1.5MHz, 600mA Synchronous Step-Down Regulator with Bypass Transistor

The LTC3403 is a high efficiency monolithic synchronous buck regulator optimized for WCDMA power amplifier applications. The output voltage can be dynamically programmed from 0.3V to 3.5V. At VOUT > 3.6V an internal bypass P-channel MOSFET connects VOUT directly to VIN, eliminating power loss through the inductor. Selectable forced continuous mode enables fast VOUT response to the controlling input.

Supply current is only 20µA in Burst Mode® operation and drops to <1µA in shutdown. The 2.5V to 5V input voltage range makes the LTC3403 ideally suited for single Li-Ion battery-powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems.

Switching frequency is internally set at 1.5MHz, 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.

The LTC3403 is available in a low profile 8-lead 3mm x 3mm DFN package.

Applications

* WCDMA Cell Phone Power Amplifiers

* Wireless Modems

* Dynamically Adjustable Output from 0.3V to 3.5V

* Very Low Quiescent Current: Only 20µA During Operation

* 600mA Output Current

* Internal P-Channel MOSFET Bypass Transistor

* High Efficiency: Up to 96%

* 1.5MHz Constant Frequency Operation

* No Schottky Diode Required

* Low Dropout Operation: 100% Duty Cycle

* 2.5V to 5V Input Voltage Range

* Drives Optional External P-Channel MOSFET

* Shutdown Mode Draws < 1µA Supply Current

* Current Mode Operation for Excellent Line and Load Transient Response

* Overtemperature Protected

* Available in 8-Lead 3mm x 3mm DFN Package