LT3466
Dual Full Function White LED
Step-Up Converter with
Built-In Schottky Diodes
FEATURES
s
s
DESCRIPTIO
s
s
s
s
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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 V
OUT
)
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
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 a low profile, small footprint
(3mm
×
3mm
×
0.75mm) DFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Main/Sub Displays
Digital Cameras, Sub-Notebook PCs
PDAs, Handheld Computers
Automotive
TYPICAL APPLICATIO
3V TO 5V
1µF
47µH
SW1
LED1
2.2µF
LT3466
FB1
CTRL1
10Ω
SHUTDOWN
AND DIMMING
CONTROL 1
FB2
R
T
GND CTRL2
SHUTDOWN
AND DIMMING
CONTROL 2
10Ω
3466 F01a
85
80
47µH
75
V
IN
SW2
V
OUT2
2.2µF
LED2
EFFICIENCY (%)
V
OUT1
70
65
60
55
50
63.4k
0
Figure 1. Li-Ion Powered Driver for 8/8 White LEDs
3466f
U
Conversion Efficiency
V
IN
= 3.6V
8/8 LEDs
5
10
LED CURRENT (mA)
3466 F01b
U
U
15
20
1
LT3466
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
OUT1
SW1
V
IN
SW2
V
OUT2
1
2
3
4
5
11
10 FB1
9 CTRL1
8 R
T
7 CTRL2
6 FB2
Input Voltage (V
IN
) ................................................... 24V
SW1, SW2 Voltages ................................................ 44V
V
OUT1
, V
OUT2
Voltages ............................................. 44V
CTRL1, CTRL2 Voltages ........................................... 24V
FB1, FB2, R
T
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
LT3466EDD
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 2.96°C/W
EXPOSED PAD (PIN 11) IS GND
MUST BE SOLDERED TO PCB
DD PART MARKING
LBBH
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Minimum Operating Voltage
Maximum Operating Voltage
FB1 Voltage
FB2 Voltage
FB1 Pin Bias Current
FB2 Pin Bias Current
Quiescent Current
Switching Frequency
Oscillator Frequency Range
Nominal R
T
Pin Voltage
Maximum Duty Cycle
The
q
denotes specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
IN
= 3V, V
CTRL1
= 3V, V
CTRL2
= 3V, unless otherwise specified.
CONDITIONS
MIN
2.7
24
q
q
TYP
MAX
UNITS
V
V
mV
mV
nA
nA
mA
µA
MHz
kHz
V
%
%
%
mA
mA
mV
mV
192
192
200
200
10
10
5
16
208
208
50
50
6
25
1.2
2000
V
FB1
= 0.2V (Note 3)
V
FB2
= 0.2V (Note 3)
V
FB1
= V
FB2
= 0.3V
CTRL1 = CTRL2 = 0V
R
T
= 48.7k
R
T
= 48.7k
R
T
= 48.7k
R
T
= 20.5k
R
T
= 267k
q
0.8
200
1
0.54
90
96
92
99
400
400
360
360
0.01
0.01
5
5
Converter 1 Current Limit
Converter 2 Current Limit
Converter 1 V
CESAT
Converter 2 V
CESAT
Switch 1 Leakage Current
Switch 2 Leakage Current
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
V
OUT1
Overvoltage Threshold
V
OUT2
Overvoltage Threshold
V
CTRL1
= V
CTRL2
= 1V
I
SW1
= 300mA
I
SW2
= 300mA
V
SW1
= 10V
V
SW2
= 10V
q
q
320
320
1.8
1.8
50
q
8
10
42
42
12
2
U
µA
µA
V
V
mV
µA
V
V
3466f
W
U
U
W W
W
LT3466
ELECTRICAL CHARACTERISTICS
PARAMETER
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)
The
q
denotes specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
IN
= 3V, V
CTRL1
= 3V, V
CTRL2
= 3V, unless otherwise specified.
CONDITIONS
I
SCHOTTKY1
= 300mA
I
SCHOTTKY2
= 300mA
V
OUT1
= 20V
V
OUT2
= 20V
600
600
Note 3:
Current flows out of the pin.
MIN
TYP
0.85
0.85
5
5
MAX
UNITS
V
V
µA
µA
µs
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.
