LTC3549 Datasheet, PDF (1/16 Pages) Linear Technology – 250mA Low VIN Buck Regulator in 2mm × 3mm DFN

LTC3549
250mA Low V_IN Buck
Regulator in 2mm × 3mm DFN
FEATURES
■ _{1.6V to 5.5V Input Voltage Range}
■ _{Internal Soft-Start}
■ _{Low Ripple Burst Mode}^® _Operation
Output Ripple: <20mV_P-P
I_Q: 50µA
■ _{2.25MHz Constant-Frequency Operation}
■ _{High Efficiency: Up to 93%}
■ _{250mA Output Current (VIN = 1.8V, VOUT = 1.2V)}
■ _{450mA Peak Inductor Current}
■ _{No Schottky Diode Required}
■ _{Low Dropout Operation: 100% Duty Cycle}
■ _{0.611V Reference Voltage}
■ _{Stable with Ceramic Capacitors}
■ _{Shutdown Mode Draws <1µA Supply Current}
■ _{Current Mode Operation for Excellent Line and Load}
Transient Response
■ _{Overtemperature Protection}
■ _{Available in a Low Profile (0.75mm) 6-Lead}
(2mm x 3mm) DFN Package
U
APPLICATIO S
■ _{2 AA-Cell Applications}
■ _{Cellular Phones}
■ _{Digital Cameras}
■ _{MP3 Players}
DESCRIPTIO
The LTC^®3549 is a high efficiency, monolithic synchronous
buck regulator using a constant-frequency, current mode
architecture. The output voltage is adjusted via an external
resistor divider.
A fixed switching frequency of 2.25MHz is supported.
This switching frequency allows the use of small surface
mount inductors and capacitors, including ceramics.
Supply current during Burst Mode operation is only 50µA
dropping to < 1µA in shutdown. The 1.6V to 5.5V input
voltage range makes the LTC3549 ideally suited for single
cell Li-Ion, Li-Metal and 2-cell alkaline, NiCd or NiMH
battery-powered applications. 100% duty cycle capabil-
ity provides low dropout operation, extending battery
life in portable systems. Burst Mode operation can be
user-enabled, increasing efficiency at light loads, further
extending battery life.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Internal
soft-start offers controlled output voltage rise time at start-
up without the need for external components.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents,
including 5481178, 6580258, 6304066, 6127815, 6498466, 6611131.
TYPICAL APPLICATIO
High Efficiency Step-Down Converter
V_IN
1.8V TO
5.5V
4.7µF
CER
LTC3549
SW
V_IN
RUN
MODE V_FB
GND
3.3µH*
22pF
137k ^200k
*TDK VLF3012AT-3R3MR87
3549 TA01
V_OUT
1.5V
4.7µF
CER
Burst Mode Efficiency, V_OUT = 1.5V
100
1
90
80
0.1
70
60
50
0.01
40
30
20
10
0
0.1
V_IN = 1.8V
V_IN = 2.5V
V_IN = 3.1V
POWER LOST
0.001
AT V_IN = 2.5V
0.0001
1
10
100
1k
LOAD CURRENT (mA)
3549 TA02
3549f
1