FEATURES
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LT3497
Dual Full Function White
LED Driver with Integrated
Schottky Diodes
DESCRIPTION
The LT
®
3497 is a dual full function step-up DC/DC con-
verter specifically designed to drive up to 12 white LEDs
(6 white LEDs in series per converter) from a Li-Ion cell. Se-
ries 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. Accurate LED dimming and
shutdown of the two LED strings can also be controlled
independently. The LT3497 features a unique high side LED
current sense that enables the part to function as a “one
wire current source;” one side of the LED string can be
returned to ground anywhere, allowing a simpler 1-wire
LED connection. Traditional LED drivers use a grounded
resistor to sense LED current, requiring a 2-wire connec-
tion to the LED string.
The 2.3MHz switching frequency allows the use of tiny
inductors and capacitors. Few external components are
needed for the dual white LED Driver: open-LED protection
and the Schottky diodes are all contained inside the 3mm
×
2mm DFN package. With such a high level of integra-
tion, the LT3497 provides a high efficiency dual white LED
driver solution in the smallest of spaces.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
True Color PWM is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Drives Up to 12 White LEDs (6 in Series per
Converter) from a 3V Supply
Two Independent Boost Converters Capable of
Driving Asymmetric LED Strings
Independent Dimming and Shutdown Control of the
Two LED Strings
High Side Sense Allows “One Wire Current Source”
per Converter
Internal Schottky Diodes
Open LED Protection (32V)
2.3MHz Switching Frequency
±5% Reference Accuracy
V
IN
Range: 2.5V to 10V
Dual Wide 250:1 True Color PWM
TM
Dimming
Requires Only 1µF Output Capacitor per Converter
Available in a 3mm
×
2mm 10-Pin DFN Package
APPLICATIONS
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Cellular Phones
PDAs, Handheld Computers
Digital Cameras
MP3 Players
GPS Receivers
TYPICAL APPLICATION
Li-Ion Power Driver for 4/4 White LEDs
V
IN
3V TO 5V
1µF
EFFICIENCY (%)
80
75
V
IN
= 3.6V
4/4LEDs
Efficiency
15µH
SW1
CAP1
10Ω
1µF
LT3497
V
IN
15µH
SW2
CAP2
10Ω
1µF
70
65
60
55
LED1
LED2
CTRL1 GND CTRL2
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 1
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 2
3497 TA01a
50
0
5
10
15
LED CURRENT (mA)
20
3497 TA01b
3497f
1
LT3497
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
LED1 1
CTRL1 2
GND 3
CTRL2 4
LED2 5
11
10 CAP1
9
8
7
6
SW1
V
IN
SW2
CAP2
Input Voltage (VIN) ...................................................10V
SW1, SW2 Voltages ..................................................35V
CAP1, CAP2 Voltages ................................................35V
CTRL1, CTRL2 Voltages ............................................10V
LED1, LED2 Voltages ................................................35V
Operating Temperature Range ................. –40°C to 85°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range................... –65°C to 125°C
DDB PACKAGE
10-LEAD (3mm
×
2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 76°C/W,
θ
JC
= 13.5°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LT3497EDDB
DDB PART MARKING
LCGT
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Minimum Operating Voltage
LED Current Sense Voltage (V
CAP1
– V
LED1
)
LED Current Sense Voltage (V
CAP2
– V
LED2
)
Offset Voltage (V
OS
) Between
(V
CAP1
– V
LED1
) – (V
CAP2
– V
LED2
) Voltages
CAP1, LED1 Pin Bias Current
CAP2, LED2 Pin Bias Current
V
CAP1
, V
LED1
Common Mode Minimum Voltage
V
CAP2
, V
LED2
Common Mode Minimum Voltage
Supply Current
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3V, V
CTRL1
= V
CTRL2
= 3V.
CONDITIONS
V
CAP1
= 16V
V
CAP2
= 16V
V
OS
= |(V
CAP1
– V
LED1
) – (V
CAP2
– V
LED2
)|
V
CAP1
= 16V, V
LED1
= 16V
V
CAP2
= 16V, V
LED2
= 16V
●
●
MIN
2.5
190
190
0
TYP
200
200
2
20
20
MAX
210
210
8
40
40
2.5
2.5
UNITS
V
mV
mV
mV
µA
µA
V
V
mA
µA
MHz
%
mA
mA
mV
mV
V
CAP1
= V
CAP2
= 16V, V
LED1
= V
LED2
= 15V,
V
CTRL1
= V
CTRL2
= 3V
V
CTRL1
= V
CTRL2
= 0V
1.8
88
●
●
6
12
2.3
92
400
400
200
200
0.1
0.1
8.5
18
2.8
Switching Frequency
Maximum Duty Cycle
Converter 1 Switch Current Limit SW1
Converter 2 Switch Current Limit SW2
Converter 1 V
CESAT
Converter 2 V
CESAT
Switch 1 Leakage Current
Switch 2 Leakage Current
I
SW1
= 200mA
I
SW2
= 200mA
V
SW1
= 16V
V
SW2
= 16V
300
300
5
5
µA
µA
3497f
2
LT3497
ELECTRICAL CHARACTERISTICS
PARAMETER
V
CTRL1
Voltage for Full LED Current
V
CTRL2
Voltage for Full LED Current
V
CTRL1
or V
CTRL2
Voltage to Turn On the IC
V
CTRL1
and V
CTRL2
Voltages to Shut Down the IC
CTRL1, CTRL2 Pin Bias Current
CAP1 Pin Overvoltage Protection
CAP2 Pin Overvoltage Protection
Schottky 1 Forward Drop
Schottky 2 Forward Drop
Schottky 1 Reverse Leakage Current
Schottky 2 Reverse Leakage Current
I
SCHOTTKY1
= 100mA
I
SCHOTTKY2
= 100mA
V
R1
= 25V
V
R2
= 25V
●
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3V, V
CTRL1
= V
CTRL2
= 3V.
