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FAN5902 — 800mA Buck Converter for 3G RFPAs
FAN5902 — 800mA Buck Converter for 3G RFPAs
May 2009
FAN5902
800mA Buck Converter for 3G RFPAs
Features
92% Efficient Synchronous Operation
2.7V to 5.5V Input Voltage Range
V
OUT
Range from 0.4V to 3.4V (or V
IN
)
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
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 V
OUT
=V
BAT
-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.
Applications
Battery-Powered 3G RFPAs
Multiband/Multimode WCDMA/CDMA Handset RF
Transceivers
RF PC Cards
Pocket PC and PDAs with Communication
Capabilities
Important
For
complete
performance specifications and
datasheet, please contact a Fairchild Semiconductor
sales representative.
Ordering Information
Part Number
FAN5902MPX
FAN5902UCX
Operating
Temperature Range
-40 to +85°C
-40 to +85°C
Package
12-Lead, 3x3.5mm, Molded Leadless
Package (MLP)
12-Bump, Wafer-Level Chip-Scale
Package (WLCSP)
Eco Status
RoHS
RoHS
Packing
Method
Tape and Reel
Tape and Reel
For Fairchild’s definition of Eco Status, please visit:
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