AS1339
6 5 0 m A R F St e p - D o w n D C - D C f o r PA, w i t h t w o L D O s
D a ta s h e e t
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.
2 Key Features
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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
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3 Applications
The AS1339 is ideal for WCDMA/NCDMA cellular
handsets, Wireless PDAs, and Smartphones.
Figure 1. Typical Operating Circuit
V
IN
2.7V to 5.5V
10µF
V
PA
0.8V to 3.75V
IN1A
PAA
PAB
IN1B
LX
2.2µH
4.7µF
PGND
NC
Analog Control
REFIN
PA ON/OFF
LDO1 ON/OFF
LDO2 ON/OFF
NC
V
IN
2.7V to 5.5V
1µF
PA_EN
EN1
AS1339
LDO1
2.85V
0.1µF
EN2
TEST
IN2
AGND
LDO2
2.85V
0.1µF
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