Fairchild FAN5902 service manual

FAN5902
800mA Buck Converter for 3G RFPAs

FAN5902 — 800mA Buck Converter for 3G RFPAs FAN5902 — 800mA Buck Converter for 3G RFPAs

May 2009

Features

 92% Efficient Synchronous Operation
 2.7V to 5.5V Input Voltage Range
 V

Range from 0.4V to 3.4V (or VIN)

OUT

 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 V
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.

OUT=VBAT

-250mV). The bypass

Important

For complete performance specifications and
datasheet, please contact a Fairchild Semiconductor
sales representative.

Ordering Information

Part Number

FAN5902MPX -40 to +85°C

FAN5902UCX -40 to +85°C

For Fairchild’s definition of Eco Status, please vis it: http://www.fairchildsemi.com/company/green/rohs_green.html.

© 2009 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5902 • Rev. 1.0.2.short

Operating

Temperature Range

Package

12-Lead, 3x3.5mm, Molded Leadless
Package (MLP)

12-Bump, Wafer-Level Chip-Scale
Package (WLCSP)

Eco Status

RoHS Tape and Reel

RoHS

Packing

Method

Tape and Reel

FAN5902 — 800mA Buck Converter for 3G RFPAs

Application Diagrams

10μF

V

BAT

2.7V to

5.5V

From Processor

From External DAC

PVIN

PVIN VOUTSNS

PVIN

VOUTSNS

AVIN

FAN5902

BPE N

SW

PGND

SYNC

EN

AGND

VCON

Figure 1. FAN5902 Circuit

DCDC

V

50m

OUT_SNS

0.4V < V

20mA < I

470nH

OUT

OUT

< V

BAT

< 800mA

V

2.2μF

OUT

10 F
0603

V

BATT

2.7V up to 5.5V

3

G
P

I

O

Processor

Base

PVIN

AVIN

BPE N

SYNC

EN

VCON

D
A
C

Bypass Sl ew

Controller

Swi tcher

Controller

SW

PGND

V

Reference

Bandgap

V

MOD E

R

FIN

P

DET

Bias

Power

Detector

AGND

RFPA

Figure 2. Typical Application

OUT_SNS

470n H

Supply

V

OUT

2.2 F
0603

0.4V up to V
Up to 800mA

V

Dynamic

Scaling

R

FOUT

Duplexer

RX

IN

OUT

© 2009 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5902 • Rev. 1.0.2.short 2

Pin Configurations

Figure 3. 12-Lead MLP

(Top View)

FAN5902 — 800mA Buck Converter for 3G RFPAs

Figure 4. 12-Bump WLCSP

(Top View)

Pin Definitions

MLP

Pin #

(*) (*) AGND

VOUTSNS

EN

VCON Analog control input from an external D-to-A converter.

AVIN Analog bias supply voltage input. Connect to PVIN.

AGND Connect to analog ground.

BPEN

SYNC

PGND

SW Switching node of the internal MOSFET switches. Connect to output inductor.

PVIN

(*) Pinout available upon request

WLCSP

Pin #

Name Description

Analog ground, reference ground for the IC. Follow PCB routing notes for
connecting this pin.

Output voltage sense pin. Connect to V
regulation.

Enables switcher when HIGH, shutdown mode when LOW. This pin should not
be left floating.

Force bypass transistor when HIGH; auto-bypass when LOW. This pin should
not be left floating

External clock synchronization input and PFM lockout. When SYNC remains
HIGH, the DC-to-DC does not allow PFM mode. Tie SYNC to AGND if not used.

Power ground of the internal MOSFET switches. Follow routing notes for
connections between PGND and AGND.

Supply voltage input to the internal MOSFET switches. Connect to input power
source.

to establish feedback path for

OUT

© 2009 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5902 • Rev. 1.0.2.short 3