LINEAR TECHNOLOGY LT3466-1 Technical data

FEATURES
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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
Fixed Frequency Operation Up to 2MHz
83% Efficiency Driving 8 White LEDs at 15mA
OUT
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
White LED and OLED Displays
Digital Cameras, Sub-Notebook PCs
PDAs, Handheld Computers
TFT - LCD Bias Supply
Automotive
LT3466-1
White LED Driver and Boost
Converter in 3mm × 3mm
DFN Package
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DESCRIPTIO
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 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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TYPICAL APPLICATIO
3V TO 5V
1µF
IN
LT3466-1
R
T
33µH
V
SHUTDOWN AND DIMMING CONTROL 2
OUT2
FB2
16V 30mA
475k
24.9k
34661 F01a
6 LEDs
33µH
SW1 SW2V
V
1µF1µF
10
OUT1
FB1
CTRL1 GND CTRL2
SHUTDOWN
AND DIMMING
CONTROL 1
63.4k
Figure 1. Li-Ion Powered Driver for 6 White LEDs and OLED Display
90
VIN = 3.6V
85
LED DRIVER
80
75
70
65
EFFICIENCY (%)
60
55
50
0
Conversion Efficiency
BOOST CONVERTER
51015
OUTPUT CURRENT (mA)
302520
34661 F01b
34661f
1
LT3466-1
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ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
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(Note 1)
Input Voltage (VIN) ................................................... 24V
SW1, SW2 Voltages ................................................ 44V
V
OUT1
, V
Voltages ............................................. 44V
OUT2
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
ELECTRICAL CHARACTERISTICS
range, otherwise specifications are at TA = 25°C. VIN = 3V, V
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
FB2 Pin Bias Current V
Quiescent Current V
Switching Frequency RT = 48.7k 0.75 1 1.25 MHz
Oscillator Frequency Range (Note 4) 200 2000 kHz
Nominal RT Pin Voltage RT = 48.7k 0.54 V
Maximum Duty Cycle RT = 48.7k 90 96 %
Converter 1 Current Limit 310 400 mA
Converter 2 Current Limit 310 400 mA
Converter 1 V
Converter 2 V
Switch 1 Leakage Current V
Switch 2 Leakage Current V
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
CTRL2 Pin Bias Current V
CESAT
CESAT
FB1
FB2
FB1
CTRL1 = CTRL2 = 0V 16 25 µA
R
= 20.5k 92 %
T
RT = 267k 99 %
I
SW1
I
SW2
SW1
SW2
CTRL1
CTRL2
The denotes specifications that apply over the full operating temperature
= 3V, V
CTRL1
= 0.2V (Note 3) 10 50 nA
= 0.8V (Note 3) 10 50 nA
= V
= 1V 5 7.5 mA
FB2
= 300mA 320 mV
= 300mA 320 mV
= 10V 0.01 5 µA
= 10V 0.01 5 µA
= 1V 6 9 12.5 µA
= 1V (Note 3) 10 120 nA
V
OUT1
SW1
V
IN
SW2
V
OUT2
10-LEAD (3mm × 3mm) PLASTIC DFN
T
JMAX
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.
CTRL2
TOP VIEW
10
9
8
7
6
FB1
CTRL1
R
T
CTRL2
FB2
DD PART MARKING
1
2
11
3
4
5
DD PACKAGE
= 125°C, θJA = 43°C/W, θJC = 3°C/W
EXPOSED PAD (PIN 11) IS GND
MUST BE SOLDERED TO PCB
= 3V, unless otherwise specified.
ORDER PART
NUMBER
LT3466EDD-1
LBRX
34661f
2
LT3466-1
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ELECTRICAL CHARACTERISTICS
range, otherwise specifications are at TA = 25°C. VIN = 3V, V
The denotes specifications that apply over the full operating temperature
CTRL1
= 3V, V
= 3V, unless otherwise specified.
CTRL2
PARAMETER CONDITIONS MIN TYP MAX UNITS
V
Overvoltage Threshold 39.5 V
OUT1
V
Overvoltage Threshold 39.5 V
OUT2
Schottky 1 Forward Drop I
Schottky 2 Forward Drop I
Schottky 1 Reverse Leakage V
Schottky 2 Reverse Leakage V
SCHOTTKY1
SCHOTTKY2
OUT1
OUT2
= 300mA 0.85 V
= 300mA 0.85 V
= 20V 5 µA
= 20V 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 3: Current flows out of the pin. Note 4: Guaranteed by design and test correlation, not production tested.
