LTC1438/LTC1439
25
14389fb
The previous instructions will yield a PC layout which has
three separate ground regions returning separately to the
bottom plates of the output capacitors: a signal ground, a
MOSFET gate/INTV
CC
ground and the ground from the
input capacitors, Schottky diode and synchronous
MOSFET. In practice, this may produce a long power
ground path from the input and output capacitors. A long,
low resistance path between the input and output capaci-
tor power grounds will not upset the operation of the
switching controllers as long as the signal and power
grounds from the IC pins does not “tap in” along this path.
APPLICATIONS INFORMATION
WUU
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current, reducing the susceptibility to both the “loop”
radiated magnetic fields and the transformer or inductor
leakage fields.
The capacitor on INTV
CC
acts as a reservoir to supply the
high transient currents to the bottom gates
and
to re-
charge the boost capacitor. This capacitor should be a
4.7µF tantalum capacitor placed as close as possible to the
INTV
CC
and PGND pins of the IC. Peak current driving the
MOSFET gates exceeds 1A. The PGND pin of the IC,
connected to this capacitor, should connect directly to the
lower plates of the output capacitors to minimize the AC
ripple on the INTV
CC
IC power supply.
TYPICAL APPLICATIONS
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LTC1438 5V/3A, 3.3V/3.5A Regulator
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
SENSE
+
1
SENSE
–
1
V
PROG1
I
TH1
POR2
C
OSC
SGND
LBI
LBO
SFB1
I
TH2
V
OSENSE2
SENSE
–
2
SENSE
+
2
RUN/SS1
BOOST 1
TGL1
SW1
V
IN
BG1
INTV
CC
PGND
BG2
EXTV
CC
SW2
TGL2
BOOST 2
RUN/SS2
LTC1438
0.1µF
22µF
35V
0.1µF
1438 TA01
+
+
1000pF
100Ω100Ω
1000pF
10Ω
V
IN
5.2V TO 28V: SWITCHING FREQUENCY = 180kHz
5V, 3A/3.3V, 3.5A
M1 TO M4: Si4412ADY
INPUT CAPACITORS ARE AVX-TPS SERIES
OUTPUT CAPACITORS ARE AVX-TPSV LEVEL II SERIES
INTV
CC
POR2
LBI
LBO
0.1µF
1000pF
1000pF
220pF
470pF
10k
10Ω
M1
M2
M4
M3
CMDSH-3
CMDSH-3
10k
221k, 1%
56pF
1k
10Ω
392k, 1%
1000pF
56pF
220pF
0.1µF
0.1µF
V
OUT1
4.7µF 16V
0.033Ω
0.033Ω
22µF
35V
+
MBRS140T3
MBRS140T3
10µH
SUMIDA
CDRH125-100MC
10µH
SUMIDA
CDRH125-100MC
+
220µF
10V
V
IN
5.2V
TO
28V
V
OUT1
5V
3A
V
OUT2
3.3V
3.5A
GND
220µF
10V
22µF
35V
+
22µF
35V
++
1N4148
1N4148
22pF
