LT3486
Dual 1.3A White LED
Step-Up Converters with
Wide Dimming
FEATURES
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DESCRIPTIO
■
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■
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■
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Wide (1000:1) PWM Dimming Range with No
ColorShift
Independent Dimming and Shutdown Control of the
LED Drivers
Drives Up to 16 White LEDs at 25mA (8 per Driver)
from a Single Li-Ion Cell
Drives Up to 16 White LEDs at 100mA (8 per Driver)
from 12V Supply
±3% LED Current Programming Accuracy
Open LED Protection: 36V Clamp Voltage
Fixed Frequency Operation: Up to 2MHz
Wide Input Voltage Range: 2.5V to 24V
Low Shutdown Current: I
CC
< 1µA
Overtemperature Protection
Available in (5mm
×
3mm
×
0.75mm) 16-Pin DFN
and 16-Pin Thermally Enhanced TSSOP Packages
The LT
®
3486 is a dual step-up DC/DC converter
specifically designed to drive up to 16 White LEDs (8 in
series per converter) at constant current from a single
Li-Ion cell. Series connection of the LEDs provides identi-
cal LED currents resulting in uniform brightness. The two
independent converters are capable of driving asymmetric
LED strings.
The dimming of the two LED strings can be controlled
independently via the respective CTRL pins. An internal
dimming system allows the dimming range to be extended
up to 1000:1 by feeding a PWM signal to the respective
PWM pins. The LT3486 operating frequency can be set with
an external resistor over a 200kHz to 2MHz range. A low
200mV feedback voltage (±3% accuracy) minimizes power
loss in the current setting resistor for better efficiency.
Additional features include output voltage limiting when
LEDs are disconnected and overtemperature protection.
The LT3486 is available in a space saving 16-pin DFN
(5mm
×
3mm
×
0.75mm) and 16-pin thermally enhanced
TSSOP packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Patent Pending.
APPLICATIO S
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Notebook PC Display
LED Camera Light for Cell Phones
Car Dashboard Lighting
Avionics Displays
TYPICAL APPLICATIO
Li-Ion Powered Driver for Camera Flash and LCD Backlighting
V
IN
3V TO 4.2V
10µF
2.2µF
LED1
AOT3218
DIMMING 1
OFF ON
SW1
OVP1
CTRL1
SHDN
PWM1
OFF ON
R
FB1
0.62Ω
0.1µF
FB1
V
C1
100k
R
T
63.4k
LT3486
L1
10µH
V
IN
L2
10µH
SW2
OVP2
CTRL2
REF
PWM2
FB2
V
C2
2.8k
4.7nF
R
FB2
8.06Ω
3486 TA01a
90
2.2µF
8 LEDs
EFFICIENCY (%)
MOVIE MODE
I
LED1
= 175mA
85
FLASH MODE
I
LED1
= 320mA
DIMMING 2
25mA
80
75
0.1µF
70
8 LEDS/25mA
3
3.2
3.4
3.6
V
IN
(V)
3.8
4
4.2
65
U
Efficiency vs V
IN
3486 TA01b
U
U
3486f
1
LT3486
ABSOLUTE
AXI U RATI GS
(Note 1)
Operating Temperature Range (Note 2) ...–40°C to 85°C
Storage Temperature Range
DFN ...................................................–65°C to 125°C
TSSOP ............................................... –65°C to 150°C
Maximum Junction Temperature .......................... 125°C
Lead Temperature (Soldering, 10sec, TSSOP) ...... 300°C
Input Voltage (V
IN
) ...................................................25V
⎯
S
⎯
H
⎯
D
⎯
N Voltage ..........................................................25V
SW1, SW2 Voltages .................................................40V
OVP1, OVP2 Voltages ...............................................40V
CTRL1, CTRL2 Voltages ...........................................10V
PWM1, PWM2 Voltages ...........................................10V
FB1, FB2 Voltages .....................................................10V
PACKAGE/ORDER I FOR ATIO
SW1
V
IN
OVP1
R
T
V
C1
FB1
CTRL1
PWM1
1
2
3
4
5
6
7
8
17
16 SW2
15 REF
14 OVP2
13 SHDN
12 V
C2
11 FB2
10 CTRL2
9
PWM2
ORDER PART
NUMBER
LT3486EDHC
DHC PART
MARKING
3486
DHC PACKAGE
16-LEAD (5mm
×
3mm) PLASTIC DFN
EXPOSED PAD (PIN 17) IS GND
MUST BE SOLDERED TO PCB
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 4°C/W
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
Maximum Operating Voltage
Feedback Voltage (FB1, FB2)
Offset between FB1 and FB2
Feedback Pin Bias Current (FB1, FB2)
Quiescent Current
Switching Frequency
Oscillator Frequency Range
Nominal R
T
Pin Voltage
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
= 3V, V
CTRL2
= 3V, V
PWM1
= 3V, V
PWM2
= 3V,
V
SHDN
= 3V, unless otherwise noted.
