Block Diagram

30050404

FIGURE 2. Functional Block Diagram

Operation Description

The LM3218 is a simple, step-down DC-DC converter with a

2.6 µH series inductor substrate optimized for powering RF

power amplifiers (PAs) in mobile phones, portable communi-

cators, 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 current mode buck architecture, with syn-

chronous rectification for high efficiency. It is designed for a

maximum load capability of 650 mA when V

and 400 mA when V

Maximum load range may vary from this depending on input

voltage, output voltage and the inductor chosen.

Efficiency is typically around 95% for a 400 mA load with 3.4V

output, 3.9V input. The LM3218 has an R

scheme to increase efficiency when V

voltage is dynamically programmable 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 LM3218 is constructed using a chip-scale 8-pin micro

SMD package and a LTCC inductor substrate. This package

offers the smallest possible integrated solution footprint for

space-critical applications such as cell phones, where board

area is an important design consideration. Use of a high

switching frequency (2 MHz) reduces the size of external

components. As shown in Figure 1, only two external capac-

itors are required for implementation. Use of this module

requires special design considerations for implementation.

(See LTCC Module Package Assembly and Use in the Appli-

cations Information section). The board mounting 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. Also, 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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