LT3466-1 Datasheet by Analog Devices Inc.

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LT3466-1 TECHNOLOGY L7H L7. a, J}, a, a, 4/ 4 i: 11??? __ L7LJL1WW
1
LT3466-1
34661f
White LED Driver and Boost
Converter in 3mm × 3mm
DFN Package
Figure 1. Li-Ion Powered Driver for 6 White LEDs and OLED Display
Drives Up to 10 White LEDs from a 3.6V Supply
Two Independent Step-Up DC/DC Converters
Independent Dimming and Shutdown Control
of the Outputs
±1.5% Output Voltage Accuracy (Boost Converter)
±4% LED Current Programming Accuracy
Internal Schottky Diodes
Internal Soft-Start Eliminates Inrush Current
Output Overvoltage Protection (39.5V Max V
OUT
)
Fixed Frequency Operation Up to 2MHz
83% Efficiency Driving 8 White LEDs at 15mA
from a 3.6V Supply
Wide Input Voltage Range: 2.7V to 24V
Tiny (3mm × 3mm) 10-Lead DFN Package
White LED and OLED Displays
Digital Cameras, Sub-Notebook PCs
PDAs, Handheld Computers
TFT - LCD Bias Supply
Automotive
LT
®
3466-1 is a dual switching regulator that combines a
white LED driver and a boost converter in a low profile,
small footprint (3mm × 3mm × 0.75mm) DFN package.
The LED driver can be configured to drive up to 10 White
LEDs in series and the boost converter can be used for
generating the LCD bias voltages or driving a secondary
OLED display. 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 LT3466-1 provides independent dimming and shut-
down control of the two converters. The operating fre-
quency can be set with an external resistor over a 200kHz
to 2MHz range. The white LED driver features a low 200mV
reference, thereby minimizing power loss in the current
setting resistor for better efficiency. The boost converter
achieves ±1.5% output voltage accuracy by the use of a
precision 0.8V reference. Protection features include out-
put overvoltage protection and internal soft-start. Wide
input supply range allows operation from 2.7V to 24V.
3V TO 5V
16V
30mA
33µH1µF
1µF1µF
6 LEDs
33µH
SHUTDOWN
AND DIMMING
CONTROL 2
SHUTDOWN
AND DIMMING
CONTROL 1
1024.9k
475k
34661 F01a
63.4k
CTRL1 GND CTRL2
RT
SW1 SW2VIN
LT3466-1
VOUT1
FB1
VOUT2
FB2
Conversion Efficiency
OUTPUT CURRENT (mA)
0
EFFICIENCY (%)
70
75
302520
34661 F01b
60
50
65
55
51015
90
85
80
BOOST CONVERTER
LED DRIVER
V
IN
= 3.6V
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
TYPICAL APPLICATIO
U
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
2
LT3466-1
34661f
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Operating Voltage 2.7 V
Maximum Operating Voltage 22 V
FB1 Voltage 192 200 208 mV
FB2 Voltage 788 800 812 mV
FB1 Pin Bias Current V
FB1
= 0.2V (Note 3) 10 50 nA
FB2 Pin Bias Current V
FB2
= 0.8V (Note 3) 10 50 nA
Quiescent Current V
FB1
= V
FB2
= 1V 5 7.5 mA
CTRL1 = CTRL2 = 0V 16 25 µA
Switching Frequency R
T
= 48.7k 0.75 1 1.25 MHz
Oscillator Frequency Range (Note 4) 200 2000 kHz
Nominal R
T
Pin Voltage R
T
= 48.7k 0.54 V
Maximum Duty Cycle R
T
= 48.7k 90 96 %
R
T
= 20.5k 92 %
R
T
= 267k 99 %
Converter 1 Current Limit 310 400 mA
Converter 2 Current Limit 310 400 mA
Converter 1 V
CESAT
I
SW1
= 300mA 320 mV
Converter 2 V
CESAT
I
SW2
= 300mA 320 mV
Switch 1 Leakage Current V
SW1
= 10V 0.01 5 µA
Switch 2 Leakage Current V
SW2
= 10V 0.01 5 µA
CTRL1 Voltage for Full LED Current 1.8 V
CTRL2 Voltage for Full Feedback Voltage 1V
CTRL1 or CTRL2 Voltage to Turn On the IC 150 mV
CTRL1 and CTRL2 Voltages to Shut Down Chip 70 mV
CTRL1 Pin Bias Current V
CTRL1
= 1V 6 9 12.5 µA
CTRL2 Pin Bias Current V
CTRL2
= 1V (Note 3) 10 120 nA
(Note 1)
Input Voltage (V
IN
) ................................................... 24V
SW1, SW2 Voltages ................................................ 44V
V
OUT1
, V
OUT2
Voltages ............................................. 44V
CTRL1, CTRL2 Voltages ........................................... 24V
FB1, FB2 Voltages ...................................................... 2V
Operating Temperature Range (Note 2) ... 40°C to 85°C
Storage Temperature Range .................. –65°C to 125°C
Junction Temperature .......................................... 125°C
ABSOLUTE AXI U RATI GS
WWWU
PACKAGE/ORDER I FOR ATIO
UU
W
T
JMAX
= 125°C, θ
JA
= 43°C/W, θ
JC
= 3°C/W
EXPOSED PAD (PIN 11) IS GND
MUST BE SOLDERED TO PCB
ORDER PART
NUMBER
DD PART MARKING
LBRX
LT3466EDD-1
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. VIN = 3V, VCTRL1 = 3V, VCTRL2 = 3V, unless otherwise specified.
