1.5MHz/2.25MHz, 600mA Synchronous Step-Down Regulator with LDO Mode

The LTC3448 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 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 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 inductors 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 feedback reference voltage. The LTC3448 is available in a low profile 3mm × 3mm DFN package or thermally enhanced 8-lead MSOP.

Protected by U.S. Patents including 5481178, 6580258, 6304066, 6127815, 6498466, 6611131. Others pending.

Applications

* Cellular Telephones

* Personal Information Appliances

* Wireless and DSL Modems

* Digital Still Cameras

* MP3 Players

* Portable Instruments

* 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