600mA Voltage-Scaling Step-Down Converter
for RF Power Amplifiers with Bypass Switch
General Description
The AAT1171 SwitchReg, a member of Analogic-
Tech's Total Power Management IC™ (TPMIC™)
product family, has been specifically designed to
dynamically control the operating voltage of a
WCDMA or CDMA power amplifier inside single
lithium-ion battery-powered 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. A low resistance MOSFET, typically 230mΩ,
provides a low dropout voltage as the battery input
voltage approaches the programmed output voltage
and the converter runs at 100% duty cycle. To fur-
ther improve system efficiency, an 85mΩ bypass
MOSFET transistor is also included to allow the PA
to be powered directly from the battery.
The AAT1171 feedback and control method gives
excellent load regulation and transient response
while maintaining small external components. The
output voltage responds in less than 30µs. The con-
verter can be synchronized to an external system
clock, forced to operate in Light Load (LL) mode for
highest efficiency at light loads, or in Pulse Width
Modulation (PWM) mode for low noise operation.
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.
AAT1171
Features
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SwitchReg
™
V
IN
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 150µs Start-Up
3x3mm 12-Pin TDFN Package
Temperature Range: -40°C to +85°C
Applications
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WCDMA or CDMA PA in Cellular Phones,
Smartphones, Feature Phones, etc.
Express Card
PCMCIA Data Cards
Typical Application
VIN
2.2µH
0.6V - 3.6V
10µF
VCC
AAT1171
BYPASS
LX
–
MODE/SYNC
EN
DAC
GNDx2
VOUT
4.7µF
V
CC2
V
CONT
V
REF
V
CC2
PA
DAC
Baseband
Processor
TX
RX
1171.2006.06.1.0
1
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