TOP VIEW
11
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
10
9
6
7
8
4
5
3
2
1FB1
CTRL1
R
T
CTRL2
FB2
V
OUT1
SW1
V
IN
SW2
V
OUT2
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/
L7LJL1WW
3
LT3466-1
34661f
PARAMETER CONDITIONS MIN TYP MAX UNITS
V
OUT1
Overvoltage Threshold 39.5 V
V
OUT2
Overvoltage Threshold 39.5 V
Schottky 1 Forward Drop I
SCHOTTKY1
= 300mA 0.85 V
Schottky 2 Forward Drop I
SCHOTTKY2
= 300mA 0.85 V
Schottky 1 Reverse Leakage V
OUT1
= 20V 5 µA
Schottky 2 Reverse Leakage V
OUT2
= 20V 5 µA
Soft-Start Time (Switcher 1) 600 µs
Soft-Start Time (Switcher 2) 600 µs
ELECTRICAL CHARACTERISTICS
The denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. VIN = 3V, VCTRL1 = 3V, VCTRL2 = 3V, unless otherwise specified.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC3466-1E 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.
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Switching Waveforms
(LED Driver)
Switching Waveforms
(Boost Converter)
VFB1 vs VCTRL1
V
OUT1
100mV/DIV
(AC-COUPLED)
V
SW1
20V/DIV
I
L1
100mA/DIV
V
IN
= 3.6V 0.5µs/DIV 34661 G01
6 LEDs AT 20mA
CIRCUIT OF FIGURE 1
V
OUT2
100mV/DIV
(AC-COUPLED)
V
SW2
20V/DIV
I
L2
100mA/DIV
V
IN
= 3.6V 0.5µs/DIV 34661 G02
V
OUT2
= 16V/30mA
CIRCUIT OF FIGURE 1
V
CTRL1
(V)
0
V
FB1
(mV)
100
150
2
34661 G03
50
00.5 11.5
250
200
V
IN
= 3.6V
6 LEDs
VFB2 vs VCTRL2
V
CTRL2
(V)
0
V
FB2
(mV)
400
600
2
34661 G16
200
300
500
100
00.5 11.5
900
800
700
V
IN
= 3.6V
V
OUT2
= 16V
TA = 25°C unless otherwise specified
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4
LT3466-1
34661f
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Quiescent Current
(CTRL1 = CTRL2 = 3V)Switch Current Limit vs Duty Cycle
Shutdown Current
(CTRL1 = CTRL2 = 0V)
Open-Circuit Output Clamp
Voltage
RT vs Oscillator Frequency
DUTY CYCLE (%)
0
CURRENT LIMIT (mA)
300
400
80
34661 G05
200
100
250
350
450
500
150
50
020 40 60 100
T
A
= –50°C
T
A
= 85°C
T
A
= 25°C
Open-Circuit Output Clamp
Voltage
Input Current with Output 1 and
Output 2 Open Circuit
OSCILLATOR FREQUENCY (kHz)
RT (k)
1000
34661 G10
10
100
600 180014001000
200
Oscillator Frequency vs VIN
TA = 25°C unless otherwise specified
V
IN
(V)
0
7
6UVLO
5
4
3
2
1
012 20
34661 G04
48 16 24
QUIESCENT CURRENT (mA)
V
IN
(V)
2
0
SHUTDOWN CURRENT (µA)
10
30
40
50
70
412 16
34661 G06
20
60
10 20 2422
6814 18
T
A
= –50°C
T
A
= 25°C
T
A
= 100°C
V
IN
(V)
38.00
OUTPUT CLAMP VOLTAGE (V)
39.00
40.00
41.00
38.50
39.50
40.50
6 101418
34661 G07
2442 8 12 16 20 22
V
OUT2
V
OUT1
R
T
= 63.4k
TEMPERATURE (°C)
50 –25
37
OUTPUT CLAMP VOLTAGE (V)
39
42
050 75
34661 G08
38
41
40
25 100 125
VOUT2
VOUT1
RT = 63.4k
V
IN
(V)
2
INPUT CURRENT (mA)
12
16
20
18
34661 G09
8
4
0468
10 12 14 16 20 2422
R
T
= 63.4k
V
IN
(V)
800
OSCILLATOR FREQUENCY (kHz)
900
1000
1100
8121620
34661 G11
24462 10141822
R
T
= 48.7k
L7LJL1WW
5
LT3466-1
34661f
TEMPERATURE (°C)
–50
0.780
FB2 VOLTAGE (V)
0.785
0.790
0.795
0.800
0.810
–25 02550
34661 G17
75 125100
0.805
VIN = 3V
VOUT2 = 16V/30mA
SCHOTTKY FORWARD DROP (mV)
0
SCHOTTKY FORWARD CURRENT (mA)
150
200
250
600 1000
34661 G14
100
50
0200 400 800
300
350
400
TEMPERATURE (°C)
–50
0
SCHOTTKY LEAKAGE CURRENT (µA)
2
4
6
8
–25 0 25 50
34661 G015
75 100
V
R
= 36V
V
R
= 20V
Schottky Forward Voltage Drop Schottky Leakage Current
CTRL Voltages to Shut Down
the IC
TEMPERATURE (°C)
–50
0
CTRL VOLTAGE (mV)
25
50
75
100
150
–25 02550
34661 G13
75 100
125
CTRL1
CTRL2
VIN = 3.6V
Oscillator Frequency
vs Temperature
TEMPERATURE (°C)
–50
800
OSCILLATOR FREQUENCY (kHz)
900
1000
1100
–25 0 25 50
34661 G12
75 100
VIN = 3.6V
RT = 48.7k
FB2 Pin Voltage vs Temperature FB2 Pin Load Regulation
LOAD CURRENT (mA)
0
–1.00
V
OUT2
/V
OUT2
(%)
–0.80
–0.60
–0.40
–0.20
V
IN
= 3V
V
OUT2
= 16V
0
10 20
34661 G18
30
TYPICAL PERFOR A CE CHARACTERISTICS
UW
TA = 25°C unless otherwise specified
L7Hl1§ég
6
LT3466-1
34661f
UU
U
PI FU CTIO S
V
OUT1
(Pin 1): Output of Converter 1. This pin is connected
to the cathode of the internal Schottky diode. Connect an
output capacitor from this pin to ground.
