LINER LT3466-1

LT3466-1
White LED Driver and Boost
Converter in 3mm × 3mm
DFN Package
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FEATURES
DESCRIPTIO
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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.
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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 VOUT)
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
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APPLICATIO S
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White LED and OLED Displays
Digital Cameras, Sub-Notebook PCs
PDAs, Handheld Computers
TFT - LCD Bias Supply
Automotive
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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The LT3466-1 provides independent dimming and shutdown control of the two converters. The operating frequency 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 output overvoltage protection and internal soft-start. Wide
input supply range allows operation from 2.7V to 24V.
TYPICAL APPLICATIO
3V TO 5V
Conversion Efficiency
33µH
33µH
1µF
90
VIN = 3.6V
85
6 LEDs
VOUT1
VIN
LT3466-1
80
VOUT2
1µF
1µF
FB1
FB2
RT GND
CTRL1
10Ω
LED DRIVER
SW2
SHUTDOWN
AND DIMMING
CONTROL 1
63.4k
16V
30mA
475k
CTRL2
SHUTDOWN
AND DIMMING
CONTROL 2
EFFICIENCY (%)
SW1
BOOST CONVERTER
75
70
65
60
55
24.9k
34661 F01a
50
0
5
10
15
20
25
30
OUTPUT CURRENT (mA)
34661 F01b
Figure 1. Li-Ion Powered Driver for 6 White LEDs and OLED Display
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LT3466-1
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ABSOLUTE
RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
Input Voltage (VIN) ................................................... 24V
SW1, SW2 Voltages ................................................ 44V
VOUT1, VOUT2 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
ORDER PART
NUMBER
TOP VIEW
10 FB1
VOUT1
1
SW1
2
VIN
3
SW2
4
8 RT
7 CTRL2
VOUT2
5
6 FB2
9 CTRL1
11
LT3466EDD-1
DD PART MARKING
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
LBRX
TJMAX = 125°C, θJA = 43°C/W, θJC = 3°C/W
EXPOSED PAD (PIN 11) IS GND
MUST BE SOLDERED TO PCB
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
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.
PARAMETER
CONDITIONS
MIN
Minimum Operating Voltage
TYP
MAX
2.7
UNITS
V
Maximum Operating Voltage
22
V
FB1 Voltage
●
192
200
208
mV
FB2 Voltage
●
788
800
812
mV
FB1 Pin Bias Current
VFB1 = 0.2V (Note 3)
10
50
nA
FB2 Pin Bias Current
VFB2 = 0.8V (Note 3)
10
50
nA
Quiescent Current
VFB1 = VFB2 = 1V
CTRL1 = CTRL2 = 0V
5
16
7.5
25
mA
µA
Switching Frequency
RT = 48.7k
0.75
1.25
MHz
Oscillator Frequency Range
(Note 4)
200
2000
kHz
Nominal RT Pin Voltage
RT = 48.7k
Maximum Duty Cycle
RT = 48.7k
RT = 20.5k
RT = 267k
Converter 1 Current Limit
Converter 2 Current Limit
1
0.54
V
●
90
96
92
99
%
%
%
●
310
400
mA
●
310
400
mA
320
mV
Converter 1 VCESAT
ISW1 = 300mA
Converter 2 VCESAT
ISW2 = 300mA
320
Switch 1 Leakage Current
VSW1 = 10V
0.01
5
µA
Switch 2 Leakage Current
VSW2 = 10V
0.01
5
µA
CTRL1 Voltage for Full LED Current
●
CTRL2 Voltage for Full Feedback Voltage
●
CTRL1 or CTRL2 Voltage to Turn On the IC
mV
1.8
V
1
V
150
mV
CTRL1 and CTRL2 Voltages to Shut Down Chip
CTRL1 Pin Bias Current
VCTRL1 = 1V
●
CTRL2 Pin Bias Current
VCTRL2 = 1V (Note 3)
●
6
70
mV
9
12.5
µA
10
120
nA
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LT3466-1
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.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VOUT1 Overvoltage Threshold
39.5
V
VOUT2 Overvoltage Threshold
39.5
V
Schottky 1 Forward Drop
ISCHOTTKY1 = 300mA
0.85
V
Schottky 2 Forward Drop
ISCHOTTKY2 = 300mA
0.85
V
Schottky 1 Reverse Leakage
VOUT1 = 20V
Schottky 2 Reverse Leakage
VOUT2 = 20V
5
µA
5
µA
Soft-Start Time (Switcher 1)
600
µs
Soft-Start Time (Switcher 2)
600
µs
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.
