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LT3486

3486f

Figure 6b. Efﬁciency Comparison for Different RT Resistors

Inductor Selection

The choice of the inductor will depend on the selection of

switching frequency of LT3486. The switching frequency

can be programmed from 200kHz to 2MHz. Higher switch-

ing frequency allows the use of smaller inductors albeit

at the cost of increased switching losses.

The inductor current ripple (ΔIL),neglectingthedropacross

the Schottky diode and the switch, is given by:

∆=

()

Vf L

IN MIN

OUT MAX

IN MIN

OUT MAX

()

(

)

()

•–

••

where:

L = Inductor

f = Operating frequency

VIN(MIN) = Minimum input voltage

VOUT(MAX) = Maximum output voltage

The ΔIL is typically set to 20% to 40% of the maximum

inductor current.

The inductor should have a saturation current rating greater

than the peak inductor current required for the application.

Also, ensure that the inductor has a low DCR (copper wire

resistance) to minimize I2R power losses. Recommended

inductor values range from 4.7µH to 22µH.

Several inductors that work well with the LT3486 are listed

in Table 1. Consult each manufacturer for more detailed in-

formation and for their entire selection of related parts.

Table 1. Recommended Inductors

MAX

CURRENT

DCR

RATING

PART

(µH)

(Ω)

(A)

VENDOR

LQH55DN150M

0.150

1.40

Murata

LQH55DN220M

0.190

1.20

(814) 237-1431

www.murata.com

A915AY-4R7M

4.7

0.045

2.49

Toko

A915AY-6R8M

6.8

0.068

2.01

(847) 297-0070

A915AY-100M

0.090

1.77

www.toko.com

A918CY-100M

0.098

1.22

A918CY-150M

0.149

0.94

CDRH4D28-100

0.048

1.30

Sumida

CDRH5D18-150

0.145

0.97

(847) 956-0666

www.sumida.com

Capacitor Selection

The small size of ceramic capacitors make them ideal

for LT3486 applications. Use only X5R and X7R types

because they retain their capacitance over wider voltage

and temperature ranges than other types such as Y5V

or Z5U. A 4.7µF or larger input capacitor is sufﬁcient for

most applications. Always use a capacitor with sufﬁcient

voltage rating.

Table 2 shows a list of several ceramic capacitor manufac-

turers. Consult the manufacturers for detailed information

on their entire selection of ceramic parts.

Table 2. Ceramic Capacitor Manufacturers

Taiyo Yuden

(408) 573-4150

www.t-yuden.com

AVX

(803) 448-9411

www.avxcorp.com

Murata

(714) 852-2001

www.murata.com

Diode Selection

Schottky diodes with their low forward voltage drop and

fast reverse recovery, are the ideal choices for LT3486

applications. The diode conducts current only during the

switch off time. The peak reverse voltage that the diode

must withstand is equal to the regulator output voltage.

APPLICATIO S I FOR ATIO

LED CURRENT (mA)

510

3486 F06b

VIN = 5V

8/8 LEDs

RT = 63.4k

RT = 21.5k

RT = 39.1k

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