SW1 (Pin 2): Switch Pin for Converter 1. Connect the
inductor at this pin.
V
IN
(Pin 3): Input Supply Pin. Must be locally bypassed
with a 1µF, X5R or X7R type ceramic capacitor.
SW2 (Pin 4): Switch Pin for Converter 2. Connect the
inductor at this pin.
V
OUT2
(Pin 5): Output of Converter 2. This pin is connected
to the cathode of the internal Schottky diode. Connect an
output capacitor from this pin to ground.
FB2 (Pin 6): Feedback Pin for Converter 2. The nominal
voltage at this pin is 800mV. Connect the resistor divider
to this pin. The feedback voltage can be programmed
as:
V
FB2
V
CTRL2
, when V
CTRL2
< 0.8V
V
FB2
= 0.8V, when V
CTRL2
> 1V
CTRL2 (Pin 7): Dimming and Shutdown Pin for Con-
verter 2. As the pin voltage is ramped from 0V to 1V, the
FB2 pin voltage tracks the CTRL2 voltage and ramps up to
0.8V. Any voltage above 1V does not affect the feedback
voltage. Do not leave the pin floating. It must be connected
to ground to disable converter 2.
R
T
(Pin 8): Timing Resistor to Program the Switching
Frequency. The switching frequency can be programmed
from 200KHz to 2MHz.
CTRL1 (Pin 9): Dimming and Shutdown Pin for Con-
verter 1. Connect this pin to ground to disable the con-
verter. As the pin voltage is ramped from 0V to 1.8V, the
LED current ramps from 0 to I
LED1
(= 200mV/R
FB1
). Any
voltage above 1.8V does not affect the LED current.
FB1 (Pin 10): Feedback Pin for Converter 1. The nominal
voltage at this pin is 200mV. Connect cathode of the lowest
LED and the feedback resistor at this pin. The LED current
can be programmed by :
I
LED1
(V
CTRL1
/5 • R
FB1
), when V
CTRL1
< 1V
I
LED1
(200mV/R
FB1
), when V
CTRL1
> 1.8V
Exposed Pad (Pin 11): The Exposed Pad must be soldered
to the PCB system ground.
L7LJL1WW LJ 4H1 \‘RS \ x: Tk \: ‘fw -—>|—>I—>I—H—>I—M—>I—H— r L LJ -’\Nv|||
7
LT3466-1
34661f
BLOCK DIAGRA
W
+
+
Σ
+
+
EAEA
PWM
COMP
R
SNS1
R
SNS2
OSC
C3
V
OUT2
DRIVER
L2
SW2
0.8V
EXPOSED
PAD
20k
FB1
CONVERTER 1 CONVERTER 2
0.2V
80k
SHDN
CTRL2
711
CTRL1
9
+
+
+
START-UP
CONTROL
REF 1.25V
PWM
LOGIC
5
4
V
IN
V
IN
R
T
3
R
T
8
FB2
R2
R1
R
FB1
34661 F02
6
+
Σ
OSC
SW1
C1
L1
DRIVER
1
2
10
V
OUT1
C2
PWM
LOGIC
OSC
RAMP
GEN
OSC
OVERVOLT
DETECTION
OVERVOLT
DETECTION
Q1 Q2
A2
A1 A1
A2
A3
PWM
COMP
A3
Figure 2. Block Diagram
L7Hl1§ég
8
LT3466-1
34661f
OPERATIO
U
Main Control Loop
The LT3466-1 uses a constant frequency, current mode
control scheme to provide excellent line and load regula-
tion. It incorporates two similar, but fully independent PWM
converters. Operation can be best understood by referring
to the Block Diagram in Figure 2. The oscillator, start-up
bias and the bandgap reference are shared between the
two converters. The control circuitry, power switch, Schot-
tky diode etc., are similar for both converters.
At power-up, the output voltages V
OUT1
and V
OUT2
are
charged up to V
IN
(input supply voltage) via their respec-
tive inductor and the internal Schottky diode. If either
CTRL1 and CTRL2 or both are pulled high, the bandgap
reference, start-up bias and the oscillator are turned on.
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 voltage at the
FB1 pin to 200mV. 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 feedback voltage.
The working of converter 2 is similar to converter 1 with
the exception that the feedback 2 reference voltage is
800mV. The error amplifier A1 in converter 2 regulates the
voltage at the FB2 pin to 800mV. If only one of the
converters is turned on, the other converter will stay off
and its output will remain charged up to V
IN
(input supply
voltage). The LT3466-1 enters into shutdown, when both
CTRL1 and CTRL2 are pulled lower than 70mV. The CTRL1
and CTRL2 pins perform independent dimming and shut-
down control for the two converters.
Minimum Output Current
The LT3466-1 can drive a 6-LED string at 3mA 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 3 shows circuit operation with 6 white LEDs at 3mA
current driven from 3.6V supply. Peak inductor current is
less than 50mA and the regulator operates in discontinu-
ous 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 300 resistor across the inductors, al-
though this will degrade efficiency.
