LT3466EDD [Linear]
Dual Full Function White LED Step-Up Converter with Built-In Schottky Diodes; 双路全功能的白光LED升压型转换器，带有内置肖特基二极管
| 型号： | LT3466EDD |
| 厂家： | 
Linear |
| 描述： | Dual Full Function White LED Step-Up Converter with Built-In Schottky Diodes |
| 文件： | 总20页 (文件大小：325K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3466
Dual Full Function White LED
Step-Up Converter with
Built-In Schottky Diodes
U
FEATURES
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.
■
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 (42V 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
Tiny (3mm × 3mm) 10-Lead DFN Package
■
■
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.
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APPLICATIO S
■
Main/Sub Displays
■
Digital Cameras, Sub-Notebook PCs
The LT3466 is available in a low profile, small footprint
(3mm × 3mm × 0.75mm) DFN package.
■
PDAs, Handheld Computers
Automotive
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
U
TYPICAL APPLICATIO
3V TO 5V
Conversion Efficiency
85
1µF
V
= 3.6V
IN
8/8 LEDs
80
75
70
65
60
55
50
47µH
SW2
47µH
SW1
V
IN
LED1
LED2
V
V
OUT2
OUT1
2.2µF
2.2µF
LT3466
FB1
FB2
R
T
CTRL1
GND CTRL2
63.4k
SHUTDOWN
SHUTDOWN
AND DIMMING
CONTROL 2
10Ω
10Ω
AND DIMMING
CONTROL 1
0
5
10
15
20
LED CURRENT (mA)
3466 F01a
3466 F01b
Figure 1. Li-Ion Powered Driver for 8/8 White LEDs
3466f
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LT3466
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ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Note 1)
Input Voltage (VIN) ................................................... 24V
SW1, SW2 Voltages ................................................ 44V
ORDER PART
TOP VIEW
NUMBER
V
1
2
3
4
5
10 FB1
OUT1
SW1
V
OUT1, VOUT2 Voltages ............................................. 44V
9
8
7
6
CTRL1
LT3466EDD
CTRL1, CTRL2 Voltages ........................................... 24V
FB1, FB2, RT Voltages ................................................ 2V
Operating Temperature Range ................ –40°C to 85°C
Storage Temperature Range .................. –65°C to 125°C
Junction Temperature .......................................... 125°C
11
V
IN
R
T
SW2
OUT2
CTRL2
FB2
V
DD PART MARKING
LBBH
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 43°C/W, θJC = 2.96°C/W
EXPOSED PAD (PIN 11) IS GND
MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. VIN = 3V, VCTRL1 = 3V, VCTRL2 = 3V, unless otherwise specified.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
Minimum Operating Voltage
Maximum Operating Voltage
FB1 Voltage
2.7
24
208
208
50
V
●
●
192
192
200
200
10
mV
mV
nA
FB2 Voltage
FB1 Pin Bias Current
FB2 Pin Bias Current
Quiescent Current
V
FB1
V
FB2
V
FB1
= 0.2V (Note 3)
= 0.2V (Note 3)
10
50
nA
= V = 0.3V
5
6
mA
FB2
CTRL1 = CTRL2 = 0V
16
25
µA
Switching Frequency
R = 48.7k
0.8
1
1.2
MHz
kHz
V
T
Oscillator Frequency Range
200
2000
Nominal R Pin Voltage
R = 48.7k
T
0.54
T
Maximum Duty Cycle
R = 48.7k
●
90
96
92
99
%
%
%
T
R = 20.5k
T
R = 267k
T
Converter 1 Current Limit
Converter 2 Current Limit
●
●
320
320
400
400
360
360
0.01
0.01
mA
mA
mV
mV
µA
µA
V
Converter 1 V
Converter 2 V
I
I
= 300mA
= 300mA
= 10V
CESAT
CESAT
SW1
SW2
Switch 1 Leakage Current
V
V
5
5
SW1
SW2
Switch 2 Leakage Current
= 10V
CTRL1 Voltage for Full LED Current
CTRL2 Voltage for Full LED Current
CTRL1 and CTRL2 Voltage to Shut Down Chip
CTRL1, CTRL2 Pin Bias Current
1.8
1.8
V
50
12
mV
µA
V
V
= V
= 1V
CTRL2
●
8
10
42
42
CTRL1
V
OUT1
V
OUT2
Overvoltage Threshold
Overvoltage Threshold
V
3466f
2
LT3466
ELECTRICAL CHARACTERISTICS
The ● denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. VIN = 3V, VCTRL1 = 3V, VCTRL2 = 3V, unless otherwise specified.