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.
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TYPICAL PERFOR A CE CHARACTERISTICS
TA = 25°C unless otherwise specified
V
OUT1
100mV/DIV
(AC-COUPLED)
V
SW1
20V/DIV
I
100mA/DIV
250
200
150
(mV)
FB1
V
100
Switching Waveforms (LED Driver)
L1
V
= 3.6V 0.5µs/DIV 34661 G01
IN
6 LEDs AT 20mA CIRCUIT OF FIGURE 1
V
vs V
50
0
0
FB1
VIN = 3.6V 6 LEDs
0.5
CTRL1
V
CTRL1
1
(V)
1.5
34661 G03
Switching Waveforms (Boost Converter)
V
OUT2
100mV/DIV
(AC-COUPLED)
V
SW2
20V/DIV
I
L2
100mA/DIV
VIN = 3.6V 0.5µs/DIV 34661 G02 V
= 16V/30mA
OUT2
CIRCUIT OF FIGURE 1
V
vs V
FB2
900
VIN = 3.6V V
800
700
600
500
(mV)
FB2
400
V
300
200
100
2
0
0
OUT2
= 16V
0.5
CTRL2
V
CTRL2
1
(V)
1.5
34661 G16
2
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LT3466-1
VIN (V)
2
0
SHUTDOWN CURRENT (µA)
10
30
40
50
70
4
12
16
34661 G06
20
60
10
20
2422
6
8
14 18
TA = –50°C
TA = 25°C
TA = 100°C
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TYPICAL PERFOR A CE CHARACTERISTICS
TA = 25°C unless otherwise specified
500
450
400
350
300
250
200
150
CURRENT LIMIT (mA)
100
50
0
0
TA = –50°C
T
A
20
DUTY CYCLE (%)
= 85°C
40
Open-Circuit Output Clamp Voltage
41.00 RT = 63.4k
40.50
40.00
39.50
39.00
OUTPUT CLAMP VOLTAGE (V)
38.50
V
V
OUT2
OUT1
60
TA = 25°C
80
34661 G05
100
Quiescent Current (CTRL1 = CTRL2 = 3V)Switch Current Limit vs Duty Cycle
7
0
UVLO
48
VIN (V)
12 20
6
5
4
3
2
QUIESCENT CURRENT (mA)
1
0
Open-Circuit Output Clamp Voltage
42
RT = 63.4k
41
40
39
38
OUTPUT CLAMP VOLTAGE (V)
16 24
V
OUT2
V
OUT1
34661 G04
Shutdown Current (CTRL1 = CTRL2 = 0V)
Input Current with Output 1 and Output 2 Open Circuit
20
RT = 63.4k
16
12
8
INPUT CURRENT (mA)
4
38.00
6 101418
VIN (V)
2442 8 12 16 20 22
34661 G07
37
–50 –25
0
TEMPERATURE (°C)
RT vs Oscillator Frequency
1000
100
4
(k)
T
R
10
600 180014001000
200
OSCILLATOR FREQUENCY (kHz)
34661 G10
50
25
75
100
Oscillator Frequency vs V
1100
RT = 48.7k
1000
900
OSCILLATOR FREQUENCY (kHz)
800
VIN (V)
0
2
125
34661 G08
8121620
468
IN
34661 G11
10 12
24462 10141822
14 16 20
VIN (V)
18
2422
34661 G09
34661f
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TYPICAL PERFOR A CE CHARACTERISTICS
LT3466-1
TA = 25°C unless otherwise specified
Oscillator Frequency vs Temperature
1100
VIN = 3.6V
= 48.7k
R
T
1000
900
OSCILLATOR FREQUENCY (kHz)
800
–50
–25 0 25 50
TEMPERATURE (°C)
75
100
34661 G12
CTRL Voltages to Shut Down the IC
150
= 3.6V
V
IN
125
100
75
50
CTRL VOLTAGE (mV)
25
0
–50
CTRL1
02550
–25
TEMPERATURE (°C)
CTRL2
Schottky Forward Voltage Drop Schottky Leakage Current
400
350
300
250
200
150
100
50
SCHOTTKY FORWARD CURRENT (mA)
0
200 400 800
0
SCHOTTKY FORWARD DROP (mV)
600
1000
34661 G14
8
6
4
2
SCHOTTKY LEAKAGE CURRENT (µA)
0
–50
–25 0 25 50
TEMPERATURE (°C)
75 100
34661 G13
VR = 36V
VR = 20V
75 100
34661 G015
FB2 Pin Voltage vs Temperature
0.810 VIN = 3V
= 16V/30mA
V
OUT2
0.805
0.800
0.795
FB2 VOLTAGE (V)
0.790
0.785
0.780
–50
02550
–25
TEMPERATURE (°C)
75 125100
34661 G17
FB2 Pin Load Regulation
0
–0.20
(%)
–0.40
OUT2
/V
–0.60
OUT2
V
–0.80
–1.00
0
10 20
LOAD CURRENT (mA)
V V
IN OUT2
= 3V
= 16V
30
34661 G18
34661f
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LT3466-1
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PI FU CTIO S
V
(Pin 1): Output of Converter 1. This pin is connected
OUT1
