1FEATURES
2• High-Efficiency PFM and PWM Modes with
Internal Synchronous Rectification
• Analog Bypass Function with Low Dropout
Resistance (45 mΩ typ.)
• Dynamically Adjustable Output Voltage, 0.4V
to 3.6V (typ.), in PFM and PWM modes
• 3A Maximum Load Current in PWM Mode
• 2.7MHz (average) PWM Switching Frequency
• Modulated Switching Frequency to Aid Rx
Band Compliance
• Operates From a Single Li-ion Cell
(2.7V to 5.5V)
• ACB Reduces Inductor Requirements and Size
• Minimum Total Solution Size by Using Small
Footprint and Case Size Inductor and
Capacitors
• 16-bump Thin DSBGA Package
• Current and Thermal Overload Protection

APPLICATIONS
• USB Datacards
• Cellular Phones
• Hand-Held Radios
• RF PC Cards
• Battery-Powered RF Devices

DESCRIPTION
The LM3253 is a DC-DC converter optimized for
powering multi-mode 2G/3G/4G RF power amplifiers
(PAs) from a single Lithium-Ion cell. The LM3253
steps down an input voltage from 2.7V to 5.5V to a
dynamically adjustable output voltage of 0.4V to 3.6V.
The output voltage is set through a VCON analog
input that adjusts the output voltage to ensure
efficient operation at all power levels of the RF PA.
The LM3253 is optimized for USB datacard
applications.
The LM3253 operates in constant frequency Pulse
Width Modulation (PWM) mode producing a small
and predictable amount of output voltage ripple. This
enables best ECTEL power requirements in GMSK
and EDGE spectral compliance, with the minimal
amount of filtering and excess headroom. When
operating in Pulse Frequency Modulation (PFM)
mode, the LM3253 enables the lowest DG09 current
consumption and therefore maximizes system
efficiency.
The LM3253 has a unique Active Current assist and analog Bypass (ACB) feature to minimize inductor
size without any loss of output regulation for the
entire battery voltage and RF output power range,
until dropout. ACB provides a parallel current path,
when needed, to limit the maximum inductor current
to 1.84A (typ.) while still driving a 3A load. The ACB
also enables operation with minimal dropout voltage.
The LM3253 is available in a small 2 mm x 2 mm
chip-scale 16-bump DSBGA package.
When considering the use of the LM3253 in a system
design, contact the Texas Instruments Sales or Field
Application engineer for a copy of the "LM3253:
DC-DC Converter for 3G/4G RF PAs PCB Layout
Considerations.”