LT3491 LINER [Linear Technology], LT3491 Datasheet - Page 7

• Manufacturer Part Number: LT3491
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
INDUCTOR SELECTION
A 10µH inductor is recommended for most LT3491 appli-
cations. Although small size and high efficiency are major
concerns, the inductor should have low core losses at
2.3MHz and low DCR (copper wire resistance). Some
small inductors in this category are listed in Table 1. The
efficiency comparison of different inductors is shown in
Figure 3.
Table 1. Recommended Inductors
PART
LQH32CN100K53
LQH2MCN100K02
SD3112-100
1001AS-100M
(TYPE D312C)
CDRH2D11
CDRH2D14
CAPACITOR SELECTION
The small size of ceramic capacitors make them ideal for
LT3491 applications. Use only X5R and X7R types be-
cause they retain their capacitance over wider temperature
ranges than other types such as Y5V or Z5U. A 1µF input
capacitor and a 1µF output capacitor are sufficient for
most applications.
Figure 3. Efficiency Comparison of Different Inductors
60
80
75
70
65
55
50
45
40
35
30
0
(µH)
10
10
10
10
10
10
L
U
5
LED CURRENT (mA)
0.5375
0.446
0.294
DCR
0.48
(Ω)
0.3
1.2
V
4 LEDs
FRONT PAGE
APPLICATION CIRCUIT
MURATA LQH2MCN100K02
MURATA LQH32CN100K53
TOKO 10001AS-100M
SUMIDA CDRH2D11
SUMIDA CDRH2D14
IN
U
= 3.6V
10
CURRENT
RATING
(mA)
550
460
450
225
280
700
W
15
3491 F03
VENDOR
Murata
www.murata.com
Cooper
www.cooperet.com
Toko
www.toko.com
Sumida
www.sumida.com
20
U
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. Recommended Ceramic Capacitor Manufacturers
OVERVOLTAGE PROTECTION
The LT3491 has an internal open-circuit protection circuit.
In the cases of output open circuit, when the LEDs are
disconnected from the circuit or the LEDs fail open circuit,
V
at a very low frequency to minimize input current. The V
and input current during output open circuit are shown in
the Typical Performance Characteristics. Figure 4 shows
the transient response when the LEDs are disconnected.
INRUSH CURRENT
The LT3491 has a built-in Schottky diode. When supply
voltage is applied to the V
through the inductor and the Schottky diode and charges
up the CAP voltage. The Schottky diode inside the LT3491
can sustain a maximum current of 1A.
CAP
200mA/DIV
10V/DIV
is clamped at 27V (typ). The LT3491 will then switch
V
CAP
I
L
Taiyo Yuden
V
CIRCUIT OF
FRONT PAGE
APPLICATION
Figure 4. Output Open-Circuit Waveform
IN
Murata
AVX
= 3.6V
LEDs DISCONNECTED
AT THIS INSTANT
500µs/DIV
IN
pin, an inrush current flows
www.t-yuden.com
www.avxcorp.com
www.murata.com
[phone]
[phone]
[phone]
3491 F04
LT3491
3491fa
7
CAP