LTC1147 Linear Technology, LTC1147 Datasheet - Page 13

• Manufacturer Part Number: LTC1147
• Description: High Efficiency Step-Down Switching Regulator Controllers
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
LTC1147 series. These items are also illustrated graphi-
cally in the layout diagram of Figure 7. Check the following
in your layout:
1. Are the signal and power grounds segregated? The
2. Does the LTC1147 SENSE
LTC1147 ground (Pin 7) must return separately to a)
the power and b) signal grounds. The power ground
(a) returns to the source anode of the Schottky diode
and (–) plate of C
as short as possible. The signal ground (b) connects
to the (–) plate of C
close to R
V
+
–
IN
BOLD LINES INDICATE HIGH CURRENT PATHS
SENSE
390pF
U
and the (+) plate of C
IN
1k
, which should have lead lengths
OUT
3300pF
U
.
–
Figure 7. LTC1147 Layout Diagram (See Board Layout Checklist)
(Pin 4) connect to a point
1
2
3
4
V
C
I
SENSE
TH
W
IN
T
LTC1147-3.3
(LTC1147L)
LTC1147-5
–
+
+
1 F
OUT
C
SENSE
PDRIVE
?
IN
1000pF
SHDN
(V
GND
U
FB
+
)
8
7
6
5
P-CH
SHUTDOWN
3. Are the SENSE
4. Does the (+) plate of C
5. Is the input decoupling capacitor (0.1 F/1 F) con-
6. On fixed output versions, is the SHDN (Pin 6) actively
For additional High Efficiency application circuits see Application Note 54.
100pF
minimum PC trace spacing? The 1000pF capacitor
between Pins 4 and 5 should be as close as possible to
the LTC1147.
P-channel MOSFET as closely as possible? This capaci-
tor provides the AC current to the P-channel MOSFET.
nected closely between V
This capacitor carries the MOSFET driver peak currents.
pulled to ground during normal operation? The SHDN
pin is high impedance and must not be allowed to float.
D1
R1
L
LTC1147-5/LTC1147L
–
R2
and SENSE
R
SENSE
IN
IN
connect to the source of the
(Pin 1) and ground (Pin 7)?
LTC1147 • F07
+
OUTPUT DIVIDER
REQUIRED WITH
ADJUSTABLE
VERSION ONLY
leads routed together with
LTC1147-3.3
+
C
OUT
V
+
OUT
–
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