PARAMETER
CONDITIONS
MIN
TYP
0.85
0.85
MAX
UNITS
V
Schottky 1 Forward Drop
Schottky 2 Forward Drop
Schottky 1 Reverse Leakage
Schottky 2 Reverse Leakage
Soft-Start Time (Switcher 1)
Soft-Start Time (Switcher 2)
I
I
= 300mA
= 300mA
SCHOTTKY1
SCHOTTKY2
V
V
OUT1
V
OUT2
= 20V
5
5
µA
µA
µs
= 20V
600
600
µs
Note 1: Absolute Maximum Ratings are those values beyond which the life
Note 3: Current flows out of the pin.
of a device may be impaired.
Note 2: The LTC3466E is guaranteed to meet specified performance from
0°C to 70°C. Specifications over the –40°C to 85°C operating range are
assured by design, characterization and correlation with statistical process
controls.
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TYPICAL PERFOR A CE CHARACTERISTICS
Switching Waveforms
Transient Response
VFB1,2 vs VCTRL1,2
250
200
150
100
50
VOUT1
VOUT1
V
A
= 3V
IN
50mV/DIV
0.5V/DIV
T
= 25°C
VSW1
20V/DIV
VCTRL1
2V/DIV
IL1
IL1
100mA/DIV
200mA/DIV
VIN = 3.6V
0.5µs/DIV
3466 G01
VIN = 3.6V
ILED1 = 20mA TO 10mA
CIRCUIT OF FIGURE 1
5µs/DIV
3466 G02
CIRCUIT OF FIGURE 1
0
0
0.5
1
1.5
2
CONTROL VOLTAGE (V)
3466 G03
3466f
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LT3466
TYPICAL PERFOR A CE CHARACTERISTICS
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Shutdown Quiescent Current
(CTRL1 = CTRL2 = 0V)
Switch Saturation Voltage (VCESAT
)
Switch Current Limit vs Duty Cycle
500
450
400
350
300
250
200
150
100
50
450
400
350
300
250
200
150
100
50
100
90
80
70
60
50
40
30
20
10
0
T
= 25°C
CE1 CE2
T
= –50°C
T
= 25°C
A
A
A
V
, V
T
= –50°C
A
T
A
= 85°C
T = 25°C
A
T
= 100°C
A
0
0
200 250
20
60
0
50 100 150
300 350 400
0
40
80
100
2
4
6
8
10 12 14 16 18 20 22 24
(V)
SWITCH CURRENT (mA)
DUTY CYCLE (%)
V
IN
3466 G04
3466 G05
3466 G06
Open-Circuit Output Clamp
Voltage
Open-Circuit Output Clamp
Voltage
Input Current with Output 1 and
Output 2 Open Circuit
12
10
8
44
43
42
41
40
45
44
T
= 25°C
= 48.7k
T
= 25°C
= 48.7k
V
= 3.6V
= 48.7k
A
T
A
T
IN
T
R
R
R
43
42
41
V
V
OUT2
OUT1
V
V
OUT2
OUT1
6
40
39
4
38
37
36
35
2
0
2
4
6
8
10 12 14 16 18 20 22 24
(V)
2
4
6
8
10 12 14 16 18 20 22 24
(V)
–50
50
0
TEMPERATURE (°C)
100
V
IN
V
IN
3466 G09
3466 G07
3466 G08
Oscillator Frequency vs VIN
RT vs Oscillator Frequency
1000
100
10
1200
R
T
= 48.7k
1100
1000
900
800
600
1000
1400
1800
200
2
4
6
8
10 12 14 16 18 20 22 24
(V)
OSCILLATOR FREQUENCY (kHz)
V
IN
3466 G10
3466 G11
3466f
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LT3466
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TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
vs Temperature
2500
Quiescent Current
(CTRL1 = CTRL2 = 3V)
6
5
4
3
2
1
0
T
= 25°C
V
= 3.6V
A
IN
2250
2000
1750
1500
1250
1000
750
R
= 20.5k
= 48.7k
T
R
T
500
0
8
12
(V)
16
20
24
4
0
50
–50
100
V
IN
TEMPERATURE (°C)
3466 G13
3466 G12
Schottky Forward Voltage Drop
Schottky Leakage Current
6
5
4
3
2
1
0
400
350
300
250
T
= 25°C
A
200
150
V
= 40V
R
V
= 20V
R
100
50
0
–50
0
50
100
200
400
800
0
1000
600
TEMPERATURE (°C)
SCHOTTKY FORWARD DROP (mV)
3466 G15
3466 G14
3466f
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LT3466
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PI FU CTIO S
VOUT1 (Pin1):OutputofConverter1.Thispinisconnected
to the cathode of the internal Schottky diode. Connect an
output capacitor from this pin to ground.