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.
V
(Pin 5): Output of Converter 2. This pin is connected
OUT2
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
V
FB2
V
= 0.8V, when V
FB2
CTRL2
, when V
CTRL2
CTRL2
> 1V
< 0.8V
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 I 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
(V
LED1
I
(200mV/R
LED1
CTRL1
/5 • R
FB1
), when V
FB1
), when V
(= 200mV/R
LED1
CTRL1
CTRL1
< 1V
> 1.8V
FB1
). Any
Exposed Pad (Pin 11): The Exposed Pad must be soldered to the PCB system ground.
6
34661f
BLOCK DIAGRA
+
+
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
7
11
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
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LT3466-1
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Figure 2. Block Diagram
34661f
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LT3466-1
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OPERATIO
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Main Control Loop
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.
At power-up, the output voltages V charged up to V
(input supply voltage) via their respec-
IN
OUT1
and V
OUT2
are
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 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.
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 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 300 resistor across the inductors, al­though this will degrade efficiency.
V
OUT1
20mV/DIV
(AC-COUPLED)
V
SW1
20V/DIV
I
L1
50mA/DIV
V
= 3.6V 0.5µs/DIV 34661 F03
IN
I
= 3mA
LED1
CIRCUIT OF FIGURE 1
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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34661f
OPERATIO
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LT3466-1
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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.
V
OUT1
10V/DIV
I
L1
200mA/DIV
200µs/DIV
LED1 DISCONNECTED AT THIS POINT
V
= 3.3V
IN
CIRCUIT OF FIGURE 1
Figure 4a. Transient Response of Switcher 1 with LED1 Disconnected from the Output
34661 F04a
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 switch­ing in an erratic mode when powered from low supply voltages.
V
SW1
50V/DIV
100mA/DIV
V
SW2
50V/DIV
100mA/DIV
I
IN
200mA/DIV
I
L1
I
L2
V
= 3.6V
IN
CIRCUIT OF FIGURE 1
1µs/DIV
34661 F04b
V
OUT1
20V/DIV
V
FB1
200mV/DIV
CTRL1
5V/DIV
V
= 3.6V
IN
6 LEDs, 20mA CIRCUIT OF FIGURE 1
200µs/DIV
Figure 4b. Output 1 Open-Circuit Waveforms Figure 5. Start-Up Waveforms
34661 F05
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9
LT3466-1
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APPLICATIO S I FOR ATIO
DUTY CYCLE
The duty cycle for a step-up converter is given by:
VVV
++–
D
OUT D IN
=
VVV
OUT D CESAT
where:
= Output voltage
V
OUT
V
= Schottky forward voltage drop
D
V
= Saturation voltage of the switch
CESAT
= Input battery voltage
V
IN
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.
SETTING THE SWITCHING FREQUENCY
OPERATING FREQUENCY SELECTION
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.
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
-1
maximum number of LEDs. The LT3466
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 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 R The nominal voltage on the R
pin is 0.54V, and the
T
pin to ground.
