LINER LT3466EDD Dual full function white led step-up converter with built-in schottky diode Datasheet

LT3466
Dual Full Function White LED
Step-Up Converter with
Built-In Schottky Diodes
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FEATURES
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DESCRIPTIO
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
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APPLICATIO S
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Main/Sub Displays
Digital Cameras, Sub-Notebook PCs
PDAs, Handheld Computers
Automotive
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 a low profile, small footprint
(3mm × 3mm × 0.75mm) DFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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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.
TYPICAL APPLICATIO
3V TO 5V
Conversion Efficiency
85
1µF
VIN = 3.6V
8/8 LEDs
80
47µH
47µH
LED1
VIN
SW2
LED2
VOUT2
VOUT1
2.2µF
2.2µF
LT3466
FB1
10Ω
SHUTDOWN
AND DIMMING
CONTROL 1
RT GND CTRL2
63.4k
SHUTDOWN
AND DIMMING
CONTROL 2
70
65
60
FB2
CTRL1
EFFICIENCY (%)
75
SW1
55
10Ω
3466 F01a
50
0
5
10
15
20
LED CURRENT (mA)
3466 F01b
Figure 1. Li-Ion Powered Driver for 8/8 White LEDs
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LT3466
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ABSOLUTE
RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
Input Voltage (VIN) ................................................... 24V
SW1, SW2 Voltages ................................................ 44V
VOUT1, VOUT2 Voltages ............................................. 44V
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
ORDER PART
NUMBER
TOP VIEW
10 FB1
VOUT1
1
SW1
2
VIN
3
SW2
4
7 CTRL2
VOUT2
5
6 FB2
LT3466EDD
9 CTRL1
11
8 RT
DD PART MARKING
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
LBBH
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
Minimum Operating Voltage
TYP
MAX
2.7
UNITS
V
Maximum Operating Voltage
24
V
FB1 Voltage
●
192
200
208
mV
FB2 Voltage
●
192
200
208
mV
FB1 Pin Bias Current
VFB1 = 0.2V (Note 3)
10
50
nA
FB2 Pin Bias Current
VFB2 = 0.2V (Note 3)
10
50
nA
Quiescent Current
VFB1 = VFB2 = 0.3V
CTRL1 = CTRL2 = 0V
5
16
6
25
mA
µA
Switching Frequency
RT = 48.7k
1
1.2
MHz
2000
kHz
0.8
Oscillator Frequency Range
200
Nominal RT Pin Voltage
RT = 48.7k
Maximum Duty Cycle
RT = 48.7k
RT = 20.5k
RT = 267k
0.54
V
●
90
96
92
99
%
%
%
Converter 1 Current Limit
●
320
400
mA
Converter 2 Current Limit
●
320
400
mA
Converter 1 VCESAT
ISW1 = 300mA
360
mV
Converter 2 VCESAT
ISW2 = 300mA
360
mV
Switch 1 Leakage Current
VSW1 = 10V
0.01
5
µA
Switch 2 Leakage Current
VSW2 = 10V
0.01
5
µA
CTRL1 Voltage for Full LED Current
1.8
V
CTRL2 Voltage for Full LED Current
1.8
V
CTRL1 and CTRL2 Voltage to Shut Down Chip
CTRL1, CTRL2 Pin Bias Current
VCTRL1 = VCTRL2 = 1V
●
8
10
50
mV
12
µA
VOUT1 Overvoltage Threshold
42
V
VOUT2 Overvoltage Threshold
42
V
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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
Schottky 1 Forward Drop
ISCHOTTKY1 = 300mA
MIN
0.85
TYP
MAX
UNITS
V
Schottky 2 Forward Drop
ISCHOTTKY2 = 300mA
0.85
V
Schottky 1 Reverse Leakage
VOUT1 = 20V
5
µA
Schottky 2 Reverse Leakage
VOUT2 = 20V
5
µA
Soft-Start Time (Switcher 1)
600
µs
Soft-Start Time (Switcher 2)
600
µs
Note 1: Absolute Maximum Ratings are those values beyond which the life
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.
Note 3: Current flows out of the pin.
