LINER LTC3201

LT3486
Dual 1.3A White LED
Step-Up Converters with
Wide Dimming
DESCRIPTION
FEATURES
Wide (1000:1) PWM Dimming Range with No
ColorShift
n Independent Dimming and Shutdown Control of the
LED Drivers
n Drives Up to 16 White LEDs at 25mA (8 per Driver)
from a Single Li-Ion Cell
n Drives Up to 16 White LEDs at 100mA (8 per Driver)
from 12V Supply
n ±3% LED Current Programming Accuracy
n Open LED Protection: 36V Clamp Voltage
n Fixed Frequency Operation: Up to 2.5MHz
n Wide Input Voltage Range: 2.5V to 24V
n Low Shutdown Current: ICC < 1µA
n Overtemperature Protection
n Available in (5mm × 3mm × 0.75mm) 16-Pin DFN
and 16-Pin Thermally Enhanced TSSOP Packages
n
APPLICATIONS
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 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 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.
Notebook PC Display
n LED Camera Light for Cell Phones
n Car Dashboard Lighting
n Avionics Displays
n
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property
of their respective owners.
TYPICAL APPLICATION
Li-Ion Powered Driver for Camera Flash and LCD Backlighting
VIN
3V TO 4.2V
Efficiency vs VIN
10µF
SW1
LED1
AOT3218
L2
10µH
SW2
VIN
OFF ON
CTRL1
CTRL2
SHDN
REF
LT3486
RFB1
0.62Ω
GND RT
75
VC2
63.4k
0.1µF
FLASH MODE
ILED1 = 320mA
80
70
FB2
FB1
VC1
0.1µF
PWM2
PWM1
OFF ON
DIMMING 2
25mA
MOVIE MODE
ILED1 = 175mA
85
8 LEDs
OVP2
OVP1
DIMMING 1
100k
2.2µF
EFFICIENCY (%)
L1
10µH
2.2µF
90
2.8k
4.7nF
RFB2
8.06Ω
3486 TA01a
65
8 LEDS/25mA
3
3.2
3.4
3.6
VIN (V)
3.8
4
4.2
3486 TA01b
3486fe
1
LT3486
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Voltage (VIN).....................................................25V
SHDN Voltage............................................................25V
SW1, SW2 Voltages ..................................................40V
OVP1, OVP2 Voltages................................................40V
CTRL1, CTRL2 Voltages.............................................10V
PWM1, PWM2 Voltages.............................................10V
FB1, FB2 Voltages......................................................10V
Operating Junction Temperature Range (Note 2)
LT3486E................................................–40°C to 85°C
LT3486I...............................................–40°C to 125°C
Storage Temperature Range
DFN ....................................................–65°C to 125°C
TSSOP................................................–65°C to 150°C
Maximum Junction Temperature........................... 125°C
Lead Temperature (Soldering, 10 sec, TSSOP)...... 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
SW1
1
16 SW2
VIN
2
15 REF
OVP1
3
14 OVP2
RT
4
VC1
5
12 VC2
FB1
6
11 FB2
CTRL1
7
10 CTRL2
PWM1
8
9
17
SW1 1
16 SW2
VIN 2
15 REF
OVP1 3
13 SHDN
RT 4
PWM2
14 OVP2
17
13 SHDN
VC1 5
12 VC2
FB1 6
11 FB2
CTRL1 7
10 CTRL2
PWM1 8
9 PWM2
DHC PACKAGE
16-LEAD (5mm × 3mm) PLASTIC DFN
EXPOSED PAD (PIN 17) IS GND
MUST BE SOLDERED TO PCB
FE PACKAGE
16-LEAD PLASTIC TSSOP
EXPOSED PAD IS GND (PIN 17)
MUST BE SOLDERED TO PCB
TJMAX = 125°C, θJA = 43°C/W, θJC = 4°C/W
TJMAX = 125°C, θJA = 38°C/W, θJC = 10°C/W
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3486EDHC#PBF
LT3486EDHC#TRPBF
3486
16-Lead (5mm × 3mm) Plastic DFN
–40°C to 85°C
LT3486EFE#PBF
LT3486EFE#TRPBF
3486EFE
16-Lead Plastic TSSOP
–40°C to 85°C
LT3486IFE#PBF
LT3486IFE#TRPBF
3486IFE
16-Lead Plastic TSSOP
–40°C to 125°C
LEAD BASED FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3486EDHC
LT3486EDHC#TR
3486
16-Lead (5mm × 3mm) Plastic DFN
–40°C to 85°C
LT3486EFE
LT3486EFE#TR
3486EFE
16-Lead Plastic TSSOP
–40°C to 85°C
LT3486IFE
LT3486IFE#TR
3486IFE
16-Lead Plastic TSSOP
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
3486fe
2
LT3486
ELECTRICAL
CHARACTERISTICS
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3V, VCTRL1 = 3V, VCTRL2 = 3V, VPWM1 = 3V, VPWM2 = 3V,
VSHDN = 3V, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
Minimum Operating Voltage
TYP
MAX
UNITS
2.5
V
Maximum Operating Voltage
Feedback Voltage (FB1, FB2)
l
194
200
24
V
206
mV
Offset between FB1 and FB2
VOS = |FB1-FB2|
0
3
6
mV
Feedback Pin Bias Current (FB1, FB2)
VFB1 = VFB2 = 0.2V (Note 3)
10
45
100
nA
Quiescent Current
VFB1 = VFB2 = 1V
SHDN = 0V, CTRL1 = CTRL2 = 0V
9
0.1
14
1
mA
µA
Switching Frequency
RT = 53.6k
RT = 20.5k
1
2.2
1.25
2.7
MHz
MHz
2500
kHz
Oscillator Frequency Range (Typical Value)
(Note 4)
Nominal RT Pin Voltage
RT = 53.6k
Maximum Duty Cycle
RT = 53.6k
RT = 20.5k
RT = 309k
l
0.75
1.7
200
l
Switch Current Limit (SW1, SW2)
0.54
V
90
96
90
98
%
%
%
1
1.3
Switch VCESAT
ISW1 = ISW2 = 0.75A
Switch Leakage Current
VSW1 = VSW2 = 10V
0.1
Error Amplifier Transconductance
∆I = ±5µA
220
1.6
300
A
mV
5
µA
µA/V
Error Amplifier Voltage Gain
120
VC1, VC2 Switching Threshold
0.85
V
VC1, VC2 Clamp Voltage
1.5
V
VC1, VC2 Source Current
VFB1 = VFB2 = 0V
25
µA
VC1, VC2 Sink Current
VFB1 = VFB2 = 1V
25
µA
VC1, VC2 Pin Leakage Current
VC1 = VC2 = 1V, VPWM1 = VPWM2 = 0V
1
10
35
36
V
75
mV
OVP1, OVP2 Overvoltage Threshold Voltage
34
CTRL1, CTRL2 Voltages to Turn Off LED1, 2 Currents
l
nA
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
l
20
PWM1, PWM2 Voltage High
l
0.9
PWM1, PWM2 Voltage Low
l
PWM1, PWM2 Pin Bias Current
VCTRL1 = VCTRL2 = 3V
VPWM1 = VPWM2 = 3V
30
µA
V
0.1
SHDN Voltage High
40
0.4
V
1
µA
1.6
V
SHDN Voltage Low
0.4
SHDN Pin Bias Current
VSHDN = 3V
REF Voltage
IREF = 10µA
REF Source Current
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 specified performance
from 0°C to 85°C and is designed, characterized and expected to meet
20
l
1.2
1.25
50
80
V
µA
1.3
V
µA
these extended temperature limits, but is not tested at –40°C and 85°C.