Overvoltage Protection
The LT3466-1 has internal overvoltage protection for both
converters. In the event the white LEDs are disconnected
from the circuit or fail open, the converter 1 output voltage
is clamped at 39.5V (typ). Figure 4(a) shows the transient
response of the circuit in Figure 1 with LED1 disconnected.
With the white LEDs disconnected, the converter 1 starts
switching at the peak current limit. The output of converter
1 starts ramping up and finally gets clamped at 39.5V (typ).
The converter 1 will then switch at low inductor current to
regulate the output voltage. Output voltage and input
current during output open circuit are shown in the Typical
Performance Characteristics graphs.
Figure 3. Switching Waveforms
V
OUT1
20mV/DIV
(AC-COUPLED)
V
SW1
20V/DIV
I
L1
50mA/DIV
V
IN
= 3.6V 0.5µs/DIV 34661 F03
I
LED1
= 3mA
CIRCUIT OF FIGURE 1
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9
LT3466-1
34661f
In the event one of the converters has an output open-circuit,
its output voltage will be clamped at 39.5V. However, the
other converter will continue functioning properly. The photo
in Figure 4b shows circuit operation with converter 1 output
open-circuit and converter 2 driving the OLED display. Con-
verter 1 starts switching at a lower inductor current and
begins skipping pulses, thereby reducing its input current.
Converter 2 continues functioning properly.
Soft-Start
The LT3466-1 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 5
shows the start-up waveforms with converter 1 driving six
LEDs at 20mA. The filtered input current, as shown in
Figure 5, is well controlled. The soft-start circuitry is less
effective when driving a higher number of LEDs.
Undervoltage Lockout
The LT3466-1 has an undervoltage lockout circuit which
shuts down both converters when the input voltage drops
below 2.1V (typ). This prevents the converter from switch-
ing in an erratic mode when powered from low supply
voltages.
OPERATIO
U
Figure 4a. Transient Response of Switcher 1 with LED1
Disconnected from the Output
Figure 4b. Output 1 Open-Circuit Waveforms Figure 5. Start-Up Waveforms
V
OUT1
10V/DIV
200µs/DIV
LED1 DISCONNECTED AT THIS POINT
V
IN
= 3.3V
CIRCUIT OF FIGURE 1
34661 F04a
I
L1
200mA/DIV
V
OUT1
20V/DIV
V
FB1
200mV/DIV
200µs/DIV
V
IN
= 3.6V
6 LEDs, 20mA
CIRCUIT OF FIGURE 1
34661 F05
I
IN
200mA/DIV
CTRL1
5V/DIV
VSW1
50V/DIV
VSW2
50V/DIV
1µs/DIV
VIN = 3.6V
CIRCUIT OF FIGURE 1
34661 F04b
IL1
100mA/DIV
IL2
100mA/DIV
‘IO in 200 500 i000 I400 i800 osciLLAmR FREDUENCV (kHz) Figure ii. Timing Resismr (n1) Valli
10
LT3466-1
34661f
OPERATING FREQUENCY SELECTION
The choice of operating frequency is determined by sev-
eral factors. There is a tradeoff 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.
Another consideration is the maximum duty cycle achiev-
able. In certain applications, the converter needs to oper-
ate at the maximum duty cycle in order to light up the
maximum number of LEDs. The LT3466
-1
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 1 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 = 38.3k)
and 2MHz (RT = 20.5k). The efficiency comparison for
different RT values is shown in Figure 7.
INDUCTOR SELECTION
The choice of the inductor will depend on the selection of
switching frequency of LT3466
-1
. The switching fre-
quency can be programmed from 200kHz to 2MHz. Higher
switching frequency allows the use of smaller inductors
albeit at the cost of increased switching losses.
APPLICATIO S I FOR ATIO
WUUU
Figure 6. Timing Resistor (RT) Value Figure 7. Efficiency Comparison for Different RT Resistors
OSCILLATOR FREQUENCY (kHz)
RT (k)
1000
34661 F06
10
100
600 180014001000
200
LED CURRENT (mA)
0
EFFICIENCY (%)
60
70
20
34661 F07
50
40 510 15
90
80
CIRCUIT OF FIGURE 1
V
IN
= 3.6V
6 LEDs R
T
= 63.4k
R
T
= 20.5k
R
T
= 38.3k
DUTY CYCLE
The duty cycle for a step-up converter is given by:
DVVV
VVV
OUT D IN
OUT D CESAT
=+
+
where:
V
OUT
= Output voltage
V
D
= Schottky forward voltage drop
V
CESAT
= Saturation voltage of the switch
V
IN
= Input battery voltage
The maximum duty cycle achievable for LT3466
-1
is 96%
(typ) when running at 1MHz switching frequency. It in-
creases to 99% (typ) when run at 200kHz and drops to
92% (typ) at 2MHz. Always ensure that the converter is not
duty-cycle limited when powering the LEDs or OLED at a
given switching frequency.
SETTING THE SWITCHING FREQUENCY
The LT3466-1 uses a constant frequency architecture that
can be programmed over a 200KHz to 2MHz 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 6.
L7LJL1WW
11
LT3466-1
34661f
APPLICATIO S I FOR ATIO
WUUU
The inductor current ripple (I
L
), neglecting the drop
across the Schottky diode and the switch, is given by :
=
()
IVV V
VfL
L
IN MIN OUT MAX IN MIN
OUT MAX
() ( ) ()
()
•–
••
where:
L = Inductor
f = Operating frequency
V
IN(MIN)
= Minimum input voltage
V
OUT(MAX)
= Maximum output voltage
The I
L
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 I
2
R power losses.