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TYPICAL PERFOR A CE CHARACTERISTICS
Switching Waveforms
Transient Response
VFB1,2 vs VCTRL1,2
VOUT1
0.5V/DIV
VSW1
20V/DIV
VCTRL1
2V/DIV
200
IL1
100mA/DIV
IL1
200mA/DIV
0.5µs/DIV
VIN = 3.6V
CIRCUIT OF FIGURE 1
3466 G01
5µs/DIV
VIN = 3.6V
ILED1 = 20mA TO 10mA
CIRCUIT OF FIGURE 1
3466 G02
FEEDBACK VOLTAGE (mV)
VOUT1
50mV/DIV
250
VIN = 3V
TA = 25°C
150
100
50
0
0
1
0.5
1.5
CONTROL VOLTAGE (V)
2
3466 G03
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LT3466
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TYPICAL PERFOR A CE CHARACTERISTICS
Switch Saturation Voltage (VCESAT)
500
TA = –50°C
450
400
350
300
250
200
150
300
250
200
150
100
50
50
0
0
100 150 200 250 300 350 400
SWITCH CURRENT (mA)
50
0
20
60
40
DUTY CYCLE (%)
80
50
40
30
20
0
100
12
43
6
8 10 12 14 16 18 20 22 24
VIN (V)
42
41
TA = 25°C
RT = 48.7k
10
VOUT2
INPUT CURRENT (mA)
OUTPUT CLAMP VOLTAGE (V)
41
4
Input Current with Output 1 and
Output 2 Open Circuit
VIN = 3.6V
44 RT = 48.7k
VOUT1
2
3466 G06
45
TA = 25°C
RT = 48.7k
42
TA = 100°C
60
Open-Circuit Output Clamp
Voltage
VOUT2
TA = 25°C
70
3466 G05
Open-Circuit Output Clamp
Voltage
43
TA = –50°C
80
10
3466 G04
44
90
TA = 85°C
350
100
0
100
TA = 25°C
SHUTDOWN CURRENT (µA)
TA = 25°C
VCE1, VCE2
400
CURRENT LIMIT (mA)
SWITCH SATURATION VOLTAGE (mV)
450
OUTPUT CLAMP VOLTAGE (V)
Shutdown Quiescent Current
(CTRL1 = CTRL2 = 0V)
Switch Current Limit vs Duty Cycle
VOUT1
40
39
38
37
8
6
4
2
36
40
2
4
6
8 10 12 14 16 18 20 22 24
VIN (V)
35
–50
0
50
0
TEMPERATURE (°C)
100
6
8 10 12 14 16 18 20 22 24
VIN (V)
3466 G09
Oscillator Frequency vs VIN
RT vs Oscillator Frequency
1000
1200
OSCILLATOR FREQUENCY (kHz)
RT (kΩ)
4
3466 G08
3466 G07
100
10
200
2
600
1000
1400
1800
OSCILLATOR FREQUENCY (kHz)
3466 G10
RT = 48.7k
1100
1000
900
800
2
4
6
8 10 12 14 16 18 20 22 24
VIN (V)
3466 G11
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LT3466
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TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
vs Temperature
Quiescent Current
(CTRL1 = CTRL2 = 3V)
6
2500
2250
5
RT = 20.5k
2000
QUIESCENT CURRENT (mA)
OSCILLATOR FREQUENCY (kHz)
TA = 25°C
VIN = 3.6V
1750
1500
1250
RT = 48.7k
1000
4
3
2
1
750
0
500
–50
0
50
100
0
TEMPERATURE (°C)
4
8
12
VIN (V)
20
16
3466 G13
3466 G12
Schottky Forward Voltage Drop
TA = 25°C
SCHOTTKY LEAKAGE CURRENT (µA)
SCHOTTKY FORWARD CURRENT (mA)
Schottky Leakage Current
6
400
350
300
250
200
150
100
50
0
24
0
200
400
800
600
SCHOTTKY FORWARD DROP (mV)
1000
3466 G14
5
4
3
VR = 40V
2
VR = 20V
1
0
–50
0
50
TEMPERATURE (°C)
100
3466 G15
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LT3466
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VOUT1 (Pin 1): Output of Converter 1. This pin is connected
to the cathode of the internal Schottky diode. Connect an
output capacitor from this pin to ground.
