MOSFET

CONTROL

LOGIC

SW

CURRENT

COMP

OSCILLATOR

ERROR

AMPLIFIER

DELAY

LOGIC

FB

SHUTDOWN

CONTROL

MAIN CONTROL

EN

FET SIZE

CONTROL

COMP

PGND

GND

SMALL

PFET

LARGE

PFET

LM3208

SNVS404B – APRIL 2006 – REVISED MARCH 2013

www.ti.com

BLOCK DIAGRAM

Figure 34. Functional Block Diagram

OPERATION DESCRIPTION

The LM3208 is a simple, step-down DC-DC converter optimized for powering 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 over a wide range of power levels from a single Li-Ion battery cell. It is

based on a current-mode buck architecture, with synchronous rectification for high efficiency. It is designed for a

mode.

Maximum load range may vary from this depending on input voltage, output voltage and the inductor chosen.

from 0.8V to 3.6V by adjusting the voltage on the control pin without the need for external feedback resistors.

This prolongs battery life by changing the PA supply voltage dynamically depending on its transmitting power.

Additional features include current overload protection and thermal overload shutdown.

The LM3208 is constructed using a chip-scale 8-pin DSBGA package. This package 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 (2MHz, typ.) reduces the size of external components. As shown in Figure 1,

only three external power components are required for implementation. Use of a DSBGA package requires

special design considerations for implementation. (See DSBGA Package Assembly and Use in the Application

Information 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 subject to high-intensity

ambient red or infrared light. In addition, the system controller should set EN low during power-up and other low

supply voltage conditions. (See Shutdown Mode in the Device Information section.)

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