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.”