The LT3486I specifications are guaranteed over the –40°C to 125°C
temperature range.
Note 3: Current flows out of the pin.
Note 4: Guaranteed by design and test correlation, not production tested.
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LT3486
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Waveforms
PWM Dimming Wavforms
ILED
200mA/DIV
VSW2
50V/DIV
IL2
500mA/DIV
IL
500mA/DIV
VSW1
10V/DIV
IL1
1A/DIV
PWM
5V/DIV
LED Current vs PWM Duty Cycle
Wide Dimming Range (1000:1)
250
1
0.1
1
10
0.1
PWM DUTY CYCLE (%)
± 5mV
200
150
100
50
0
100
250
VIN = 3.6V
TA = 25°C
FEEDBACK VOLTAGE (mV)
FEEDBACK VOLTAGE (mV)
1
0.5
1.5
CONTROL VOLTAGE (V)
0
3486 G01
37
VIN = 3.6V
TA = 50°C
100
TA = 25°C
80
TA = 100°C
OUTPUT CLAMP VOLTAGE (V)
SHDN PIN BIAS CURRENT (µA)
100
50
60
40
1
0.5
1.5
CONTROL VOLTAGE (V)
0
Open-Circuit Output Clamp
Voltage vs VIN
37
VIN = 3.6V
RT = 63.4k
36
2
3486 G04
Open-Circuit Output Clamp
Voltage vs Temperature
120
TA = 25°C
TA = –50°C
150
3486 G03
SHDN Pin Bias Current
(CTRL1 = CTRL2 = 3V)
140
TA = 85°C
200
0
2
OUTPUT CLAMP VOLTAGE (V)
ILED (mA)
10
0.01
0.01
VFB vs VCTRL
(Temperature Variation)
VFB vs VCTRL
VIN = 12V
8/8 LEDs
PWM FREQ = 100Hz
3486 G18
VIN = 12V
0.2ms/DIV
8/8 LEDs
PWM FREQ = 1kHz
3486 G17
0.5µs/DIV
VIN = 3.6V
8 LEDs/25mA
2 LEDs/320mA
CIRCUIT OF FRONT PAGE APPLICATION
100
TA = 25°C unless otherwise specified.
VOUT2
VOUT1
35
34
VIN = 3.6V
RT = 63.4k
36
VOUT1
VOUT2
35
34
20
0
0
4
16
12
8
SHDN PIN VOLTAGE (V)
20
24
3486 G05
33
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
3486 G06
33
2
4
6
8 10 12 14 16 18 20 22 24
VIN (V)
3486 G07
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LT3486
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C
RT = 63.4k
1000
RT vs Oscillator Frequency
Oscillator Frequency vs VIN
1100
15
RT (kΩ)
INPUT CURRENT (mA)
20
OSCILLATOR FREQUENCY (kHz)
Input Current with Output 1 and
Output 2 Open Circuit
TA = 25°C unless otherwise specified.
10
100
5
0
4
2
6
10
8 10 12 14 16 18 20 22 24
VIN (V)
0
500
1000
1500
2000
OSCILLATOR FREQUENCY (kHz)
Oscillator Frequency
vs Temperature
12
RT = 309k
100
–50
–25
100
6
4
VIN = 3.6V
SHDN = 3V
CTRL1 = CTRL2 = 3V
2
0
4
6
PWM 1
PWM 2
0
–0.5
0
30
40
50 60 70 80
DUTY CYCLE (%)
90
100
3486 G14
6
8
4
PWM PIN VOLTAGE (V)
10
3486 G13
REF Voltage Load Regulation
VIN = 3.6V
TA = –50°C
1.25
REF VOLTAGE (V)
1.20
1.26
1.24
TA = 85°C
1.15
TA = 25°C
1.10
1.05
1.00
0.95
20
2
1.30
1.22
900
VIN = 3.6V
0.5
–1.0
8 10 12 14 16 18 20 22 24
VIN (V)
1.28
REF VOLTAGE (V)
CURRENT LIMIT (mA)
1300
800
3486 G10
REF Voltage vs Temperature
1.30
1000
8 10 12 14 16 18 20 22 24
VIN (V)
3486 G12
Switch Current Limit
vs Duty Cycle
1100
6
UVLO
8
0
125
1200
4
PWM Pin Input Bias Current
3486 G11
1400
2
1.0
2
0
25
50
75
TEMPERATURE (°C)
950
900
2500
PWM PIN CURRENT (µA)
1000
1000
Quiescent Current vs VIN
10
QUIESCENT CURRENT (mA)
OSCILLATOR FREQUENCY (kHz)
10000
RT = 53.6k
1050
3486 G09
3486 G08
RT = 22.1k
RT = 53.6k
1.20
–50
–25
50
0
75
25
TEMPERATURE (°C)
100
125
0.90
VIN = 3.6V
TA = 25°C
0
20 40 60 80 100 120 140 160 180 200
REF LOAD CURRENT (µA)
3468 G16
3486 G15
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LT3486
PIN FUNCTIONS
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.
