Fairchild FAN5902 3G RF功放电源解决方案

Fairchild公司的FAN5902是高效率低噪音同步降压DC/DC转换器,设计用于给3G手机和其它移动设备的RF功率放大器供电.输入电压2.7V-5.5V,输出电流高达800mA,输出电压从0.4V到3.4V动态调整,正比于0.2V-1.7V模拟输入电压,从而得到最佳的功率附加效率(PAE).本文介绍了FAN5902的主要特性和典型应用电路.

FAN5902:800mA Buck Converter for 3G RFPAs

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 800mA 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-250mV). 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 470nH. 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.

FAN5902主要特性:

92% Efficient Synchronous Operation

2.7V to 5.5V Input Voltage Range

VOUT Range from 0.4V to 3.4V (or VIN)

Up to 800mA 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 470nH 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

FAN5902应用:

Battery-Powered 3G RFPAs

Multiband/Multimode WCDMA/CDMA Handset RF Transceivers

RF PC Cards

Pocket PC and PDAs with Communication Capabilities



图1.FAN5902电路



图2.FAN5902典型应用电路图