Datasheet

LTC1772B
12
1772bfa
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 LTC1772B. These items are illustrated graphically in
the layout diagram in Figure 7. Check the following in
your layout:
1. Is the Schottky diode closely connected between ground
(Pin 2) and drain of the external MOSFET?
2. Does the (+) plate of C
IN
connect to the sense resistor
as closely as possible? This capacitor provides AC
current to the MOSFET.
3. Is the input decoupling capacitor (0.1μF) 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. Is the trace from SENSE
–
(Pin 4) to the Sense resistor
kept short? Does the trace connect close to R
SENSE
?
6. Keep the switching node PGATE away from sensitive
small signal nodes.
7. Does the V
FB
pin connect directly to the feedback
resistors? The resistive divider R1 and R2 must be
connected between the (+) plate of C
OUT
and signal
ground.
Figure 7. LTC1772B Layout Diagram (See PC Board Layout Checklist)
L1
M1
R1
BOLD LINES INDICATE HIGH CURRENT PATHS
R2
D1
R
SENSE
V
IN
V
OUT
1772 F06
0.1μF
C
OUT
C
ITH
R
ITH
+
C
IN
+
I
TH
/RUN
LTC1772B
GND
V
FB
6
5
4
1
2
3
PGATE
V
IN
SENSE
–