CTRL2 (Pin 7): Dimming and Shutdown Pin for Con-
verter 2. Connect this pin to ground to disable the con-
verter. As the pin voltage is ramped from 0V to 1.6V, the
LED current ramps from 0 to ILED2 (= 200mV/RFB2). Any
voltage above 1.6V does not affect the LED current.
SW1 (Pin 2): Switch Pin for Converter 1. Connect the
inductor at this pin.
RT (Pin 8): Timing Resistor to Program the Switching
Frequency. The switching frequency can be programmed
from 200KHz to 2MHz.
VIN (Pin 3): Input Supply Pin. Must be locally bypassed
with a 1µF, X5R or X7R type ceramic capacitor.
SW2 (Pin 4): Switch Pin for Converter 2. Connect the
inductor at this pin.
CTRL1 (Pin 9): Dimming and Shutdown Pin for Con-
verter 1. Connect this pin to ground to disable the con-
verter. As the pin voltage is ramped from 0V to 1.6V, the
LED current ramps from 0 to ILED1 (= 200mV/RFB1). Any
voltage above 1.6V does not affect the LED current.
V
OUT2 (Pin5):OutputofConverter2.Thispinisconnected
to the cathode of the internal Schottky diode. Connect an
output capacitor from this pin to ground.
FB2 (Pin 6): Feedback Pin for Converter 2. The nominal
voltageatthispinis200mV.Connectcathodeofthelowest
LED and the feedback resisitor at this pin. The LED current
can be programmed by :
FB1 (Pin 10): Feedback Pin for Converter 1. The nominal
voltageatthispinis200mV.Connectcathodeofthelowest
LED and the feedback resistor at this pin. The LED current
can be programmed by :
I
LED2 ≈ (200mV/RFB2), when VCTRL2 > 1.6V
LED2 ≈ (VCTRL2/5 • RFB2), when VCTRL2 < 1V
I
LED1 ≈ (200mV/RFB1), when VCTRL1 > 1.6V
LED1 ≈ (VCTRL1/5 • RFB1), when VCTRL1 < 1V
I
I
ExposedPad(Pin11):TheExposedPadmustbesoldered
to the PCB system ground.
3466f
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LT3466
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BLOCK DIAGRA
3466f
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LT3466
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OPERATIO
Main Control Loop
Minimum Output Current
The LT3466 uses a constant frequency, current mode
control scheme to provide excellent line and load regula-
tion. It incorporates two identical, but fully independent
PWM converters. Operation can be best understood by
referring to the Block Diagram in Figure 2. The oscillator,
start-up bias and the bandgap reference are shared be-
tween the two converters. The control circuitry, power
switch, Schottky diode etc., are all identical for both the
converters.
The LT3466 can drive an 8-LED string at 2.5mA LED
current without pulse skipping. As current is further
reduced, the device may begin skipping pulses. This will
result in some low frequency ripple, although the LED
current remains regulated on an average basis down to
zero.ThephotoinFigure 3showscircuitoperationwith16
white LEDs (eight per converter) at 2.5mA current driven
from3.6Vsupply. Peakinductorcurrentislessthan50mA
and the regulator operates in discontinuous mode imply-
ing that the inductor current reached zero during the
discharge phase. After the inductor current reaches zero,
the switch pin exhibits ringing due to the LC tank circuit
formed by the inductor in combination 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 applica-
tion of a 300Ω resistor across the inductors, although this
will degrade efficiency.
At power-up, the output voltages VOUT1 and VOUT2 are
charged up to VIN (input supply voltage) via their respec-
tive inductor and the internal Schottky diode. If either
CTRL1 and CTRL2 or both are pulled high, the bandgap
reference, start-up bias and the oscillator are turned on.
Working of the main control loop can be understood by
following the operation of converter 1. At the start of each
oscillator cycle, the power switch Q1 is turned on. A
voltage proportional to the switch current is added to a
stabilizing ramp and the resulting sum is fed into the
positive terminal of the PWM comparator A2. When this
voltage exceeds the level at the negative input of A2, the
PWM logic turns off the power switch. The level at the
negative input of A2 is set by the error amplifier A1, and is
simply an amplified version of the difference between the
feedback voltage and the 200mV reference voltage. In this
manner, the error amplifier A1 regulates the feedback
voltage to 200mV reference voltage. The output of the
error amplifier A1 sets the correct peak current level in
inductor L1 to keep the output in regulation. The CTRL1
pin voltage is used to adjust the reference voltage.