SW1 (Pin 2): Switch Pin for Converter 1. Connect the
inductor at this pin.
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.
CTRL2 (Pin 7): Dimming and Shutdown Pin for Converter␣ 2. Connect this pin to ground to disable the converter. 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.
RT (Pin 8): Timing Resistor to Program the Switching
Frequency. The switching frequency can be programmed
from 200KHz to 2MHz.
VOUT2 (Pin 5): Output of Converter 2. This pin is connected
to the cathode of the internal Schottky diode. Connect an
output capacitor from this pin to ground.
CTRL1 (Pin 9): Dimming and Shutdown Pin for Converter␣ 1. Connect this pin to ground to disable the converter. 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.
FB2 (Pin 6): Feedback Pin for Converter 2. The nominal
voltage at this pin is 200mV. Connect cathode of the lowest
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
voltage at this pin is 200mV. Connect cathode of the lowest
LED and the feedback resistor at this pin. The LED current
can be programmed by :
ILED2 ≈ (200mV/RFB2), when VCTRL2 > 1.6V
ILED1 ≈ (200mV/RFB1), when VCTRL1 > 1.6V
ILED2 ≈ (VCTRL2/5 • RFB2), when VCTRL2 < 1V
ILED1 ≈ (VCTRL1/5 • RFB1), when VCTRL1 < 1V
Exposed Pad (Pin 11): The Exposed Pad must be soldered
to the PCB system ground.
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C2
RFB1
10
1
FB1
PWM
LOGIC
PWM
COMP
A2
RSNS1
DRIVER
CONVERTER 1
OSC
OVERVOLT
DETECTION
SW1
Q1
2
–
+
VOUT1
L1
–
+
A3
EA
A1
Σ
20k
+
+
–
C1
RT
9
VIN
START-UP
CONTROL
REF 1.25V
CTRL1
SHDN
OSC
3
7
CTRL2
80k
0.2V
Figure 2. LT3466 Block Diagram
80k
0.2V
RAMP
GEN
OSC
8
RT
20k
+
+
–
Σ
A1
EA
A3
11
EXPOSED
PAD
–
+
Q2
4
A2
OSC
PWM
LOGIC
VOUT2
FB2
OVERVOLT
DETECTION
CONVERTER 2
PWM
COMP
DRIVER
RSNS2
SW2
L2
–
+
VIN
6
5
3466 F02
RFB2
C3
LT3466
BLOCK DIAGRA
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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 regulation. 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 between 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. The photo in Figure␣ 3 shows circuit operation with 16
white LEDs (eight per converter) at 2.5mA current driven
from 3.6V supply. Peak inductor current is less than 50mA
and the regulator operates in discontinuous mode implying 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 application 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 respective 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.
If only one of the converters is turned on, the other converter will stay off and its output will remain charged up to
VIN (input supply voltage). The LT3466 enters into shutdown, 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.
VOUT1
10mV/DIV
VSW1
20V/DIV
IL1
50mA/DIV
0.5µs/DIV
VIN = 3.6V
ILED1 = 2.5mA
CIRCUIT OF FIGURE 1
3466 F03
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
circuit or fail open, the converter output voltage is clamped
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.
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LT3466
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OPERATIO
In the event one of the converters has an output opencircuit, its output voltage will be clamped at 42V. However,
the other converter will continue functioning properly. 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, reducing 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 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
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.
IIN
100mA/DIV
IL1
500mA/DIV
VOUT1
5V/DIV
VSW2
50V/DIV
VFB1
200mV/DIV
IL2
200mA/DIV
CRTL1
2V/DIV
VIN = 3.6V
CIRCUIT OF FIGURE 1
(8/8 LEDs)
1µs/DIV
3466 F04
Figure 4. Output 1 Open-Circuit Waveforms
VIN = 3.6V
4 LEDs, 20mA
L = 15µH
C = 0.47µF
100µs/DIV
3466 F05
Figure 5. Start-Up Waveforms
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LT3466
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APPLICATIO S I FOR ATIO
DUTY CYCLE
The duty cycle for a step-up converter is given by:
D=
VOUT + VD – VIN
VOUT + VD – VCESAT
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.
