LTC3408 1.5MHz, 600mA Synchronous Step-Down Regulator with Bypass Transistor UFEATURESDESCRIPTIO ■ Dynamically Adjustable Output from 0.3V to 3.5V The LTC®3408 is a high efficiency monolithic synchro- ■ 600mA Output Current nous buck regulator optimized for WCDMA power ampli- ■ Internal 0.08 Ω P-Channel MOSFET Bypass fier applications. The output voltage can be dynamically Transistor programmed from 0.3V to 3.5V. At VOUT > 3.6V an internal ■ High Efficiency: Up to 96% 0.08Ω bypass P-channel MOSFET connects VOUT directly ■ 1.5MHz Constant Frequency Operation to VIN, eliminating power loss through the inductor. ■ No Schottky Diode Required The input voltage range is 2.5V to 5V making the LTC3408 ■ Low Dropout Operation: 100% Duty Cycle ideally suited for single Li-Ion battery-powered applica- ■ 2.5V to 5V Input Voltage Range tions. 100% duty cycle provides low dropout operation, ■ Shutdown Mode Draws < 1µA Supply Current extending battery life in portable systems. ■ Current Mode Operation for Excellent Line and Load Transient Response Switching frequency is internally set at 1.5MHz, allowing ■ Overtemperature Protected the use of small surface mount inductors and capacitors. ■ Available in 8-Lead 3mm × 3mm DFN Package The internal synchronous switch increases efficiency and eliminates the need for an external Schottky diode. UAPPLICATIO S The LTC3408 is available in a low profile (0.75mm) 8-lead 3mm × 3mm DFN package. ■ WCDMA Cell Phone Power Amplifiers ■ Wireless Modems , LTC and LT are registered trademarks of Linear Technology Corporation. U.S. Patent Numbers: 5481178, 6580258, 6304066, 6127815, 6498466, 6611131 UTYPICAL APPLICATIOWCDMA Transmitter Power SupplyEfficiency Power Lost vs Load Current 1 100 V 4.7µH* 90 IN VOUT 2.7V VIN SW 3× VREF 80 TO 5V C † IN COUT** 600mA 10µF LTC3408 4.7µF 70 EFFICIENCY (%) CER CER 0.1 60 RUN VOUT REF 50 OUTPUT GND 40 WCDMA PROGRAMMING 0.01 RF PA POWER LOST (W) DAC 30 VOUT = 1.2V 20 *MURATA LQH32CN4R7M11 VOUT = 1.5V ** 3403 TA01 TAIYO YUDEN JMK212BJ475MG VOUT = 1.8V 10 †TAIYO YUDEN JMK212BJ106MN VOUT = 2.5V 0.01 0 1 10 100 1000 LOAD CURRENT (mA) 3408 F04 3408f 1
