LTC3718 Linear Technology, LTC3718 Datasheet - Page 17

• Manufacturer Part Number: LTC3718
• Description: Low Input Voltage DC/DC Controller
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
and double check the assumed T
Now check the power dissipation of the top MOSFET at
current limit with
C
temperature. The output capacitors are chosen for a low
IN
T
T
www.DataSheet4U.com
P
P
J
J
BOT
is chosen for an RMS current rating of about 6A at
TOP
= 50 C + (0.18W)(50 C/W) = 59 C
= 50 C + (0.87W)(50 C/W) = 93.5 C
0 18
2 5
0 87
1 25
1 7 2 5
.
.
2 5
.
.
.
.
V
2 5
V
W
V
W
PGOOD
– .
.
1 25
.
V
9 9
90 C
U
.
V
A
V
9 9
= 1.35:
2
.
U
9 9
1 35 0 013
A
.
2
.
R
100k
PG
2
A
C1 820pF
60
R
10k
2
R1
J
Figure 7. Design Example: 1.25V/ 6A at 300kHz from 2.5V
( . )( .
pF
12.1k
1 15 0 013
.
in the MOSFET:
R
W
F1
4.75k
237k
R
39.2k
R
R
R2
ON
C
100pF
300
C2
R
10k
0.1 F
F3
C
kHz
SS
10
11
12
1
2
3
4
5
6
7
8
9
RUN/SS
V
PGOOD
V
I
SGND1
I
V
V
SHDN
SGND2
V
U
TH
ON
ON
RNG
FB1
REF
FB2
)
LTC3718
1000pF
37.4k
R
C
F4
F2
SENSE
SENSE
BOOST
PGND1
INTV
PGND2
SW1
SW2
V
V
BG
IN1
IN2
TG
CC
+
–
24
23
22
21
20
19
18
17
16
15
14
13
ESR of 0.005 to minimize output voltage changes due to
inductor ripple current and load steps. The ripple voltage
will be only:
However, a 0A to 6A load step will cause an output change
of up to:
The inductor for the boost converter is selected by first
choosing an allowable ripple current. The boost converter
will be operating in discontinous mode. If we select a ripple
current of 170mA for the boost converter, then:
The complete circuit is shown in Figure 7.
L
V
V
D
CMDSH-3
C
0.33 F
C
10 F
OUT(RIPPLE)
OUT(STEP)
B
B
VCC1
(
170
3 3 1
.
C
4.7 F
IN2
mA
V
M1
IRF7811A
M2
IRF7811A
)( .
= I
1 4
= I
= (2.6A) (0.005 ) = 13mV
3 3
5
1 H
.
LOAD
L1
MHz
V
L(MAX)
V
C
22 F
IN1
2
D1
B340A
D2
B340A
(ESR) = (6A) (0.005 ) = 30mV
)
3718 F07
(ESR)
4 7
.
L2
4.7 H
D3
MBR0520
H
C
270 F
C
330 F
OUT
2
IN2
V
2.5V
V
1.25V
IN
OUT
6A
LTC3718
17
3718fa