LM3279_16 Datasheet, PDF (12/37 Pages) Texas Instruments – Buck-Boost Converter

LM3279
SNVS970C – MARCH 2013 – REVISED OCTOBER 2014
7 Detailed Description
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7.1 Overview
The LM3279 buck-boost converter provides high-efficiency, low-noise power for RF power amplifiers (PAs) in
mobile phones, portable communicators and similar battery powered RF devices. It is designed to allow the RF
PA to operate at maximum efficiency for a wide range of power levels from a single Li-Ion battery cell. The
capability of LM3279 to provide an output voltage lower than as well as higher than the input battery voltage
enables the PA to operate with high linearity for a wide range of battery voltages, thereby extending the usable
voltage range of the battery. The converter feedback loop is internally compensated for both buck and boost
operation, and the architecture is such that it provides seamless transition between buck and boost mode of
operation. The LM3279 operates in energy-saving Pulse Frequency Modulation (PFM) mode for increased
efficiencies and current savings during low-power RF transmission modes. The output voltage is dynamically
programmable from 0.4 V to 4.2 V by either programming the VSET value in register 00h, or adjusting the
voltage on the control pin VCON. The fast output voltage transient response of LM3279 makes it suitable for
adaptively adjusting the PA supply voltage depending on its transmitting power which improves systems
efficiency and prolongs battery life
Additional features include current-overload protection, output overvoltage clamp, and thermal-overload
shutdown.
The LM3279 is constructed using a chip-scale 16-bump DSBGA package that offers the smallest possible size
for space-critical applications such as cell phones where board area is an important design consideration. Use of
a high switching frequency (2.4 MHz, typ.) reduces the size of external components. As shown in Figure 24 and
Figure 27, only three external power components are required for circuit operation. Use of a DSBGA package
requires special design considerations for implementation. (See DSBGA Package Assembly And Use in the
Layout section.) Its fine bump-pitch requires careful board design and precision assembly equipment. Use of this
package is best suited for opaque-case applications where its edges are not subjected to high-intensity ambient
red or infrared light. In addition, the system controller should set VIO = LOW (or EN if system implementation
with analog VCON) during power-up and other low supply-voltage conditions.
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