CONDITIONS
MIN
2.5
●
V
OS
= |FB1-FB2|
V
FB1
= V
FB2
= 0.2V (Note 3)
V
FB1
= V
FB2
= 1V
⎯
S
⎯
H
⎯
D
⎯
N = 0V, CTRL1 = CTRL2 = 0V
R
T
= 53.6k
(Note 4)
R
T
= 53.6k
2
U
U
W
W W
U
W
TOP VIEW
SW1 1
V
IN
2
OVP1 3
R
T
4
V
C1
5
FB1 6
CTRL1 7
PWM1 8
17
16 SW2
15 REF
14 OVP2
13 SHDN
12 V
C2
11 FB2
10 CTRL2
9 PWM2
ORDER PART
NUMBER
LT3486EFE
FE PART
MARKING
3486EFE
FE PACKAGE
16-LEAD PLASTIC TSSOP
EXPOSED PAD IS GND (PIN 17)
MUST BE SOLDERED TO PCB
T
JMAX
= 125°C,
θ
JA
= 38°C/W,
θ
JC
= 10°C/W
TYP
MAX
24
206
6
100
14
1
1.25
2000
UNITS
V
V
mV
mV
nA
mA
µA
MHz
kHz
V
194
0
10
200
3
45
9
0.1
1
0.54
0.75
200
3486f
LT3486
The
ELECTRICAL CHARACTERISTICS
25°C. V
●
denotes the specifications whichVapply over the full operating
= 3V, V
= 3V, V
= 3V,
= 3V, V
= 3V,
temperature range, otherwise specifications are at T =
A
IN
CTRL1
CTRL2
PWM1
PWM2
V
SHDN
= 3V, unless otherwise noted.
PARAMETER
Maximum Duty Cycle
CONDITIONS
R
T
= 53.6k
R
T
= 20.5k
R
T
= 309k
I
SW1
= I
SW2
= 0.75A
V
SW1
= V
SW2
= 10V
∆I = ±5µA
●
MIN
90
TYP
96
90
98
1.3
300
0.1
220
120
0.85
1.5
25
25
1
36
MAX
UNITS
%
%
%
A
mV
µA
µA/V
V
V
µA
µA
nA
V
mV
mV
V
µA
V
V
µA
V
V
µA
V
µA
Switch Current Limit (SW1, SW2)
Switch V
CESAT
Switch Leakage Current
Error Amplifier Transconductance
Error Amplifier Voltage Gain
V
C1
, V
C2
Switching Threshold
V
C1
, V
C2
Clamp Voltage
V
C1
, V
C2
Source Current
V
C1
, V
C2
Sink Current
V
C1
, V
C2
Pin Leakage Current
OVP1, OVP2 Overvoltage Threshold Voltage
CTRL1, CTRL2 Voltages to Turn Off LED1, 2 Currents
CTRL1, CTRL2 Voltages to Turn On LED1, 2 Currents
CTRL1, CTRL2 Voltages for Full LED1, 2 Currents
CTRL1, CTRL2 Pin Bias Current
PWM1, PWM2 Voltage High
PWM1, PWM2 Voltage Low
PWM1, PWM2 Pin Bias Current
SHDN Voltage High
SHDN Voltage Low
SHDN Pin Bias Current
REF Voltage
REF Source Current
1
5
V
FB1
= V
FB2
= 0V
V
FB1
= V
FB2
= 1V
V
C1
= V
C2
= 1V, V
PWM1
= V
PWM2
= 0V
34
●
10
38
75
V
CTRL1
= V
CTRL2
= 3V
●
●
●
150
1.8
20
0.9
30
40
0.4
1
0.4
V
PWM1
= V
PWM2
= 3V
1.6
V
SHDN
= 3V
I
REF
= 10µA
●
0.1
1.2
50
20
1.25
80
1.3
Note 1:
Absolute maximum ratings are those beyond which the life of a
device may be impaired.
Note 2:
The LT3486E is guaranteed to meet specified performance from
0°C to 70°C and is designed, characterized and expected to meet these
extended temperature limits, but is not tested at –40°C and 85°C.
Note 3:
Current flows out of the pin.
Note 4:
Guaranteed by design and test correlation, not production tested.
