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PDF LTC3466 Data sheet ( Hoja de datos )
| Número de pieza | LTC3466 | |
| Descripción | Dual Full Function White LED Step-Up Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
■ Drives Up to 20 White LEDs (10 in Series
per Converter) from a 3.6V Supply
■ Two Independent Step-Up Converters Capable of
Driving Asymmetric LED Strings
■ Independent Dimming and Shutdown Control
of the Two LED Strings
■ Internal Schottky Diodes
■ Internal Soft-Start Eliminates Inrush Current
■ Open LED Protection (39.5V Max VOUT)
■ Fixed Frequency Operation Up to 2MHz
■ 81% Efficiency Driving 16 White LEDs at 15mA
(Eight per Driver) from a 3.6V Supply
■ Wide Input Voltage Range: 2.7V to 24V
■ Available in 10-Pin DFN and 16-Pin Thermally
Enhanced TSSOP Packages
U
APPLICATIO S
■ Main/Sub Displays
■ Digital Cameras, Sub-Notebook PCs
■ PDAs, Handheld Computers
■ Automotive
LT3466
www.DataSheet4U.com
Dual Full Function White LED
Step-Up Converter with
Built-In Schottky Diodes
DESCRIPTIO
LT®3466 is a dual full function step-up DC/DC converter
specifically designed to drive up to 20 White LEDs (10 in
series per converter) with a constant current. Series
connection of the LEDs provides identical LED currents
resulting in uniform brightness and eliminating the need
for ballast resistors and expensive factory calibration.
The two independent converters are capable of driving
asymmetric LED strings. The dimming of the two LED
strings can also be controlled independently. The LT3466
is ideal for providing backlight for main and sub-displays
in cell phones and other handheld devices.
The LT3466 operating frequency can be set with an
external resistor over a 200kHz to 2MHz range. A low
200mV feedback voltage minimizes power loss in the
current setting resistor for better efficiency. Additional
features include output voltage limiting when LEDs are
disconnected and internal soft-start.
The LT3466 is available in the 10-pin (3mm × 3mm ×
0.75mm) DFN and 16-pin thermally enhanced TSSOP
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
3V TO 5V
1µF
L1
47µH
L2
47µH
LED1
2.2µF
SW1
VOUT1
VIN
SW2
VOUT2
LT3466
2.2µF
LED2
FB1 FB2
CTRL1 RT GND CTRL2
10Ω OFF ON 63.4k
SHUTDOWN
AND DIMMING
CONTROL 1
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 2
10Ω
3466 F01a
Figure 1. Li-Ion Powered Driver for 8/8 White LEDs
Conversion Efficiency
85
VIN = 3.6V
8/8 LEDs
80
75
70
65
60
55
50
0
5 10 15
LED CURRENT (mA)
20
3466 F01b
3466fa
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LT3466
www.DataSheet4U.com
RT vs Oscillator Frequency
1000
Oscillator Frequency vs VIN
1200
RT = 48.7k
1100
100 1000
900
10
200
600 1000 1400 1800
OSCILLATOR FREQUENCY (kHz)
3466 G10
Oscillator Frequency
vs Temperature
2500
VIN = 3.6V
2250
2000
RT = 20.5k
1750
1500
1250
1000
RT = 48.7k
750
500
–50
0 50
TEMPERATURE (°C)
100
3466 G12
Schottky Forward Voltage Drop
400
TA = 25°C
350
300
250
200
150
100
50
0
0 200 400 600 800 1000
SCHOTTKY FORWARD DROP (mV)
3466 G14
800
2 4 6 8 10 12 14 16 18 20 22 24
VIN (V)
3466 G11
Quiescent Current
(CTRL1 = CTRL2 = 3V)
6
TA = 25°C
5
4
3
2
1
0
0 4 8 12 16 20 24
VIN (V)
3466 G13
Schottky Leakage Current
6
5
4
3
VR = 36V
2
VR = 20V
1
0
–50
0 50
TEMPERATURE (°C)
100
3466 G15
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5
5 Page 
APPLICATIO S I FOR ATIO
INDUCTOR SELECTION
The choice of the inductor will depend on the selection of
the switching frequency of the LT3466. The switching
frequency can be programmed from 200kHz to 2MHz.
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 10µH to 68µH.
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
MAX CURRENT
L DCR RATING
(µH) (Ω) (mA)
LQH32CN100
LQH32CN150
LQH43CN330
10 0.44
15 0.58
33 1.00
300
300
310
ELL6RH330M
ELL6SH680M
33 0.38
68 0.52
600
500
A914BYW330M
A914BYW470M
A920CY680M
CDRH2D18150NC
CDRH4D18-330
CDRH5D18-680
33 0.45
47 0.73
68 0.40
15 0.22
33 0.51
68 0.84
440
360
400
350
310
430
VENDOR
Murata
(814) 237-1431
www.murata.com
Panasonic
(714) 373-7939
www.panasonic.com
Toko
www.toko.com
Sumida
(847) 956-0666
www.sumida.com
LT3466
www.DataSheet4U.com
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 1µF 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
INRUSH CURRENT
The LT3466 has built-in Schottky diodes. When supply
voltage is applied to the VIN pin, an inrush current flows
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:
IPK
=
VIN – 0.6
ωL
where:
ω= 1
LCOUT
Table 3 gives inrush peak current for some component
selections.
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| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3466.PDF ] | |
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