14

LTC3403

3403f

Figure 7. Suggested Layout

Figure 8

8

7

6

5

1

2

3

4

REF

MODE

RUN

GDR

GND

SW

L1

LTC3403

TO DAC

VIA TO REF

VIA TO GND

3403 F07

SW

GDR

4

1

8

LTC3403

LTC3403 F08

2.7V

TO 5V

MODE

RUN

REF

2

6

5

7

GND

DAC

3

†

10

µF

CER

4.7

µF

CER

2.2

µH*

1000pF

10k

*

**

†

MURATA LQH32CN2R2M11

TAIYO YUDEN JMK212BJ475MG

TAIYO YUDEN JMK212BJ106MN

PC Board Layout Checklist

When laying out the printed circuit board, the following

checklist should be used to ensure proper operation of the

LTC3403. These items are also illustrated graphically in

Figures 6 and 7. Check the following in your layout:

1. The power traces, consisting of the GND trace, the SW

wide.

possible? This capacitor provides the AC drive to the

internal power MOSFETs.

Design Example

As a design example, assume the LTC3403 is used in a

single lithium-ion battery-powered cellular phone applica-

down to about 2.7V. The load current requirement is a

maximum of 0.6A but most of the time it will be in standby

mode, requiring only 2mA. Efficiency at both low and high

load currents is important. Output voltage is 2.5V. With

this information we can calculate L using Equation (1),

L

fI

V

V

V

L

OUT

OUT

IN

=

∆









1

1

()(

)

–

(2)

f = 1.5MHz in Equation (2) gives:

L

V

MHz

mA

V

V

H

=









=µ

25

1 5

240

1

25

42

281

.

.(

)

–

.

.

.

A 2.2

µH inductor works well for this application. For best

efficiency choose a 720mA or greater inductor with less

than 0.2

Ω series resistance.

ESR of less than 0.25

Ω. In most cases, a ceramic capaci-

tor will satisfy this requirement.

APPLICATIO S I FOR ATIO