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TYPICAL PERFOR A CE CHARACTERISTICS
TA = 25°C unless otherwise specified
Switching Waveforms
(LED Driver)
Switching Waveforms
(Boost Converter)
VOUT1
100mV/DIV
(AC-COUPLED)
VOUT2
100mV/DIV
(AC-COUPLED)
VSW1
20V/DIV
VSW2
20V/DIV
IL2
100mA/DIV
IL1
100mA/DIV
VIN = 3.6V
0.5µs/DIV
6 LEDs AT 20mA
CIRCUIT OF FIGURE 1
VIN = 3.6V
0.5µs/DIV
VOUT2 = 16V/30mA
CIRCUIT OF FIGURE 1
34661 G01
VFB1 vs VCTRL1
250
34661 G02
VFB2 vs VCTRL2
900
VIN = 3.6V
6 LEDs
VIN = 3.6V
800 VOUT2 = 16V
200
700
VFB2 (mV)
VFB1 (mV)
600
150
100
500
400
300
200
50
100
0
0
0.5
1
1.5
2
VCTRL1 (V)
0
0
0.5
1
1.5
2
VCTRL2 (V)
34661 G03
34661 G16
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LT3466-1
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TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise specified
500
7
TA = –50°C
450
UVLO
TA = 85°C
350
300
250
200
150
100
5
4
3
2
1
50
80
0
100
4
8
12
VIN (V)
16
Open-Circuit Output Clamp
Voltage
OUTPUT CLAMP VOLTAGE (V)
OUTPUT CLAMP VOLTAGE (V)
42
40.50
40.00
VOUT2
39.50
VOUT1
39.00
38.50
38.00
4
6
8 10 12 14 16 18 20 22 24
VIN (V)
4
6
8 10 12 14 16 18 20 22 24
VIN (V)
34661 G06
Input Current with Output 1 and
Output 2 Open Circuit
20
41
40
VOUT1
39
38
37
–50
RT = 63.4k
16
VOUT2
12
8
4
–25
50
25
0
75
TEMPERATURE (°C)
100
125
0
2
4
6
8 10 12 14 16 18 20 22 24
VIN (V)
34661 G08
34661 G09
Oscillator Frequency vs VIN
RT vs Oscillator Frequency
1000
1100
OSCILLATOR FREQUENCY (kHz)
RT (kΩ)
20
2
RT = 63.4k
34661 G07
100
10
200
TA = 100°C
30
Open-Circuit Output Clamp
Voltage
RT = 63.4k
2
40
34661 G04
34661 G05
41.00
TA = 25°C
0
24
20
INPUT CURRENT (mA)
60
40
DUTY CYCLE (%)
50
10
0
20
0
TA = –50°C
60
SHUTDOWN CURRENT (µA)
QUIESCENT CURRENT (mA)
CURRENT LIMIT (mA)
70
TA = 25°C
6
400
0
Shutdown Current
(CTRL1 = CTRL2 = 0V)
Quiescent Current
(CTRL1 = CTRL2 = 3V)
Switch Current Limit vs Duty Cycle
600
1000
1400
1800
OSCILLATOR FREQUENCY (kHz)
34661 G10
RT = 48.7k
1000
900
800
2
4
6
8 10 12 14 16 18 20 22 24
VIN (V)
34661 G11
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LT3466-1
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TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise specified
Oscillator Frequency
vs Temperature
150
VIN = 3.6V
RT = 48.7k
VIN = 3.6V
125
CTRL1
CTRL VOLTAGE (mV)
OSCILLATOR FREQUENCY (kHz)
1100
CTRL Voltages to Shut Down
the IC
1000
900
100
CTRL2
75
50
25
800
–50
–25
0
25
50
TEMPERATURE (°C)
75
0
–50
100
–25
75
0
25
50
TEMPERATURE (°C)
34661 G12
34661 G13
Schottky Forward Voltage Drop
Schottky Leakage Current
8
SCHOTTKY LEAKAGE CURRENT (µA)
SCHOTTKY FORWARD CURRENT (mA)
400
350
300
250
200
150
100
50
0
200
800
600
SCHOTTKY FORWARD DROP (mV)
0
400
6
4
VR = 36V
VR = 20V
2
0
–50
1000
–25
75
0
25
50
TEMPERATURE (°C)
FB2 Pin Load Regulation
FB2 Pin Voltage vs Temperature
0
VIN = 3V
VOUT2 = 16V/30mA
VIN = 3V
VOUT2 = 16V
–0.20
∆VOUT2/VOUT2 (%)
FB2 VOLTAGE (V)
0.805
0.800
0.795
0.790
–0.40
–0.60
–0.80
0.785
0.780
–50
100
34661 G015
34661 G14
0.810
100
–1.00
–25
75
0
25
50
TEMPERATURE (°C)
100
125
34661 G17
0
10
20
LOAD CURRENT (mA)
30
34661 G18
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LT3466-1
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PI FU CTIO S
VOUT1 (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.
