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AAT1171

600mA Voltage-Scaling Step-Down Converter for RF Power Amplifiers with Bypass Switch

Analog Technology Inc 

AAT1171

600mA Voltage-Scaling Step-Down Converter

for RF Power Amplifiers with Bypass Switch

General Description

Features

SwitchReg™

The AAT1171 SwitchReg dynamically controls the

operating voltage of a WCDMA or CDMA power

amplifier inside single-cell, lithium-ion battery-pow-

ered systems. The AAT1171 outputs a voltage

between 0.6V and 3.6V, thereby optimizing the

amplifier efficiency at both low and high transmit

levels.

The AAT1171 output voltage is controlled via an

analog signal from the baseband processor. It can

deliver 600mA of continuous load current while

maintaining a low 45µA of no load quiescent current.

The 2MHz switching frequency minimizes the size of

external components while keeping switching losses

low. To further improve system efficiency, an 85mΩ

bypass MOSFET transistor is also included to allow

the PA to be powered directly from the battery.

The AAT1171 maintains high efficiency thoughout

the entire load range in Light Load (LL) mode, and

can be forced into Pulse Wide Modulation (PWM)

mode for low noise operation or can be synchro-

nized to an external clock.

The AAT1171 is available in a Pb-free, space-sav-

ing TDFN33-12 package and is rated over the

-40°C to +85°C temperature range.

• VIN Range: 2.7V to 5.5V

• Variable Output Voltage: 0.6V to 3.6V

• 600mA Output Current

• DAC Input: 0.2V to 1.2V

• High Output Accuracy: ±3%

• 45µA No Load Quiescent Current

• Internal Soft Start Limits Startup Current and

Output Voltage Overshoot

• Synchronizable to External 19.8MHz System

Clock

• Over-Temperature and Current Limit Protection

• Integrated 85mΩ Bypass MOSFET

• 2MHz Operation

• PWM/LL Control with Override

• Fast Start-Up:

— 50µs (AAT1171-4, AAT1171-5)

— 150µs (AAT1171-1)

• 100% Duty Cycle Operation

• <30µs Output Voltage Response Time

• 3x3mm 12-Pin TDFN Package

• Temperature Range: -40°C to +85°C

Applications

• WCDMA or CDMA PA in Cellular Phones,

Smartphones, Feature Phones, etc.

• Express Card

• PCMCIA Data Cards

Typical Application

CIN

–

4.7μF

VIN

VCC

LX

AAT1171-1/

AAT1171-4

BYPASS

VOUT

MODE/SYNC

EN

DAC GNDx2

L1

2.2μH

0.6V - 3.6V

COUT

4.7μF

VCC2 VCONT

VREF

VCC2

PA

DAC

TX

Baseband

Processor

RX

VIN

VCC

L1

4.7μH

LX

0.6V - 3.6V

CIN

–

4.7μF

AAT1171-5

BYPASS

VOUT

MODE/SYNC

EN

DAC GNDx2

COUT

10μF

VCC2 VCONT

VREF

VCC2

PA

DAC

TX

Baseband

Processor

RX

1171.2007.08.1.1

1

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