LTC1872
10
1872fa
For more information
www.linear.com/LTC1872
applicaTions inForMaTion
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC1872. These items are illustrated graphically in
the layout diagram in Figure 5. Check the following in
your layout:
1. The Schottky diode should be closely connected
between the output capacitor and the drain of the
external MOSFET.
2. The (+) plate of C
IN
should connect to the sense resis-
tor as closely as possible. This capacitor provides AC
current to the inductor.
3. The input decoupling capacitor (0.1µF) should be
connected closely between V
IN
(Pin 5) and ground
(Pin 2).
4. Connect the end of R
SENSE
as close to V
IN
(Pin 5) as
possible. The V
IN
pin is the SENSE
+
of the current
comparator.
5. The trace from SENSE
–
(Pin 4) to the Sense resistor
should be kept short. The trace should connect close
to R
SENSE
.
6. Keep the switching node NGATE away from sensitive
small signal nodes.
7. The V
FB
pin should connect directly to the feedback
resistors. The resistive divider R1 and R2 must be
connected between the (+) plate of C
OUT
and signal
ground.
L1
M1
BOLD LINES INDICATE HIGH CURRENT PATHS
D1
R
S
V
OUT
V
IN
1872 F05
0.1µF
C
ITH
R
ITH
R2
R1
C
IN
+
I
TH
/RUN
LTC1872
GND
V
FB
6
5
4
1
2
3
NGATE
V
IN
SENSE
–
C
OUT
+
Figure 5. LTC1872 Layout Diagram (See PC Board Layout Checklist)
