LT3466
Dual Full Function White LED
Step-Up Converter with
Built-In Schottky Diodes
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 (39.5V 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
Available in 10-Pin DFN and 16-Pin Thermally
Enhanced TSSOP Packages
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.
APPLICATIO S
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Main/Sub Displays
Digital Cameras, Sub-Notebook PCs
PDAs, Handheld Computers
Automotive
TYPICAL APPLICATIO
3V TO 5V
1µF
L1
47µH
SW1
LED1
2.2µF
LT3466
FB1
CTRL1
10Ω
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 1
FB2
R
T
GND CTRL2
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 2
10Ω
3466 F01a
85
L2
47µH
V
IN
SW2
V
OUT2
2.2µF
LED2
EFFICIENCY (%)
80
75
V
OUT1
70
65
60
55
50
63.4k
0
Figure 1. Li-Ion Powered Driver for 8/8 White LEDs
3466fa
U
Conversion Efficiency
V
IN
= 3.6V
8/8 LEDs
5
10
LED CURRENT (mA)
3466 F01b
U
U
15
20
1
LT3466
ABSOLUTE
AXI U
RATI GS
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 (Note 2) ... –40°C to 85°C
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
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
Offset Voltage (V
OS
) Between FB1 and FB2 Voltages
FB1 Pin Bias Current
FB2 Pin Bias Current
Quiescent Current
Switching Frequency
Oscillator Frequency Range
Nominal R
T
Pin Voltage
Maximum Duty Cycle
The
●
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
●
●
V
OS
= |FB1 – FB2|
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
(Note 4)
R
T
= 48.7k
R
T
= 48.7k
R
T
= 20.5k
R
T
= 267k
●
2
U
U
W
W W
U
W
(Note 1)
Maximum Junction Temperature ......................... 125°C
Storage Temperature Range
DFN .................................................. –65°C to 125°C
TSSOP .............................................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec, TSSOP) ..... 300°C
TOP VIEW
GND
NC
VOUT1
SW1
V
IN
SW2
V
OUT2
GND
1
2
3
4
5
6
7
8
17
16 GND
15 FB1
14 CTRL1
13 NC
12 R
T
11 CTRL2
10 FB2
9
GND
ORDER PART
NUMBER
LT3466EFE
FE PART MARKING
3466EFE
FE PACKAGE
16-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 38°C/W,
θ
JC(PAD)
= 10°C/W
EXPOSED PAD (PIN 17) IS GND
MUST BE SOLDERED TO PCB
TYP
MAX
UNITS
V
V
mV
mV
mV
nA
nA
mA
µA
MHz
kHz
V
%
%
%
3466fa
192
192
0
200
200
1.5
10
10
5
16
208
208
7.5
50
50
7.5
25
1.2
2000
0.8
200
1
0.54
90
96
92
99
LT3466
ELECTRICAL CHARACTERISTICS
PARAMETER
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 or CTRL2 Voltage to Turn-On the IC
CTRL1 and CTRL2 Voltages to Shut Down the IC
CTRL1, CTRL2 Pin Bias Current
V
OUT1
Overvoltage-Lockout Threshold
V
OUT2
Overvoltage-Lockout Threshold
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)
(Note 5)
(Note 5)
The
●
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
320
320
TYP
400
400
360
360
0.01
0.01
MAX
UNITS
mA
mA
mV
mV
I
SW1
= 300mA
I
SW2
= 300mA
V
SW1
= 10V
V
SW2
= 10V
●
●
5
5
µA
µA
V
V
mV
1.8
1.8
150
50
mV
µA
V
V
V
V
V
CTRL1
= V
CTRL2
= 1V
V
OUT1
Rising
V
OUT2
Rising
I
SCHOTTKY1
= 300mA
I
SCHOTTKY2
= 300mA
V
OUT1
= 20V
V
OUT2
= 20V
●
8
10
39.5
39.5
0.85
0.85
12
5
5
600
600
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 LT3466E 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.
Note 4:
Guaranteed by design and test correlation, not production tested.
Note 5:
Current limit is guaranteed by design and/or correlation to static
test. Slope compensation reduces current limit at high duty cycle.
TYPICAL PERFOR A CE CHARACTERISTICS
Switching Waveforms
V
OUT1
50mV/DIV
V
SW1
20V/DIV
I
L1
100mA/DIV
V
OUT1
0.5V/DIV
V
CTRL1
2V/DIV
I
L1
200mA/DIV
0.5µs/DIV
V
IN
= 3.6V
CIRCUIT OF FIGURE 1
U W
Transient Response
3466 G01
50µs/DIV
V
IN
= 3.6V
I
LED1
= 20mA TO 10mA
CIRCUIT OF FIGURE 1
3466 G02
3466fa
3
LT3466
TYPICAL PERFOR A CE CHARACTERISTICS
V
FB
vs V
CTRL
250
V
IN
= 3V
T
A
= 25°C
FEEDBACK VOLTAGE (mV)
FEEDBACK VOLTAGE (mV)
FEEDBACK VOLTAGE (mV)
200
150
100
50
0
0
1
0.5
1.5
CONTROL VOLTAGE (V)
Switch Saturation Voltage (V
CESAT
)
450
500
T
A
= 25°C
V
CE1
, V
CE2
450
400
SWITCH SATURATION VOLTAGE (mV)
400
350
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 Clamp Voltage
vs V
IN
40.5
T
A
= 25°C
R
T
= 63.4k
OUTPUT CLAMP VOLTAGE (V)
OUTPUT CLAMP VOLTAGE (V)
V
OUT2
39.5
V
OUT1
INPUT CURRENT (mA)
40.0
39.0
38.5
2
4
6
8 10 12 14 16 18 20 22 24
V
IN
(V)
3466 G07
4
U W
2
3466 G03
V
FB
vs V
CTRL
(Temperature Variation)
250
T
A
= –45°C
T
A
= 25°C
T
A
= 85°C
250
±5mV
200
Distribution of V
FB
vs V
CTRL
V
IN
= 3V
T
A
= 25°C
MAX
MIN
150
±4mV
TYP
200
150
100
100
±4mV
50
50
0
0
0
1
0.5
1.5
CONTROL VOLTAGE (V)
2
3466 G17
0
1
0.5
1.5
CONTROL VOLTAGE (V)
2
3466 G16
Switch Current Limit vs Duty Cycle
T
A
= –50°C
T
A
= 25°C
Shutdown Quiescent Current
(CTRL1 = CTRL2 = 0V)
100
90
80
70
60
50
40
30
20
10
T
A
= –50°C
T
A
= 25°C
T
A
= 100°C
60
40
DUTY CYCLE (%)
80
100
3466 G05
0
2
4
6
8 10 12 14 16 18 20 22 24
V
IN
(V)
3466 G06
Open-Circuit Clamp Voltage
vs Temperature
42
Input Current with Output 1 and
Output 2 Open Circuit
25
T
A
= 25°C
R
T
= 63.4k
V
IN
= 3.6V
R
T
= 63.4k
41
20
40
15
V
OUT2
V
OUT1
39
10
38
5
37
–50
0
50
0
TEMPERATURE (°C)
100
3466 G08
2
4
6
8 10 12 14 16 18 20 22 24
V
IN
(V)
3466 G09
3466fa
LT3466
TYPICAL PERFOR A CE CHARACTERISTICS
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
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
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
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
= 36V
2
V
R
= 20V
1
0
–50
0
50
TEMPERATURE (°C)
100
3466 G15
3466fa
5
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