LTC3448_15 Datasheet, PDF (1/20 Pages) Linear Technology – 1.5MHz/2.25MHz, 600mA Synchronous Step-Down Regulator with LDO Mode

FEATURES
■ _{High Efficiency: Up to 96%}
■ _{Very Low Quiescent Supply Current: 32µA During}
Linear Regulator Operation
■ _{600mA Output Current (Buck Converter)}
■ _{Optionally Operates as Linear Regulator Below}
3mA—External or Automatic ON/OFF
■ _{2.5V to 5.5V Input Voltage Range}
■ _{1.5MHz or 2.25MHz Constant Frequency Operation}
or External Synchronization
■ _{No Schottky Diode Required}
■ _{Low Dropout Operation: 100% Duty Cycle}
■ _{0.6V Reference Allows Low Output Voltages}
■ _{Shutdown Mode Draws < 1µA Supply Current}
■ _{Current Mode Operation for Excellent Line and}
Load Transient Response
■ _{Overtemperature Protected}
■ _{Low Profile (3mm × 3mm) 8-Lead DFN and 8-Lead}
MSOP Packages
U
APPLICATIO S
■ _{Cellular Telephones}
■ _{Personal Information Appliances}
■ _{Wireless and DSL Modems}
■ _{Digital Still Cameras}
■ _{MP3 Players}
■ _{Portable Instruments}
, LTC and LT are registered trademarks 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. Others pending.
LTC3448
1.5MHz/2.25MHz, 600mA
Synchronous Step-Down
Regulator with LDO Mode
DESCRIPTIO
The LTC^®3448 is a high efficiency, monolithic, synchronous
buck regulator using a constant frequency, current mode
architecture. Supply current during operation is only 32µA
(linear regulator mode) and drops to <1µA in shutdown. The
2.5V to 5.5V input voltage range makes the LTC3448 ide-
ally suited for single Li-Ion battery-powered applications.
100% duty cycle provides low dropout operation, extend-
ing battery life in portable systems. At moderate output load
levels, PWM pulse skipping mode operation provides very
low output ripple voltage for noise sensitive applications.
The LTC3448 automatically switches into linear regulator
operation at very low load currents to maintain <5mV_P-P
output voltage ripple. Supply current in this mode is
typically 32µA. The switch to linear regulator mode occurs
at a threshold of 3mA. Linear regulator operation can be set
to on, off or automatic turn on/off.
Switching frequency is selectable at either 1.5MHz or
2.25MHz, allowing the use of small surface mount induc-
tors and capacitors.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.6V feed-
back reference voltage. The LTC3448 is available in a low
profile 3mm × 3mm DFN package or thermally enhanced
8-lead MSOP.
TYPICAL APPLICATIO
1.5V High Efficiency Regulator with Automatic LDO Mode
V_IN
2.5V TO 5.5V
C_IN
4.7µF
V_IN
SW
RUN V_OUT
LTC3448
MODE
FREQ V_FB
SYNC
GND
2.2µH
22pF ^474k
316k
C_OUT
4.7µF
V_OUT
1.5V
3448 TA01a
Efficiency and Power Loss vs Load Current
100 _{VIN = 3.6V}
1
90 VOUT = 1.5V
80 ^{TA = 25°C}
0.1
70
EFFICIENCY
60
POWER LOSS
50
0.01
40
30
0.001
20
10
0
0.0001
0.001
0.01
0.1
0.0001
1
LOAD CURRENT (A)
23448 TA01b
3448f
1