1
LTC1911-1.5/LTC1911-1.8
1911f
APPLICATIO S
U
FEATURES
DESCRIPTIO
U
TYPICAL APPLICATIO
U
Low Noise, High Efficiency,
Inductorless Step-Down
DC/DC Converter
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.
■
Low Noise Constant Frequency Operation
■
2.7V to 5.5V Input Voltage Range
■
No Inductors
■
Typical Efficiency 25% Higher Than LDOs
■
Shutdown Disconnects Load from V
IN
■
Output Voltage: 1.8V ±4% or 1.5V ±4%
■
Output Current: 250mA
■
Low Operating Current: I
IN
= 180µA Typ
■
Low Shutdown Current: I
IN
= 10µA Typ
■
Oscillator Frequency: 1.5MHz
■
Soft-Start Limits Inrush Current at Turn On
■
Short-Circuit and Overtemperature Protected
■
Available in an 8-Pin MSOP Package
, LTC and LT are registered trademarks of Linear Technology Corporation.
■
Handheld Computers
■
Cellular Phones
■
Smart Card Readers
■
Portable Electronic Equipment
■
Handheld Medical Instruments
■
Low Power DSP Supplies
V
IN
C2
+
C2
–
GND
8
6
7
5
1
2
3
4
SS/SHDN
V
OUT
C1
+
C1
–
LTC1911-1.8
1µF*
1-CELL Li-Ion
OR
3-CELL NiMH
10µF*
*CERAMIC CAPACITOR
10µF*
1911 TA01
V
OUT
= 1.8V
I
OUT
= 250mA
1µF*
2.7V TO 5.5V INPUT
Single Cell Li-Ion to 1.8V DC/DC Converter
Efficiency
Burst Mode is a registered trademark of Linear Technology Corporation.
*U.S. Patent #6,438,005
INPUT VOLTAGE (V)
2
30
EFFICIENCY (%)
40
50
60
70
80
90
3456
1911 G05
IDEAL LDO
250mA100mA
V
OUT
= 1.8V