AS1339
650mA RF Step-Down DC-DC for PA, with two LDOs
Datasheet
www.austriamicrosystems.com Revision 1.04 1 - 25
1 General Description
The AS1339 is a high-frequency step-down converter
optimized for dynamically powering the power amplifier
(PA) in WCDMA or NCDMA handsets. The device uses
a 110mΩ typical bypass FET to power the PA directly
from the battery during high-power transmission. The IC
integrates two 10mA low-noise, low-dropout regulators
(LDOs) for PA biasing.
With a switching frequency of 2MHz, the device allows
optimization for smallest solution size or highest
efficiency. The AS1339 supports fast switching using
small ceramic 10μF input and 4.7µF output capacitors to
maintain low ripple voltage.
The AS1339 uses an analog input driven by an external
DAC to control the output voltage linearly for continuous
PA power adjustment. The gain from REFIN to OUT is
2.5V/V. At high-duty cycle, the device automatically
switches to a bypass mode, connecting the input to the
output through a low-impedance MOSFET. The LDOs
are designed for low-noise operation, wherein each LDO
in the device is individually enabled through its own logic
control interface. The device is available in a 16-pin
WLP (2x2mm) package.
Figure 1. Typical Operating Circuit
2 Key Features
! Fixed Switching Frequency: 2MHz
! PA Step-Down Converter
! Low Dropout Voltage
! Low Output-Voltage Ripple
! Dynamic Output Voltage Control (0.8V to 3.75V)
! 30µs Settling Time for 0.8V to 3.4V Output Voltage
Change
! 650mA Output Drive Capability
! Two 10mA Low-Noise LDOs
! Low Shutdown Current
! Supply Voltage Range: 2.7V to 5.5V
! Thermal Shutdown
! 16-pin WLP (2x2mm) package
3 Applications
The AS1339 is ideal for WCDMA/NCDMA cellular
handsets, Wireless PDAs, and Smartphones.
LDO2 ON/OFF
LDO1 ON/OFF
Analog Control
PA ON/OFF
IN2
EN2
EN1
REFIN
PA_EN
IN1B
IN1A
PAB
PAA
LX
PGND
NC
LDO1
LDO2
2.85V
2.85V
V
PA
0.8V to 3.75V
V
IN
2.7V to 5.5V
4.7µF
10µF
V
IN
2.7V to 5.5V
2.2µH
AS1339
AGND
0.1µF
0.1µF
1µF
TEST
NC