T
current that flows into the timing resistor is used to charge and discharge an internal oscillator capacitor. A graph for selecting the value of R
for a given operating
T
frequency is shown in the Figure 6.
1000
100
(k)
T
R
10
600 180014001000
200
OSCILLATOR FREQUENCY (kHz)
34661 F06
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
CIRCUIT OF FIGURE 1
= 3.6V
V
IN
6 LEDs
80
70
60
EFFICIENCY (%)
50
40
0
5
LED CURRENT (mA)
RT = 63.4k
RT = 38.3k
10
RT = 20.5k
15
20
34661 F07
Figure 6. Timing Resistor (RT) Value
10
Figure 7. Efficiency Comparison for Different RT Resistors
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APPLICATIO S I FOR ATIO
LT3466-1
The inductor current ripple (∆IL), neglecting the drop across the Schottky diode and the switch, is given by :
VV V
=
IN MIN OUT MAX IN MIN
I
L
•–
() ( ) ()
()
VfL
OUT MAX
••
()
where:
L = Inductor
f = Operating frequency
V
V
= Minimum input voltage
IN(MIN)
OUT(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
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 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
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 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:
V
–.:06
PK
IN
=
ω
L
I
where
1
=
ω
LC
OUT
Table 3 gives inrush peak current for some component selections.
Table 3. Inrush Peak Current
VIN (V) L (µH) C
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
(µF) IP (A)
OUT
34661f
11
LT3466-1
VV
R
R
OUT2
08 1
1
2
=+
⎛ ⎝
⎞ ⎠
.
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WUUU
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 R
(Figure 1). The feedback reference is 200mV.
FB1
In order to have accurate LED current, precision resistors are preferred (1% is recommended).
FB
200
=
I
LED11
Value Selection
FB1
I
(mA) R
LED1
5 40.2
10 20.0
15 13.3
20 10.0
25 8.06
FB1
(Ω)
R
Table 4. R
mV
Most White LEDs are driven at maximum currents of 15mA to 20mA.
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 100kΩ.
C1 1µF
LT3466-1
CTRL1
34661 F08
R1
10k
PWM
10kHz TYP
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:
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
. As the CTRL1 pin voltage increases
LED1
beyond 1.8V, it has no effect on the LED current.
The LED current can be set by:
I
(V
LED1
I
(200mV/R
LED1
CTRL1
/5 • R
FB1
), when V
FB1
), when V
CTRL1
CTRL1
< 1V
> 1.8V
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 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:
V
V
FB2
V
0.8V, when V
FB2
CTRL2
, when V
CTRL2
CTRL2
> 1V
< 0.8V
34661f
12
WUUU
VIRVVV
IN MAX BASE BASE BE Q OUT CE Q( ) () ()
+• + = +
121
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APPLICATIO S I FOR ATIO
LT3466-1
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
R
1
VV
=+
OUT FB22
⎛ ⎜
1
⎟ ⎠
R
2
) is given by:
OUT2
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.
900
VIN = 3.6V
= 16V
V
OUT2
800
700
600
500
(mV)
FB2
400
V
300
200
100
0
0
0.8
0.4 V
CTRL2
Figure 9. V
FB2
(V)
vs V
1.61.2
CTRL2
2
34661 F09
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.
3V TO 5V
C
IN
I
R
C
OUT1
1µF
R
FB1
10
: TAIYO YUDEN JMK107BJ105
C
IN
: TAIYO YUDEN GMK316BJ105
C
OUT1
, C
C
OUT2
L1, L2: TOKO D52LC Q1: PHILIPS BC807
: TAIYO YUDEN TMK316BJ474
OUT3
L1
33µH
SW1 SW2V
IN
V
OUT1
LT3466-1
FB1
R
CTRL1 CTRL2
T
1µF
63.4k 1%
V
BASE
L2 33µH
OUT2
FB2
ONOFFONOFF
BASE
Q1
+– V
CE(SAT)
R1
475k
C
OUT2
0.47µF
Figure 10. Li-Ion Powered Driver for 6 White LEDs and a Secondary OLED Display with Output Disconnect
The R
I
LOAD
I
BASE
I
BASE
all conditions. The h
resistor can be calculated as:
BASE
= 30mA
I
LOAD
=
h
04.