VIN (Pin 2): Input Supply Pin. Must be locally bypassed
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 VC pin low.
RT (Pin 4): Timing Resistor to Program the Switching
Frequency. The switching frequency can be programmed
from 200kHz to 2.5MHz.
VC1, VC2 (Pins 5, 12): The VC Pins are the Outputs of the
Internal Error Amplifier. 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 (RFB)
to the respective feedback pin. The LED current in each
string can be programmed by:
ILED @ 200mV/RFB, when VCTRL > 1.8V
ILED @ VCTRL/(5RFB), when VCTRL < 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 ILED = (200mV/RFB). Any voltage 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 VC pin
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.
3486fe
6
LT3486
BLOCK DIAGRAM
SW1
1
RT
VIN
4
2
SW2
16
14 OVP2
OVP1 3
OVERVOLT
DETECTION
OV1
EN1
CONVERTER1
OVERVOLT
DETECTION
CONVERTER2
OSC
Q1
OSC
A3
–
+
+
–
VC1 5
0.2V
+
–
+
EN1
8
REF 1.25V
0.2V
+
–
+
–
EA
12 VC2
7
PWM1 CTRL1
OV2
EN2
START-UP
CONTROL
20k
A2
A1
SHDN
80k
PWM
COMP
+
+
EA
A1
CONVERTER1
CONTROL
OSC
RSNS2
–
A2
OV1
EN2
+
A3
RSNS1
PWM
COMP
PWM
LOGIC
Q2
RAMP
GEN
+
OV2
DRIVER
OSC
PWM
LOGIC
20k
6
13
15
11
FB1
SHDN
REF
FB2
80k
CONVERTER 2
CONTROL
10
9
CTRL2 PWM2
17
3486 F01
EXPOSED
PAD
Figure 1. LT3486 Block Diagram
3486fe
7
LT3486
OPERATION
Main Control Loop
The LT3486 uses a constant frequency, current mode
control scheme to provide excellent line and load regulation.
It incorporates two identical, but fully independent PWM
converters. Operation can be best understood by referring
to the block diagram in Figure 1. The oscillator, start-up
bias and the bandgap reference are shared between the two
converters. The control circuitry, power switch, dimming
control etc., are all identical for both converters.
At power-up, the output capacitors of both converters are
charged up to VIN (input supply voltage) via their respective
inductor and the Schottky diode. If the SHDN pin is taken
above 1.6V, the bandgap reference, start-up bias and the
oscillator are turned on. Grounding the SHDN pin shuts
down the part.
The CTRL1 and CTRL2 pins perform independent dimming
and shutdown control for the two converters. Taking
the CTRL pins high, enables the respective converters.
Connecting these pins to ground, shuts down each
converter by pulling their respective VC pin low.
Working of the main control loop can be understood by
following the operation of converter 1. At the start of
each oscillator cycle, the power switch Q1 is turned on.
A voltage proportional to the switch current is added to
a stabilizing ramp and the resulting sum is fed into the
positive terminal of the PWM comparator A2. When this
voltage exceeds the level at the negative input of A2, the
PWM logic turns off the power switch. The level at the
negative input of A2 is set by the error amplifier A1, and
is simply an amplified version of the difference between
the feedback voltage and the 200mV reference voltage. In
this manner, the error amplifier A1 regulates the feedback
voltage to 200mV reference voltage. The output of the
error amplifier A1 sets the correct peak current level in
inductor L1 to keep the output in regulation. The CTRL1
pin voltage is used to adjust the reference voltage.
The PWM1, 2 control pins are used to extend the dimming
range for the individual converter. The LED current in each
string can be controlled down to µA levels by feeding
a PWM signal to these pins. Refer to the Applications
Information section for more detail.
If only one of the converters is turned on, the other converter
will stay off and its output will remain charged up to VIN
(input supply voltage).
Minimum Output Current
The LT3486 can drive an 8-LED string at 4mA LED current
without pulse skipping. As current is further reduced, the
device may begin skipping pulses. This will result in some
low frequency ripple, although the LED current remains
regulated on an average basis down to zero. The photo
in Figure 2 shows circuit operation with 8 white LEDs
at 4mA current driven from 3.6V supply. Peak inductor
current is less than 200mA and the regulator operates in
discontinuous mode implying that the inductor current
reached zero during the discharge phase. After the inductor
current reaches zero, the switch pin exhibits ringing due to
the LC tank circuit formed by the inductor in combination
with switch and diode capacitance. This ringing is not
harmful; far less spectral energy is contained in the ringing
than in the switch transitions. The ringing can be damped
by application of a 300Ω resistor across the inductors,
although this will degrade efficiency.
VOUT2
10mV/DIV
VSW2
20V/DIV
IL2
200mA/DIV
VIN = 3.6V
0.5µs/DIV
ILED2 = 4mA (8 LEDs)
CIRCUIT OF FRONT PAGE APPLICATION
3486 F02
Figure 2. Switching Waveforms
Open-Circuit Protection
The LT3486 has internal open-circuit protection for both
the converters. Connect the overvoltage protection pins
(OVP1, OVP2) to the output of the respective converter.
When the LEDs are disconnected from the circuit or fail
open, the on-chip voltage detectors monitor the voltages at
the OVP1 and OVP2 pins and limits these voltages to 36V
(typ) by turning off the respective switcher. The converter
will then switch at a very low frequency to minimize the
input current. Output voltage and input current during
3486fe
8
LT3486
OPERATION
output open circuit are shown in the Typical Performance
Characteristics graphs.
