LTC3878 Linear Technology Corporation, LTC3878 Datasheet - Page 19

• Manufacturer Part Number: LTC3878
• Description: Wide Operating Range No RSENSE Step-Down Controller
• Manufacturer: Linear Technology Corporation

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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.
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APPLICATIONS INFORMATION
Use planes for V
fi ltering 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
system).
Place decoupling capacitor C
pins with short, direct trace connections.
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.
IN
, V
BOLD LINES INDICATE HIGH CURRENT PATHS
R1
R2
OUT
C
C
SS
C1
IN
, GND or to any other DC rail in your
R
and V
C
OUT
C
C2
R
C2
ON
to maintain good voltage
1
2
3
4
5
6
7
8
next to the I
Figure 8. LTC3878 Layout Diagram Without Ground Plane
RUN/SS
PGOOD
V
FCB
I
SGND
I
V
TH
ON
RNG
FB
LTC3878
BOOST
INTV
PGND
SW
TH
V
BG
NC
TG
CC
IN
and SGND
16
15
14
13
12
11
10
9
+
C
C
D
VCC
B
B
C
F
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R
Place M2 as close to the controller as possible, keeping
the PGND, BG and SW traces short.
Keep the high dV/dT SW, BOOST and TG nodes away
from sensitive small-signal nodes.
Connect the input capacitor(s), C
power MOSFETs. This capacitor carries the MOSFET AC
current.
Connect the INTV
to the INTV
Connect the top driver boost capacitor, C
the BOOST and SW pins.
Connect the V
and PGND pins.
F
M2
C
OUT
CC
D1
and PGND pins.
M1
IN
L
pin decoupling C
CC
decoupling capacitor C
C
IN
3878 F08
F
+
–
–
+
closely to the V
V
LTC3878
V
IN
IN
OUT
, close to the
B
, closely to
VCC
19
closely
3878f
IN