEEDBACK
NETWORK)
SW3
PV_IN
C1
PGND
SW2
L2
C3
V_OUT2
3545 F03
(VIA TO FEEDBACK
NETWORK)
(VIA TO FEEDBACK
NETWORK)
V_OUT1
Figure 3. Layout Diagram
35451fb
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