LTC3878
19
3878fa
l Use planes for V
IN
and V
OUT
to maintain good voltage
filtering and to keep power losses low.
l 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).
l Place decoupling capacitor C
C2
next to the I
TH
and SGND
pins with short, direct trace connections.
When laying out a printed circuit board without a ground
plane, use the following checklist to ensure proper operation
of the controller. These items are illustrated in Figure 7.
l Segregate the signal and power grounds. All small-signal
components should return to the SGND pin at one point.
SGND and PGND should be tied together underneath
the IC and then connect directly to the source of M2.
l Place M2 as close to the controller as possible, keeping
the PGND, BG and SW traces short.
l Keep the high dV/dT SW, BOOST and TG nodes away
from sensitive small-signal nodes.
l Connect the input capacitor(s), C
IN
, close to the
power MOSFETs. This capacitor carries the MOSFET AC
current.
l Connect the INTV
CC
decoupling capacitor C
VCC
closely
to the INTV
CC
and PGND pins.
l Connect the top driver boost capacitor, C
B
, closely to
the BOOST and SW pins.
l Connect the V
IN
pin decoupling C
F
closely to the V
IN
and PGND pins.
Figure 8. LTC3878 Layout Diagram Without Ground Plane
applicaTions inForMaTion
16
15
14
13
12
11
10
9
C
C2
BOLD LINES INDICATE HIGH CURRENT PATHS
C
C1
C
SS
R
ON
R
C
R
F
3878 F08
1
2
3
4
5
6
7
8
RUN/SS
PGOOD
V
RNG
FCB
I
TH
SGND
I
ON
V
FB
BOOST
TG
SW
PGND
BG
INTV
CC
V
IN
NC
C
B
M2
M1
D
B
C
F
C
VCC
C
OUT
C
IN
V
IN
V
OUT
+
–
+
–
LTC3878
L
R1
R2
+