Figure 3a shows the transient response of switcher 1 with
the LEDs disconnected from the output. When the LED1
string is disconnected from the output, the voltage at the
feedback pin (FB1) drops to 0V. As a result, the error
amplifier charges up the VC node to the clamp voltage
level of 1.5V (typ). The converter starts switching at peak
current limit and ramps up the output voltage. When the
output voltage reaches the OVP clamp voltage level of 36V
(typ), the LT3486 shuts off the converter by pulling the VC
node to ground. The converter then regulates the output
voltage at 36V (typ) by switching at a very low frequency.
In the event one of the converters has an output opencircuit, its output voltage will be clamped at 36V (typ).
However, the other converter will continue functioning
properly. The photo in Figure 3b shows circuit operation
with converter 1 output open-circuit and converter 2
driving eight LEDs at 25mA. Converter 1 starts switching
at a very low frequency, reducing its input current.
IL1
1A/DIV
Soft-Start
The LT3486 has a separate internal soft-start circuitry for
each converter. Soft-start helps to limit the inrush current
during start-up. Soft-start is achieved by clamping the
output of the error amplifier during the soft-start period.
This limits the peak inductor current and ramps up the
output voltage in a controlled manner.
The converter enters into soft-start mode whenever
the respective CTRL pin is pulled from low to high.
Figure 4 shows the start-up waveforms with converter 2 driving eight LEDs at 25mA. The filtered input
current, as shown in Figure 4, is well controlled. The
soft-start circuit is more effective when driving a smaller
number of LEDs.
Undervoltage Lockout
The LT3486 has an undervoltage lockout circuit which
shuts down both the converters when the input voltage
drops below 2.1V (typ). This prevents the converter
to operate in an erratic mode when powered from low
supply voltages.
Overtemperature Protection
VOUT1
20V/DIV
VC1
2V/DIV
VIN = 3.6V
CIRCUIT OF
FRONT PAGE
APPLICATION
100µs/DIV
3486 F03a
LED1 DISCONNECTED
AT THIS INSTANT
Figure 3a. Transient Response of Switcher 1 with LED1
Disconnected from the Output
The maximum allowable junction temperature for
LT3486 is 125°C. In normal operation, the IC’s junction
temperature should be kept below 125°C at an ambient
temperature of 85°C or less. If the junction temperature exceeds 150°C, the internal thermal shutdown
circuitry kicks in and turns off both the converters.
The converters will remain off until the die temperature
falls below 150°C.
IIN
200mA/DIV
IL1
1A/DIV
VOUT2
10V/DIV
VOUT1
1V/DIV
AC COUPLED
VFB2
200mV/DIV
IL2
500mA/DIV
CTRL2
5V/DIV
VIN = 3.6V
2ms/DIV
CIRCUIT OF FRONT PAGE APPLICATION
LED1 DISCONNECTED
3486 F03b
Figure 3b. Switching Waveforms with Output 1 Open Circuit
VIN = 3.6V
0.5ms/DIV
8 LEDs, 25mA
CIRCUIT OF FRONT PAGE APPLICATION
Figure 4. Start-Up Waveforms
3486 F04
3486fe
9
LT3486
APPLICATIONS INFORMATION
Duty Cycle
Operating Frequency Selection
The duty cycle for a step-up converter is given by:
The choice of operating frequency is determined by several factors. There is a trade-off between efficiency and
component size. Higher switching frequency allows the
use of smaller inductors albeit at the cost of increased
switching losses and decreased efficiency.
D=
VOUT + VD – VIN
VOUT + VD – VCESAT
where:
VOUT = Output voltage
VD = Schottky forward voltage drop
VCESAT = Saturation voltage of the switch
VIN = Input battery voltage
The maximum duty cycle achievable for LT3486 is 96%
(typ) when running at 1MHz switching frequency. It increases to 98% (typ) when run at 200kHz and drops to
90% (typ) at 2MHz. Always ensure that the converter is
not duty-cycle limited when powering the LEDs at a given
switching frequency.
Another consideration is the maximum duty cycle achievable. In certain applications the converter needs to operate
at the maximum duty cycle in order to light up the maximum
number of LEDs. The LT3486 has a fixed oscillator off-time
and a variable on-time. As a result, the maximum duty
cycle increases as the switching frequency is decreased.
The circuit of Figure 6a is operated with different values
of timing resistor (RT). RT is chosen so as to run the converters at 800kHz (RT = 63.4k), 1.25MHz (RT = 39.1k) and
2MHz (RT = 21.5k). The CTRL pins are used to provide
dimming for the respective LED strings. The efficiency
comparison for different RT values is shown in Figure 6b.
Setting the Switching Frequency
5V
The LT3486 uses a constant frequency architecture that
can be programmed over a 200kHz to 2.5MHz range
with a single external timing resistor from the RT pin to
ground. The nominal voltage on the RT pin is 0.54V, and the
current that flows into the timing resistor is used to charge
and discharge an internal oscillator capacitor. A graph for
selecting the value of RT for a given operating frequency
is shown in the Figure 5.
D1
D2
L1
10µH
COUT1
2.2µF
SW1
25mA
1000
L2
10µH
COUT2
2.2µF
VIN
SW2
OVP1
OVP2
CTRL1
CTRL2
OFF ON
SHDN
REF
PWM1
1.25V
PWM2
CREF
0.1µF
FB2
FB1
GND
2.8k
8.06Ω
25mA
REF
LT3486
VC1
RT (kΩ)
CIN
10µF
4.7nF
RT
VC2
RT
2.8k
4.7nF
CIN: 10V, X7R
COUT1, COUT2: 35V, X5R
D1, D2: ZETEX ZHCS400
L1, L2: TOKO D53LC TYPE A
100
8.06Ω
3486 F06a
Figure 6a. 5V to 8/8 White LEDs
10
0
500
1000
1500
2000
OSCILLATOR FREQUENCY (kHz)
2500
3486 G09
Figure 5. Timing Resistor (RT) Value
3486fe
10
LT3486
APPLICATIONS INFORMATION
90
Several inductors that work well with the LT3486 are listed
in Table 1. Consult each manufacturer for more detailed
information and for their entire selection of related parts.
