LINEAR TECHNOLOGY LT3486 Technical data
FEATURES
LT3486
Dual 1.3A White LED
Step-Up Converters with
Wide Dimming
U
DESCRIPTIO
■
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 2.5MHz
■
Wide Input Voltage Range: 2.5V to 24V
■
Low Shutdown Current: I
■
Overtemperature Protection
■
Available in (5mm × 3mm × 0.75mm) 16-Pin DFN
CC
< 1µA
and 16-Pin Thermally Enhanced TSSOP Packages
U
APPLICATIO S
■
Notebook PC Display
■
LED Camera Light for Cell Phones
■
Car Dashboard Lighting
■
Avionics Displays
The LT®3486 is a dual step-up DC/DC converter
specifi cally 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 identical 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 2.5MHz range. A low
200mV feedback voltage (±3% accuracy) minimizes power
loss in the current setting resistor for better effi ciency.
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.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
Li-Ion Powered Driver for Camera Flash and LCD Backlighting
V
IN
3V TO 4.2V
2.2µF
AOT3218
OFF ON
LED1
DIMMING 1
OFF ON
100k
R
FB1
0.62Ω
L1
10µHL210µH
SW1 SW2
OVP1
CTRL1
SHDN
PWM1
FB1
V
V
IN
LT3486
C1
0.1µF
RTGND
10µF
63.4k
U
CTRL2
PWM2
OVP2
REF
FB2
V
C2
2.8k
4.7nF
DIMMING 2
2.2µF
0.1µF
R
FB2
8.06Ω
3486 TA01a
8 LEDs
25mA
90
85
80
75
EFFICIENCY (%)
70
8 LEDS/25mA
65
3
Effi ciency vs V
MOVIE MODE
= 175mA
I
LED1
I
3.4 3.6 3.8
3.2
VIN (V)
FLASH MODE
= 320mA
LED1
IN
4 4.2
3486 TA01b
3486fa
1
LT3486
WW
W
ABSOLUTE AXI U RATI GS
U
(Note 1)
Input Voltage (VIN) ...................................................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
UUW
FOR ATIOPACKAGE/ORDER I
SW1
1
V
2
IN
OVP1
3
R
4
T
V
5
C1
FB1
6
CTRL1
7
PWM1
8
16-LEAD (5mm × 3mm) PLASTIC DFN
T
JMAX
DHC PACKAGE
EXPOSED PAD (PIN 17) IS GND
MUST BE SOLDERED TO PCB
= 125°C, θJA = 43°C/W, θJC = 4°C/W
16
SW2
15
REF
14
OVP2
13
17
SHDN
12
V
FB2
11
CTRL2
10
PWM2
9
C2
ORDER PART
NUMBER
LT3486EDHC
DHC PART
MARKING
3486
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
TOP VIEW
1
SW1
2
V
IN
3
OVP1
4
R
T
V
C1
FB1
CTRL1
PWM1
EXPOSED PAD IS GND (PIN 17)
MUST BE SOLDERED TO PCB
= 125°C, θJA = 38°C/W, θJC = 10°C/W
T
JMAX
17
5
6
7
8
FE PACKAGE
16-LEAD PLASTIC TSSOP
16
SW2
15
REF
14
OVP2
SHDN
13
V
12
C2
FB2
11
CTRL2
10
PWM2
9
ORDER PART
NUMBER
LT3486EFE
FE PART
MARKING
3486EFE
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 specifi ed with wider operating temperature ranges.
The
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifi cations are at T
= 3V, unless otherwise noted.
V
SHDN
= 25°C. VIN = 3V, V
A
●
denotes the specifi cations which apply over the full operating
CTRL1
= 3V, V
CTRL2
= 3V, V
PWM1
= 3V, V
PWM2
= 3V,
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Operating Voltage 2.5 V
Maximum Operating Voltage 24 V
●
Feedback Voltage (FB1, FB2)
194 200 206 mV
Offset between FB1 and FB2 VOS = |FB1-FB2| 0 3 6 mV
Feedback Pin Bias Current (FB1, FB2) V
Quiescent Current V
= V
FB1
FB1
⎯S⎯H⎯D⎯
= 0.2V (Note 3) 10 45 100 nA
FB2
= V
= 1V 9 14 mA
FB2
N = 0V, CTRL1 = CTRL2 = 0V 0.1 1 µA
Switching Frequency RT = 53.6k 0.75 1 1.25 MHz
R
= 20.5k
T
●
1.7 2.2 2.7 MHz
Oscillator Frequency Range (Typical Value) (Note 4) 200 2500 kHz
Nominal RT Pin Voltage RT = 53.6k 0.54 V
2
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LT3486
The
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifi cations are at T
= 3V, unless otherwise noted.