VIN (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.
VOUT2 (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:
VFB2 ≈ VCTRL2, when VCTRL2 < 0.8V
VFB2 = 0.8V, when VCTRL2 > 1V
CTRL2 (Pin 7): Dimming and Shutdown Pin for Converter 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.
RT (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 Converter 1. Connect this pin to ground to disable the converter. As the pin voltage is ramped from 0V to 1.8V, the
LED current ramps from 0 to ILED1 (= 200mV/RFB1). 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 :
ILED1 ≈ (VCTRL1/5 • RFB1), when VCTRL1 < 1V
ILED1 ≈ (200mV/RFB1), when VCTRL1 > 1.8V
Exposed Pad (Pin 11): The Exposed Pad must be soldered
to the PCB system ground.
34661f
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C2
RFB1
10
1
FB1
PWM
LOGIC
PWM
COMP
A2
RSNS1
DRIVER
CONVERTER 1
OSC
OVERVOLT
DETECTION
SW1
Q1
2
–
+
VOUT1
L1
–
+
A3
EA
A1
Σ
20k
+
+
–
C1
RT
9
VIN
START-UP
CONTROL
REF 1.25V
CTRL1
SHDN
OSC
3
7
CTRL2
0.8V
Figure 2. Block Diagram
80k
0.2V
RAMP
GEN
OSC
8
RT
+
+
–
Σ
A1
EA
A3
11
EXPOSED
PAD
–
+
Q2
4
A2
OSC
PWM
LOGIC
VOUT2
FB2
OVERVOLT
DETECTION
CONVERTER 2
PWM
COMP
DRIVER
RSNS2
SW2
L2
–
+
VIN
6
5
34661 F02
R2
R1
C3
LT3466-1
BLOCK DIAGRA
34661f
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LT3466-1
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OPERATIO
Main Control Loop
Minimum Output Current
The LT3466-1 uses a constant frequency, current mode
control scheme to provide excellent line and load regulation. 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, Schottky diode etc., are similar for both converters.
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 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.
At power-up, the output voltages VOUT1 and VOUT2 are
charged up to VIN (input supply voltage) via their respective 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 VIN (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 shutdown control for the two converters.
VOUT1
20mV/DIV
(AC-COUPLED)
VSW1
20V/DIV
IL1
50mA/DIV
0.5µs/DIV
VIN = 3.6V
ILED1 = 3mA
CIRCUIT OF FIGURE 1
34661 F03
Figure 3. Switching Waveforms
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.
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LT3466-1
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OPERATIO
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. Converter 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.
VOUT1
10V/DIV
IL1
200mA/DIV
Undervoltage Lockout
200µs/DIV
34661 F04a
LED1 DISCONNECTED AT THIS POINT
VIN = 3.3V
CIRCUIT OF FIGURE 1
Figure 4a. Transient Response of Switcher 1 with LED1
Disconnected from the Output
VSW1
50V/DIV
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 switching in an erratic mode when powered from low supply
voltages.
IIN
200mA/DIV
IL1
100mA/DIV
VOUT1
20V/DIV
VSW2
50V/DIV
VFB1
200mV/DIV
IL2
100mA/DIV
CTRL1
5V/DIV
VIN = 3.6V
1µs/DIV
CIRCUIT OF FIGURE 1
34661 F04b
Figure 4b. Output 1 Open-Circuit Waveforms
VIN = 3.6V
200µs/DIV
6 LEDs, 20mA
CIRCUIT OF FIGURE 1
34661 F05
Figure 5. Start-Up Waveforms
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LT3466-1
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APPLICATIO S I FOR ATIO
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 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.
