May 2009

© 2009 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FAN5902 • Rev. 1.0.2.short

FAN5902

800mA Buck Converter for 3G RFPAs

Features

92% Efficient Synchronous Operation

2.7V to 5.5V Input Voltage Range

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

Applications

Battery-Powered 3G RFPAs

Multiband/Multimode WCDMA/CDMA Handset RF

Transceivers

RF PC Cards

Pocket PC and PDAs with Communication

Capabilities

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 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

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.

Important

For

complete

performance

specifications

and

datasheet, please contact a Fairchild Semiconductor

sales representative.

Ordering Information

Part Number

Operating

Temperature Range

Package

Eco Status

Packing

Method

FAN5902MPX

-40 to +85°C

12-Lead, 3x3.5mm, Molded Leadless

Package (MLP)

RoHS

Tape and Reel

FAN5902UCX

-40 to +85°C

12-Bump, Wafer-Level Chip-Scale

Package (WLCSP)

RoHS

Tape and Reel