VIN = 5V
8/8 LEDs
80
EFFICIENCY (%)
RT = 63.4k
70
Table 1. Recommended Inductors
RT = 21.5k
MAX
DCR
(Ω)
CURRENT
RATING
(A)
LQH55DN150M
LQH55DN220M
15
22
0.150
0.190
1.40
1.20
Murata
(814) 237-1431
www.murata.com
A915AY-4R7M
A915AY-6R8M
A915AY-100M
A918CY-100M
A918CY-150M
4.7
6.8
10
10
15
0.045
0.068
0.090
0.098
0.149
2.49
2.01
1.77
1.22
0.94
Toko
(847) 297-0070
www.toko.com
CDRH4D28-100
CDRH5D18-150
10
15
0.048
0.145
1.30
0.97
Sumida
(847) 956-0666
www.sumida.com
PART
50
40
30
L
(µH)
RT = 39.1k
60
0
5
10
15
LED CURRENT (mA)
25
20
3486 F06b
Figure 6b. Efficiency Comparison for Different RT Resistors
Inductor Selection
The choice of the inductor will depend on the selection of
switching frequency of LT3486. The switching frequency
can be programmed from 200kHz to 2.5MHz. Higher
switching frequency allows the use of smaller inductors
albeit at the cost of increased switching losses.
The inductor current ripple (∆IL), neglecting the drop
across the Schottky diode and the switch, is given by:
∆I = VIN(MIN) • (VOUT (MAX) – VIN(MIN) )
L
VOUT (MAX) • f • L
where:
L = Inductor
Capacitor Selection
The small size of ceramic capacitors make them ideal
for LT3486 applications. Use only X5R and X7R types
because they retain their capacitance over wider voltage
and temperature ranges than other types such as Y5V
or Z5U. A 4.7µF or larger input capacitor is sufficient for
most applications. Always use a capacitor with sufficient
voltage rating.
Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information
on their entire selection of ceramic parts.
Table 2. Ceramic Capacitor Manufacturers
Taiyo Yuden
(408) 573-4150
www.t-yuden.com
VIN(MIN) = Minimum input voltage
AVX
VOUT(MAX) = Maximum output voltage
(803) 448-9411
www.avxcorp.com
Murata
(714) 852-2001
www.murata.com
f = Operating frequency
The ∆IL is typically set to 20% to 40% of the maximum
inductor current.
The inductor should have a saturation current rating greater
than the peak inductor current required for the application.
Also, ensure that the inductor has a low DCR (copper wire
resistance) to minimize I2R power losses. Recommended
inductor values range from 4.7µH to 22µH.
VENDOR
Diode Selection
Schottky diodes with their low forward voltage drop and
fast reverse recovery, are the ideal choices for LT3486
applications. The diode conducts current only during the
switch off time. The peak reverse voltage that the diode
must withstand is equal to the regulator output voltage.
3486fe
11
LT3486
APPLICATIONS INFORMATION
The average forward current in normal operation is equal
to the output current, and the peak current is equal to the
peak inductor current. A Schottky diode rated at 1A is sufficient for most LT3486 applications. Some recommended
Schottky diodes are listed in Table 3.
200mV
ILED1
200mV
RFB2 =
ILED2
Table 3. Recommended Schottky Diodes
Table 4. RFB Value Selection
PART NUMBER
RFB1 =
VR (V)
IAVG (A)
MANUFACTURER
ILED (mA)
RFB (Ω)
MBR0530
MBRM120E
30
20
0.5
1
On Semiconductor
www.onsemi.com
5
40.2
ZLLS400
ZLLS1000
ZHCS400
ZHCS1000
40
40
40
40
0.4
1
0.4
1
Zetex
www.zetex.com
10
20.0
15
13.3
20
10.0
25
8.06
When the LT3486 is set up for PWM dimming operation,
choose a Schottky diode with low reverse leakage current.
During PWM dimming operation, the output capacitor is
required to hold up the charge in the PWM “off” period.
A low reverse leakage Schottky helps in that mode of operation. The Zetex ZLLS400 and ZLLS1000 are available
in a small surface mount package and are a good fit for
this application.
MOSFET Selection
The power MOSFET used in LT3486 applications with wide
dimming range requirements should be chosen based on
the maximum drain-source voltage. The maximum drain
current ID(MAX) and gate-to-source voltages should also
be considered when choosing the FET.
Choose a MOSFET with maximum VDS (drain source) voltage greater than the output clamp voltage i.e., 36V (typ).
Fairchild Semiconductor’s FDN5630 (60V, 1.7A N‑channel
FET) is a good fit for most LT3486 applications. For dimming low current LEDs (~25mA), Fairchild 2N7002 is a
good alternative.
Programming LED Current
The current in each LED string can be set independently
by the choice of resistors RFB1 and RFB2 respectively
(see front page application). The feedback reference is
200mV. In order to have accurate LED current, precision
resistors are preferred (1% is recommended).
Most low power white LEDs are driven at maximum currents of 15mA to 25mA. The LT3486 can be used to power
high power LEDs as well. Refer to the Typical Applications
for more detail.
Dimming Control
The dimming of the two LED strings can be controlled
independently by modulating the respective CTRL and
PWM pins. There are two ways to control the intensity
of the LEDs.
Adjusting the LED Current Value
Controlling the current flowing through the LEDs controls
the intensity of the LEDs.This is the easiest way to control
the intensity of the LEDs. The LED forward current can be
controlled by modulating the DC voltage at the respective
CRTL pin. The PWM pins are not in use when appying
this scheme. They must be connected to a 0.9V supply or
higher. The DC voltage at the CTRL pin can be modulated
in two ways.
(a) Using a DC Voltage Source
For some applications, the preferred method of brightness
control is a variable DC voltage fed to the CTRL pins. The
CTRL1, CTRL2 pin voltage can be modulated to set the
dimming of the respective LED string. As the voltage on
the CTRL1, CTRL2 pin increases from 0V to 1.8V, the LED
current increases from 0 to ILED. As the CTRL1, CTRL2
pin voltage increases beyond 1.8V, it has no effect on the
LED current.
