FAN5902 Datasheet | Fairchild Semiconductor

- 800m A Buck Converter for 3G RFPAs .. May 2009 FAN5902 800m A Buck Converter for 3G RFPAs Features - - - - - - - - - - - - - 92% Efficient Synchronous Operation 2.7V to 5.5V Input Voltage Range VOUT Range from 0.4V to 3.4V (or VIN) Up to 800m A Output Current 20µs Step Response 30µs Bypass Transition Time 50mΩ Integrated Bypass FET with Controlled Slew Rate for Low Battery Voltage Operation 6MHz PWM Operation Allows 470n H Small Form Factor Inductor 100% Duty Cycle for Low Dropout Operation Thermal Shutdown Input Under-Voltage Lockout 12-Lead MLP (0.8mm Maximum) 12-Bump WLCSP Description The FAN5902 is a high-efficiency, low-noise, synchronous, step-down DC-to-DC converter designed for powering the radio frequency power amplifiers (RFPA) in 3G mobile handsets and other mobile applications. It provides up to 800m A of output current over an input voltage range of 2.7V to 5.5V. The output voltage can be dynamically adjusted from 0.4V up to 3.4V, proportional to an analog input voltage ranging from 0.2V to 1.7V provided by an external DAC. This allows supplying the RFPA with the voltage level that provides optimum Power Added Efficiency (PAE). An integrated bypass FET automatically switches on when the battery voltage drops too close to the output voltage (when VOUT=VBAT-250m V). The bypass transition is controlled by a slew rate controller to limit the inrush current and reduce the RFPA gain deviation. The FAN5902 offers fast transition times, allowing changes to the output voltage in less than 20µs. The FAN5902 operates at 6MHz, enabling the use of a small, low-value inductor of 470n H. A current-mode control loop with fast transient response ensures excellent line and load regulation. The FAN5902 improves the RFPA power efficiency and increases the talk/connection time in 3G handsets. The FAN5902 is available in a 12-lead MLP package and 12-bump WLCSP. Applications - - - - Battery-Powered 3G RFPAs Multiband/Multimode WCDMA/CDMA Handset RF...