Recommended inductor values range from 10µH to 68µH.
Several inductors that work well with the LT3466
-1
are listed
in Table 1. Consult each manufacturer for more detailed
information and for their entire selection of related parts.
Table 1. Recommended Inductors
MAX CURRENT
L DCR RATING
PART (µH) () (mA) VENDOR
LQH32CN100 10 0.44 300 Murata
LQH32CN150 15 0.58 300 (814) 237-1431
LQH43CN330 33 1.00 310 www.murata.com
ELL6RH330M 33 0.38 600 Panasonic
ELL6SH680M 68 0.52 500 (714) 373-7939
www.panasonic.com
A914BYW330M 33 0.45 440 Toko
A914BYW470M 47 0.73 360 www.toko.com
A920CY680M 68 0.40 400
CDRH2D18150NC 15 0.22 0.35A Sumida
CDRH4D18-330 33 0.51 0.31A (847) 956-0666
CDRH5D18-680 68 0.84 0.43A www.sumida.com
CAPACITOR SELECTION
The small size of ceramic capacitors make them ideal for
LT3466-1 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 1µF input capacitor is sufficient for most applica-
tions. Always use a capacitor with sufficient voltage rating.
Table 2 shows a list of several ceramic capacitor manufac-
turers. 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
AVX (803) 448-9411
www.avxcorp.com
Murata (714) 852-2001
www.murata.com
INRUSH CURRENT
The LT3466-1 has built-in Schottky diodes. When supply
voltage is applied to the V
IN
pin, an inrush current flows
through the inductor and the Schottky diode and charges
up the output capacitor. Both Schottky diodes in the
LT3466
-1
can sustain a maximum of 1A current. The
selection of inductor and capacitor value should ensure
the peak of the inrush current to be below 1A.
For low DCR inductors, which is usually the case for this
application, the peak inrush current can be simplified as
follows:
IV
L
where
LC
PK IN
OUT
=
=
–.
:
06
1
ω
ω
Table 3 gives inrush peak current for some component
selections.
Table 3. Inrush Peak Current
V
IN
(V) L (µH) C
OUT
(µF) I
P
(A)
5 15 0.47 0.78
5 33 1.00 0.77
5 47 2.2 0.95
5 68 1.00 0.53
9 47 0.47 0.84
12 33 0.22 0.93
L7Hl1§ég
12
LT3466-1
34661f
Typically peak inrush current will be less than the value
calculated above. This is due to the fact that the DC
resistance in the inductor provides some damping result-
ing in a lower peak inrush current.
SETTING THE LED CURRENT
The current in the LED string can be set by the choice of the
resistor R
FB1
(Figure 1). The feedback reference is 200mV.
In order to have accurate LED current, precision resistors
are preferred (1% is recommended).
RmV
I
FB LED
11
200
=
Table 4. RFB1 Value Selection
I
LED1
(mA) R
FB1
()
5 40.2
10 20.0
15 13.3
20 10.0
25 8.06
Most White LEDs are driven at maximum currents of
15mA to 20mA.
DIMMING WHITE LEDS
The LED current in the driver can be set by modulating the
CTRL1 pin. There are two different ways to control the
intensity of white LEDs.
Using a DC Voltage
For some applications, the preferred method of brightness
control is a variable DC voltage to adjust the LED current.
The CTRL1 pin voltage can be modulated to set the
dimming of the LED string. As the voltage on the CTRL1
pin increases from 0V to 1.8V, the LED current increases
from 0 to I
LED1
. As the CTRL1 pin voltage increases
beyond 1.8V, it has no effect on the LED current.
The LED current can be set by:
I
LED1
(V
CTRL1
/5 • R
FB1
), when V
CTRL1
< 1V
I
LED1
(200mV/R
FB1
), when V
CTRL1
> 1.8V
APPLICATIO S I FOR ATIO
WUUU
Feedback voltage variation versus control voltage is given
in the Typical Performance Characteristics graphs.
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 8) by an RC network and fed to the CTRL1 pin.
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 pin, which
is 100k.
34661 F08
C1
1µF
PWM
10kHz TYP
R1
10k
LT3466-1
CTRL1
Figure 8. Dimming Control Using a Filtered PWM Signal
SETTING THE BOOST OUTPUT VOLTAGE
The LT3466-1 regulates the voltage at the FB2 pin to 0.8V.
The output voltage of the boost converter (V
OUT2
) is set by
a resistor divider according to the formula:
VV
R
R
OUT2 08 1 1
2
=+
.
Choose 1% resistors for better accuracy. The FB2 input
bias current is quite low, on the order of 10nA (typ). Large
resistor values (R1 ~ 1M) can be used in the divider
network maximizing efficiency.
PROGRAMMING THE BOOST OUTPUT VOLTAGE
The output voltage of the boost converter can be modu-
lated by applying a variable DC voltage at the CTRL2 pin
The nominal voltage at the FB2 pin is 800mV. As the
voltage on the CTRL2 pin is ramped from 0V to 1V, the FB2
pin voltage ramps up to 0.8V. The feedback voltage can be
programmed as:
V
FB2
V
CTRL2
, when V
CTRL2
< 0.8V
V
FB2
0.8V, when V
CTRL2
> 1V
Ty; flit. I, . 13 r2 fl E Rhmxwfixwxw JéLf: f L7LJL1WW
13
LT3466-1
34661f
APPLICATIO S I FOR ATIO
WUUU
Figure 9 shows the feedback voltage variation versus the
control voltage. As seen in Figure 9, the linearity of the
graph allows the feedback voltage to be set accurately via
the control voltage.
