LTC3450

9

3450fa

Inductor Selection

Inductors in the range of 47µH to 100µH with saturation

for use with the LTC3450. Ferrite core materials are

strongly recommended for their superior high frequency

performance characteristics. A bobbin or toroid type core

will reduce radiated noise. Inductors meeting these re-

quirements are listed in Table 1.

Table 1. Recommended Inductors

PART

L

MAX DCR HEIGHT

NUMBER

(µH)

(Ω)

(mm)

VENDOR

CLQ4D10-470

47

1.28

1.2

Sumida

CLQ4D10-101

100

3.15

(847) 956-0666

CMD4D08-470

47

1.6

1.0

www.sumida.com

DO1606-473

47

1.1

2.0

Coilcraft

DO1606-104

100

2.3

(847) 639-6400

DT1608-473

47

0.34

2.92

www.coilcraft.com

DT1608-104

100

1.1

LQH43MN470J03 47

1.5

2.6

Murata

LQH43MN101J03 100

2.5

www.murata.com

DU6629-470M

47

0.64

2.92

Coev Magnetics

DU6629-101M

100

1.27

www.circuitprotection.com

Capacitor Selection

The boost converter requires two capacitors. The input

capacitor should also be an X5R type between 2.2µF and

10µF. A larger capacitor (10µF) should be used if lower

output ripple is desired or the output load required is close

to the 10mA maximum.

The charge pumps require flying capacitors of at least

0.1µF to obtain specified performance. Ceramic X5R types

are strongly recommended for their low ESR and ESL and

capacitance versus bias voltage stability. The filter capaci-

tor on V2X should be at least 0.1µF. A 0.47µF or larger

0.1µF or larger. Please be certain that the capacitors used

are rated for the maximum voltage with adequate safety

margin. Refer to Table 2 for a listing of capacitor vendors.

Table 2. Capacitor Vendor Information

Supplier

Phone

Website

AVX

(803) 448-9411

www.avxcorp.com

Murata

(714) 852-2001

www.murata.com

Taiyo Yuden

(408) 573-4150

www.t-yuden.com

APPLICATIO S I FOR ATIO

Soft-Start

Soft-start operation provides a gradual increase in the

current drawn from the input power source (usually a

battery) during initial startup of the LTC3450, eliminating

the inrush current which is typical in most boost convert-

ers. This reduces stress on the input power source, boost

inductor and output capacitor, reduces voltage sag on the

battery and increases battery life. The rate at which the

input current will increase is set by two external compo-

2). Upon initial application of power or release of a pull

down switch on SHDN, the voltage on SHDN will increase

time constant SHDN will rise to approximately 63.2% of

SHDN, no switching will occur because the shutdown

threshold is 0.77V (typ). From 0.77V to 1V the maximum

switch pin current capability of the LTC3450 will gradually

increase from near zero to the maximum current limit. An

SHDN is driven high with a logic signal, the input current

will gradually increase to its maximum value in approxi-

mately 50µs.

5 SHDN

3450 F02

6.8nF

1M

5%

Figure 2. Soft-Start Component Configuration

Printed Circuit Board Layout Guidelines

High speed operation of the LTC3450 demands careful

attention to PCB layout. You will not get advertised perfor-

mance with careless layout. Figure 3 shows the recom-

mended component placement for a single layer PCB. A

multilayer board with a separate ground plane is ideal but

not absolutely necessary.