LTC1707 LINER [Linear Technology], LTC1707 Datasheet - Page 11

• Manufacturer Part Number: LTC1707
• Description: High Efficiency Monolithic Synchronous Step-Down Switching Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
A second, more severe transient is caused by switching in
loads with large (>1 F) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with C
deliver enough current to prevent this problem if the load
switch resistance is low and it is driven quickly. The only
solution is to limit the rise time of the switch drive so that
the load rise time is limited to approximately (25 • C
Thus, a 10 F capacitor charging to 3.3V would require a
250 s rise time, limiting the charging current to about
130mA.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
LTC1707. These items are also illustrated graphically in
the layout diagram of Figure 7. Check the following in your
layout:
OUT
, causing a rapid drop in V
U
OPTIONAL
U
BOLD LINES INDICATE HIGH CURRENT PATHS
R
C
W
OUT
C
C2
C
. No regulator can
SS
C
C1
Figure 7. LTC1707 Layout Diagram
U
C
1
2
3
4
REF
I
RUN/SS
V
GND
TH
FB
LOAD
LTC1707
SYNC/MODE
).
V
REF
V
SW
1. Are the signal and power grounds segregated? The
2. Does the V
3. Does the (+) plate of C
4. Keep the switching node SW away from sensitive small-
IN
LTC1707 signal ground consists of the resistive
divider, the optional compensation network (R
C
the (–) plate of C
LTC1707. The power ground traces should be kept
short, direct and wide. The signal ground and power
ground should converge to a common node in a star-
ground configuration.
resistors? The resistive divider R1/R2 must be con-
nected between the (+) plate of C
possible? This capacitor provides the AC current to the
internal power MOSFETs.
signal nodes.
8
7
6
5
C1
), C
R2
R1
L1
SS
, C
+
REF
FB
C
pin connect directly to the feedback
and C
OUT
IN
V
, the (–) plate of C
OUT
+
–
C2
IN
C
. The power ground consists of
IN
1707 F07
connect to V
+
V
+
–
IN
OUT
OUT
and signal ground.
LTC1707
IN
and Pin 4 of the
as closely as
11
C
and