LTC3718 Linear Technology, LTC3718 Datasheet - Page 18

• Manufacturer Part Number: LTC3718
• Description: Low Input Voltage DC/DC Controller
• Manufacturer: Linear Technology

LTC3718
APPLICATIO S I FOR ATIO
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
• Place C
• Place LTC3718 chip with Pins 13 to 24 facing the
• Use an immediate via to connect the components to
• Use compact plane for switch node (SW) to improve
• Use planes for V
18
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it should be as close as possible to the layer with power
MOSFETs.
compact area. It may help to have some components
on the bottom side of the board.
power components. Keep the components connected
to Pins 1 to 12 close to LTC3718 (noise sensitive
components).
ground plane including SGND and PGND of LTC3718.
Use several bigger vias for power components.
cooling of the MOSFETs and to keep EMI down.
filtering and to keep power losses low.
IN
, C
OUT
, MOSFETs, D1 and inductor all in one
IN
U
and V
C1
U
OUT
R
R
R
ON
F3
C
to maintain good voltage
C2
R
F5
C
W
SS
10
11
12
1
2
3
4
5
6
7
8
9
RUN/SS
V
PGOOD
V
I
SGND1
I
V
V
SHDN
SGND2
V
TH
ON
ON
RNG
FB1
REF
FB2
LTC3718
R
Figure 8. LTC3718 Layout Diagram
F4
SENSE
SENSE
INTV
BOOST
PGND1
PGND2
U
SW1
SW2
V
V
BG
IN1
IN2
TG
CC
+
–
24
23
22
21
20
19
18
17
16
15
14
13
D
C
B
IN2
D3
C
C
VCC
B
• Flood all unused areas on all layers with copper.
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
• Place M2 as close to the controller as possible, keep-
• Connect the input capacitor(s) C
• Keep the high dV/dt SW, BOOST and TG nodes away
• Connect the INTV
• Connect the top driver boost capacitor C
Flooding with copper will reduce the temperature rise
of power component. You can connect the copper
areas to any DC net (V
rail in your system).
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.
ing the PGND, BG and SW traces short.
MOSFETs. This capacitor carries the MOSFET AC
current.
from sensitive small-signal nodes.
to the INTV
the BOOST and SW pins.
L2
M1
M2
BOLD LINES INDICATE HIGH CURRENT PATHS
CC
L1
and PGND pins.
D2
CC
decoupling capacitor C
IN
, V
OUT
C
IN
C
, GND or to any other DC
OUT
3718 F08
IN
+
–
close to the power
V
V
OUT
IN
B
VCC
closely to
closely
3718fa