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LM2698 Demoboard

Posted: 03 Oct 2003     Print Version  Bookmark and Share

Keywords:POWER 

/ARTICLES/2003OCT/A/2003OCT03_AMD_POW_ICT_AN.PDF

LM2698 Demoboard

Introduction

A printed circuit board has been developed to aid in the

design and evaluation of the LM2698 DC-DC boost con-

verter. This application note contains information about the

board.

General Description

The LM2698 is a general purpose, high frequency DC-DC

converter. This board is intended to demonstrate the primary

advantages of the LM2698. The LM2698 is able to operate

at 1.25MHz switching frequency, yielding extremely high

power density. The low RDS(ON) internal MOSFET allows for

high conversion efficiency. It uses a current mode control

scheme, giving superior line and load regulation. The

LM2698 is a Simple Switcher.TM, which includes Switchers

Made Simple software for fast, effective designs.

The LM2698 demoboard will operate with the following pa-

rameters:

4.5V VIN 9V

VOUT = 12V

0 IOUT 400mA*

Note: * See Figure 2 for IOUT vs VIN

Note 1: The inductance affects the stability of the converter. See the COM-

PENSATION section in the datasheet for tips on optimizing the inductance

value, especially for input voltages less than 5V. To operate this demoboard

at voltages below 4.5V with the supplied 105H inductor and remain in a safe

stability region, use a 1.25 MHz switching frequency (if VIN > 5V, a 600 kHz

or 1.25 MHz switching frequency is acceptable).

Note 2: When operating the LM2698 at 1.25 MHz switching frequency, it is

recommended to increase the bypass capacitance, CBYP, to 0.220 5F.

20023001

FIGURE 1. LM2698 Demoboard Schematic

National Semiconductor

Application Note 1202

Mark Hartman

October 2001

LM2698DemoboardAN-1202

) 2002 National Semiconductor Corporation AN200230 www.national.com

TABLE 1. Bill of Materials

Component Value Description Model Number

COUT 105F Output Capacitor TMK432BJ106MM (Taiyo Yuden)

CIN 225F Input Capacitor LMK432BJ226MM (Taiyo Yuden)

CC 4.7nF Compensation Capacitor VJ0805Y472MXAAT (Vishay)

CBYP 0.15F Bypass Capacitor VJ0805Y104KXAAT (Vishay)

D 1A, 20V Schottky Power Diode MBRM120LT3 (ON-Semiconductor)

L 105H Power Inductor CDRH6D38-100 (Sumida)

RC 24.9k Compensation Resistor CRCW 0805 2492 FRT1 (Vishay)

RFB1 30.1k Top Feedback Resistor CRCW 0805 3012 FRT1 (Vishay)

RFB2 3.48k Bottom Feedback Resistor CRCW 0805 3481 FRT1 (Vishay)

TABLE 2. Jumper Settings

Jumper Setting Description

J1 600 kHz 600 kHz switching frequency

1.25 MHz 1.25 MHz switching frequency

J2 Run LM2698 is regulating

SD LM2698 is shutdown

Maximum Output Current

The current limit of the LM2698 is with respect to the switch

current. This means that the maximum output current to the

load is dependent on duty cycle. With a fixed VOUT, the

maximum output current will be a function of VIN, as shown

in Figure 2.

20023002

FIGURE 2. Maximum Output Current vs Input Voltage

AN-1202

www.national.com 2

20023004

FIGURE 3. LM2698 Demoboard Top Layer Layout

20023003

FIGURE 4. LM2698 Demoboard Bottom Layer Layout

AN-1202

www.national.com3

Notes

LIFE SUPPORT POLICY

NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT

DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL

COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or

systems which, (a) are intended for surgical implant

into the body, or (b) support or sustain life, and

whose failure to perform when properly used in

accordance with instructions for use provided in the

labeling, can be reasonably expected to result in a

significant injury to the user.

2. A critical component is any component of a life

support device or system whose failure to perform

can be reasonably expected to cause the failure of

the life support device or system, or to affect its

safety or effectiveness.

National Semiconductor

Corporation

Americas

Email: support@nsc.com

National Semiconductor

Europe

Fax: +49 (0) 180-530 85 86

Email: europe.support@nsc.com

Deutsch Tel: +49 (0) 69 9508 6208

English Tel: +44 (0) 870 24 0 2171

Frangais Tel: +33 (0) 1 41 91 8790

National Semiconductor

Asia Pacific Customer

Response Group

Tel: 65-2544466

Fax: 65-2504466

Email: ap.support@nsc.com

National Semiconductor

Japan Ltd.

Tel: 81-3-5639-7560

Fax: 81-3-5639-7507

www.national.com

AN-1202LM2698Demoboard

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.





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