VOUT1
10mV/DIV
VSW1
20V/DIV
IL1
50mA/DIV
VIN = 3.6V
0.5µs/DIV
3466 F03
ILED1 = 2.5mA
CIRCUIT OF FIGURE 1
Figure 3. Switching Waveforms
Open-Circuit Protection
The LT3466 has internal open-circuit protection for both
the converters. When the LEDs are disconnected from the
circuitorfailopen,theconverteroutputvoltageisclamped
at 42V. The converter will then switch at a very low
frequency to minimize the input current. Output voltage
and input current during output open circuit are shown in
the Typical Performance Characteristics graphs.
If only one of the converters is turned on, the other con-
verter will stay off and its output will remain charged up to
VIN (input supply voltage). The LT3466 enters into shut-
down, when both CTRL1 and CTRL2 are pulled lower than
50mV. The CTRL1 and CTRL2 pins perform independent
dimming and shutdown control for the two converters.
3466f
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LT3466
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OPERATIO
In the event one of the converters has an output open-
circuit, itsoutputvoltagewillbeclampedat42V. However,
theotherconverterwillcontinuefunctioningproperly. The
photo in Figure 4 shows circuit operation with converter 1
output open-circuit and converter 2 driving eight LEDs at
20mA. Converter 1 switches at a lower frequency, reduc-
ing its input current.
The converter enters into soft-start mode whenever the
respective CTRL pin is pulled from low to high. Figure 5
shows the start-up waveforms with converter 1 driving
four LEDs at 20mA. The filtered input current, as shown in
Figure 5, is well controlled. The soft-start circuit is less
effective when driving a higher number of LEDs.
Undervoltage Lockout
Soft-Start
The LT3466 has an undervoltage lockout circuit which
shuts down both the converters when the input voltage
drops below 2.1V (typ). This prevents the converter to
operate in an erratic mode when powered from low supply
voltages.
The LT3466 has a separate internal soft-start circuitry for
each converter. Soft-start helps to limit the inrush current
during start-up. Soft-start is achieved by clamping the
output of the error amplifier during the soft-start period.
This limits the peak inductor current and ramps up the
output voltage in a controlled manner.
VSW1
50V/DIV
IIN
100mA/DIV
IL1
VOUT1
500mA/DIV
5V/DIV
VSW2
50V/DIV
VFB1
200mV/DIV
IL2
CRTL1
2V/DIV
200mA/DIV
VIN = 3.6V
CIRCUIT OF FIGURE 1
(8/8 LEDs)
1µs/DIV
3466 F04
VIN = 3.6V
4 LEDs, 20mA
L = 15µH
100µs/DIV
3466 F05
C = 0.47µF
Figure 4. Output 1 Open-Circuit Waveforms
Figure 5. Start-Up Waveforms
3466f
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LT3466
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APPLICATIO S I FOR ATIO
DUTY CYCLE
current that flows into the timing resistor is used to
charge and discharge an internal oscillator capacitor. A
graph for selecting the value of RT for a given operating
frequency is shown in the Figure 6.
The duty cycle for a step-up converter is given by:
V
OUT + VD – V
IN
D =
V
OUT + VD – VCESAT
OPERATING FREQUENCY SELECTION
where:
The choice of operating frequency is determined by sev-
eral factors. There is a tradeoff between efficiency and
component size. Higher switching frequency allows the
use of smaller inductors albeit at the cost of increased
switching losses and decreased efficiency.
V
OUT = Output voltage
VD = Schottky forward voltage drop
VCESAT = Saturation voltage of the switch
VIN = Input battery voltage
Another consideration is the maximum duty cycle achiev-
able. In certain applications, the converter needs to oper-
ate at the maximum duty cycle in order to light up the
maximum number of LEDs. The LT3466 has a fixed
oscillator off-time and a variable on-time. As a result, the
maximumdutycycleincreasesastheswitchingfrequency
is decreased.
The maximum duty cycle achievable for LT3466 is 96%
(typ) when running at 1MHz switching frequency. It in-
creases to 99% (typ) when run at 200kHz and drops to
92%(typ)at2MHz.Alwaysensurethattheconverterisnot
duty-cycle limited when powering the LEDs at a given
switching frequency.
The circuit of Figure 1 is operated with different values of
timing resistor (RT). RT is chosen so as to run the
converters at 800kHz (RT = 63.4k), 1.25MHz (RT = 39.1k)
and 2MHz (RT = 20.5k). The efficiency comparison for
different RT values is shown in Figure 7.
SETTING THE SWITCHING FREQUENCY
The LT3466 uses a constant frequency architecture that
can be programmed over a 200KHz to 2MHz range with a
single external timing resistor from the RT pin to ground.
