LTC3448| Datasheet

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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 32uA (linear regulator mode) and drops to <1uA in shutdown. The 2.5V to 5.5V input voltage range makes the LTC3448 ideally suited for single Li-Ion battery-powered applications. 100% duty cycle provides low dropout operation, extending 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 <5mVP-P output voltage ripple. Supply current in this mode is typically 32uA. 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 inductors and cap
acitors. 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 feedback reference voltage. The LTC3448 is available in a low profile 3mm 3mm DFN package or thermally enhanced 8-lead MSOP.

FEATURES

High Efficiency: Up to 96% Very Low Quiescent Supply Current: 32uA 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 < 1uA 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

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.

TYPICAL APPLICATIO
VIN 2.5V TO 5.5V CIN 4.7uF VIN

Efficiency and Power Loss vs Load Current
100 90 80 70 EFFICIENCY (%) VIN = 3.6V VOUT = 1.5V TA = 25 C 1

1.5V High Efficiency Regulator with Automatic LDO Mode
2.2uH SW 474k COUT 4.7uF VOUT RUN LTC3448 MODE VFB FREQ SYNC GND VOUT 1.5V 22pF

60 50 40 30

EFFICIENCY POWER LOSS 0.01

316k

20 10 0 0.0001

3448 TA01a

U

U

U

0.1 POWER LOSS (W)

0.001

0.0001 0.001 0.01 0.1 LOAD CURRENT (A) 1
23448 TA01b

3448f

1

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LTC3448 DATASHEET