LTC1871 Linear Technology, LTC1871 Datasheet - Page 29

• Manufacturer Part Number: LTC1871
• Description: Wide Input Range/ No RSENSE Current Mode Boost/ Flyback and SEPIC Controller
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
5. With an minimum input voltage of 5V, only logic-level
And so the inductor value is:
The component chosen is a BH Electronics BH510-
1007, which has a saturation current of 8A.
power MOSFETs should be considered. Because the
maximum duty cycle is 71.4%, the maximum SENSE
pin threshold voltage is reduced from its low duty cycle
typical value of 150mV to approximately 120mV.
Assuming a MOSFET junction temperature of 125 C,
the room temperature MOSFET R
than:
L
2
V
•
IN MIN
(
I
C
47pF
L
C2
•
)
f
R
33k
•
C
105k
C
6.8nF
D
1%
C1
U
R2
MAX
C
C
D1:
12.1k
IN
DC
, C
1%
, C
R1
U
OUT1
OUT2
2 1 5 300
: KEMET T495X476K020AS
: TAIYO YUDEN TMK432BJ106MM
• . •
INTERNATIONAL RECTIFIER 30BQ040
R
80.6k
1%
T
Figure 18a. 4.5V to 15V Input, 12V/2A Output SEPIC Converter
5
W
DS(ON)
1
2
3
4
5
R3
1M
RUN
I
FB
FREQ
MODE/SYNC
Figure 18b. SEPIC Efficiency vs Output Current
TH
k
100
95
90
85
80
75
70
65
60
55
50
45
• .
LTC1871
0.001
should be less
0 714 4
U
INTV
V
SENSE
IN
GATE
GND
V
= 4.5V
CC
0.01
IN
OUTPUT CURRENT (A)
V
10
9
8
7
6
IN
V
= 15V
H
IN
L1, L2: BH ELECTRONICS BH510-1007 (*COUPLED INDUCTORS)
M1:
= 12V
0.1
C
4.7 F
X5R
VCC
INTERNATIONAL RECTIFIER IRF7811W
V
MODE = INTV
For a SEPIC converter, the switch BV
greater than V
an IRF7811W, which is rated to 30V, and has a maxi-
mum room temperature R
R
O
+
DS ON
= 12V
0 12
1
1 5
.
(
.
C
47 F
IN
L1*
1871 F18b
)
•
CC
1 2 1 5
10
•
M1
. • .
V
SENSE MAX
10 F
X5R
C
25V
1
I
DC
O MAX
IN(MAX)
(
•
(
L2*
•
D1
)
12 5
+ V
)
5
•
.
+
1
O
DS(ON)
, or 27V. This comes close to
1
C
47 F
20V
OUT1
2
1
2
1
of 12m at V
12 7
•
1871 F018a
.
C
10 F
25V
X5R
DSS
T
OUT2
2
m
•
GND
LTC1871
V
4.5V to 15V
V
12V
1.5A
(2A PEAK)
IN
OUT
rating must be
V
V
O
IN MIN
(
GS
1
V
29
= 4.5V.
D
)
1