The nominal voltage on the RT pin is 0.54V, and the
1000
100
10
85
CIRCUIT OF FIGURE 1
R
= 63.4k
T
V
= 3.6V
IN
80
75
8/8 LEDs
R
T
= 39.1k
70
65
60
55
50
R
T
= 20.5k
600
1000
1400
1800
200
5
10
LED CURRENT (mA)
20
0
15
OSCILLATOR FREQUENCY (kHz)
3466 F06
3466 F07
Figure 6. Timing Resistor (RT) Value
Figure 7. Efficiency Comparison for Different RT Resistors
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LT3466
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APPLICATIO S I FOR ATIO
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INDUCTOR SELECTION
CAPACITOR SELECTION
The choice of the inductor will depend on the selection of
switching frequency of LT3466. The switching frequency
canbeprogrammedfrom200kHzto2MHz.Higherswitch-
ing frequency allows the use of smaller inductors albeit at
the cost of increased switching losses.
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.
The inductor current ripple (∆IL), neglecting the drop
across the Schottky diode and the switch, is given by :
Table2showsalistofseveralceramiccapacitormanufac-
turers. Consultthemanufacturersfordetailedinformation
on their entire selection of ceramic parts.
V
• VOUT(MAX) – V
IN(MIN)
(
)
IN(MIN)
∆IL =
VOUT(MAX) • f •L
Table 2. Ceramic Capacitor Manufacturers
Taiyo Yuden
(408) 573-4150
www.t-yuden.com
where:
L = Inductor
f = Operating frequency
AVX
(803) 448-9411
www.avxcorp.com
Murata
(714) 852-2001
www.murata.com
VIN(MIN) = Minimum input voltage
VOUT(MAX) = Maximum output voltage
INRUSH CURRENT
The ∆IL is typically set to 20% to 40% of the maximum
inductor 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.
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.
Recommendedinductorvaluesrangefrom10µHto68µH.
SeveralinductorsthatworkwellwiththeLT3466arelisted
in Table 1. Consult each manufacturer for more detailed
information and for their entire selection of related parts.
For low DCR inductors, which is usually the case for this
application, the peak inrush current can be simplified as
follows:
Table 1. Recommended Inductors
MAX CURRENT
V – 0.6
L
(µH)
DCR
(Ω)
RATING
(mA)
IN
IPK
=
PART
VENDOR
ωL
LQH32CN100
LQH32CN150
LQH43CN330
10
15
33
0.44
0.58
1.00
300
300
310
Murata
(814) 237-1431
www.murata.com
where:
1
ω =
ELL6RH330M
ELL6SH680M
33
68
0.38
0.52
600
500
Panasonic
(714) 373-7939
www.panasonic.com
LCOUT
Table 3 gives inrush peak current for some component
selections.
A914BYW330M
A914BYW470M
A920CY680M
33
47
68
0.45
0.73
0.40
440
360
400
Toko
www.toko.com
CDRH2D18150NC
CDRH4D18-330
CDRH5D18-680
15
33
68
0.22
0.51
0.84
0.35A
0.31A
0.43A
Sumida
(847) 956-0666
www.sumida.com
3466f
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LT3466
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APPLICATIO S I FOR ATIO
Table 3. Inrush Peak Current
Using a DC Voltage
V
(V)
L (µH)
15
C
(µF)
I (A)
P
IN
OUT
Forsomeapplications,thepreferredmethodofbrightness
control is a variable DC voltage to adjust the LED current.
TheCTRL1,CTRL2pinvoltagecanbemodulatedtosetthe
dimming of the respective LED string. As the voltage on
the CTRL1, CTRL2 pin increases from 0V to 1.6V, the LED
current increases from 0 to ILED1,2. As the CTRL1, CTRL2
pin voltage increases beyond 1.6V, it has no effect on the
LED current.
5
0.47
0.78
0.77
0.95
0.53
0.84
0.93
5
5
33
1.00
2.2
47
5
68
1.00
0.47
0.22
9
47
12
33
Typically peak inrush current will be less than the value
calculated above. This is due to the fact that the DC
resistance in the inductor provides some damping result-
ing in a lower peak inrush current.
The LED current can be set by:
I
LED1,2 ≈ (200mV/RFB1,2), when VCTRL1,2 > 1.6V
LED1,2 ≈ (VCTRL1,2/5 • RFB1,2), when VCTRL1,2 < 1V
I
Feedback voltage variation versus control voltage is given
in the Typical Performance Characteristics graphs.
PROGRAMMING LED CURRENT
The LED current of each LED string can set independently
by the choice of resistors RFB1 and RFB2 respectively
(Figure 2). The feedback reference is 200mV. In order to
have accurate LED current, precision resistors are pre-
ferred (1% is recommended).