3486fe
12
LT3486
APPLICATIONS INFORMATION
The LED current can be set by:
Pulse-Width Modulation (PWM)
ILED ≈ (200mV/RFB), when VCTRL > 1.8V
Adjusting the forward current flowing in the LEDs changes
the intensity of the LEDs, as explained in the previous section. However, a change in forward current also changes the
color of the LEDs. The chromaticity of the LEDs changes
with the change in forward current. Many applications
cannot tolerate any shift in the color of the LEDs. Controlling the intensity of the LEDs via applying a PWM signal
allows dimming of the LEDs without changing the color.
ILED ≈ (VCTRL/5 • RFB), when VCTRL < 1V
Feedback voltage variation versus control voltage is given
in the Typical Performance Characteristics graphs.
(b) Using a Filtered PWM Signal
A variable duty cycle PWM can be used to control the brightness of the LED string. The PWM signal is filtered (Figure
7) by an RC network and fed to the CTRL1, CTRL2 pins.
Dimming the LEDs via a PWM signal essentially involves
turning the LEDs on and off at the PWM frequency. The
human eye has a limit of 60 frames per second. By increasing the PWM frequency to say, 80Hz, the eye can
be deceived into believing that the pulsed light source is
continously on. Additionally by modulating the duty cycle
(amount of “on-time”), the intensity of the LEDs can be
controlled. The color of the LEDs remains unchanged in
this scheme since the LED current value is either zero or
a constant value.
The corner frequency of R1, C1 should be much lower
than the frequency of the PWM signal. R1 needs to be
much smaller than the internal impedance in the CTRL
pins, which is 100kΩ.
LT3486
R1
10k
PWM
10kHz TYP
CTRL1,2
C1
1µF
Figure 8(a) shows a 12V to 8/8 white LED driver. The PWM
dimming control method requires an external NMOS tied
to the cathode of the lowest LED in the string, as shown in
3486 F07
Figure 7. Dimming Control Using a Filtered PWM Signal
12V (TYP)
9V TO 15V
L1
10µH
COUT1
2.2µF
100mA
L2
10µH
5V
D1
D2
C1 1µF
SW1
LUXEON
LEDs
LXCL-PWF1
CIN
10µF
VIN
SW2
OVP1
OVP2
VIN
CTRL1
CTRL2
OFF ON
SHDN
PWM2
RT
VC1
100k
2.2nF
100mA
21.5k
RFB1 COUT1, COUT2: 35V, X5R OR X7R
2Ω CIN: 25V, X5R OR X7R
C1: 10V, X5R OR X7R
CREF: 6.3V, X5R OR X7R
3.65k
2.2nF
D1, D2: ZETEX ZLLS1000
L1, L2: TOKO D53LC (TYPE A)
Q1, Q2: FAIRCHILD FDN5630
ILED
200mA/DIV
IL
500mA/DIV
PWM
5V/DIV
VC2
22pF
3.65k
Q1
CREF
0.1µF
FB2
FB1
PWM
FREQ
1kHz
LUXEON
LEDs
LXCL-PWF1
VIN
REF
LT3486
PWM1
DIMMING
INPUT 1
COUT2
2.2µF
Q2
RFB2
2Ω
DIMMING
INPUT 2
PWM
FREQ?
1kHz
100k
VIN = 12V
0.2ms/DIV
8/8 LEDs
PWM FREQ = 1kHz
3486 G18
Figure 8b. PWM Dimming Waveforms
3486 TA10a
Figure 8a. 12V to 8/8 White LEDs
3486fe
13
LT3486
APPLICATIONS INFORMATION
the figure. A PWM logic input is applied to the gate of the
NMOS and the PWM pin of the LT3486. When the PWM
input is taken high, the LEDs are connected to the RFB
resistor and a current ILED = 200mV/RFB flows through
the LEDs. When the PWM input is taken low, the LEDs are
disconnected and turn off. The low PWM input applied to
the LT3486 ensures that the respective converter turns
off and its VC pin goes high impedance. This ensures that
the capacitor connected to the VC pin retains its voltage
which in turn allows the LEDs to turn on faster, as shown
in Figure 8(b). The CTRL pin is not used to modulate the
LED current in the scheme. It can be connected to a supply voltage greater than 1.8V.
The dimming control pins (PWM1, PWM2) can be used
to extend the dimming range for the individual switching
converters. The LED current can be controlled down to
µA levels by feeding a PWM signal with frequencies in the
range of 80Hz to 50kHz. The LED current can be controlled
by PWM frequencies above 50kHz but the controllable
current decreases with increasing frequency. Pulling the
PWM pins below 0.4V disables the respective switcher.
Taking it higher than 0.9V resumes normal operation.
Connect these pins to 0.9V or higher if not in use.
Figure 9 shows the LED current variation vs PWM duty
cycle. The LED current is controlled by applying a PWM of
frequency 100Hz, 1kHz and 25kHz to the circuit of Figure  8a.
As seen in the curves, the LED string is able to get a wide
(1000:1) dimming range with PWM frequency of 100Hz.
The dimming range decreases as PWM frequency goes up.
Board Layout Consideration
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To prevent electromagnetic interference (EMI) problems,
proper layout of high frequency switching paths is essential.
Minimize the length and area of all traces connected to the
switching node pins (SW1 and SW2). Keep the feedback
pins (FB1 and FB2) away from the switching nodes.
The DFN and FE packages both have an exposed paddle
that must be connected to the system ground. The
ground connection for the feedback resistors should
be tied directly to the ground plane and not shared with
any other component, except the RT resistor, ensuring a
clean, noise-free connection. Recommended component
placement for the DFN package is shown in the Figure 10.
