LTC1911-1.5_15 Datasheet, PDF (1/12 Pages) Linear Technology – Low Noise, High Efficiency, Inductorless Step-Down DC/DC Converter

LTC1911-1.5/LTC1911-1.8
Low Noise, High Efficiency,
Inductorless Step-Down
DC/DC Converter
FEATURES
s _{Low Noise Constant Frequency Operation}
s _{2.7V to 5.5V Input Voltage Range}
s _{No Inductors}
s _{Typical Efficiency 25% Higher Than LDOs}
s _{Shutdown Disconnects Load from VIN}
s _{Output Voltage: 1.8V ±4% or 1.5V ±4%}
s _{Output Current: 250mA}
s _{Low Operating Current: IIN = 180µA Typ}
s _{Low Shutdown Current: IIN = 10µA Typ}
s _{Oscillator Frequency: 1.5MHz}
s _{Soft-Start Limits Inrush Current at Turn On}
s _{Short-Circuit and Overtemperature Protected}
s _{Available in an 8-Pin MSOP Package}
U
APPLICATIO S
s _{Handheld Computers}
s _{Cellular Phones}
s _{Smart Card Readers}
s _{Portable Electronic Equipment}
s _{Handheld Medical Instruments}
s _{Low Power DSP Supplies}
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
*U.S. Patent #6,438,005
DESCRIPTIO
The LTC^®1911 is a switched capacitor step-down DC/DC
converter that produces a 1.5V or 1.8V regulated output
from a 2.7V to 5.5V input. The part uses switched capaci-
tor fractional conversion to achieve high efficiency over the
entire input range. No inductors are required. Internal cir-
cuitry controls the step-down conversion ratio to optimize
efficiency as the input voltage and load conditions vary.*
Typical efficiency is over 25% higher than that of a linear
regulator.
A unique constant frequency architecture provides a low
noise regulated output as well as lower input noise than
conventional charge pump regulators. High frequency
operation (f_OSC = 1.5MHz) simplifies output filtering to
further reduce conducted noise. To optimize efficiency,
the part enters Burst Mode^® operation under light load
conditions.
Low operating current (180µA with no load, 10µA in
shutdown) and low external parts count (two 1µF flying
capacitors and two 10µF bypass capacitors) make the
LTC1911 ideally suited for space constrained battery-
powered applications. The part is short-circuit and
overtemperature protected, and is available in an 8-pin
MSOP package.
TYPICAL APPLICATIO
Single Cell Li-Ion to 1.8V DC/DC Converter
2.7V TO 5.5V INPUT
1-CELL Li-Ion
OR
3-CELL NiMH
10µF*
1µF*
*CERAMIC CAPACITOR
LTC1911-1.8
1 _{VIN SS/SHDN} 8
2 _C2+
6
V_OUT
3 _C2–
C1^{+ 7}
4 _GND
C1^{– 5}
1µF*
V_OUT = 1.8V
I_OUT = 250mA
10µF*
1911 TA01
Efficiency
90
80
100mA
70
250mA
60
50
IDEAL LDO
40
V_OUT = 1.8V
30
2
3
4
5
INPUT VOLTAGE (V)
6
1911 G05
1911f
1