Fairchild FAN5903 Specifications Manual

5903 — ck C verter w ith yp ass M e fo r 3G /3.5G /4G

December 2011

FAN5903 Buck Converter with Bypass Mode for 3G/3.5G/4G PAs

Features Description

 2.7V to 5.5V Input Voltage Range FAN5903 is a high-efficiency, low-noise, synchronous, step-down, DC-DC converter designed for powering

 VOUT Range from 0.4V to 3.50V (or VIN)

3G/3.5G/4G RF Power Amplifiers (PAs) in handsets and  Small Form Factor Inductor other mobile applications. The output voltage may be dynamically varied from

o 2012 470n H or 540n H for Minimal PCB Area

0.40V to 3.50V, proportional to an analog input VCON,

o 2020 1.0µH for Higher Efficiency

ranging from 0.16V to 1.40V provided by an external  Bypass Dropout at 500m A, 60m V Typical DAC. This allows the PA to be supplied with the voltage that enables maximum power-added efficiency.

 100% Duty Cycle for Low Dropout Operation

An integrated bypass FET automatically switches on

 Input Under-Voltage Lockout / Thermal Shutdown when battery voltage drops close to the desired output

voltage (VOUT=VBAT-200m V). The DC-DC switches back

 1.34mm x 1.29mm, 9-Bump, 0.4mm-Pitch WLCSP

to Synchronous Mode when the voltage dropout

 3MHz / 6MHz Selectable Switching Frequency to exceeds 375m V. The integrated bypass FET is also Facilitate System Optimization enabled when VCON is nominally greater than to 1.5V.

 High-Efficiency PFM Operation at Low Power The FAN5903 offers fast transition times, enabling changes to the output voltage in less than 10µs for

 Sleep Mode for Very Low IQ Operation

power transitions. Moreover, a Current-Mode control  Up to 96% Efficient Synchronous Operation at loop with fast transient response ensures excellent line High-Power Conditions and load regulation. Light-load efficiency is optimized by operating in PFM

 10µs Output Voltage Step Response for Early

Mode for load currents typically less than 100m A.

Power Loop Settling

The switching frequency may be set to 3MHz or 6MHz, enabling further optimization of system performance.

Applications

The FAN5903 typically uses a single, small-form-factor inductor of 540n H. Efficiency may be further optimized

 Dynamic Supply Bias for 3G/3.5G and 4G PAs

using a 1.0µH inductor when running at 3MHz.

 Power Supply for WCDMA/LTE PAs

When output regulation is not required, the FAN5903 may be placed in Sleep Mode by setting VCON nominally

Resources to 100m V. This ensures a very low IQ (<70µA) while

enabling a fast return to output regulation. The

For more information or a full copy of this datasheet,

FAN5903 enables significant current reduction and

please contact a Fairchild representative.

increased talk time and is available in a 1.34mm x 1.29mm, 9-bump, 0.40mm-pitch, WLCSP package.

Ordering Information

Operating

Part Number Package Packing Method

Temperature Range

1.34mm x 1.29mm, 9-bump, 0.4mm Pitch,

FAN5903UCX -40 to +85°C Tape and Reel

Wafer-Level Chip-Scale Package (WLCSP)

© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN5903 • Rev. 1.0.7