LTC1871-1_15 Datasheet, PDF (1/36 Pages) Linear Technology – Wide Input Range, No RSENSE Current Mode Boost, Flyback and SEPIC Controller

FEATURES
n _{High Efficiency (No Sense Resistor Required)}
n _{Wide Input Voltage Range: 2.5V to 36V}
n _{Current Mode Control Provides Excellent}
Transient Response
n _{High Maximum Duty Cycle (92% Typ)}
n _{±2% RUN Pin Threshold with 100mV Hysteresis}
n _{±1% Internal Voltage Reference}
n _{Ultra Low Pulse Skip Threshold for Wide Input}
Range Applications
n _{Micropower Shutdown: IQ = 10μA}
n _{Programmable Operating Frequency}
(50kHz to 1MHz) with One External Resistor
n _{Synchronizable to an External Clock Up to 1.3 × fOSC}
n _{User-Controlled Pulse Skip or Burst Mode}^® _Operation
n _{Internal 5.2V Low Dropout Voltage Regulator}
n _{Output Overvoltage Protection}
n _{Capable of Operating with a Sense Resistor for High}
Output Voltage Applications
n _{Small 10-Lead MSOP Package}
APPLICATIONS
n _{Telecom Power Supplies}
n _{Portable Electronic Equipment}
LTC1871-1
Wide Input Range, No R_SENSE™
Current Mode Boost,
Flyback and SEPIC Controller
DESCRIPTION
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 applications are possible
with the LTC1871-1 by connecting the SENSE pin to a
resistor in the source of the power MOSFET.
The IC’s operating frequency can be set with an external
resistor over a 50kHz to 1MHz range, and can be synchro-
nized to an external clock using the MODE/SYNC pin.
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.
The LTC1871-1 is available in the 10-lead MSOP package.
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
No R_SENSE is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
TYPICAL APPLICATION
R_C
22k
C_C1
6.8nF
C_C2
47pF
R2
37.4k
1%
R1
12.1k
1%
R_T
80.6k
1%
RUN
SENSE
I_TH
V_IN
LTC1871-1
FB
FREQ
INTV_CC
GATE
MODE/SYNC GND
L1
1μH
D1
M1
C_{VCC +}
4.7μF
X5R
C_IN
22μF
6.3V
×2
C_IN: TAIYO YUDEN JMK325BJ226MM
C_OUT1: PANASONIC EEFUEOJ151R
C_OUT2: TAIYO YUDEN JMK325BJ226MM
D1: MBRB2515L
L1: SUMIDA CEP125-H 1R0MH
M1: FAIRCHILD FDS7760A
V_IN
3.3V
V_OUT
5V
+ ^COUT1
150μF
7A
(10A PEAK)
6.3V
×4
C_OUT2
22μF
6.3V
X5R
×2
GND
18711 F01a
Figure 1. High Efficiency 3.3V Input, 5V Output Boost Converter (Bootstrapped)
Efficiency of Figure 1
100
90
Burst Mode
80
OPERATION
70
PULSE-SKIP
60
MODE
50
40
30
0.001
0.01
0.1
1
OUTPUT CURRENT (A)
10
18711 F01b
18711fb
1