The boost converter output voltage (V
OUT2
) is given by:
VV R
R
OUT FB22
11
2
=+
Thus a linear change in the feedback (FB2) voltage results
in a linear change in the boost output voltage (V
OUT2
).
Connect the CTRL2 pin to ground to disable converter 2.
Do not leave the pin floating. Unlike the CTRL1 pin, which
has an internal 100k pull-down resistor, the CTRL2 pin
input impedance is very high (>100M). A small amount
of board leakage current is sufficient to turn on the
converter 2.
The R
BASE
resistor can be calculated as:
I
LOAD
= 30mA
II
h
BASE LOAD
FE MIN
=04.
()
I
BASE
must be chosen such that Q1 is in saturation under
all conditions. The h
FE(MIN)
can be obtained from the
Philips BC807 data sheet as:
h
FE(MIN)
100
This yields worst case I
BASE
as:
ImA mA
BASE
=
30
0 4 100 075
.( ) .
R
BASE
is given by:
VIRVVV
IN MAX BASE BASE BE Q OUT CE Q( ) () ()
+• + = +
121
Thus R VV V V
I
BASE
OUT IN MAX CE Q BE Q
B
;––
( ) () ()
=+
211
AASE
Figure 10. Li-Ion Powered Driver for 6 White LEDs and a
Secondary OLED Display with Output Disconnect
CTRL1 CTRL2
R
T
SW1 SW2V
IN
3V TO 5V
16V
30mA
L2
33µH
C
IN
1µFR
BASE
I
BASE
V
CE(SAT)
C
OUT1
1µF
C
OUT2
0.47µF
63.4k
1%
L1
33µH
LT3466-1
C
IN
: TAIYO YUDEN JMK107BJ105
C
OUT1
: TAIYO YUDEN GMK316BJ105
C
OUT2
, C
OUT3
: TAIYO YUDEN TMK316BJ474
L1, L2: TOKO D52LC
Q1: PHILIPS BC807
V
OUT1
FB1
R
FB1
10
R2
24.9k
R1
475k
34661 F10
V
OUT2
FB2
ONOFFONOFF
C
OUT3
0.47µF
Q1
+–
Figure 9. VFB2 vs VCTRL2
OUTPUT DISCONNECT
The LT3466-1 can be used for powering white LEDs
(Channel 1) and an OLED display or, LCD bias (Channel 2).
Some OLED displays require load isolation in order to
reduce the current drained from the battery in shutdown.
The LT3466-1 output can be configured to provide output
disconnect by the use of only one resistor, R
BASE
, and a
PNP transistor, Q1, as shown in Figure 10.
As a design example, we target a Li-Ion powered driver for
6 white LEDs and an OLED display (16V at 30mA). We can
choose a general purpose PNP switching transistor like
Philips BC807 (Q1) to provide isolation.
V
CTRL2
(V)
0
V
FB2
(mV)
400
600
2
34661 F09
200
300
500
100
00.4 0.8 1.61.2
900
800
700
V
IN
= 3.6V
V
OUT2
= 16V
y f 5’ If gr
14
LT3466-1
34661f
1
2
3
4
5
10
9
8
7
6
COUT1
RFB1
RT
CTRL1
CTRL2
34661 F10
R2
R1
COUT2
CIN
VIN
GND
GND
L1
L2 11
Figure 11. Recommended Component Placement
APPLICATIO S I FOR ATIO
WUUU
The V
CE(SAT)
and V
BE(SAT)
values for the transistor Q1 can
be obtained from the Philips BC807 data sheet:
RVV
mA
BASE =+1650109
075
–..
.
R
BASE
= 13.6k
Picking the closest 1% resistor value yields:
R
BASE
= 14k
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 essen-
tial. Minimize the length and area of all traces connected to
the switching node pins (SW1 and SW2). Keep the feed-
back pins (FB1 and FB2) away from the switching nodes.
The DFN package has 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 R
T
resistor, ensuring a clean, noise-free con-
nection. Recommended component placement is shown
in the Figure 11.
