WLAN/BT

Module

System

Boost/Bypass

2.7 V to 4.5 V

2G

3G/4G

10 µF

10 µF

DC/DC

DC/DC

10 µF + 4.7 µF (0402)

FB

EN

VIN

SW

3 V - 5.5 V

2.2 µF

2.2 µF

GND

0.47 µH

LM3281

3.3 V

GPO

MODE

LM3281

SNVSA38 – NOVEMBER 2014

www.ti.com

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LM3281 is a high efficiency DC-DC converter optimized to power Wireless Connectivity Solutions in cell

phones, portable communication devices or other battery-powered RF devices. The device is designed to

operate from an input supply voltage between 3 V and 5.5 V with a maximum load current of 1.2 A. It operates in

PWM mode for medium to heavy load conditions and in ECO mode for light load conditions to optimize for best

efficiency , transient performance and output voltage ripple at varying load conditions. In PWM mode the LM3281

converter operates with nominal switching frequency of 6 MHz, thus enabling use of smaller size capacitors and

inductor. The converter operates in ECO mode at lighter load conditions to maintain high efficiency. In this mode

a period of switching burst charges the output capacitor to the regulation target. This is followed by a period of no

switching where the output voltages coasts to a lower voltage threshold due to light load current consumption.

Upon reaching this lower voltage threshold, the cycle repeats by starting a new switching burst. The LM3281

automatically transitions into Analog Bypass operation as input voltage approaches output voltage.

Figure 17 shows one of many application configurations for LM3281. A battery-connected system boost bypass

(normally part of system PMU) provides input supply to LM3281 which in turn very efficiently converts this input

to a fixed 3.3-V output with superior transient response and output noise, thereby saving the Wireless

Connectivity Solution from having to operate from a higher supply voltage, such as a direct connection to a

battery or a system boost/bypass. This results in significant power dissipation savings and consequently cooler

operation for the connectivity solution without sacrificing its RF performance. In applications where low voltage

battery operation is not a significant feature, system boost/bypass can be eliminated, and the LM3281 can be

directly connected to a battery for high efficiency power conversion and excellent RF performance. These types

8.2 Typical Application

Figure 17. LM3281 Typical Application

14

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