Datasheet

LTC3852
27
3852f
LTC3852
C
S
C
C1
C
C2
C
FF
C
INTVCC
C
FLY
R
B
R
S1
C
SS
C
FLTR
R
FREQ
R
PGOOD
V
PULL-UP
R
C
R
A
C
OUT1
C
IN2
C
OUT2
C
B
D
B
R
SENSE
D1
M2
M1
C
IN1
+
–
L1
V
IN
–
+
V
OUT
3852 F13
PGOOD
FREQ/PLLFLTR
MODE/PLLIN
RUN
SHDN
TRACK/SS
I
TH
V
FB
SENSE
–
SENSE
+
SW
TG
BOOST
V
IN2
V
IN1
INTV
CC
V
PUMP
BG
GND1, 2
C
–
C
+
R
S2
+
+
ONOFF
Figure 13. LTC3852 Switching Regulator Layout Diagram
APPLICATIONS INFORMATION
ground. The 47pF to 100pF capacitor should be as
close as possible to the LTC3852. Be careful locating
the feedback resistors too far away from the LTC3852.
The V
FB
line should not be routed close to any other
nodes with high slew rates.
3. Are the SENSE
–
and SENSE
+
leads routed together
with minimum PC trace spacing? The fi lter capacitor
between SENSE
+
and SENSE
–
should be as close as
possible to the LTC3852. Ensure accurate current
sensing with Kelvin connections as shown in Figure 14.
Series resistance can be added to the SENSE lines to
increase noise rejection and to compensate for the ESL
of R
SENSE
.
4. Does the (+) terminal of C
IN
connect to the drain of
the topside MOSFET(s) as closely as possible? This
capacitor provides the AC current to the MOSFET(s).
5. Is the INTV
CC
ceramic decoupling capacitor connected
closely between INTV
CC
and GND2? This capacitor
carries the MOSFET driver peak currents.
6. Keep the switching node (SW), top gate node (TG) and
boost node (BOOST) away from sensitive small-signal
SENSE
+
SENSE
–
HIGH
CURRENT
PATH
3852 F14
CURRENT SENSE
RESISTOR
(R
SENSE
)
nodes, especially from the voltage and current sensing
feedback pins. All of these nodes have very large and
fast moving signals and therefore should be kept on
the “output side” of the LTC3852 and occupy minimum
PC trace area.
Figure 14. Kelvin Sensing R
SENSE
Layout Considerations (Charge Pump)
Due to the high switching frequency and high transient
currents produced by the charge pump, careful board layout
is necessary for optimum performance. A true ground
plane and short connections to all the external capacitors