3486f
3
LT3486
TYPICAL PERFOR A CE CHARACTERISTICS
Switching Waveforms
V
SW2
50V/DIV
I
L2
500mA/DIV
V
SW1
10V/DIV
I
L1
1A/DIV
0.5µs/DIV
V
IN
= 3.6V
8 LEDs/25mA
2 LEDs/320mA
CIRCUIT OF FRONT PAGE APPLICATION
3486 G17
LED Current vs PWM Duty Cycle
Wide Dimming Range (1000:1)
100
V
IN
= 12V
8/8 LEDs
PWM FREQ = 100Hz
FEEDBACK VOLTAGE (mV)
250
10
I
LED
(mA)
FEEDBACK VOLTAGE (mV)
1
0.1
0.01
0.01
1
10
0.1
PWM DUTY CYCLE (%)
SHDN Pin Bias Current
(CTRL1 = CTRL2 = 3V)
140
VIN = 3.6V
SHDN PIN BIAS CURRENT (µA)
120
100
80
60
40
20
0
0
4
16
12
8
SHDN PIN VOLTAGE (V)
20
24
3486 G05
OUTPUT CLAMP VOLTAGE (V)
OUTPUT CLAMP VOLTAGE (V)
TA = 50°C
TA = 25°C
TA = 100°C
36
4
U W
3486 G01
T
A
= 25°C unless otherwise specified.
PWM Dimming Wavforms
I
LED
200mA/DIV
I
L
500mA/DIV
PWM
5V/DIV
V
IN
= 12V
0.2ms/DIV
8/8 LEDs
PWM FREQ = 1kHz
3486 G18
V
FB
vs V
CTRL
250
V
IN
= 3.6V
T
A
= 25°C
200
200
V
FB
vs V
CTRL
(Temperature Variation)
±
5mV
T
A
= 85°C
150
150
T
A
= –50°C
T
A
= 25°C
100
100
50
50
100
0
0
1
0.5
1.5
CONTROL VOLTAGE (V)
0
2
3486 G03
0
1
0.5
1.5
CONTROL VOLTAGE (V)
2
3486 G04
Open-Circuit Output Clamp
Voltage vs Temperature
37
37
V
IN
= 3.6V
R
T
= 63.4k
V
OUT2
V
OUT1
35
36
Open-Circuit Output Clamp
Voltage vs V
IN
V
IN
= 3.6V
R
T
= 63.4k
V
OUT1
35
V
OUT2
34
34
33
–50
33
–25
75
0
25
50
TEMPERATURE (°C)
100
125
2
4
6
8 10 12 14 16 18 20 22 24
V
IN
(V)
3486 G07
3486 G06
3486f
LT3486
TYPICAL PERFOR A CE CHARACTERISTICS
Input Current with Output 1 and
Output 2 Open Circuit
20
T
A
= 25°C
R
T
= 63.4k
1000
OSCILLATOR FREQUENCY (kHz)
INPUT CURRENT (mA)
15
R
T
(kΩ)
10
5
0
2
4
6
8 10 12 14 16 18 20 22 24
V
IN
(V)
3486 G08
Oscillator Frequency vs
Temperature
10000
OSCILLATOR FREQUENCY (kHz)
12
10
QUIESCENT CURRENT (mA)
R
T
= 22.1k
R
T
= 53.6k
8
6
4
2
0
–25
0
25
50
75
TEMPERATURE (°C)
100
125
PWM PIN CURRENT (µA)
1000
R
T
= 309k
100
–50
Switch Current Limit vs
Duty Cycle
1800
1700
CURRENT LIMIT (mA)
1600
1500
1400
1300
1200
20
30
40
REF VOLTAGE (V)
1.30
V
IN
= 3.6V
1.28
REF VOLTAGE (V)
50 60 70 80
DUTY CYCLE (%)
U W
90
T
A
= 25°C unless otherwise specified.
R
T
vs Oscillator Frequency
1100
Oscillator Frequency vs V
IN
R
T
= 53.6k
1050
100
1000
950
10
900
0
500
1000
1500
2000
OSCILLATOR FREQUENCY (kHz)
2500
3486 G09
2
4
6
8 10 12 14 16 18 20 22 24
V
IN
(V)
3486 G10
Quiescent Current vs V
IN
1.0
PWM Pin Input Bias Current
V
IN
= 3.6V
UVLO
0.5
PWM 1
0
PWM 2
– 0.5
SHDN = 3V
CTRL1 = CTRL2 = 3V
0
2
4
6
8 10 12 14 16 18 20 22 24
V
IN
(V)
3486 G12
–1.0
0
2
6
8
4
PWM PIN VOLTAGE (V)
10
3486 G13
3486 G11
REF Voltage vs Temperature
1.30
REF Voltage Load Regulation
1.25
1.20
T
A
= 85°C
1.15
1.10
1.05
1.00
T
A
= 25°C
T
A
= –50°C
V
IN
= 3.6V
1.26
1.24
1.22
0.95
1.20
–50
0.90
–25
50
25
0
75
TEMPERATURE (°C)
100
125
0
20 40 60 80 100 120 140 160 180 200
REF LOAD CURRENT (µA)
3468 G16
V
IN
= 3.6V
T
A
= 25°C
100
3486 G14
3486 G15
3486f
5
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