LTC1775 LINER [Linear Technology], LTC1775 Datasheet - Page 20

• Manufacturer Part Number: LTC1775
• Description: High Power No RSENSE TM Current Mode Synchronous Step-Down Switching Regulator
• Manufacturer: LINER [Linear Technology]

LTC1775
APPLICATIO S I FOR ATIO
20
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
LTC1775. These items are also illustrated graphically in
the layout diagram of Figure 12. Check the following in
your layout:
1) Connect the TK lead directly to the drain of the topside
2) The power ground pin connects directly to the source of
3) The LTC1775 signal ground pin should connect to the
MOSFET. Then connect the drain to the (+) plate of C
This capacitor provides the AC current to the top
MOSFET.
the bottom N-channel MOSFET. Then connect the source
to the anode of the Schottky diode (if used) and (–) plate
of C
possible.
(–) plate of C
ground at the source of the bottom MOSFET. All small-
signal components (R2, C
directly to SGND.
IN
, which should have as short lead lengths as
OUT
BOLD LINES INDICATE HIGH CURRENT PATHS
OPTIONAL 5V EXTV
WITH V
. Connect the (–) plate of C
OUTPUT DIVIDER
U
CONNECTION
R2
REQUIRED
R1
C
C
PROG
SS
C1
U
OPEN
R
INTV
C
OPEN
CLK
EXT
SS
CC
CC
, C
1
2
3
4
5
6
7
8
W
C
, etc.) should return
EXTV
SYNC
RUN/SS
FCB
I
SGND
V
V
TH
PROG
OSENSE
CC
LTC1775
Figure 12. LTC1775 Layout Diagram
OUT
INTV
BOOST
PGND
U
SW
V
TG
BG
TK
CC
IN
to power
16
15
14
13
12
11
10
9
IN
.
D
B
4) Keep the switch node SW away from sensitive small-
5) Connect the INTV
6) Does the V
7) For applications with multiple switching power con-
C
B
+
signal nodes. Ideally the switch node should be placed
on the opposite side of the power MOSFETs from the
LTC1775.
to the INTV
capacitor carries the MOSFET gate drive current.
the load? In adjustable applications, the resistive di-
vider (R1, R2) must be connected between the load and
signal ground. Place the divider near the LTC1775 in
order to keep the high impedance V
verters connected to the same V
filter capacitance for the LTC1775 is not shared with the
other converters. AC input current from another con-
verter will cause substantial input voltage ripple that
may interfere with proper operation of the LTC1775. A
few inches of PC trace or wire (L
between C
sharing.
C
VCC
+
M2
M1
IN
C
OSENSE
OUT
CC
L
and the V
TRACE
L1
pin and the power ground pin. This
D1
CC
pin connect as close as possible to
+
decoupling capacitor C
IN
C
IN
supply is sufficient to prevent
1775 F12
IN
+
–
–
+
, ensure that the input
V
V
IN
OUT
OSENSE
TRACE
node short.
VCC
100nH)
closely