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
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 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 maximum duty cycle achievable for LT3466-1 is 96%
(typ) when running at 1MHz switching frequency. It increases 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.
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.
SETTING THE SWITCHING FREQUENCY
INDUCTOR SELECTION
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.
The choice of the inductor will depend on the selection of
switching frequency of LT3466-1. The switching frequency can be programmed from 200kHz to 2MHz. Higher
switching frequency allows the use of smaller inductors
albeit at the cost of increased switching losses.
90
1000
CIRCUIT OF FIGURE 1
VIN = 3.6V
6 LEDs
EFFICIENCY (%)
RT (kΩ)
80
100
RT = 63.4k
RT = 20.5k
70
RT = 38.3k
60
50
10
200
600
1000
1400
1800
OSCILLATOR FREQUENCY (kHz)
34661 F06
Figure 6. Timing Resistor (RT) Value
40
0
5
10
15
20
LED CURRENT (mA)
34661 F07
Figure 7. Efficiency Comparison for Different RT Resistors
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LT3466-1
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APPLICATIO S I FOR ATIO
The inductor current ripple (∆IL), neglecting the drop
across the Schottky diode and the switch, is given by :
∆IL =
(
VIN(MIN) • VOUT(MAX) – VIN(MIN)
)
VOUT(MAX) • f • L
where:
Z5U. A 1µF 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
L = Inductor
Taiyo Yuden
(408) 573-4150
www.t-yuden.com
f = Operating frequency
AVX
VIN(MIN) = Minimum input voltage
(803) 448-9411
www.avxcorp.com
Murata
(714) 852-2001
www.murata.com
VOUT(MAX) = Maximum output voltage
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 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
L
(µH)
MAX
DCR
(Ω)
CURRENT
RATING
(mA)
LQH32CN100
LQH32CN150
LQH43CN330
10
15
33
0.44
0.58
1.00
300
300
310
Murata
(814) 237-1431
www.murata.com
ELL6RH330M
ELL6SH680M
33
68
0.38
0.52
600
500
Panasonic
(714) 373-7939
www.panasonic.com
A914BYW330M
A914BYW470M
A920CY680M
33
47
68
0.45
0.73
0.40
440
360
400
Toko
www.toko.com
CDRH2D18150NC
CDRH4D18-330
CDRH5D18-680
15
33
68
0.22
0.51
0.84
0.35A
0.31A
0.43A
PART
VENDOR
Sumida
(847) 956-0666
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
INRUSH CURRENT
The LT3466-1 has built-in Schottky diodes. When supply
voltage is applied to the VIN 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:
IPK =
VIN – 0.6
ωL
where:
ω=
1
LCOUT
Table 3 gives inrush peak current for some component
selections.
Table 3. Inrush Peak Current
VIN (V)
L (µH)
COUT (µF)
IP (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
34661f
11
LT3466-1
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APPLICATIO S I FOR ATIO
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 resulting 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 RFB1 (Figure 1). The feedback reference is 200mV.
In order to have accurate LED current, precision resistors
are preferred (1% is recommended).
RFB1 =
200mV
ILED1
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 100kΩ.
PWM
10kHz TYP
Table 4. RFB1 Value Selection
ILED1 (mA)
Feedback voltage variation versus control voltage is given
in the Typical Performance Characteristics graphs.
RFB1 (Ω)
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 ILED1. As the CTRL1 pin voltage increases
beyond 1.8V, it has no effect on the LED current.
The LED current can be set by:
LT3466-1
R1
10k
CTRL1
C1
1µF
34661 F08
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 (VOUT2) is set by
a resistor divider according to the formula:
⎛ R1⎞
VOUT2 = 0.8V ⎜ 1+ ⎟
⎝ R2⎠
Choose 1% resistors for better accuracy. The FB2 input
bias current is quite low, on the order of 10nA (typ). Large
resistor values (R1 ~ 1MΩ) can be used in the divider
network maximizing efficiency.
