LT3465 Ver la hoja de datos (PDF) - Linear Technology
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LT3465 Datasheet PDF : 12 Pages
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LT3465
APPLICATIO S I FOR ATIO
discontinuous mode, meaning the inductor current
reaches zero during the discharge phase. After the induc-
tor current reaches zero, the SW pin exhibits ringing due
to the LC tank circuit formed by the inductor in combina-
tion with switch and diode capacitance. This ringing is
not harmful; far less spectral energy is contained in the
ringing than in the switch transitions. The ringing can be
damped by application of a 300Ω resistor across the
inductor, although this will degrade efficiency.
Inductor Selection
A 22µH inductor is recommended for most LT3465 appli-
cations. Although small size and high efficiency are major
concerns, the inductor should have low core losses at
1.2MHz and low DCR (copper wire resistance). Some
inductors in this category with small size are listed in
Table␣ 1. The efficiency comparison of different inductors
is shown in Figure 4.
Table 1. Recommended Inductors
PART
NUMBER
CURRENT RATING
DCR (Ω)
(mA)
LQH32CN220
0.71
250
ELJPC220KF
4.0
160
CDRH3D16-220 0.53
350
LB2012B220M 1.7
75
LEM2520-220
5.5
125
MANUFACTURER
Murata
814-237-1431
www.murata.com
Panasonic
714-373-7334
www.panasonic.com
Sumida
847-956-0666
www.sumida.com
Taiyo Yuden
408-573-4150
www.t-yuden.com
Taiyo Yuden
408-573-4150
www.t-yuden.com
Capacitor Selection
The small size of ceramic capacitors makes them ideal for
LT3465 applications. X5R and X7R types are recom-
mended because they retain their capacitance over wider
voltage and temperature ranges than other types such as
85
VIN = 3.6V
4 LEDS
80
75
70
65
60
MURATA LQH32CN220
55
TAIYO YUDEN LB2012B220M
TAIYO YUDEN CB2012B220
50
0
5
10
15
20
LED CURRENT (mA)
3465 F04
Figure 4. Efficiency Comparison of Different Inductors
Y5V or Z5U. A 1µF input capacitor and a 0.22µF output
capacitor are sufficient for most LT3465 applications.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER
PHONE
URL
Taiyo Yuden
408-573-4150
www.t-yuden.com
Murata
814-237-1431
www.murata.com
Kemet
408-986-0424
www.kemet.com
Soft-Start
The LT3465 has an internal soft-start circuit to limit the
input current during circuit start-up. The circuit start-up
waveforms are shown in Figure 5.
IIN 50mA/DIV
VOUT 5V/DIV
VFB 100mV/DIV
CTRL 5V/DIV
VIN = 3.6V
4 LEDs, 20mA
L = 22µH
C = 0.22µF
200µs/DIV
3465 F05
Figure 5. Start-Up Waveforms
6
sn3465 3465is
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