Using a Filtered PWM Signal
A variable duty cycle PWM can be used to control the
brightness of the LED string. The PWM signal is filtered
(Figure 8) by an RC network and fed to the CTRL1, CTRL2
pins.
200mV
RFB1
RFB2
=
=
ThecornerfrequencyofR1,C1shouldbemuchlowerthan
the frequency of the PWM signal. R1 needs to be much
smaller than the internal impedance in the CTRL pins,
which is 100kΩ.
ILED1
200mV
ILED2
Table 4. RFB1,2 Value Selection
LT3466
R1
10k
I
(mA)
R
(Ω)
LED1,2
FB1,2
PWM
10kHz TYP
CTRL1,2
5
40.2
C1
1µF
3466 F08
10
15
20
25
20.0
13.3
10.0
8.06
Figure 8. Dimming Control Using a Filtered PWM Signal
LOW INPUT VOLTAGE APPLICATIONS
Most White LEDs are driven at maximum currents of
15mA to 20mA.
The LT3466 can be used in low input voltage applications.
The input supply voltage to LT3466 must be 2.7V or
higher. However, the inductors can be run off a lower
battery voltage. This technique allows the LEDs to be
powered off two alkaline cells. Most portable devices have
a3.3Vlogicsupplyvoltagewhichcanbeusedtopowerthe
LT3466. The LEDs can be driven straight from the battery,
resulting in higher efficiency.
DIMMING CONTROL
Therearetwodifferenttypesofdimmingcontrolcircuits.
The LED current in the two drivers can be set indepen-
dently by modulating the CTRL1 and CTRL2 pins
respectively.
3466f
12
LT3466
W U U
APPLICATIO S I FOR ATIO
U
Figure 9 shows four LEDs being run off two AA cells. The
battery is connected to the inductors and the chip is
powered off 3.3V logic supply voltage.
BOARD LAYOUT CONSIDERATION
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To prevent electromagnetic interference (EMI) problems,
proper layout of high frequency switching paths is essen-
tial. Minimizethelengthandareaofalltracesconnectedto
the switching node pins (SW1 and SW2). Keep the feed-
back pins (FB1 and FB2) away from the switching nodes.
3.3V
2 AA CELLS
1.8V to 3V
0.1µF
1µF
15µH
L1
L2
15µH
SW1
V
SW2
IN
V
V
OUT2
OUT1
The DFN package has an exposed paddle that must be
connected to the system ground. The ground connection
for the feedback resistors should be tied directly to the
ground plane and not shared with any other component,
except the RT resistor, ensuring a clean, noise-free con-
nection. Recommended component placement is shown
in the Figure 10.
1µF
1µF
LT3466
FB1
FB2
R
T
CTRL1
CTRL2
10Ω
10Ω
63.4k
1%
3466 F09
Figure 9. 2 AA Cells to Four White LEDs
HIGH INPUT VOLTAGE APPLICATIONS
GND
The input voltage to LT3466 can be as high as 24V. This
gives it the flexibility of driving a large number of LEDs
when being run off a higher voltage. The maximum num-
ber of LEDs that can be driven is constrained by the
converter output voltages being clamped at 42V.
C
OUT1
R
FB1
C
IN
CTRL1
CTRL2
10
9
1
2
3
4
5
R
T
L1
L2
V
IN
11
8
The LT3466 can be used to power 20 White LEDs (10 per
converter) at 20mA when running off two Li-Ion cells in
series.
