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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com

201999B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013

AAT1171

600mA Voltage-Scaling Step-Down Converter

for RF Power Amplifiers with Bypass Switch

DATA SHEET

Functional Description

The AAT1171 is a 600mA 2MHz peak current mode syn-

chronous step-down (buck) converter designed to oper-

ate from a single-cell lithium-ion battery with a 2.7V to

4.2V input range. The output voltage is dynamically

programmed by the DAC input voltage.

To maximize converter efficiency over all load conditions,

the converter automatically transitions to a variable fre-

quency light load (LL) mode when the load is less than

100mA. When combined with the very low quiescent

current, the LL mode maintains a high efficiency over the

complete load range. For noise sensitive applications,

the converter can be forced into a fixed frequency PWM

mode. Provisions are also made for synchronization of

the converter to an external system clock.

The synchronous buck converter power output devices

are sized at 230mΩ for a 600mA full load output current.

In addition to the converter output, an additional low

resistance bypass MOSFET (85mΩ) can be connected

improve headroom and extend the WCDMA PA full power

range. This reduces the battery voltage necessary for a

WCDMA RF power amplifier to meet linearity require-

ments, thus extending operating time. In dual mode

systems, the bypass mode may also be used when the

WCDMA RF power amplifier is in GSM mode. Bypass

mode is activated by setting the bypass input high or by

forcing the baseband DAC output voltage to 1.3V.

The AAT1171 requires only three external components

frequency reduces the inductor size required to 2.2μH

for the AAT1171-1/AAT1171-4 and 4.7μH for the

AAT1171-5. This reduces the DC resistance and improves

the converter efficiency while minimizing the inductor

Functional Block Diagram

Logic

DH

DL

Comp

Error

Amp

VOUT

VCC

VIN

LX

AGND

PGND

DAC

EN

BYPASS

MODE/SYNC

MODE/SYNC

Interface