ltc1871ems-7-trpbf Linear Technology Corporation, ltc1871ems-7-trpbf Datasheet - Page 29

• Manufacturer Part Number: ltc1871ems-7-trpbf
• Description: Wide Input Range, No Rsense Current Mode Boost, Flyback And Sepic Controller
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
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 • I
V
IN(MIN)
C
47pF
C2
L
• f
R
33k
C
105k
C
6.8nF
• D
C1
1%
R2
MAX
C
C
D1:
12.1k
IN
DC
, C
1%
R1
, C
OUT1
=
OUT2
2 • 1.5 • 300k
: 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
1
2
3
4
5
R3
1M
DS(ON)
RUN
I
FB
FREQ
MODE/SYNC
TH
Figure 18b. SEPIC Effi ciency vs Output Current
LTC1871-1
• 0.714 = 4μH
100
95
90
85
80
75
70
65
60
55
50
45
should be less
0.001
INTV
SENSE
GATE
GND
V
V
CC
IN
IN
= 4.5V
0.01
10
9
8
7
6
OUTPUT CURRENT (A)
V
IN
L1, L2: BH ELECTRONICS BH510-1007 (*COUPLED INDUCTORS)
M1:
V
= 15V
IN
= 12V
C
4.7μF
X5R
0.1
VCC
INTERNATIONAL RECTIFIER IRF7811W
For a SEPIC converter, the switch BV
greater than V
an IRF7811W, which is rated to 30V, and has a maximum
room temperature R
+
R
=
V
MODE = INTV
O
DS(ON)
0.12
= 12V
1.5
1
C
47μF
IN
L1*
18711 F18b
•
•
M1
1.2 • 1.5
CC
10μF
10
X5R
V
C
25V
DC
SENSE(MAX)
1
I
O(MAX)
IN(MAX)
•
L2*
D1
•
DS(ON)
12.5
+ V
+
5
•
1
O
, or 27V. This comes close to
C
47μF
20V
×2
1+
OUT1
of 12mΩ at V
+ 1
2
1
= 12.7m
18711 F018a
LTC1871-1
•
C
10μF
25V
X5R
×2
OUT2
DSS
T
GND
V
4.5V to 15V
V
12V
1.5A
(2A PEAK)
IN
OUT
•
rating must be
GS
V
V
IN(MIN)
O
= 4.5V.
+ V
1
29
D
18711fb
+ 1