FE MIN
()
must be chosen such that Q1 is in saturation under
can be obtained from the
FE(MIN)
Philips BC807 data sheet as:
h
This yields worst case I
I
BASE
R
BASE
100
FE(MIN)
=
0 4 100
is given by:
mA
30 .( )
BASE
075
.
as:
mA
Thus R
;
BASE
VV V V
=
––
211
OUT IN MAX CE Q BE Q
+
( ) () ()
I
B
AASE
R2
24.9k
34661 F10
16V 30mA
C
OUT3
0.47µF
34661f
13
LT3466-1
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APPLICATIO S I FOR ATIO
The V
CE(SAT)
and V
BE(SAT)
values for the transistor Q1 can
be obtained from the Philips BC807 data sheet:
R
R
BASE
BASE
VV
=
= 13.6k
+1650109
–..
mA
075
.
Picking the closest 1% resistor value yields:
R
= 14k
BASE
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
ground plane and not shared with any other component, except the R
resistor, ensuring a clean, noise-free con-
T
nection. Recommended component placement is shown in the Figure 11.
GND
C
IN
V
GND
C
OUT1
R
FB1
L1
IN
L2
C
OUT2
Figure 11. Recommended Component Placement
1
2
11
3
4
5
10
9
8
7
6
R2
R1
CTRL1
R
T
CTRL2
34661 F10
14
34661f
U
www.BDTIC.com/LINEAR
TYPICAL APPLICATIO S
Li-Ion Powered 4 White LEDs Driver and 12V Boost Converter
3V TO 5V
C
IN
1µF
12V 30mA AT V 60mA AT V
R1
R2
64.9k
34661 TA01a
4 LEDs
C
OUT1
0.47µF
R
FB1
10
C
: TAIYO YUDEN JMK107BJ105
IN
: TAIYO YUDEN EMK212BJ474
C
OUT1
: TAIYO YUDEN EMK212BJ105
C
OUT2
L1, L2: MURATA LQH32CN150K53
L1
15µH
SW1 SW2V
IN
V
OUT1
LT3466-1
FB1
R
CTRL1 CTRL2
T
38.3k 1%
V
OUT2
FB2
L2 15µH
909k
C
OUT2
1µF
ONOFFONOFF
IN IN
= 3V = 5V
Efficiency vs Load Current
90
4 LEDs/20mA V
OUT2
85
80
75
EFFICIENCY (%)
70
65
60
0
10
= 12V
VIN = 3V
20 30 40
LOAD CURRENT (mA)
LT3466-1
VIN = 5V
50 60
34661 TA01b
Li-Ion Powered Driver for 6 White LEDs and OLED Display
3V TO 5V
6 LEDs
R
FB1
10
: TAIYO YUDEN JMK107BJ105
C
IN
C
OUT1
L1, L2: 33µH TOKO D52LC
SW1 SW2V
V
C
OUT1
1µF
, C
OUT2
OUT1
FB1
CTRL1 GND CTRL2
SHUTDOWN
AND DIMMING
CONTROL 1
: TAIYO YUDEN GMK316BJ105
L1
33µH
63.4k
IN
LT3466-1
R
T
L2
33µH
V
SHUTDOWN AND DIMMING CONTROL 2
OUT2
FB2
1µF
C 1µF
OUT2
16V 30mA
R1 475k
R2
24.9k
34661 TA02a
90
85
LED DRIVER
80
75
70
65
EFFICIENCY (%)
60
VIN = 3.6V
55
6 LEDs V
OUT2
50
0
Conversion Efficiency
BOOST CONVERTER
= 16V
51015
OUTPUT CURRENT (mA)
302520
34661 TA02b
34661f
15
LT3466-1
www.BDTIC.com/LINEAR
TYPICAL APPLICATIO S
Li-Ion Powered Driver for 6 White LEDs and OLED with Output Disconnect
U
V
OUT2
20V/DIV
6 LEDs
L1
33µH
C
OUT1
1µF
R
FB1
10
: TAIYO YUDEN JMK107BJ105
C
IN
: TAIYO YUDEN GMK316BJ105
C
OUT1
, C
C
OUT2
OUT3
L1, L2: 33µH TOKO D52LC Q1: PHILIPS BC807
V
FB1
CTRL1 CTRL2
: TAIYO YUDEN TMK316BJ474