PROGRAMMING THE BOOST OUTPUT VOLTAGE
The output voltage of the boost converter can be modulated 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:
ILED1 ≈ (VCTRL1/5 • RFB1), when VCTRL1 < 1V
VFB2 ≈ VCTRL2, when VCTRL2 < 0.8V
ILED1 ≈ (200mV/RFB1), when VCTRL1 > 1.8V
VFB2 ≈ 0.8V, when VCTRL2 > 1V
34661f
12
LT3466-1
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APPLICATIO S I FOR ATIO
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.
3V TO 5V
CIN
1µF
L1
33µH
The boost converter output voltage (VOUT2) is given by:
VOUT 2
L2
33µH
SW1
⎛ R1⎞
= VFB2 ⎜ 1+ ⎟
⎝ R2⎠
Thus a linear change in the feedback (FB2) voltage results
in a linear change in the boost output voltage (VOUT2).
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 (>100MΩ). A small amount
of board leakage current is sufficient to turn on the
converter 2.
VIN
SW2
FB1
CTRL1
OFF ON
16V
30mA
COUT3
0.47µF
R1
475k
COUT2
0.47µF
LT3466-1
RFB1
10Ω
RBASE
Q1
+
–
VCE(SAT)
VOUT2
VOUT1
COUT1
1µF
IBASE
FB2
RT
R2
24.9k
CTRL2
OFF ON
63.4k
1%
34661 F10
CIN: TAIYO YUDEN JMK107BJ105
COUT1: TAIYO YUDEN GMK316BJ105
COUT2, COUT3: TAIYO YUDEN TMK316BJ474
L1, L2: TOKO D52LC
Q1: PHILIPS BC807
Figure 10. Li-Ion Powered Driver for 6 White LEDs and a
Secondary OLED Display with Output Disconnect
900
VIN = 3.6V
800 VOUT2 = 16V
The RBASE resistor can be calculated as:
ILOAD = 30mA
700
VFB2 (mV)
600
IBASE =
500
400
ILOAD
0 . 4hFE(MIN)
300
IBASE must be chosen such that Q1 is in saturation under
all conditions. The hFE(MIN) can be obtained from the
Philips BC807 data sheet as:
200
100
0
0
0.4
0.8
1.2
VCTRL2 (V)
1.6
2
34661 F09
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, RBASE, and a
PNP transistor, Q1, as shown in Figure 10.
hFE(MIN) ≅ 100
This yields worst case IBASE as:
IBASE =
30mA
≅ 0 . 75mA
0 . 4(100)
RBASE is given by:
VIN(MAX ) + IBASE • RBASE + VBE(Q1) = VOUT 2 + VCE(Q1)
Thus; RBASE =
VOUT 2 – VIN(MAX ) + VCE(Q1) – VBE(Q1)
IBASE
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.
34661f
13
LT3466-1
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APPLICATIO S I FOR ATIO
The VCE(SAT) and VBE(SAT) values for the transistor Q1 can
be obtained from the Philips BC807 data sheet:
RBASE =
16 V – 5V + 0 . 1 – 0 . 9
0 . 75mA
ground plane and not shared with any other component,
except the RT resistor, ensuring a clean, noise-free connection. Recommended component placement is shown
in the Figure 11.
