LM3242

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SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015

7 Detailed Description

7.1 Overview

The LM3242 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 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.

There are five modes of operation depending on the current required: PWM (Pulse Width Modulation), ECO

(ECOnomy), BP (Bypass), Sleep, and Shutdown. (See Table 1.) The LM3242 operates in PWM mode at higher

load current conditions. Lighter loads cause the device to automatically switch into ECO mode. Shutdown mode

turns the device off and reduces battery consumption to 0.1 µA (typical).

500-mA load with 3.3-V output, 3.9-V input. The output voltage is dynamically programmable from 0.4 V to 3.6 V

by adjusting the voltage on the control pin (VCON) without the need for external feedback resistors. This 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 LM3242 is constructed using a chip-scale 9-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 the Typical Application Circuit, 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.) 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. Also, the system controller must set EN low during power-up and other low supply

voltage conditions. (See Shutdown Mode.)

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