7
6
R
FB2
C
OUT2
3466 F10
GND
Figure 10. Recommended Component Placement
3466f
13
LT3466
U
TYPICAL APPLICATIO S
Li-Ion to 2/4 White LEDs
Conversion Efficiency
3V TO 5V
85
80
75
V
= 3.6V
IN
2/4 LEDs
C
IN
1µF
L1
15µH
L2
15µH
70
65
60
55
50
SW1
V
SW2
IN
V
OUT1
V
OUT2
C
C
OUT2
0.47µF
OUT1
1µF
LT3466
FB1
FB2
R
R
T
R
FB2
10Ω
CTRL1
CTRL2
FB1
10Ω
5
10
20
0
15
LED CURRENT (mA)
3466 TA01a
38.3k
1%
3466 TA01b
C
C
C
: TAIYO YUDEN JMK107BJ105
IN
: TAIYO YUDEN LMK212BJ105
OUT1
: TAIYO YUDEN EMK212BJ474
OUT2
L1, L2: MURATA LQH32CN150
Li-Ion to 5/5 White LEDs
Conversion Efficiency
3V TO 5V
85
80
75
V
= 3.6V
IN
5/5 LEDs
C
IN
1µF
L1
15µH
L2
15µH
70
65
60
55
50
SW1
V
SW2
IN
V
V
OUT2
OUT1
C
C
OUT1
0.47µF
OUT2
0.47µF
LT3466
FB1
FB2
R
R
T
R
CTRL1
CTRL2
FB1
FB2
10Ω
10Ω
0
5
10
15
20
LED CURRENT (mA)
38.3k
1%
3466 TA02a
3466 TA02b
C
C
: TAIYO YUDEN JMK107BJ105
IN
OUT1 OUT2
, C
: TAIYO YUDEN GMK212BJ474
L1, L2: MURATA LQH32CN150
3466f
14
LT3466
U
TYPICAL APPLICATIO S
Li-Ion to 6/6 White LEDs
Conversion Efficiency
3V TO 5V
85
80
75
V
= 3.6V
IN
6/6 LEDs
C
IN
1µF
L1
33µH
L2
33µH
70
65
60
55
50
SW1
V
SW2
IN
V
OUT1
V
OUT2
C
C
OUT2
1µF
OUT1
1µF
LT3466
FB1
FB2
R
T
CTRL1
CTRL2
5
10
20
0
15
R
R
FB2
FB1
10Ω
10Ω
LED CURRENT (mA)
63.4k
1%
3466 TA03b
3466 TA03a
C
: TAIYO YUDEN JMK107BJ105
IN
OUT1 OUT2
C
, C
: TAIYO YUDEN GMK316BJ105
L1, L2: TOKO A914BYW-330M
Li-Ion to 7/7 White LEDs
Conversion Efficiency
3V TO 5V
85
80
75
V
= 3.6V
IN
7/7 LEDs
C
IN
1µF
L1
33µH
L2
33µH
70
65
60
55
50
SW1
V
SW2
IN
V
OUT1
V
OUT2
C
C
OUT2
1µF
OUT1
1µF
LT3466
FB1
FB2
R
T
CTRL1
CTRL2
5
10
20
0
15
LED CURRENT (mA)
63.4k
1%
R
R
FB2
10Ω
FB1
3466 TA04b
10Ω
3466 TA04a
C
: TAIYO YUDEN JMK107BJ105
IN
OUT1 OUT2
C
, C
: TAIYO YUDEN GMK316BJ105
L1, L2: TOKO A914BYW-330M
3466f
15
LT3466
U
TYPICAL APPLICATIO S
Li-Ion to 8/8 White LEDs
3V TO 5V
Conversion Efficiency
85
80
75
V
= 3.6V
IN
8/8 LEDs
C
IN
1µF
L1
47µH
L2
47µH
70
65
60
55
50
SW1
V
SW2
IN
V
V
OUT2
OUT1
C
C
OUT1
2.2µF
OUT2
2.2µF
LT3466
FB1
FB2
R
T
CTRL1
CTRL2
5
10
20
0
15
LED CURRENT (mA)
63.4k
1%
3466 TA05b
R
R
FB2
FB1
10Ω
10Ω
C
C
: TAIYO YUDEN JMK107BJ105
IN
OUT1 OUT2
L1, L2: TOKO A918CE-470M
3466 TA05a
, C
: TAIYO YUDEN GMK325BJ225
Li-Ion to 9/9 White LEDs
Conversion Efficiency
3V TO 5V
90
V
= 3.6V
IN
9/9 LEDs
C
IN
85
80
75
70
65
60
1µF
L1
68µH
L2
68µH
SW1
V
SW2
IN
V
V
OUT2
OUT1
C
OUT1
1µF
C
OUT2
1µF
LT3466
FB1
FB2
R
T
CTRL1
CTRL2
4
8
0
12
LED CURRENT (mA)
147k
1%
3466 TA06b
R
R
C
C
: TAIYO YUDEN JMK107BJ105
FB1
FB2
IN
OUT1 OUT2
16.5Ω
16.5Ω
, C
: TAIYO YUDEN UMK325BJ105
L1, L2: TOKO A920CY-680M
3466 TA06a
3466f
16
LT3466
U
TYPICAL APPLICATIO S
Li-Ion to 10/10 White LEDs
Conversion Efficiency
3V TO 5V
90
85
80
75
70
65
60
V
= 3.6V
IN
10/10 LEDs
C
IN
1µF
L1
68µH
L2
68µH
SW1
V
IN
SW2
V
V
OUT2
OUT1
C
C
OUT2
1µF
OUT1
1µF
LT3466
FB1
FB2
R
T
CTRL1
CTRL2
4
8
0
12
LED CURRENT (mA)
147k
1%
3466 TA07b
R
R
FB2
C
C
: TAIYO YUDEN JMK107BJ105
IN
OUT1 OUT2
L1, L2: TOKO A920CY-680M
FB1
16.5Ω
16.5Ω
, C
: TAIYO YUDEN UMK325BJ105
3466 TA07a
2 AA Cells to 2/2 White LEDs
Conversion Efficiency
3.3V
75
70
65
60
55
50
V
= 2.4V
IN
2/2 LEDs
C
IN1
V
CC
0.1µF
1.8V TO 3V
C
IN2
L1
15µH
L2
1µF
15µH
SW1
V
SW2
IN
V
V
OUT2