RBASE = 13.6k
Picking the closest 1% resistor value yields:
RBASE = 14k
GND
COUT1
RFB1
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 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
CIN
10
1
L1
3
L2
CTRL1
9
2
VIN
RT
11
8
4
7
5
6
R2
CTRL2
R1
COUT2
34661 F10
GND
Figure 11. Recommended Component Placement
34661f
14
LT3466-1
U
TYPICAL APPLICATIO S
Li-Ion Powered 4 White LEDs Driver and 12V Boost Converter
3V TO 5V
Efficiency vs Load Current
CIN
1µF
4 LEDs
L2
15µH
SW1
VIN
SW2
VOUT2
VOUT1
COUT1
0.47µF
R1
909k
COUT2
1µF
LT3466-1
FB1
RFB1
10Ω
FB2
RT
CTRL1
OFF ON
R2
64.9k
CTRL2
38.3k
1%
OFF ON
4 LEDs/20mA
VOUT2 = 12V
85
EFFICIENCY (%)
L1
15µH
90
12V
30mA AT VIN = 3V
60mA AT VIN = 5V
VIN = 5V
80
VIN = 3V
75
70
65
34661 TA01a
60
CIN: TAIYO YUDEN JMK107BJ105
COUT1: TAIYO YUDEN EMK212BJ474
COUT2: TAIYO YUDEN EMK212BJ105
L1, L2: MURATA LQH32CN150K53
0
10
20
30
40
LOAD CURRENT (mA)
50
60
34661 TA01b
Li-Ion Powered Driver for 6 White LEDs and OLED Display
3V TO 5V
L1
33µH
SW1
L2
33µH
VIN
Conversion Efficiency
1µF
90
85
SW2
LED DRIVER
6 LEDs
COUT1
1µF
VOUT1
LT3466-1
COUT2
1µF
FB1
FB2
RT GND
CTRL1
RFB1
10Ω
VOUT2
SHUTDOWN
AND DIMMING
CONTROL 1
63.4k
CIN: TAIYO YUDEN JMK107BJ105
COUT1, COUT2: TAIYO YUDEN GMK316BJ105
L1, L2: 33µH TOKO D52LC
16V
30mA
R1
475k
EFFICIENCY (%)
80
BOOST CONVERTER
75
70
65
60
VIN = 3.6V
6 LEDs
VOUT2 = 16V
CTRL2
SHUTDOWN
AND DIMMING
CONTROL 2
R2
24.9k
34661 TA02a
55
50
0
5
10
15
20
25
30
OUTPUT CURRENT (mA)
34661 TA02b
34661f
15
LT3466-1
U
TYPICAL APPLICATIO S
Li-Ion Powered Driver for 6 White LEDs and OLED with Output Disconnect
3V TO 5V
14k
CIN
1µF
L1
33µH
Q1
L2
33µH
COUT3
0.47µF
6 LEDs
SW1
COUT1
1µF
VIN
VOUT2
COUT2
0.47µF
LT3466-1
CTRL1
OFF ON
R1
475k
SW2
VOUT1
FB1
RFB1
10Ω
16V
30mA
FB2
RT
R2
24.9k
CTRL2
63.4k
1%
OFF ON
34661 TA03a
CIN: TAIYO YUDEN JMK107BJ105
COUT1: TAIYO YUDEN GMK316BJ105
COUT2, COUT3: TAIYO YUDEN TMK316BJ474
L1, L2: 33µH TOKO D52LC
Q1: PHILIPS BC807
Conversion Efficiency
90
VOUT2
20V/DIV
VIN = 3.6V
VOUT2 = 16V
EFFICIENCY (%)
80
IL2
200mA/DIV
CTRL2
5V/DIV
VIN = 3.6V
VOUT2 = 16V
2ms/DIV
34661 TA03c
70
60
50
40
0
5
10
15
20
LOAD CURRENT (mA)
25
30
34661 TA03b
34661f
16
LT3466-1
U
TYPICAL APPLICATIO S
Li-Ion Powered Driver for 6 White LEDs and OLED with Output Disconnect
3V TO 5V
CIN
1µF
L1
33µH
6 LEDs
L2
33µH
SW1
VIN
COUT3
0.47µF
R1
475k
SW2
VOUT1
COUT1
1µF
VOUT2
COUT2
0.47µF
LT3466-1
FB1
RFB1
10Ω
CTRL1
OFF ON
16V
30mA
Q1
FB2
RT
R2
24.9k
CTRL2
63.4k
1%
CIN: TAIYO YUDEN JMK107BJ105
COUT1: TAIYO YUDEN GMK316BJ105
COUT2, COUT3: TAIYO YUDEN TMK316BJ474
L1, L2: 33µH TOKO D52LC
Q1: SILICONIX TPO610
OFF ON
34661 TA04a
NOTE: ENSURE THAT VOUT2 > VIN(MAX) + 5V
Conversion Efficiency
90
VIN = 3.6V
85 VOUT2 = 16V
VOUT2
20V/DIV
EFFICIENCY (%)
80
IL2
200mA/DIV
CTRL2
5V/DIV
75
70
65
60
VIN = 3.6V
VOUT2 = 16V
2ms/DIV
34661 TA04c
55
50
0
5
10
20
15
LOAD CURRENT (mA)
25
30
34661 TA04b
34661f
17
LT3466-1
U
TYPICAL APPLICATIO S
Li-Ion to 10 White LEDs and LCD Bias (±8V) with Output Disconnect
3V TO 5V
CIN
1µF
L1
68µH
C1
0.1µF
–8V
10mA
L2
33µH
