LT3466 Linear Technology, LT3466 Datasheet - Page 11

• Manufacturer Part Number: LT3466
• Description: Dual Full Function White LED Step-Up Converter with Built-In Schottky Diodes
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
INDUCTOR SELECTION
The choice of the inductor will depend on the selection of
switching frequency of LT3466. 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 ( I
across the Schottky diode and the switch, is given by :
where:
The I
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 I
Recommended inductor values range from 10 H to 68 H.
Several inductors that work well with the LT3466 are listed
in Table 1. Consult each manufacturer for more detailed
information and for their entire selection of related parts.
Table 1. Recommended Inductors
PART
LQH32CN100
LQH32CN150
LQH43CN330
ELL6RH330M
ELL6SH680M
A914BYW330M
A914BYW470M
A920CY680M
CDRH2D18150NC
CDRH4D18-330
CDRH5D18-680
L = Inductor
f = Operating frequency
V
V
IN(MIN)
OUT(MAX)
I
L
L
is typically set to 20% to 40% of the maximum
V
IN MIN
= Minimum input voltage
(
= Maximum output voltage
)
( H)
V
•
10
15
33
33
68
33
47
68
15
33
68
L
OUT MAX
U
V
OUT MAX
(
MAX
DCR
0.44
0.58
1.00
0.38
0.52
0.45
0.73
0.40
0.22
0.51
0.84
( )
(
U
)
• •
CURRENT
)
f L
RATING
–
0.35A
0.31A
0.43A
(mA)
300
300
310
600
500
440
360
400
L
V
), neglecting the drop
IN MIN
W
(
2
R power losses.
)
VENDOR
Murata
[phone]
www.murata.com
Panasonic
[phone]
www.panasonic.com
Toko
www.toko.com
Sumida
[phone]
www.sumida.com
U
CAPACITOR SELECTION
The small size of ceramic capacitors make them ideal for
LT3466 applications. Use only X5R and X7R types be-
cause they retain their capacitance over wider voltage and
temperature ranges than other types such as Y5V or Z5U.
A 1 F 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
INRUSH CURRENT
The LT3466 has built-in Schottky diodes. When supply
voltage is applied to the V
through the inductor and the Schottky diode and charges
up the output voltage. Both the Schottky diodes in the
LT3466 can sustain a maximum of 1A current. The selec-
tion of inductor and capacitor value should ensure the
peak of the inrush current to be below 1A.
For low DCR inductors, which is usually the case for this
application, the peak inrush current can be simplified as
follows:
Table 3 gives inrush peak current for some component
selections.
where
I
PK
:
V
LC
IN
1
OUT
– .
L
0 6
IN
pin, an inrush current flows
[phone]
www.t-yuden.com
[phone]
www.avxcorp.com
[phone]
www.murata.com
LT3466
11
3466f