FAN5903 Datasheet, PDF (1/3 Pages) Fairchild Semiconductor – Buck Converter with Bypass Mode for 3 G / 3.5 G / 4 G PAs

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October 2012
FAN5903
Buck Converter with Bypass Mode for 3 G / 3.5 G / 4 G PAs
Features
 2.7 V to 5.5 V Input Voltage Range
 V_OUT Range from 0.4 V to 3.5 V (or V_IN)
 Small Form Factor Inductor
o 2012 470 nH or 540 nH for Minimal PCB Area
o 2520 1.0 µH for Higher Efficiency
 Bypass Dropout at 500 mA, 60 mV Typical
 100% Duty Cycle for Low Dropout Operation
 Input Under-Voltage Lockout / Thermal Shutdown
 1.34 mm x 1.29 mm, 9-Bump, 0.4 mm-Pitch
WLCSP
 3 MHz / 6 MHz Selectable Switching Frequency to
Facilitate System Optimization
 High-Efficiency PFM Operation at Low Power
 Sleep Mode for Very Low I_Q Operation
 Up to 96% Efficient Synchronous Operation at
High-Power Conditions
 10 µs Output Voltage Step Response for Early
Power Loop Settling
Applications
 Dynamic Supply Bias for 3G/3.5G and 4G PAs
 Power Supply for WCDMA/LTE PAs
Resources
For more information or a full copy of this datasheet,
please contact a Fairchild representative.
Description
FAN5903 is a high-efficiency, low-noise, synchronous,
step-down, DC-DC converter designed for powering
3 G / 3.5 G / 4 G RF Power Amplifiers (PAs) in handsets
and other mobile applications.
The output voltage may be dynamically varied from
0.40 V to 3.50 V, proportional to an analog input V_CON,
ranging from 0.16 V to 1.40 V provided by an external
DAC. This allows the PA to be supplied with the voltage
that enables maximum power-added efficiency.
An integrated bypass FET automatically switches on
when battery voltage drops close to the desired output
voltage (V_OUT=V_BAT-200 mV). The DC-DC switches back
to Synchronous Mode when the voltage dropout
exceeds 375 mV. The integrated bypass FET is also
enabled when V_CON is nominally greater than to 1.5 V.
The FAN5903 offers fast transition times, enabling
changes to the output voltage in less than 10 µs for
power transitions. Moreover, a Current-Mode control
loop with fast transient response ensures excellent line
and load regulation.
Light-load efficiency is optimized by operating in PFM
Mode for load currents typically less than 100 mA.
The switching frequency may be set to 3 MHz or 6 MHz,
enabling further optimization of system performance.
The FAN5903 typically uses a single, small-form-factor
inductor of 540 nH. Efficiency may be further optimized
using a 1.0 µH inductor when running at 3 MHz.
When output regulation is not required, the FAN5903
may be placed in Sleep Mode by setting V_CON nominally
to 50 mV. This ensures a very low I_Q (<70 µA) while
enabling a fast return to output regulation. The
FAN5903 enables significant current reduction and
increased talk time and is available in a 1.34 mm x
1.29 mm, 9-bump, 0.40 mm-pitch, WLCSP package.
Ordering Information
Part Number
FAN5903UCX
Operating
Temperature Range
-40 to +85°C
Package
1.34 mm x 1.29 mm, 9-bump, 0.4 mm Pitch,
Wafer-Level Chip-Scale Package (WLCSP)
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.8
Packing Method
Tape and Reel
www.fairchildsemi.com