Datasheet
18
LTC3718
3718fa
Figure 8. LTC3718 Layout Diagram
C
SS
C2
R
C
RUN/SS
V
ON
PGOOD
V
RNG
I
TH
SGND1
I
ON
V
FB1
V
REF
SHDN
SGND2
V
FB2
BOOST
TG
SW1
SENSE
+
SENSE
–
PGND1
BG
INTV
CC
V
IN1
V
IN2
PGND2
SW2
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
LTC3718
C1
R
ON
R
F3
R
F4
R
F5
C
IN2
L2 BOLD LINES INDICATE HIGH CURRENT PATHS
M2 D2
3718 F08
L1
D3
C
VCC
C
B
M1
D
B
V
IN
+
–
V
OUT
C
OUT
C
IN
APPLICATIO S I FOR ATIO
WUUU
PC Board Layout Checklist
When laying out a PC board follow one of the two
suggested approaches. The simple PC board layout
requires a dedicated ground plane layer. Also, for higher
currents, it is recommended to use a multilayer board to
help with heat sinking power components.
• The ground plane layer should not have any traces and
it should be as close as possible to the layer with power
MOSFETs.
• Place C
IN
, C
OUT
, MOSFETs, D1 and inductor all in one
compact area. It may help to have some components
on the bottom side of the board.
• Place LTC3718 chip with Pins 13 to 24 facing the
power components. Keep the components connected
to Pins 1 to 12 close to LTC3718 (noise sensitive
components).
• Use an immediate via to connect the components to
ground plane including SGND and PGND of LTC3718.
Use several bigger vias for power components.
• Use compact plane for switch node (SW) to improve
cooling of the MOSFETs and to keep EMI down.
• Use planes for V
IN
and V
OUT
to maintain good voltage
filtering and to keep power losses low.
• Flood all unused areas on all layers with copper.
Flooding with copper will reduce the temperature rise
of power component. You can connect the copper
areas to any DC net (V
IN
, V
OUT
, GND or to any other DC
rail in your system).
When laying out a printed circuit board, without a ground
plane, use the following checklist to ensure proper opera-
tion of the controller. These items are also illustrated in
Figure 8.
• Segregate the signal and power grounds. All small
signal components should return to the SGND pin at
one point which is then tied to the PGND pin close to
the source of M2.
• Place M2 as close to the controller as possible, keep-
ing the PGND, BG and SW traces short.
• Connect the input capacitor(s) C
IN
close to the power
MOSFETs. This capacitor carries the MOSFET AC
current.
• Keep the high dV/dt SW, BOOST and TG nodes away
from sensitive small-signal nodes.
• Connect the INTV
CC
decoupling capacitor C
VCC
closely
to the INTV
CC
and PGND pins.
• Connect the top driver boost capacitor C
B
closely to
the BOOST and SW pins.