3V TO 5V
SW1 SW2V
OUT1
LT3466-1
14k
C
IN
1µF
L2 33µH
IN
V
OUT2
FB2
R
T
63.4k 1%
ONOFFONOFF
C
OUT3
0.47µF
C
OUT2
0.47µF
Q1
16V 30mA
R1 475k
R2
24.9k
34661 TA03a
Conversion Efficiency
90
VIN = 3.6V
= 16V
V
OUT2
80
200mA/DIV
CTRL2
5V/DIV
I
L2
34661 TA03c
V
= 3.6V
IN OUT2
= 16V
2ms/DIVV
70
60
EFFICIENCY (%)
50
40
0
10 15 20
5
LOAD CURRENT (mA)
25 30
34661 TA03b
34661f
16
TYPICAL APPLICATIO S
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Li-Ion Powered Driver for 6 White LEDs and OLED with Output Disconnect
6 LEDs
U
R
FB1
10
C
OUT1
1µF
3V TO 5V
L1
33µH
SW1 SW2V
V
OUT1
LT3466-1
FB1
R
CTRL1 CTRL2
IN
T
63.4k 1%
C
1µF
V
IN
OUT2
FB2
L2 33µH
LT3466-1
16V
Q1
C
OUT3
0.47µF
C
OUT2
0.47µF
ONOFFONOFF
30mA
R1 475k
R2
24.9k
34661 TA04a
V
OUT2
20V/DIV
I
200mA/DIV
CTRL2
5V/DIV
: TAIYO YUDEN JMK107BJ105
C
IN
: TAIYO YUDEN GMK316BJ105
C
OUT1
, C
C
OUT2
L1, L2: 33µH TOKO D52LC Q1: SILICONIX TPO610
: TAIYO YUDEN TMK316BJ474
OUT3
NOTE: ENSURE THAT V
OUT2
> V
IN(MAX)
+ 5V
Conversion Efficiency
90
VIN = 3.6V
= 16V
V
OUT2
85
80
L2
34661 TA04c
V
= 3.6V
IN OUT2
= 16V
2ms/DIVV
75
70
65
EFFICIENCY (%)
60
55
50
0
510 20
15
LOAD CURRENT (mA)
25
34661 TA04b
30
34661f
17
LT3466-1
www.BDTIC.com/LINEAR
U
TYPICAL APPLICATIO S
Li-Ion to 10 White LEDs and LCD Bias (±8V) with Output Disconnect
10 LEDs
R
FB1
16.5
: TAIYO YUDEN JMK107BJ105
C
IN
: TAIYO YUDEN UMK325BJ105
C
OUT1
, C
C
OUT2
C1, C2: TAIYO YUDEN UMK212BJ104 D1, D2: PHILIPS BAT54S L1: 68µH TOKO D52LC L2: 33µF TOKO D52LC
L1
68µH
SW1 SW2V
V
C
OUT1
1µF
: TAIYO YUDEN GMK316BJ105
OUT3
OUT1
FB1
CTRL1 CTRL2
ONOFF
3V TO 5V
IN
LT3466-1
R
T
147k
1µF
V
C
OUT2
IN
FB2
L2 33µH
ONOFF
C1
0.1µF
C2
0.1µF
D1
–8V 10mA
C
OUT2
1µF
D2
909k
10k
34661 TA05a
C 1µF
8V 10mA
OUT3
+8V OUTPUT
10V/DIV
–8V OUTPUT
10V/DIV
CTRL2
5V/DIV
= 3.6V
IN
+8V/10mA –8V/10mA
Conversion Efficiency
84
VIN = 3.6V 10 LEDs
82
+8V/10mA –8V/10mA
80
78
EFFICIENCY (%)
76
2ms/DIVV
34661 TA05c
74
72
0
468
2
LED CURRENT (mA)
10 12
34661 TA05b
18
34661f
PACKAGE DESCRIPTIO
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LT3466-1
U
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 SIDES)2.15 ±0.05
PACKAGE OUTLINE
0.25 ± 0.05
2.38 ±0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
PIN 1
TOP MARK
(SEE NOTE 6)
0.200 REF
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
0.50 BSC
(2 SIDES)
3.00 ±0.10 (4 SIDES)
0.75 ±0.05
1.65 ± 0.10 (2 SIDES)
0.00 – 0.05
R = 0.115
TYP
2.38 ±0.10 (2 SIDES)
BOTTOM VIEW—EXPOSED PAD
106
15
0.25 ± 0.05
0.50 BSC
0.38 ± 0.10
(DD10) DFN 1103
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.