at. mm | LE. «W 4/ 4/ 4H «W 4/ IV_.V_.V_.V_.V_.V __ L7LJL1WW
15
LT3466-1
34661f
TYPICAL APPLICATIO S
U
CTRL1 GND CTRL2
R
T
SW1 SW2V
IN
3V TO 5V
16V
30mA
L2
33µH
1µF
C
OUT1
1µFC
OUT2
1µF
6 LEDs
L1
33µH
LT3466-1
SHUTDOWN
AND DIMMING
CONTROL 2
C
IN
: TAIYO YUDEN JMK107BJ105
C
OUT1
, C
OUT2
: TAIYO YUDEN GMK316BJ105
L1, L2: 33µH TOKO D52LC
SHUTDOWN
AND DIMMING
CONTROL 1
V
OUT1
FB1
R
FB1
10R2
24.9k
R1
475k
34661 TA02a
V
OUT2
FB2
63.4k
OUTPUT CURRENT (mA)
0
EFFICIENCY (%)
70
75
302520
34661 TA02b
60
50
65
55
51015
90
85
80
BOOST CONVERTER
LED DRIVER
V
IN
= 3.6V
6 LEDs
V
OUT2
= 16V
Li-Ion Powered Driver for 6 White LEDs and OLED Display
Conversion Efficiency
CTRL1 CTRL2
RT
SW1 SW2VIN
3V TO 5V
12V
30mA AT VIN = 3V
60mA AT VIN = 5V
L2
15µH
CIN
1µF
COUT1
0.47µF
COUT2
1µF
38.3k
1%
L1
15µH
LT3466-1
CIN: TAIYO YUDEN JMK107BJ105
COUT1: TAIYO YUDEN EMK212BJ474
COUT2: TAIYO YUDEN EMK212BJ105
L1, L2: MURATA LQH32CN150K53
VOUT1
FB1
RFB1
10
R2
64.9k
R1
909k
34661 TA01a
VOUT2
FB2
ONOFFONOFF
4 LEDs
Li-Ion Powered 4 White LEDs Driver and 12V Boost Converter
Efficiency vs Load Current
LOAD CURRENT (mA)
0
60
EFFICIENCY (%)
65
70
75
80
90
10 20 30 40
34661 TA01b
50 60
85 VIN = 5V
VIN = 3V
4 LEDs/20mA
VOUT2 = 12V
J? 5’ Z” Z” )7 f” ”kw—144444444441) W1 . L7Hl1§ég
16
LT3466-1
34661f
TYPICAL APPLICATIO S
U
Li-Ion Powered Driver for 6 White LEDs and OLED with Output Disconnect
Conversion Efficiency
LOAD CURRENT (mA)
0
40
EFFICIENCY (%)
50
60
70
80
90
510 15 20
34661 TA03b
25 30
VIN = 3.6V
VOUT2 = 16V
CTRL1 CTRL2
R
T
SW1 SW2V
IN
3V TO 5V
L2
33µH
Q1
C
IN
1µF
C
OUT1
1µF
C
OUT2
0.47µF
63.4k
1%
L1
33µH
LT3466-1
C
IN
: TAIYO YUDEN JMK107BJ105
C
OUT1
: TAIYO YUDEN GMK316BJ105
C
OUT2
, C
OUT3
: TAIYO YUDEN TMK316BJ474
L1, L2: 33µH TOKO D52LC
Q1: PHILIPS BC807
V
OUT1
FB1
R
FB1
10
R2
24.9k
14k
34661 TA03a
V
OUT2
FB2
16V
30mA
R1
475k
ONOFFONOFF
C
OUT3
0.47µF
6 LEDs
V
OUT2
20V/DIV
2ms/DIVV
IN
= 3.6V
V
OUT2
= 16V
34661 TA03c
I
L2
200mA/DIV
CTRL2
5V/DIV
L7LJL1WW
17
LT3466-1
34661f
TYPICAL APPLICATIO S
U
Li-Ion Powered Driver for 6 White LEDs and OLED with Output Disconnect
Conversion Efficiency
CTRL1 CTRL2
RT
SW1 SW2VIN
3V TO 5V
Q1
L2
33µH
CIN
1µF
COUT1
1µF
COUT2
0.47µF
63.4k
1%
L1
33µH
LT3466-1
CIN: TAIYO YUDEN JMK107BJ105
COUT1: TAIYO YUDEN GMK316BJ105
COUT2, COUT3: TAIYO YUDEN TMK316BJ474
L1, L2: 33µH TOKO D52LC
Q1: SILICONIX TPO610
NOTE: ENSURE THAT VOUT2 > VIN(MAX) + 5V
VOUT1
FB1
RFB1
10
R2
24.9k
34661 TA04a
VOUT2
FB2
16V
30mA
R1
475k
ONOFFONOFF
COUT3
0.47µF
6 LEDs
LOAD CURRENT (mA)
0
EFFICIENCY (%)
65
70
75
15 25
34661 TA04b
60
55
50 510 20
80
85
90
30
V
IN
= 3.6V
V
OUT2
= 16V
VOUT2
20V/DIV
2ms/DIVVIN = 3.6V
VOUT2 = 16V
34661 TA04c
IL2
200mA/DIV
CTRL2
5V/DIV
L7Hl1§ég
18
LT3466-1
34661f
TYPICAL APPLICATIO S
U
Li-Ion to 10 White LEDs and LCD Bias (±8V) with Output Disconnect
Conversion Efficiency
CTRL1 CTRL2
R
T
SW1 SW2V
IN
3V TO 5V
–8V
10mA
8V
10mA
L2
33µH
C
IN
1µF
C
OUT1
1µF
147k
C
IN
: TAIYO YUDEN JMK107BJ105
C
OUT1
: TAIYO YUDEN UMK325BJ105
C
OUT2
, C
OUT3
: TAIYO YUDEN GMK316BJ105
C1, C2: TAIYO YUDEN UMK212BJ104
D1, D2: PHILIPS BAT54S
L1: 68µH TOKO D52LC
L2: 33µF TOKO D52LC
L1
68µH
10 LEDs
LT3466-1
V
OUT1
FB1
R
FB1
16.5
34661 TA05a
V
OUT2
FB2
ONOFFONOFF
C
OUT2
1µF
C
OUT3
1µF
909k
10k
C1
0.1µFD1
D2
C2
0.1µF
LED CURRENT (mA)
0
72
EFFICIENCY (%)
74
76
78
80
84
2468
34661 TA05b
10 12
82
VIN = 3.6V
10 LEDs
+8V/10mA
–8V/10mA
+8V OUTPUT
10V/DIV
–8V OUTPUT
10V/DIV
2ms/DIVV
IN
= 3.6V
+8V/10mA
–8V/10mA
34661 TA05c
CTRL2
5V/DIV