VIAs TO VIN PLANE
VOUT1
VOUT2
OVP1
100
REF
RT
OVP2
SHDN
LED CURRENT (mA)
10
VC1
VIN
1
SW1
1
16
2
15
3
14
4
FB1
0.1
0.01
0.01
PWM FREQ = 100Hz
PWM FREQ = 1kHz
PWM FREQ = 25kHz
1
10
0.1
PWM DUTY CYCLE (%)
100
3486 F09
Figure 9. LED Current Variation vs PWM Duty Cycle
LED1
CTRL1
17
SW2
VC2
VIN
13
5
12
6
11
7
10
8
9
CTRL2
LED2
VIN
PWM1
VIAs TO VIN PLANE
FB2
PWM2
3486 F10
VIAs TO GROUND PLANE
Figure 10. Recommended Layout for LT3486
3486fe
14
LT3486
TYPICAL APPLICATIONS
Li-Ion Cell Powered Driver for Camera Flash and LCD Backlighting
VIN
3V TO 5V
CIN
10µF
D1
D2
L1
10µH
COUT1
2.2µF
LED1
AOT3218
SW1
320mA
DIMMING 1
OFF ON
L2
10µH
SW2
VIN
OVP1
OVP2
CTRL1
CTRL2
SHDN
LT3486
OFF ON
RT
VC1
Q1
REF
2.8k
4.7nF
0.1µF
RFB2
8.06Ω
3486 TA02a
CIN: 6.3V, X5R OR X7R DIELECTRIC
COUT1, COUT2: 35V, X5R OR X7R
D1: ZETEX ZHCS1000
D2: ZETEX ZHCS400
L1, L2: TOKO D53LC (TYPE A)
Q1: FAIRCHILD FDN5630
Efficiency vs VIN
90
MOVIE MODE
ILED1 = 175mA
85
EFFICIENCY (%)
100k
CREF
0.1µF
VC2
63.4k
RFB1
0.62Ω
25mA
FB2
FB1
0V
DIMMING 2
PWM2
PWM1
5V
COUT2
2.2µF
FLASH MODE
ILED1 = 320mA
80
75
70
65
8 LEDS/25mA
3
3.2
3.4
3.6
VIN (V)
3.8
4
4.2
3486 TA01b
3486fe
15
LT3486
TYPICAL APPLICATIONS
1 Li-Ion Cell to 8/8 White LEDs
3V TO 5V
CIN
10µF
D1
D2
L1
10µH
COUT1
2.2µF
SW1
8 LEDs
25mA
L2
10µH
VIN
OVP2
VIN
CTRL1
CTRL2
OFF ON
SHDN
LT3486
2.8k
100k
4.7nF
REF
CREF
0.1µF
25mA
VC2
2.8k
63.4k
COUT1, COUT2: 35V, X5R OR X7R
CIN: 10V, X5R OR X7R
8.06Ω
VIN
FB2
RT
VC1
Q1
8 LEDs
PWM2
FB1
PWM1
100Hz
SW2
OVP1
PWM1
5V
COUT2
2.2µF
4.7nF
PWM2
100Hz
Q2
D1, D2: ZETEX ZLLS400
L1, L2: TOKO D53LC (TYPE A)
Q1, Q2: FAIRCHILD 2N7002
8.06Ω
100k
3486 TA05A
Wide (250:1) Dimming Range
(LED Current 0.1mA to 25mA)
LED Current and Efficiency vs PWM Duty Cycle
80
EFFICIENCY (%)
25
EFFICIENCY
70
20
65
15
LED CURRENT
60
10
10
1
0.10
5
55
50
VIN = 3.6V
8/8 LEDs
PWM FREQ = 100Hz
30
LED CURRENT (mA)
75
100
35
VIN = 3.6V
8/8 LEDs
LED CURRENT (mA)
85
0
20
40
60
0
100
80
0.01
0.1
PWM DUTY CYCLE (%)
1
10
DUTY CYCLE (%)
100
3486 TA05d
3486 TA05b
PWM Dimming Waveforms
LED CURRENT
20mA/DIV
IL
200mA/DIV
PWM
5V/DIV
VIN = 3.6V
CTRL1 = 3.6V
8 LEDs/25mA
PWM FREQ = 100Hz
2ms/DIV
3486 TA05c
3486fe
16
LT3486
TYPICAL APPLICATIONS
5V to 16/16 White LEDs
5V
D5
C3
1µF
CIN
1µF
D3
16 LEDs
L1
15µH
C1
0.1µF
L2
15µH
SW2
VIN
OVP1
OVP2
VIN
CTRL1
CTRL2
OFF ON
SHDN
REF
LT3486
100k
CREF
0.1µF
63.4k
4.7nF
8.06Ω
CIN: 6.3V, X5R OR X7R
COUT1, COUT2: 35V, X5R OR X7R
C1-C4: 50V, X5R OR X7R
CREF: 6.3V, X5R OR X7R
VC2
22pF
4.02k
4.7nF
35
VIN = 5V
16/16 LEDs
80
EFFICIENCY (%)
20
70
15
65
LED CURRENT
60
10
5
55
50
0
20
40
60
80
LED CURRENT (mA)
25
EFFICIENCY
100k
D1, D2: ZETEX ZLLS400
D3-D6: PHILIPS BAV99W
L1, L2: TOKO D53LC (TYPE A)
Q1, Q2: FAIRCHILD 2N7002
3486 TA08a
PWM Dimming Waveforms
ILED
50mA/DIV
30
75
PWM FREQ
200Hz
Q2
8.06Ω
LED Current and Efficiency vs PWM Duty Cycle
85
25mA
FB2
RT
VC1
Q1
COUT2
2.2µF
VIN
PWM2
FB1
4.02k
16 LEDs
C2
0.1µF
D2
SW1
PWM1
PWM FREQ
200Hz
C4
1µF
D4
D1
COUT1
2.2µF
25mA
D6
IL
500mA/DIV
PWM
5V/DIV
L = 15µH
PWM FREQ = 200Hz
1ms/DIV
3486 TA08c
0
100
PWM DUTY CYCLE (%)
3486 TA08b
3486fe
17
LT3486
PACKAGE DESCRIPTION
DHC Package
16-Lead Plastic DFN (5mm × 3mm)
(Reference LTC DWG # 05-08-1706)
5.00 ±0.10
(2 SIDES)
R = 0.20
TYP
0.65 ±0.05
3.50 ±0.05
1.65 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
PACKAGE
OUTLINE
2.20 ±0.05
R = 0.115
TYP
9
0.40 ± 0.10
16
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
PIN 1
NOTCH
0.75 ±0.05
0.200 REF
0.25 ± 0.05
0.50 BSC
4.40 ±0.05
(2 SIDES)
0.00 – 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WJED-1) IN JEDEC
PACKAGE OUTLINE MO-229
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
8
1
0.25 ± 0.05
0.50 BSC
(DHC16) DFN 1103
4.40 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
FE Package
16-Lead Plastic TSSOP (4.4mm)
Package
(Reference LTCFE
DWG
# 05-08-1663 Rev I)
16-Lead Plastic TSSOP (4.4mm)
(Reference
LTC DWG
05-08-1663BC
Rev I)
Exposed
Pad #Variation
Exposed Pad Variation BC
4.90 – 5.10*
(.193 – .201)
