LOAD CURRENT (mA)

0

100

200

300

400

70

80

90

100

500

5 - 12V Boost

^y_ s Υ]}v

LM2731

³;´

SW

FB

GND

SHDN

U1

R3

51K

SHDN

GND

C1

2.2PF

R2

13.3K

CF

220pF

D1

MBR0520

R1/117K

L1/10PH

C2

4.7PF

12V

OUT

500mA

(TYP)

LM2731

www.ti.com

SNVS217G – MAY 2004 – REVISED SEPTEMBER 2015

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 device will operate with input voltage range from 2.7 V to 14 V and provide a regulated output voltage. This

device is optimized for high-efficiency operation with minimum number of external components. For component

selection, see Detailed Design Procedure.

8.2 Typical Application

Figure 24. Application Schematic

Figure 25. Efficiency vs Load Current

8.2.1 Design Requirements

The device must be able to operate at any voltage within the recommended operating range. The load current

must be defined in order to properly size the inductor, input, and output capacitors. The inductor must be able to

handle full expected load current as well as the peak current generated during load transients and start-up.

Inrush current at start-up will depend on the output capacitor selection. More details are provided in Detailed

Design Procedure.

The device has a shutdown pin which is used to disable the device. This pin is active-LOW and care must be

taken that the voltage on this pin does not exceed VIN + 0.3 V. This pin must also not be left floating.

8.2.2 Detailed Design Procedure

8.2.2.1 Selecting the External Capacitors

The best capacitors for use with the LM2731 are multi-layer ceramic capacitors. These capacitors have the

lowest ESR (equivalent series resistance) and highest resonance frequency which makes them optimum for use

with high-frequency switching converters.

When selecting a ceramic capacitor, only X5R and X7R dielectric types should be used. Other types such as

Z5U and Y5F have such severe loss of capacitance due to effects of temperature variation and applied voltage,

they may provide as little as 20% of rated capacitance in many typical applications. Always consult capacitor

manufacturer’s data curves before selecting a capacitor. High-quality ceramic capacitors can be obtained from

Taiyo-Yuden, AVX, and Murata.

Copyright © 2004–2015, Texas Instruments Incorporated

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