CONDITIONS
V
CAP1
= 16V
V
CAP2
= 16V
●
●
●
MIN
1.5
1.5
100
TYP
MAX
UNITS
V
V
mV
50
100
30
30
32
32
0.8
0.8
4
4
34
34
mV
nA
V
V
V
V
µA
µA
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LT3497E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
3497f
3
LT3497
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Saturation Voltage
(V
CESAT
)
450
SWITCH SATURATION VOLTAGE (mV)
400
350
–50°C
300
125°C
250
200
150
100
50
0
0
50
100 150 200 250 300 350 400
SWITCH CURRENT (mA)
3497 G01
(T
A
= 25°C unless otherwise specified)
Shutdown Current
(V
CTRL1
= V
CTRL2
= 0V)
15
–50°C
SHUTDOWN CURRENT (µA)
12
25°C
9
125°C
Schottky Forward Voltage Drop
400
SCHOTTKY FORWARD CURRENT (mA)
350
300
250
125°C
200
25°C
150
–50°C
100
50
0
0
0
800
600
SCOTTKY FORWARD DROP (mV)
200
400
1000
3497 G02
25°C
6
3
0
2
4
V
IN
(V)
6
8
10
3497 G03
Sense Voltage (V
CAP
– V
LED
)
vs V
CTRL
240
25°C
OUTPUT CLAMP VOLTAGE (V)
200
SENSE VOLTAGE (mV)
160
–50°C
120
80
40
0
0
500
1000
V
CTRL
(mV)
1500
2000
3497 G04
Open-Circuit Output Clamp
Voltage
34
30
25
INPUT CURRENT (mA)
33
Input Current in Output Open
Circuit
150°C
20
15
25°C
10
–50°C
5
125°C
–50°C
32
25°C
31
125°C
30
0
2
4
V
IN
(V)
6
8
10
3497 G05
0
2
4
6
V
IN
(V)
8
10
3497 G06
Switching Waveform
V
SW
10V/DIV
V
CAP
50mV/DIV
V
CAP
5V/DIV
V
CTRL
5V/DIV
Transient Response
I
L
100mA/DIV
200ms/DIV
V
IN
= 3.6V
FRONT PAGE
APPLICATION CIRCUIT
3497 G07
I
L
200mA/DIV
1ms/DIV
V
IN
= 3.6V
FRONT PAGE
APPLICATION CIRCUIT
3497 G08
3497f
4
LT3497
TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Current
7
125°C
6
QUIESCENT CURRENT (mA)
5
4
3
2
1
0
0
2
4
V
IN
(V)
3497 G09
(T
A
= 25°C unless otherwise specified)
Schottky Leakage Current vs
Temperature (–50°C to 125°C)
3
SCHOTTKY LEAKAGE CURRENT (µA)
Current Limit vs Temperature
500
25°C
–50°C
CURRENT LIMIT (mA)
450
2
400
24V
1
350
16V
0
–50
6
8
10
300
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
–25
75
0
25
50
TEMPERATURE (°C)
100
125
3497 G11
3497 G12
Open-Circuit Output Clamp Voltage
vs Temperature (–50°C to 125°C)
36
30
25
INPUT CURRENT (mA)
34
20
15
10
5
28
–50
Input Current in Output Open
Circuit vs Temperature
(–50°C to 125°C)
V
IN
= 3V
SWITCHING FREQUENCY (MHz)
2.60
2.50
2.40
2.30
2.20
2.10
2.00
1.90
50
25
75
0
TEMPERATURE (°C)
100
125
Switching Frequency vs
Temperature
V
IN
= 3.6V
OUTPUT CLAMP VOLTAGE (V)
32
30
–25
75
0
25
50
TEMPERATURE (°C)
100
125
0
–50 –25
1.80
–50 –25
0
50
75
25
TEMPERATURE (°C)
100
125
3497 G13
3497 G14
3497 G15
Sense Voltage (V
CAP
– V
LED
)
vs V
CAP
208
206
Sense Voltage vs Temperature
204
SENSE VOLTAGE (mV)
SENSE VOLTAGE (mV)
25
30
3497 G16
202
200
125°C
25°C
–50°C
198
196
194
192
188
5
10
20
15
V
CAP
(V)
190
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
3497 G17
3497f
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