LTC1871-1
TM
SENSE
Wide Input Range, No R
Current Mode Boost,
Flyback and SEPIC Controller
U
FEATURES
DESCRIPTIO
The LTC®1871-1 is a wide input range, current mode,
boost, flyback or SEPIC controller that drives an N-
channel power MOSFET and requires very few external
components. It eliminates the need for a current sense
resistor by utilizing the power MOSFET’s on-resistance,
thereby maximizing efficiency. Higher output voltage
applicationsarepossiblewiththeLTC1871-1byconnect-
ing the SENSE pin to a resistor in the source of the power
MOSFET.
■
High Efficiency (No Sense Resistor Required)
■
Wide Input Voltage Range: 2.5V to 36V
■
Current Mode Control Provides Excellent
Transient Response
■
High Maximum Duty Cycle (92% Typ)
■
±2% RUN Pin Threshold with 100mV Hysteresis
■
±1% Internal Voltage Reference
■
Ultra Low Pulse Skip Threshold for Wide Input
Range Applications
■
Micropower Shutdown: IQ = 10μA
The IC’s operating frequency can be set with an external
resistorovera50kHzto1MHzrange, andcanbesynchro-
nized to an external clock using the MODE/SYNC pin.
■
Programmable Operating Frequency
(50kHz to 1MHz) with One External Resistor
■
Synchronizable to an External Clock Up to 1.3 × fOSC
User-Controlled Pulse Skip or Burst Mode® Operation
The LTC1871-1 differs from the LTC1871 by having a
lower pulse skip threshold, making it ideal for applica-
tions requiring constant frequency operation at light
loads. The lower pulse skip threshold also helps maintain
constant frequency operation in applications with a wide
input voltage range. For applications requiring primary-
to-secondary side isolation, please refer to the LTC1871
datasheet.
■
■
Internal 5.2V Low Dropout Voltage Regulator
Output Overvoltage Protection
Capable of Operating with a Sense Resistor for High
Output Voltage Applications
Small 10-Lead MSOP Package
■
■
■
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APPLICATIO S
TheLTC1871-1isavailableinthe10-leadMSOPpackage.
■
Telecom Power Supplies
Portable Electronic Equipment
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
■
Corporation. No R
is a trademark of Linear Technology Corporation. All other
SENSE
trademarks are the property of their respective owners.
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TYPICAL APPLICATIO
V
IN
3.3V
Efficiency of Figure 1
L1
1μH
100
90
80
70
60
50
40
30
D1
RUN
SENSE
V
OUT
5V
Burst Mode
OPERATION
I
TH
V
IN
7A
C
R
OUT1
C
+
(10A PEAK)
LTC1871-1
INTV
150μF
6.3V
×4
22k
FB
PULSE-SKIP
MODE
CC
C
6.8nF
C1
R1
12.1k
1%
C
OUT2
FREQ
GATE
GND
M1
22μF
6.3V
X5R
×2
C
IN
C
VCC
+
R2
37.4k
1%
R
T
80.6k
1%
MODE/SYNC
22μF
6.3V
×2
C
C2
47pF
4.7μF
X5R
GND
1871 F01a
C
C
C
:
TAIYO YUDEN JMK325BJ226MM
: PANASONIC EEFUEOJ151R
D1: MBRB2515L
IN
L1: SUMIDA CEP125-H 1R0MH
M1: FAIRCHILD FDS7760A
OUT1
OUT2
0.001
0.01
0.1
1
10
: TAIYO YUDEN JMK325BJ226MM
OUTPUT CURRENT (A)
1871 F01b
Figure 1. High Efficiency 3.3V Input, 5V Output Boost Converter (Bootstrapped)
18711fa
1