34661f
19
LT3466-1
www.BDTIC.com/LINEAR
TYPICAL APPLICATIO
Li-Ion to 8 White LEDs and ±15V TFT LCD Bias Supply
3V TO 5V
L1
33µH
SW1 SW2V
8 LEDs
C
OUT1
1µF
V
OUT1
FB1
CTRL1 CTRL2
IN
LT3466-1
R
T
1µF
V
U
C
IN
OUT2
FB2
L2 33µH
C1
0.1µF
475k
26.7k
Conversion Efficiency
D1
–15V 10mA
C
OUT3
1µF
15V 10mA
C
OUT2
1µF
86
VIN = 3.6V 8 LEDs
84
+15V/10mA –15V/10mA
82
80
EFFICIENCY (%)
78
76
R
FB1
13.3
CIN: TAIYO YUDEN JMK107BJ105
, C
C
OUT1
OUT2
C1: TAIYO YUDEN UMK212BJ104 L1, L2: 33µH TOKO D52LC D1: PHILIPS BAT54S
ONOFF
, C
: TAIYO YUDEN GMK316BJ105
OUT3
63.4k
ONOFF
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
LT1618 Constant Current, Constant Voltage 1.4MHz, High Efficiency VIN: 1.6V to 18V, V
Boost Regulator MS/EDD Packages
LT1932 Constant Current, 1.2MHz, High Efficiency White LED Boost VIN: 1V to 10V, V
Regulator ThinSOT
LT1937 Constant Current, 1.2MHz, High Efficiency White LED Boost VIN: 2.5V to 10V, V
Regulator ThinSOT, SC70 Packages
LTC®3200-5 Low Noise, 2MHz, Regulated Charge Pump White LED Driver VIN: 2.7V to 4.5V, V
LTC3202 Low Noise, 1.5MHz, Regulated Charge Pump White LED Driver VIN: 2.7V to 4.5V, V
LTC3205 High Efficiency, Multidisplay LED Controller VIN: 2.8V to 4.5V, V
LTC3216 1A Low Noise High Current LED Charge Pump with Independent VIN: 2.9V to 4.4V, V
Flash/Torch Current Control DFN Package
LTC3453 500mA Synchronous Buck-Boost High Current LED Driver VIN: 2.7V to 5.5V, V
in Q FN QFN Package
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Boost Regulator with Integrated Schottky Diode ThinSOT Package
LT3466 Dual Constant Current, 2MHz High Efficiency White LED Boost VIN: 2.7V to 24V, V
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Current Protection DFN/TSSOP Packages
ThinSOT is a trademark of Linear Technology Corporation.
Linear Technology Corporation
20
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
www.linear.com
34661 TA06a
74
TM
Package
ThinSOT Package
MS/EDD Packages
QFN-24 Package
0
2.5
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
5 7.5 10
LED CURRENT (mA)
12.5 15
34661 TA06b
= 34V, IQ = 1.8mA, ISD < 1µA,
= 34V, IQ = 1.2mA, ISD < 1µA,
= 34V, IQ = 1.9mA, ISD < 1µA,
= 5V, IQ = 8mA, ISD < 1µA,
= 5.5V, IQ = 5mA, ISD < 1µA,
= 6V, IQ = 50µA, ISD < 1µA,
= 5.5V, IQ = 300µA, ISD < 2.5µA,
= 5.5V, IQ = 0.6mA, ISD < 6µA,
= 34V, IQ = 1.9mA, ISD < 1µA,
= 40V, IQ = 5mA, ISD < 16µA,
= 40V, IQ = 6.5mA, ISD < 1µA,
34661f
LT/TP 0705 500 • PRINTED IN USA
© LINEAR TECHNOLOGY CORPORATION 2005
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