10 LEDs
SW1
COUT1
1µF
D1
VIN
COUT2
1µF
C2
0.1µF
SW2
D2
VOUT2
VOUT1
8V
10mA
LT3466-1
909k
FB1
RFB1
16.5Ω
CTRL1
OFF ON
FB2
RT
CTRL2
147k
COUT3
1µF
10k
OFF ON
CIN: TAIYO YUDEN JMK107BJ105
COUT1: TAIYO YUDEN UMK325BJ105
COUT2, COUT3: TAIYO YUDEN GMK316BJ105
C1, C2: TAIYO YUDEN UMK212BJ104
D1, D2: PHILIPS BAT54S
L1: 68µH TOKO D52LC
L2: 33µF TOKO D52LC
34661 TA05a
Conversion Efficiency
84
+8V OUTPUT
10V/DIV
VIN = 3.6V
10 LEDs
+8V/10mA
–8V/10mA
EFFICIENCY (%)
82
–8V OUTPUT
10V/DIV
CTRL2
5V/DIV
VIN = 3.6V
+8V/10mA
–8V/10mA
2ms/DIV
34661 TA05c
80
78
76
74
72
0
2
4
6
8
LED CURRENT (mA)
10
12
34661 TA05b
34661f
18
LT3466-1
U
PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
0.675 ±0.05
3.50 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
PACKAGE
OUTLINE
0.25 ± 0.05
0.50
BSC
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
TYP
6
3.00 ±0.10
(4 SIDES)
0.38 ± 0.10
10
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD10) DFN 1103
5
0.200 REF
1
0.75 ±0.05
0.00 – 0.05
0.25 ± 0.05
0.50 BSC
2.38 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
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
34661f
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
LT3466-1
U
TYPICAL APPLICATIO
Li-Ion to 8 White LEDs and ±15V TFT LCD Bias Supply
3V TO 5V
SW1
COUT1
1µF
VIN
15V
10mA
LT3466-1
OFF ON
86
475k
COUT2
1µF
FB2
26.7k
CTRL2
63.4k
VIN = 3.6V
8 LEDs
+15V/10mA
–15V/10mA
84
COUT3
1µF
VOUT2
FB1
RFB1
13.3Ω
D1
SW2
VOUT1
CTRL1 RT
Conversion Efficiency
–15V
10mA
L2
33µH
L1
33µH
8 LEDs
C1
0.1µF
EFFICIENCY (%)
CIN
1µF
82
80
78
76
OFF ON
74
34661 TA06a
CIN: TAIYO YUDEN JMK107BJ105
COUT1, COUT2, COUT3: TAIYO YUDEN GMK316BJ105
C1: TAIYO YUDEN UMK212BJ104
L1, L2: 33µH TOKO D52LC
D1: PHILIPS BAT54S
0
2.5
5
7.5
10
LED CURRENT (mA)
12.5
15
34661 TA06b
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DESCRIPTION
COMMENTS
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VIN: 2.9V to 4.4V, VOUT(MAX) = 5.5V, IQ = 300µA, ISD < 2.5µA,
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500mA Synchronous Buck-Boost High Current LED Driver
in Q FN
VIN: 2.7V to 5.5V, VOUT(MAX) = 5.5V, IQ = 0.6mA, ISD < 6µA,
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LT3465/LT3465A
Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED
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VIN: 2.7V to 16V, VOUT(MAX) = 34V, IQ = 1.9mA, ISD < 1µA,
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LT3466
Dual Constant Current, 2MHz High Efficiency White LED Boost
Regulator with Integrated Schottky Diode
VIN: 2.7V to 24V, VOUT(MAX) = 40V, IQ = 5mA, ISD < 16µA,
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3A, Full Featured DC/DC Converter with Soft-Start and Inrush
Current Protection
VIN: 2.5V to 24V, VOUT(MAX) = 40V, IQ = 6.5mA, ISD < 1µA,
DFN/TSSOP Packages
ThinSOT is a trademark of Linear Technology Corporation.
34661f
20
Linear Technology Corporation
LT/TP 0705 500 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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