V
SHDN
= 25°C. VIN = 3V, V
A
●
denotes the specifi cations which apply over the full operating
CTRL1
= 3V, V
CTRL2
= 3V, V
PWM1
= 3V, V
PWM2
= 3V,
PARAMETER CONDITIONS MIN TYP MAX UNITS
Maximum Duty Cycle R
R
R
= 53.6k
T
= 20.5k 90 %
T
= 309k 98 %
T
●
90 96 %
Switch Current Limit (SW1, SW2) 1 1.3 A
Switch V
Switch Leakage Current V
I
CESAT
SW1
SW1
= I
= 0.75A 300 mV
SW2
= V
= 10V 0.1 5 µA
SW2
Error Amplifi er Transconductance ∆I = ±5µA 220 µA/V
Error Amplifi er Voltage Gain 120
VC1, VC2 Switching Threshold 0.85 V
VC1, VC2 Clamp Voltage 1.5 V
VC1, VC2 Source Current V
VC1, VC2 Sink Current V
VC1, VC2 Pin Leakage Current VC1 = VC2 = 1V, V
FB1
FB1
= V
= 0V 25 µA
FB2
= V
= 1V 25 µA
FB2
PWM1
= V
= 0V 1 10 nA
PWM2
OVP1, OVP2 Overvoltage Threshold Voltage 34 36 38 V
CTRL1, CTRL2 Voltages to Turn Off LED1, 2 Currents
●
75 mV
CTRL1, CTRL2 Voltages to Turn On LED1, 2 Currents 150 mV
CTRL1, CTRL2 Voltages for Full LED1, 2 Currents 1.8 V
CTRL1, CTRL2 Pin Bias Current V
PWM1, PWM2 Voltage High
PWM1, PWM2 Voltage Low
PWM1, PWM2 Pin Bias Current V
CTRL1
PWM1
= V
= V
= 3V
CTRL2
= 3V 0.1 1 µA
PWM2
●
20 30 40 µA
●
0.9 V
●
0.4 V
SHDN Voltage High 1.6 V
SHDN Voltage Low 0.4 V
SHDN Pin Bias Current V
REF Voltage I
REF Source Current
= 3V 20 µA
SHDN
= 10µA 1.2 1.25 1.3 V
REF
●
50 80 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 LT3486E is guaranteed to meet specifi ed 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 fl ows out of the pin.
Note 4: Guaranteed by design and test correlation, not production tested.
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LT3486
TYPICAL PERFOR
Switching Waveforms PWM Dimming Wavforms
UW
CE CHARACTERISTICSA
TA = 25°C unless otherwise specifi ed.
V
SW2
50V/DIV
I
L2
500mA/DIV
V
SW1
10V/DIV
I
L1
1A/DIV
VIN = 3.6V
8 LEDs/25mA
2 LEDs/320mA
CIRCUIT OF FRONT PAGE APPLICATION
LED Current vs PWM Duty Cycle
Wide Dimming Range (1000:1)
100
VIN = 12V
8/8 LEDs
PWM FREQ = 100Hz
10
(mA)
1
LED
I
0.1
0.01
0.01 1 10 100
0.1
PWM DUTY CYCLE (%)
0.5µs/DIV
3486 G01
3486 G17
vs V
V
FB
CTRL
250
VIN = 3.6V
= 25°C
T
A
200
150
100
FEEDBACK VOLTAGE (mV)
50
0
0
0.5
CONTROL VOLTAGE (V)
200mA/DIV
500mA/DIV
1
I
LED
PWM
5V/DIV
1.5
I
L
VIN = 12V
8/8 LEDs
PWM FREQ = 1kHz
2
3486 G03
0.2ms/DIV
VFB vs V
3486 G18
CTRL
(Temperature Variation)
250
200
TA = –50°C
150
100
FEEDBACK VOLTAGE (mV)
50
0
0
0.5
CONTROL VOLTAGE (V)
± 5mV
1
TA = 85°C
TA = 25°C
1.5
2
3486 G04
SHDN Pin Bias Current
(CTRL1 = CTRL2 = 3V)
140
VIN = 3.6V
120
100
80
60
40
SHDN PIN BIAS CURRENT (µA)
20
0
01220
48
SHDN PIN VOLTAGE (V)
TA = 50°C
TA = 25°C
TA = 100°C
16 24
4
3486 G05
Open-Circuit Output Clamp
Voltage vs Temperature
37
= 3.6V
V
IN
= 63.4k
R
T
36
35
34
OUTPUT CLAMP VOLTAGE (V)
33
–50
–25 0 25 50
TEMPERATURE (°C)
V
OUT1
V
OUT2
75 100 125
3486 G06
Open-Circuit Output Clamp
Voltage vs V
37
= 3.6V
V
IN
= 63.4k
R
T
36
35
34
OUTPUT CLAMP VOLTAGE (V)
33
4
2
IN
V
OUT1
6
12
8
10
V
IN
(V)
V
OUT2
18
14
16
22 24
20
3486 G07
3486fa
UW
0
TYPICAL PERFOR A CE CHARACTERISTICS
Input Current with Output 1 and
Output 2 Open Circuit
20
15
T
A
R
= 25°C
= 63.4k
T
R
vs Oscillator Frequency Oscillator Frequency vs V
T
1000
LT3486
TA = 25°C unless otherwise specifi ed.
