LTC3854 LINER [Linear Technology], LTC3854 Datasheet - Page 18

• Manufacturer Part Number: LTC3854
• Description: Small Footprint, Wide VIN Range Synchronous Step-Down DC/DC Controller
• Manufacturer: LINER [Linear Technology]

LTC3854
applicaTions inForMaTion
sudden step change in output voltage if the load switch
resistance is low and it is driven quickly. If the ratio of
C
should be controlled so that the load rise time is limited
to approximately 25 • C
require a 250μs rise time, limiting the charging current
to about 200mA.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3854. These items are also illustrated graphically
in the layout diagram of Figure 4. Check the following in
your layout:

LOAD
to C
OUT
is greater than 1:50, the switch rise time
47pF
R
C
C
SS
LOAD
C
C
. Thus a 10μF capacitor would
1000pF
C
C2
11
12
3
2
1
RUN/SS
ITH
V
SENSE
SENSE
FB
LTC3854
–
+
Figure 4. LTC3854 Layout Diagram
BOOST
INTV
GND
SW
V
BG
TG
CC
IN
6
5
4
10
9
8
7
R1
R2
+
+
C
4.7µF
OUT
1) Are the signal and power grounds segregated? The
2) Does the V
D
B
LTC3854 GND pin should tie to the ground plane close
to the output capacitor(s). The low current or signal
ground trace should make a single point connection
directly to the GND pin. The synchronous MOSFET
source pins should connect to the input capacitor(s)
ground.
tors? The resistive divider R1, R2 must be connected
between the (+) plate of C
47pF to 100pF capacitor should be as close as possible
to the LTC3854. Be careful locating the feedback resis-
tors too far away from the LTC3854. The V
not be routed close to any other nodes with high slew
rates.
C
B
M1
R
L1
FB
SENSE
pin connect directly to the feedback resis-
M2
D1
C
IN
OUT
3854 F04
and signal ground. The
V
V
OUT
+
–
–
+
IN
FB
line should
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