OUT1
C
C
OUT2
1µF
OUT1
1µF
LT3466
FB1
FB2
R
R
FB2
10Ω
FB1
R
T
CTRL1
CTRL2
10Ω
3466 TA08a
63.4k
1%
0
5
10
15
20
LED CURRENT (mA)
C
C
C
: TAIYO YUDEN EMK107BJ104
: TAIYO YUDEN JMK107BJ105
OUT1 OUT2
L1, L2: MURATA LQH32CN150
IN1
IN2
3466 TA08b
, C
: TAIYO YUDEN GMK316BJ105
3466f
17
LT3466
U
TYPICAL APPLICATIO S
2 Li-Ion Cells to 10/10 White LEDs
Conversion Efficiency
6V TO 9V
90
85
80
75
70
65
60
55
50
V
= 7V
IN
10/10 LEDs
C
IN
1µF
L1
L2
47µH
47µH
SW1
V
SW2
IN
V
V
OUT2
OUT1
C
C
OUT1
0.47µF
OUT2
0.47µF
LT3466
FB1
FB2
R
T
CTRL1
CTRL2
10
0
5
15
20
LED CURRENT (mA)
63.4k
1%
3466 TA09b
R
R
FB2
C
C
: TAIYO YUDEN LMK212BJ105
FB1
IN
OUT1 OUT2
10Ω
10Ω
, C
: TAIYO YUDEN UMK316BJ474
L1, L2: TOKO A914BYW-470M
3466 TA09a
3466f
18
LT3466
U
PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
0.675 ±0.05
3.50 ±0.05
2.15 ±0.05 (2 SIDES)
1.65 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50
BSC
2.38 ±0.05
(2 SIDES)
R = 0.115
TYP
6
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
0.38 ± 0.10
10
3.00 ±0.10
(4 SIDES)
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 5)
(DD10) DFN 0403
5
1
0.25 ± 0.05
0.50 BSC
0.75 ±0.05
0.200 REF
2.38 ±0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
2. ALL DIMENSIONS ARE IN MILLIMETERS
3. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
4. EXPOSED PAD SHALL BE SOLDER PLATED
5. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
3466f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
19
LT3466
U
TYPICAL APPLICATIO
Conversion Efficiency
12V to 25/25 White LEDs
V
IN
12V
85
80
75
70
65
60
55
50
V
= 12V
IN
25/25 LEDs
C
IN
1µF
C2
C7
0.1µF
0.1µF
D5
D6
D1
D2
V
V
LED1
LED2
L1
L2
33µH
33µH
C9
C4
0.1µF
C8
0.1µF
C3
0.1µF
0.1µF
D3
D4
D7
D8
25
LEDs
25
LEDs
C5
0.1µF
C10
0.1µF
SW1
V
SW2
IN
V
V
OUT2
OUT1
C11
0.22µF
C6
0.22µF
LT3466
0
5
10
15
FB1
CTRL1
FB2
LED CURRENT (mA)
R
FB2
13.3Ω
R
FB1
13.3Ω
3466 TA10b
R
T
CTRL2
3466 TA10a
C
: TAIYO YUDEN EMK316BJ105
IN
20.5k
1%
C3-C5, C8-C10: TAIYO YUDEN UMK212BJ104
C2, C7: TAIYO YUDEN HMK316BJ104
C6, C11: TAIYO YUDEN UMK316BJ224
D1-D8: PHILIPS BAV99
L1, L2: MURATA LQH32CN330
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Up to 16 White LEDs, V : 1.6V to 18V, V
LT1618
Constant Current, Constant Voltage 1.24MHz, High Efficiency
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Up to 6 White LEDs, V : 2.7V to 4.5V, I = 6.5mA, I < 1µA,
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Up to 8 White LEDs, V : 2.7V to 4.5V, I = 5mA, I < 1µA,
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Up to 4 (Main), 2 (Sub) and RGB, V : 2.8V to 4.5V,
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LT3465/LT3465A
Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED
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Up to Six White LEDs, V : 2.7V to 16V, V
= 34V,
OUT(MAX)
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Q
SD
ThinSOT is a trademark of Linear Technology Corporation.
3466f
LT/TP 0104 1K • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
20
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
LINEAR TECHNOLOGY CORPORATION 2004
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