1100
1050
R
= 53.6k
T
IN
10
INPUT CURRENT (mA)
5
0
4
6
2
12
8
10
VIN (V)
Oscillator Frequency vs
Temperature
10000
= 22.1k
R
T
= 53.6k
R
1000
OSCILLATOR FREQUENCY (kHz)
T
= 309k
R
T
100
–50
–25 0 25 50 75 100
TEMPERATURE (°C)
100
(kΩ)
T
R
10
0
14
16
18
22 24
20
3486 G08
QUIESCENT CURRENT (mA)
125
3486 G11
500 2500200015001000
OSCILLATOR FREQUENCY (kHz)
Quiescent Current vs V
12
10
8
6
4
2
0
0
UVLO
10 14 18 22 24
81216
6
4
V
IN
3486 G09
IN
SHDN = 3V
CTRL1 = CTRL2 = 3V
202
(V)
3486 G12
1000
950
OSCILLATOR FREQUENCY (kHz)
900
6
4
2
12
10
8
VIN (V)
PWM Pin Input Bias Current
1.0
V
= 3.6V
IN
0.5
PWM 1
PWM 2
4
PWM PIN CURRENT (µA)
–0.5
–1.0
0
2
0
PWM PIN VOLTAGE (V)
18
14
16
6
22 24
20
3486 G10
8
1
Switch Current Limit vs
Duty Cycle
1800
V
= 3.6V
IN
1700
1600
1500
1400
CURRENT LIMIT (mA)
1300
1200
20
40 60
30 50
DUTY CYCLE (%)
REF Voltage vs Temperature
1.30
V
= 3.6V
IN
1.28
1.26
1.24
REF VOLTAGE (V)
1.22
1.20
80
70
90
3486 G14
100
–50 –25
0
TEMPERATURE (°C)
50
25
75
100
125
3486 G15
REF Voltage Load Regulation
1.30
1.25
1.20
1.15
1.10
1.05
REF VOLTAGE (V)
1.00
0.95
V
= 3.6V
IN
T
= 25°C
A
0.90
0
40 80 120 20014020 60 100 180
REF LOAD CURRENT (µA)
TA = 25°C
TA = –50°C
TA = 85°C
160
3468 G16
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5
LT3486
PI FU CTIO S
UUU
SW1, SW2 (Pins 1, 16): The SW Pins are the Collectors
of the Internal Power Transistors. Connect the inductors
and Schottky diodes to these pins. Minimize trace area
at these pins to minimize EMI.
(Pin 2): Input Supply Pin. Must be locally bypassed
V
IN
with an X5R or X7R type ceramic capacitor.
OVP1, OVP2 (Pins 3, 14): Output Overvoltage Protection
Pins. Connect these pins to the output capacitors. The
on-chip voltage detectors monitor the voltages at these
pins and limit it to 36V (typ) by turning off the respective
switcher and pulling its V
(Pin 4): Timing Resistor to Program the Switching
R
T
Frequency. The switching frequency can be programmed
from 200kHz to 2.5MHz.
, VC2 (Pins 5, 12): The VC Pins are the Outputs of the
V
C1
Internal Error Amplifi er. The voltages at these pins control
the peak switch currents. Connect a resistor and capacitor
compensation network from these pin to ground.
FB1, FB2 (Pins 6, 11): The LT3486 regulates the voltage
at each feedback pin to 200mV. Connect the cathode of
the lowest LED in the string and the feedback resistor
) to the respective feedback pin. The LED current in
(R
FB
each string can be programmed by:
≅ 200mV/RFB, when V
I
LED
I
LED
≅ V
/(5RFB), when V
CTRL
pin low.
C
CTRL
CTRL
> 1.8V
< 1V
CTRL1, CTRL2 (Pins 7, 10): The CTRL pins are used to
provide dimming and shutdown control for the individual
switching converters. Connecting these to ground shuts
down the respective converter. As the voltages on these
pins is ramped from 0V to 1.8V, the LED current in each
converter ramps from 0 to I
age above 1.8V does not affect the LED current.
PWM1, PWM2 (Pins 8, 9): The PWM control pins can
be used to extend the dimming range for the individual
switching converter. The LED current in each string can
be controlled down to µA levels by feeding a PWM signal
to these pins. When the PWM pin voltage is taken below
0.4V, the respective converter is turned off and its V
is disconnected from the internal circuitry. Taking it higher
than 0.9V resumes normal operation. Connect these pins
to 0.9V supply or higher, if not in use.
SHDN (Pin 13): Shutdown Pin for the Device. Connect it
to 1.6V or higher to enable device; 0.4V or less to disable
device.
REF (Pin 15): The internal bandgap reference (1.25V) is
available at this pin. Bypass with a 0.1µF X5R or X7R ceramic capacitor. Draw no more than 50µA from this pin.
Exposed Pad (Pin 17): Ground. The exposed pad of the
package provides an electrical contact to ground and good
thermal connection to the printed circuit board (PCB).
Solder the exposed pad to the PCB system ground.
= (200mV/RFB). Any volt-
LED
pin
C
6
3486fa
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