OPERATING FREQUENCY SELECTION
where:
VOUT = Output voltage
VD = Schottky forward voltage drop
VCESAT = Saturation voltage of the switch
VIN = Input battery voltage
The maximum duty cycle achievable for LT3466 is 96%
(typ) when running at 1MHz switching frequency. It increases to 99% (typ) when run at 200kHz and drops to
92% (typ) at 2MHz. Always ensure that the converter is not
duty-cycle limited when powering the LEDs at a given
switching frequency.
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
The choice of operating frequency is determined by several 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.
Another consideration is the maximum duty cycle achievable. In certain applications, the converter needs to operate 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
maximum duty cycle increases as the switching frequency
is decreased.
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.
1000
85
CIRCUIT OF FIGURE 1
VIN = 3.6V
80 8/8 LEDs
RT = 63.4k
RT = 39.1k
EFFICIENCY (%)
RT (kΩ)
75
100
70
RT = 20.5k
65
60
55
10
200
600
1000
1400
1800
OSCILLATOR FREQUENCY (kHz)
3466 F06
Figure 6. Timing Resistor (RT) Value
50
0
5
10
15
20
LED CURRENT (mA)
3466 F07
Figure 7. Efficiency Comparison for Different RT Resistors
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LT3466
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APPLICATIO S I FOR ATIO
INDUCTOR SELECTION
CAPACITOR 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 switching 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 because 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 :
∆IL =
(
VIN(MIN) • VOUT(MAX) – VIN(MIN)
)
VOUT(MAX) • f • L
Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information
on their entire selection of ceramic parts.
Table 2. Ceramic Capacitor Manufacturers
where:
L = Inductor
f = Operating frequency
Taiyo Yuden
(408) 573-4150
www.t-yuden.com
AVX
(803) 448-9411
www.avxcorp.com
Murata
(714) 852-2001
www.murata.com
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
L
(µH)
MAX
DCR
(Ω)
CURRENT
RATING
(mA)
LQH32CN100
LQH32CN150
LQH43CN330
10
15
33
0.44
0.58
1.00
300
300
310
Murata
(814) 237-1431
www.murata.com
ELL6RH330M
ELL6SH680M
33
68
0.38
0.52
600
500
Panasonic
(714) 373-7939
www.panasonic.com
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
PART
VENDOR
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 selection 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.
Sumida
(847) 956-0666
www.sumida.com
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LT3466
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APPLICATIO S I FOR ATIO
Table 3. Inrush Peak Current
Using a DC Voltage
VIN (V)
L (µH)
COUT (µF)
IP (A)
5
15
0.47
0.78
5
33
1.00
0.77
5
47
2.2
0.95
5
68
1.00
0.53
9
47
0.47
0.84
12
33
0.22
0.93
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 resulting in a lower peak inrush current.
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 preferred (1% is recommended).
200mV
ILED1
200mV
=
ILED2
RFB1 =
RFB2
For some applications, the preferred method of brightness
control is a variable DC voltage to adjust the LED current.
The CTRL1, CTRL2 pin voltage can be modulated to set the
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.
The LED current can be set by:
ILED1,2 ≈ (200mV/RFB1,2), when VCTRL1,2 > 1.6V
ILED1,2 ≈ (VCTRL1,2/5 • RFB1,2), when VCTRL1,2 < 1V
Feedback voltage variation versus control voltage is given
in the Typical Performance Characteristics graphs.
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.
The corner frequency of R1, C1 should be much lower than
the frequency of the PWM signal. R1 needs to be much
smaller than the internal impedance in the CTRL pins,
which is 100kΩ.
Table 4. RFB1,2 Value Selection
ILED1,2 (mA)
RFB1,2 (Ω)
5
40.2
10
20.0
15
13.3
20
10.0
25
8.06
Most White LEDs are driven at maximum currents of
15mA to 20mA.
DIMMING CONTROL
There are two different types of dimming control circuits.
