LTC1142-ADJ Linear Technology, LTC1142-ADJ Datasheet - Page 15

• Manufacturer Part Number: LTC1142-ADJ
• Description: Dual High Efficiency Synchronous Step-Down Switching Regulators
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
To prevent stray pickup a 100pF capacitor is suggested
across R1 located close to the LTC1142HV-ADJ/LTC1142L-
ADJ as in Figure 6. The external divider network must be
placed across C
to signal ground. Refer to the Board Layout Checklist.
Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
V
V
OUT3
IN3
BOLD LINES INDICATE HIGH CURRENT PATHS
–
+
–
+
Figure 6. LTC1142-ADJ External Feedback Network
R
SENSE3
[PIN 2(16)]
[PIN 4(18)]
SGND
V
FB
OUT
C
with the negative plate of C
IN3
D1
U U
+
L1
C
N-CH
100pF
OUT3
SHUTDOWN (3.3V OUTPUT)
P-CH
Figure 7. LTC1142 Layout Diagram (see Board Layout Checklist)
R1
C
T5
V
IN5
R2
W
1 F
1k
3300pF
+
+
R
SENSE
C
OUT
OUT
10
11
12
13
14
1142 F06
1
2
3
4
5
6
7
8
9
V
OUT
U
returned
NC
PDRIVE 5
SENSE
SHUTDOWN 3
SGND3
PGND3
NC
NDRIVE 3
NC
V
C
INT V
I
SENSE
TH5
IN5
T5
CC5
+
–
3
5
1000pF
LTC1142
1000pF
SHUTDOWN 5
NDRIVE 5
PDRIVE 3
SENSE
SENSE
INT V
LTC1142. These items are also illustrated graphically in
the layout diagram of Figure 7. In general each block
should be self-contained with little cross coupling for best
performance. Check the following in your layout:
1. Are the signal and power grounds segregated? The
2. Does the LTC1142 Sense
3. Are the Sense
PGND5
SGND5
LTC1142/LTC1142L/LTC1142HV
V
LTC1142 signal ground [Pin 3 (17) for the LTC1142, Pin
4 (18) for LTC1142-ADJ] must return to the (–) plate of
C
N-channel MOSFET, anode of the Schottky diode,
and (–) plate of C
lengths as possible.
point close to R
minimum PC trace spacing? The 1000pF capacitor
I
TH3
CC3
C
NC
NC
NC
IN3
–
+
T3
OUT
3
5
28
27
26
25
24
23
22
21
20
19
18
17
16
15
. The power ground returns to the source of the
SHUTDOWN (5V OUTPUT)
3300pF
+
1 F
V
–
IN3
and Sense
SENSE
IN
1k
, which should have as short lead
P-CH
and the (+) plate of C
C
T3
–
+
N-CH
C
OUT5
, Pin 28 (14) connect to a
leads routed together with
+
D2
L2
C
IN5
R
SENSE5
OUT
–
15
+
–
+
V
1142 F07
V
OUT5
?
IN5