TYPICAL PERFOR A CE CHARACTERISTICS
Switching Waveforms
V
OUT1
50mV/DIV
V
SW1
20V/DIV
I
L1
100mA/DIV
V
OUT1
0.5V/DIV
FEEDBACK VOLTAGE (mV)
V
CTRL1
2V/DIV
I
L1
200mA/DIV
0.5µs/DIV
V
IN
= 3.6V
CIRCUIT OF FIGURE 1
U W
Transient Response
250
V
FB1,2
vs V
CTRL1,2
V
IN
= 3V
T
A
= 25°C
200
150
100
3466 G01
5µs/DIV
V
IN
= 3.6V
I
LED1
= 20mA TO 10mA
CIRCUIT OF FIGURE 1
3466 G02
50
0
0
1
0.5
1.5
CONTROL VOLTAGE (V)
2
3466 G03
3466f
3
LT3466
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Saturation Voltage (V
CESAT
)
450
SWITCH SATURATION VOLTAGE (mV)
400
350
T
A
= 25°C
V
CE1
, V
CE2
CURRENT LIMIT (mA)
300
250
200
150
100
50
0
0
50
100 150 200 250 300 350 400
SWITCH CURRENT (mA)
3466 G04
350
300
250
200
150
100
50
0
0
20
T
A
= 85°C
SHUTDOWN CURRENT (µA)
Open-Circuit Output Clamp
Voltage
44
T
A
= 25°C
R
T
= 48.7k
OUTPUT CLAMP VOLTAGE (V)
OUTPUT CLAMP VOLTAGE (V)
42
41
40
39
38
37
36
INPUT CURRENT (mA)
43
42
V
OUT2
V
OUT1
41
40
2
4
6
8 10 12 14 16 18 20 22 24
V
IN
(V)
3466 G07
R
T
vs Oscillator Frequency
1000
OSCILLATOR FREQUENCY (kHz)
1200
R
T
(kΩ)
100
10
200
600
1000
1400
1800
OSCILLATOR FREQUENCY (kHz)
3466 G10
4
U W
Switch Current Limit vs Duty Cycle
500
450
400
T
A
= –50°C
T
A
= 25°C
100
90
80
70
60
50
40
30
20
10
60
40
DUTY CYCLE (%)
80
100
3466 G05
Shutdown Quiescent Current
(CTRL1 = CTRL2 = 0V)
T
A
= –50°C
T
A
= 25°C
T
A
= 100°C
0
2
4
6
8 10 12 14 16 18 20 22 24
V
IN
(V)
3466 G06
Open-Circuit Output Clamp
Voltage
45
V
IN
= 3.6V
44 R
T
= 48.7k
V
OUT2
V
OUT1
Input Current with Output 1 and
Output 2 Open Circuit
12
10
8
6
4
2
0
T
A
= 25°C
R
T
= 48.7k
43
35
–50
50
0
TEMPERATURE (°C)
100
3466 G08
2
4
6
8 10 12 14 16 18 20 22 24
V
IN
(V)
3466 G09
Oscillator Frequency vs V
IN
R
T
= 48.7k
1100
1000
900
800
2
4
6
8 10 12 14 16 18 20 22 24
V
IN
(V)
3466 G11
3466f
LT3466
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
vs Temperature
2500
2250
OSCILLATOR FREQUENCY (kHz)
6
V
IN
= 3.6V
QUIESCENT CURRENT (mA)
2000
1750
1500
1250
1000
750
500
–50
Schottky Forward Voltage Drop
400
T
A
= 25°C
SCHOTTKY FORWARD CURRENT (mA)
350
300
250
200
150
100
50
0
0
800
600
SCHOTTKY FORWARD DROP (mV)
200
400
1000
3466 G14
SCHOTTKY LEAKAGE CURRENT (µA)
U W
0
Quiescent Current
(CTRL1 = CTRL2 = 3V)
T
A
= 25°C
R
T
= 20.5k
5
4
3
2
1
0
R
T
= 48.7k
50
100
3466 G12
0
4
8
TEMPERATURE (°C)
12
V
IN
(V)
16
20
24
3466 G13
Schottky Leakage Current
6
5
4
3
V
R
= 40V
2
V
R
= 20V
1
0
–50
0
50
TEMPERATURE (°C)
100
3466 G15
3466f
5
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