3.58
(.141)
16 1514 13 12 11
6.60 ±0.10
4.50 ±0.10
0.48
(.019)
REF
3.58
(.141)
2.94
(.116)
10 9
DETAIL B
6.40
2.94
(.252)
(.116)
BSC
SEE NOTE 4
0.45 ±0.05
1.05 ±0.10
0.51
(.020)
REF
DETAIL B IS THE PART OF
THE LEAD FRAME FEATURE
FOR REFERENCE ONLY
NO MEASUREMENT PURPOSE
0.65 BSC
1 2 3 4 5 6 7 8
RECOMMENDED SOLDER PAD LAYOUT
4.30 – 4.50*
(.169 – .177)
0.09 – 0.20
(.0035 – .0079)
0.50 – 0.75
(.020 – .030)
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
MILLIMETERS
2. DIMENSIONS ARE IN
(INCHES)
3. DRAWING NOT TO SCALE
0.25
REF
1.10
(.0433)
MAX
0° – 8°
0.65
(.0256)
BSC
0.195 – 0.30
(.0077 – .0118)
TYP
0.05 – 0.15
(.002 – .006)
FE16 (BC) TSSOP REV I 1210
4. RECOMMENDED MINIMUM PCB METAL SIZE
FOR EXPOSED PAD ATTACHMENT
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
3486fe
18
LT3486
REVISION HISTORY
(Revision history begins at Rev D)
REV
DATE
DESCRIPTION
D
03/10
Corrected the Part Number in Description Section and Order Information
PAGE NUMBER
E
01/11
1, 2
Updated Typical Value for Switching Frequency Parameter in Electrical Characteristics
3
Updated FE package drawing
18
3486fe
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
19
LT3486
TYPICAL APPLICATION
12V to 8/8 White LEDs
12V (TYP)
9V TO 15V
L1
10µH
COUT1
2.2µF
CIN
10µF
L2
10µH
LED Current and Efficiency
vs PWM Duty Cycle
5V
D1
COUT2
2.2µF
D2
C1 1µF
90
120
EFFICIENCY
100mA
SW2
VIN
OVP1
OVP2
VIN
CTRL1
CTRL2
OFF ON
SHDN
REF
LT3486
RT
VC1
PWM
FREQ
1kHz
100k
2.2nF
100mA
22pF
21.5k
RFB1 COUT1, COUT2: 35V, X5R OR X7R
2Ω CIN: 25V, X5R OR X7R
C1: 10V, X5R OR X7R
CREF: 6.3V, X5R OR X7R
DIMMING
INPUT 2
PWM
FREQ?
1kHz
100k
3.65k
2.2nF
80
Q2
D1, D2: ZETEX ZLLS1000
L1, L2: TOKO D53LC (TYPE A)
Q1, Q2: FAIRCHILD FDN5630
RFB2
2Ω
80
LED CURRENT
75
60
70
40
65
VC2
3.65k
Q1
CREF
0.1µF
FB2
FB1
DIMMING
INPUT 1
VIN
PWM2
PWM1
LUXEON
LEDs
LXCL-PWF1
100
60
VIN = 12V
8/8 LEDs
0
20
LED CURRENT (mA)
SW1
LUXEON
LEDs
LXCL-PWF1
EFFICIENCY (%)
85
20
0
100
40
60
80
PWM DUTY CYCLE (%)
3486 TA10b
3486 TA10a
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1618
Constant Current, Constant Voltage 1.24MHz, High Efficiency
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Up to 16 White LEDs, VIN: 1.6V to 18V, VOUT(MAX) = 34V,
IQ = 1.8mA, ISD < 1µA, MS Package
LT1932
Constant Current, 1.2MHz, High Efficiency White LED Boost
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Up to 8 White LEDs, VIN: 1V to 10V, VOUT(MAX) = 34V,
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LT1937
Constant Current, 1.2MHz, High Efficiency White LED Boost
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IQ = 1.9mA, ISD < 1µA, ThinSOT, SC70 Packages
LTC3200
Low Noise, 2MHz, Regulated Charge Pump White LED Driver
MS Package
Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 8mA, ISD < 1µA,
LTC3200-5
Low Noise, 2MHz, Regulated Charge Pump White LED Driver
ThinSOT Package
Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 8mA, ISD < 1µA,
LTC3201
Low Noise, 1.7MHz, Regulated Charge Pump White LED Driver
MS Package
Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 6.5mA, ISD < 1µA,
LTC3202
Low Noise, 1.5MHz, Regulated Charge Pump White LED Driver
MS Package
Up to 8 White LEDs, VIN: 2.7V to 4.5V, IQ = 5mA, ISD < 1µA,
LTC3205
High Efficiency, Multidisplay LED Controller
Up to 4 (Main), 2 (Sub) and RGB, VIN: 2.8V to 4.5V,
IQ = 50µA, ISD < 1µA, QFN-24 Package
LT3465/LT3465A
Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED
Boost Regulator with Integrated Schottky Diode
Up to Six White LEDs, VIN: 2.7V to 16V, VOUT(MAX) = 34V,
IQ = 1.9mA, ISD < 1µA, ThinSOT Package
LT3466
Dual Full Function White LED Boost Regulator with Integrated
Schottky Diode
Drives Up to 20 LEDs, VIN: 2.7V to 24V, VOUT(MAX) = 40V,
IQ = 5mA, ISD < 16µA, DFN Package
3486fe
20 Linear Technology Corporation
LT 0111 REV E • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
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 LINEAR TECHNOLOGY CORPORATION 2008