The LED current in the two drivers can be set independently by modulating the CTRL1 and CTRL2 pins
respectively.
PWM
10kHz TYP
LT3466
R1
10k
CTRL1,2
C1
1µF
3466 F08
Figure 8. Dimming Control Using a Filtered PWM Signal
LOW INPUT VOLTAGE APPLICATIONS
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
a 3.3V logic supply voltage which can be used to power the
LT3466. The LEDs can be driven straight from the battery,
resulting in higher efficiency.
3466f
12
LT3466
U
W
U U
APPLICATIO S I FOR ATIO
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.
3.3V
2 AA CELLS
1.8V to 3V
0.1µF
1µF
L2
15µH
L1
15µH
SW1
VIN
SW2
VOUT1
1µF
VOUT2
1µF
LT3466
FB1
CTRL1
FB2
RT
CTRL2
10Ω
10Ω
63.4k
1%
3466 F09
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 essential. Minimize the length and area of all traces connected to
the switching node pins (SW1 and SW2). Keep the feedback pins (FB1 and FB2) away from the switching nodes.
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 connection. Recommended component placement is shown
in the Figure 10.
Figure 9. 2 AA Cells to Four White LEDs
HIGH INPUT VOLTAGE APPLICATIONS
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 number of LEDs that can be driven is constrained by the
converter output voltages being clamped at 42V.
The LT3466 can be used to power 20 White LEDs (10 per
converter) at 20mA when running off two Li-Ion cells in
series.
GND
COUT1
RFB1
CIN
10
1
L1
9
2
VIN
3
L2
CTRL1
RT
11
8
4
7
5
6
CTRL2
RFB2
COUT2
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
CIN
1µF
VIN = 3.6V
2/4 LEDs
80
L2
15µH
SW1
COUT1
1µF
VIN
SW2
VOUT2
VOUT1
LT3466
FB1
RFB1
10Ω
EFFICIENCY (%)
75
L1
15µH
COUT2
0.47µF
RT
65
60
55
FB2
CTRL1
70
RFB2
10Ω
CTRL2
38.3k
1%
50
0
5
10
15
20
LED CURRENT (mA)
3466 TA01a
3466 TA01b
CIN: TAIYO YUDEN JMK107BJ105
COUT1: TAIYO YUDEN LMK212BJ105
COUT2: TAIYO YUDEN EMK212BJ474
L1, L2: MURATA LQH32CN150
Li-Ion to 5/5 White LEDs
Conversion Efficiency
3V TO 5V
85
VIN = 3.6V
5/5 LEDs
80
CIN
1µF
SW1
COUT1
0.47µF
VIN
SW2
VOUT2
VOUT1
LT3466
FB1
RFB1
10Ω
CTRL1
EFFICIENCY (%)
75
L2
15µH
L1
15µH
COUT2
0.47µF
CTRL2
38.3k
1%
65
60
55
FB2
RT
70
RFB2
10Ω
3466 TA02a
50
0
5
10
15
20
LED CURRENT (mA)
3466 TA02b
CIN: TAIYO YUDEN JMK107BJ105
COUT1, COUT2: 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
VIN = 3.6V
6/6 LEDs
80
CIN
1µF
L2
33µH
SW1
COUT1
1µF
EFFICIENCY (%)
75
L1
33µH
VIN
SW2
VOUT1
VOUT2
LT3466
FB1
COUT2
1µF
CTRL1
RT
65
60
55
FB2
RFB1
10Ω
70
CTRL2
50
0
RFB2
10Ω
63.4k
1%
5
10
15
20
LED CURRENT (mA)
3466 TA03b
3466 TA03a
CIN: TAIYO YUDEN JMK107BJ105
COUT1, COUT2: TAIYO YUDEN GMK316BJ105
