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LM3241

SNOSB38C – JANUARY 2009 – REVISED NOVEMBER 2017

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7 Detailed Description

7.1 Overview

The LM3241 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. The device 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. The design is based on a voltage-mode buck architecture, with synchronous rectification for high efficiency.

The device is designed for a maximum load capability of 750 mA in PWM mode. Maximum load range may vary

from this depending on input voltage, output voltage, and the inductor chosen.

Three modes of operation are available depending on the current required: pulse width modulation (PWM), Eco-

mode (economy mode), and shutdown. The LM3241 operates in PWM mode at higher load-current conditions.

Lighter loads cause the device to automatically switch into Eco-mode. Shutdown mode turns off the device and

reduces battery consumption to 0.1 µA (typical).

Precision of the DC PWM-mode output voltage is ±2% for 3.4 VOUT. Efficiency is around 95% (typical) for a 500-

mA load with a 3.3-V output and 3.9-V input. The output voltage is dynamically programmable from 0.6 V to 3.4

V by adjusting the voltage on the control pin (VCON) without the need for external feedback resistors. This

feature ensures longer battery life by being able to change the PA supply voltage dynamically depending on its

transmitting power.

Additional features include current overload protection and thermal overload shutdown.

The LM3241 is constructed using a chip-scale, 6-bump 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 (6 MHz, typical) reduces the size of external components. As

shown in Figure 29, only three external power components are required for implementation. Use of a DSBGA

package requires special design considerations for implementation (for more information see the DSBGA

Package Assembly and Use section.) The fine-bump pitch of the package 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 the Shutdown Mode section).