R=Dfi57 ' (4 STDES) (2 593(8) 1 1 ‘777 300mm 155mm,, \ T T T PW T \‘ TOP MARK (SEE NOTE 5) O 0 75 :0 05 4‘2 as :OT ‘4 :Huurufls (“ms + BOTTOM VIEwiEX NOTE T DRAWTNG TO BE MADE A JEDEC PACKAGE OUTLWE M07229 vARTATION O CHECK THE LTC WEBSTTE DATA SHEET FOR CURRENT STATUS OE vARIAT 2 DRAWWG NOT TO SCALE 3 ALL DTMENSTONS ARE W MTLLTMETERS 4 DTMENSTONS OE EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT WCLUD MOLD ELASH MOLD FLASH, TE PRESENT SHALL NOT EXCEED O 15mm ON 5 EXPOSED PAD SHAL e SHADED AREA IS ON TOP AND BOTTOM O L7LJL1WW
19
LT3466-1
34661f
U
PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
3.00 ±0.10
(4 SIDES)
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
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
0.38 ± 0.10
BOTTOM VIEW—EXPOSED PAD
1.65 ± 0.10
(2 SIDES)
0.75 ±0.05
R = 0.115
TYP
2.38 ±0.10
(2 SIDES)
15
106
PIN 1
TOP MARK
(SEE NOTE 6)
0.200 REF
0.00 – 0.05
(DD10) DFN 1103
0.25 ± 0.05
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1.65 ±0.05
(2 SIDES)2.15 ±0.05
0.50
BSC
0.675 ±0.05
3.50 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
L7Hl1§ég
20
LT3466-1
34661f
LT/TP 0705 500 • PRINTED IN USA
© LINEAR TECHNOLOGY CORPORATION 2005
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
FAX: (408) 434-0507
www.linear.com
TYPICAL APPLICATIO
U
Li-Ion to 8 White LEDs and ±15V TFT LCD Bias Supply
Conversion Efficiency
PART NUMBER DESCRIPTION COMMENTS
LT1618 Constant Current, Constant Voltage 1.4MHz, High Efficiency V
IN
: 1.6V to 18V, V
OUT(MAX)
= 34V, I
Q
= 1.8mA, I
SD
< 1µA,
Boost Regulator MS/EDD Packages
LT1932 Constant Current, 1.2MHz, High Efficiency White LED Boost V
IN
: 1V to 10V, V
OUT(MAX)
= 34V, I
Q
= 1.2mA, I
SD
< 1µA,
Regulator ThinSOTTM Package
LT1937 Constant Current, 1.2MHz, High Efficiency White LED Boost V
IN
: 2.5V to 10V, V
OUT(MAX)
= 34V, I
Q
= 1.9mA, I
SD
< 1µA,
Regulator ThinSOT, SC70 Packages
LTC®3200-5 Low Noise, 2MHz, Regulated Charge Pump White LED Driver V
IN
: 2.7V to 4.5V, V
OUT(MAX)
= 5V, I
Q
= 8mA, I
SD
< 1µA,
ThinSOT Package
LTC3202 Low Noise, 1.5MHz, Regulated Charge Pump White LED Driver V
IN
: 2.7V to 4.5V, V
OUT(MAX)
= 5.5V, I
Q
= 5mA, I
SD
< 1µA,
MS/EDD Packages
LTC3205 High Efficiency, Multidisplay LED Controller V
IN
: 2.8V to 4.5V, V
OUT(MAX)
= 6V, I
Q
= 50µA, I
SD
< 1µA,
QFN-24 Package
LTC3216 1A Low Noise High Current LED Charge Pump with Independent V
IN
: 2.9V to 4.4V, V
OUT(MAX)
= 5.5V, I
Q
= 300µA, I
SD
< 2.5µA,
Flash/Torch Current Control DFN Package
LTC3453 500mA Synchronous Buck-Boost High Current LED Driver V
IN
: 2.7V to 5.5V, V
OUT(MAX)
= 5.5V, I
Q
= 0.6mA, I
SD
< 6µA,
in Q FN QFN Package
LT3465/LT3465A Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED V
IN
: 2.7V to 16V, V
OUT(MAX)
= 34V, I
Q
= 1.9mA, I
SD
< 1µA,
Boost Regulator with Integrated Schottky Diode ThinSOT Package
LT3466 Dual Constant Current, 2MHz High Efficiency White LED Boost V
IN
: 2.7V to 24V, V
OUT(MAX)
= 40V, I
Q
= 5mA, I
SD
< 16µA,
Regulator with Integrated Schottky Diode DFN Package
LT3479 3A, Full Featured DC/DC Converter with Soft-Start and Inrush V
IN
: 2.5V to 24V, V
OUT(MAX)
= 40V, I
Q
= 6.5mA, I
SD
< 1µA,
Current Protection DFN/TSSOP Packages
ThinSOT is a trademark of Linear Technology Corporation.
RELATED PARTS
CTRL1 CTRL2
R
T
SW1 SW2V
IN
3V TO 5V
–15V
10mA
15V
10mA
L2
33µH
C
IN
1µF
C1
0.1µF
C
OUT1
1µF
C
OUT2
1µF
D1
C
OUT3
1µF
L1
33µH
LT3466-1
V
OUT1
FB1
R
FB1
13.3
26.7k
475k
34661 TA06a
V
OUT2
FB2
63.4k
8 LEDs
ONOFFONOFF
C
IN
: TAIYO YUDEN JMK107BJ105
C
OUT1
, C
OUT2
, C
OUT3
: TAIYO YUDEN GMK316BJ105
C1: TAIYO YUDEN UMK212BJ104
L1, L2: 33µH TOKO D52LC
D1: PHILIPS BAT54S
LED CURRENT (mA)
0
74
EFFICIENCY (%)
76
78
80
82
86
2.5 5 7.5 10
34661 TA06b
12.5 15
84
VIN = 3.6V
8 LEDs
+15V/10mA
–15V/10mA

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