L1, L2: TOKO A914BYW-330M
Li-Ion to 7/7 White LEDs
Conversion Efficiency
3V TO 5V
85
CIN
1µF
VIN = 3.6V
7/7 LEDs
80
SW1
COUT1
1µF
VIN
SW2
VOUT2
VOUT1
LT3466
FB1
CTRL1
EFFICIENCY (%)
75
L2
33µH
L1
33µH
COUT2
1µF
65
60
55
FB2
RT
70
CTRL2
50
0
RFB1
10Ω
63.4k
1%
5
10
15
20
LED CURRENT (mA)
RFB2
10Ω
3466 TA04b
3466 TA04a
CIN: TAIYO YUDEN JMK107BJ105
COUT1, COUT2: TAIYO YUDEN GMK316BJ105
L1, L2: TOKO A914BYW-330M
3466f
15
LT3466
U
TYPICAL APPLICATIO S
Li-Ion to 8/8 White LEDs
Conversion Efficiency
3V TO 5V
85
VIN = 3.6V
8/8 LEDs
80
CIN
1µF
SW1
COUT1
2.2µF
EFFICIENCY (%)
75
L2
47µH
L1
47µH
VIN
SW2
VOUT2
VOUT1
LT3466
FB1
COUT2
2.2µF
RT
65
60
55
FB2
CTRL1
70
CTRL2
50
5
0
RFB1
10Ω
3466 TA05a
Conversion Efficiency
3V TO 5V
90
CIN
1µF
EFFICIENCY (%)
COUT1
1µF
SW2
VOUT1
VIN = 3.6V
9/9 LEDs
85
L2
68µH
VIN
20
RFB2
10Ω
Li-Ion to 9/9 White LEDs
SW1
15
3466 TA05b
CIN: TAIYO YUDEN JMK107BJ105
COUT1, COUT2: TAIYO YUDEN GMK325BJ225
L1, L2: TOKO A918CE-470M
L1
68µH
10
LED CURRENT (mA)
63.4k
1%
VOUT2
LT3466
COUT2
1µF
80
75
70
65
FB1
CTRL1
FB2
RT
CTRL2
60
0
147k
1%
RFB1
16.5Ω
CIN: TAIYO YUDEN JMK107BJ105
COUT1, COUT2: TAIYO YUDEN UMK325BJ105
L1, L2: TOKO A920CY-680M
4
8
12
LED CURRENT (mA)
3466 TA06b
RFB2
16.5Ω
3466 TA06a
3466f
16
LT3466
U
TYPICAL APPLICATIO S
Li-Ion to 10/10 White LEDs
Conversion Efficiency
3V TO 5V
90
CIN
1µF
L2
68µH
VIN
SW2
VOUT2
VOUT1
COUT1
1µF
EFFICIENCY (%)
85
L1
68µH
SW1
VIN = 3.6V
10/10 LEDs
COUT2
1µF
LT3466
80
75
70
65
FB1
CTRL1
FB2
RT
60
CTRL2
4
0
RFB1
16.5Ω
RFB2
16.5Ω
CIN: TAIYO YUDEN JMK107BJ105
COUT1, COUT2: TAIYO YUDEN UMK325BJ105
L1, L2: TOKO A920CY-680M
3466 TA07a
Conversion Efficiency
3.3V
CIN1
0.1µF
L1
15µH
SW1
VIN
SW2
VOUT2
COUT2
1µF
LT3466
FB1
RFB1
10Ω
CTRL1
FB2
RT
CTRL2
63.4k
1%
CIN1: TAIYO YUDEN EMK107BJ104
CIN2: TAIYO YUDEN JMK107BJ105
COUT1, COUT2: TAIYO YUDEN GMK316BJ105
L1, L2: MURATA LQH32CN150
VIN = 2.4V
2/2 LEDs
70
L2
15µH
VOUT1
COUT1
1µF
75
EFFICIENCY (%)
CIN2
1µF
12
3466 TA07b
2 AA Cells to 2/2 White LEDs
VCC
1.8V TO 3V
8
LED CURRENT (mA)
147k
1%
65
60
55
RFB2
10Ω
3466 TA08a
50
0
5
10
15
20
LED CURRENT (mA)
3466 TA08b
3466f
17
LT3466
U
TYPICAL APPLICATIO S
2 Li-Ion Cells to 10/10 White LEDs
Conversion Efficiency
90
6V TO 9V
CIN
1µF
SW1
COUT1
0.47µF
80
L2
47µH
VIN
SW2
VOUT1
VOUT2
LT3466
FB1
CTRL1
EFFICIENCY (%)
L1
47µH
COUT2
0.47µF
65
50
CTRL2
CIN: TAIYO YUDEN LMK212BJ105
COUT1, COUT2: TAIYO YUDEN UMK316BJ474
L1, L2: TOKO A914BYW-470M
70
55
0
5
10
15
20
LED CURRENT (mA)
63.4k
1%
RFB1
10Ω
75
60
FB2
RT
VIN = 7V
10/10 LEDs
85
3466 TA09b
RFB2
10Ω
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
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
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
3.00 ±0.10
(4 SIDES)
0.38 ± 0.10
10
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 5)
(DD10) DFN 0403
5
0.200 REF
1
0.75 ±0.05
0.00 – 0.05
0.25 ± 0.05
0.50 BSC
2.38 ±0.10
(2 SIDES)
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
19
LT3466
U
TYPICAL APPLICATIO
Conversion Efficiency
12V to 25/25 White LEDs
VIN
12V
C2
0.1µF
VLED1
L1
33µH
D6
C4
0.1µF
D7
25
LEDs
C5
0.1µF
C7
0.1µF
D2
C8
0.1µF
C3
0.1µF
C9
0.1µF
D3
D4
D8
SW1
C6
0.22µF
VIN
SW2
VOUT1
VOUT2
LT3466
C10
0.1µF
25
LEDs
RT
70
65
60
55
C11
0.22µF
50
FB2
CTRL1
75
0
FB1
RFB1
13.3Ω
D1
VLED2
L2
33µH
VIN = 12V
25/25 LEDs
80
EFFICIENCY (%)
D5
85
CIN
1µF
CTRL2
10
5
LED CURRENT (mA)
RFB2
13.3Ω
15
3466 TA10b
3466 TA10a
CIN: TAIYO YUDEN EMK316BJ105
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
20.5k
1%
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1618
Constant Current, Constant Voltage 1.24MHz, High Efficiency
Boost Regulator
Up to 16 White LEDs, VIN: 1.6V to 18V, VOUT(MAX) = 34V,
IQ = 1.8mA, ISD < 1µA, MS Package
LT1932
Constant Current, 1.2MHz, High Efficiency White LED Boost
Regulator
Up to 8 White LEDs, VIN: 1V to 10V, VOUT(MAX) = 34V,
IQ = 1.2mA, ISD < 1µA, ThinSOTTM Package
LT1937
Constant Current, 1.2MHz, High Efficiency White LED Boost
Regulator
Up to 4 White LEDs, VIN: 2.5V to 10V, VOUT(MAX) = 34V,
IQ = 1.9mA, ISD < 1µA, ThinSOT, SC70 Packages
LTC3200
Low Noise, 2MHz, Regulated Charge Pump White LED Driver
Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 8mA, ISD < 1µA,
MS Package
LTC3200-5
Low Noise, 2MHz, Regulated Charge Pump White LED Driver
Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 8mA, ISD < 1µA,
ThinSOT Package
LTC3201
Low Noise, 1.7MHz, Regulated Charge Pump White LED Driver
Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 6.5mA, ISD < 1µA,
MS Package
LTC3202
Low Noise, 1.5MHz, Regulated Charge Pump White LED Driver
Up to 8 White LEDs, VIN: 2.7V to 4.5V, IQ = 5mA, ISD < 1µA,
MS Package
LTC3205
High Efficiency, Multidisplay LED Controller
Up to 4 (Main), 2 (Sub) and RGB, VIN: 2.8V to 4.5V,
IQ = 50µA, ISD < 1µA, QFN-24 Package
LT3465/LT3465A
Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED
Boost Regulator with Integrated Schottky Diode
Up to Six White LEDs, VIN: 2.7V to 16V, VOUT(MAX) = 34V,
IQ = 1.9mA, ISD < 1µA, ThinSOT Package
ThinSOT is a trademark of Linear Technology Corporation.
3466f
20
Linear Technology Corporation
LT/TP 0104 1K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2004
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