LT3486 データシートの表示（PDF） - Linear Technology

部品番号

コンポーネント説明

メーカー

LT3486

Dual 1.3A White LED Step-Up Converters with Wide Dimming

Linear Technology 

LT3486

APPLICATIONS INFORMATION

90

VIN = 5V

8/8 LEDs

80

RT = 63.4k

70

RT = 21.5k

60

RT = 39.1k

50

40

30

0

5

10

15

20

25

LED CURRENT (mA)

3486 F06b

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 2.5MHz. Higher

switching frequency allows the use of smaller inductors

albeit at the cost of increased switching losses.

The inductor current ripple (∆IL), neglecting the drop

across the Schottky diode and the switch, is given by:

( ) ∆IL

=

VIN(MIN) • VOUT(MAX) – VIN(MIN)

VOUT(MAX) • f • L

where:

L = Inductor

f = Operating frequency

VIN(MIN) = Minimum input voltage

VOUT(MAX) = Maximum output voltage

The ∆IL 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

information and for their entire selection of related parts.

Table 1. Recommended Inductors

L

PART

(µH)

LQH55DN150M 15

LQH55DN220M 22

A915AY-4R7M 4.7

A915AY-6R8M 6.8

A915AY-100M

10

A918CY-100M

10

A918CY-150M

15

CDRH4D28-100 10

CDRH5D18-150 15

MAX

DCR

(Ω)

0.150

0.190

0.045

0.068

0.090

0.098

0.149

0.048

0.145

CURRENT

RATING

(A)

1.40

1.20

2.49

2.01

1.77

1.22

0.94

1.30

0.97

VENDOR

Murata

(814) 237-1431

www.murata.com

Toko

(847) 297-0070

www.toko.com

Sumida

(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

AVX

Murata

(408) 573-4150

www.t-yuden.com

(803) 448-9411

www.avxcorp.com

(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.

3486fe

11

Share Link: