LT3466EDD-1#PBF_技术文档

LT3466-1

White LED Driver and Boost

Converter in 3mm × 3mm

DFN Package

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FEATURES

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.

■

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

)

■

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

to2MHzrange.ThewhiteLEDdriverfeaturesalow200mV

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.

■

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

, LTC and LT are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

■

Automotive

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TYPICAL APPLICATIO

3V TO 5V

Conversion Efficiency

1µF

90

33µH

V

IN

= 3.6V

85

80

75

70

65

60

55

50

LED DRIVER

SW1

V

SW2

IN

BOOST CONVERTER

16V

6 LEDs

V

OUT2

LT3466-1

OUT1

30mA

1µF

475k

FB1

FB2

R

CTRL1

GND

CTRL2

T

63.4k

SHUTDOWN

AND DIMMING

CONTROL 1

SHUTDOWN

AND DIMMING

CONTROL 2

10Ω

24.9k

0

5

10

15

20

25

30

OUTPUT CURRENT (mA)

34661 F01a

34661 F01b

Figure 1. Li-Ion Powered Driver for 6 White LEDs and OLED Display

34661f

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LT3466-1

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ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

(Note 1)

TOP VIEW

Input Voltage (V_IN) ................................................... 24V

SW1, SW2 Voltages ................................................ 44V

ORDER PART

NUMBER

V

1

2

3

4

5

10 FB1

OUT1

SW1

V

_OUT1, V_OUT2Voltages ............................................. 44V

9

8

7

6

CTRL1

LT3466EDD-1

11

V

R

T

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

IN

SW2

OUT2

CTRL2

FB2

V

DD PART MARKING

LBRX

DD PACKAGE

10-LEAD (3mm × 3mm) PLASTIC DFN

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 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

CTRL1

●

denotes specifications that apply over the full operating temperature

range, otherwise specifications are at T = 25°C. V = 3V, V

= 3V, V

= 3V, unless otherwise specified.

A

IN

CTRL2

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

V

Minimum Operating Voltage

Maximum Operating Voltage

FB1 Voltage

2.7

22

208

812

50

V

●

192

788

200

800

10

mV

nA

FB2 Voltage

FB1 Pin Bias Current

FB2 Pin Bias Current

Quiescent Current

V

FB1

V

FB2

V

FB1

= 0.2V (Note 3)

= 0.8V (Note 3)

10

50

nA

= V = 1V

5

16

7.5

25

mA

µA

FB2

CTRL1 = CTRL2 = 0V

Switching Frequency

R = 48.7k

0.75

200

1

1.25

MHz

kHz

V

T

Oscillator Frequency Range

(Note 4)

2000

Nominal R Pin Voltage

R = 48.7k

T

0.54

T

Maximum Duty Cycle

R = 48.7k

T

R = 267k

T

●

90

96

92

99

%

T

R = 20.5k

Converter 1 Current Limit

Converter 2 Current Limit

●

310

400

320

0.01

mA

mV

µA

V

Converter 1 V

Converter 2 V

I

= 300mA

= 10V

CESAT

SW1

SW2

Switch 1 Leakage Current

V

5

SW1

Switch 2 Leakage Current

= 10V

SW2

CTRL1 Voltage for Full LED Current

CTRL2 Voltage for Full Feedback Voltage

CTRL1 or CTRL2 Voltage to Turn On the IC

●

1.8

1

V

150

mV

µA

nA

CTRL1 and CTRL2 Voltages to Shut Down Chip

CTRL1 Pin Bias Current

70

V

= 1V

●

6

9

12.5

120

CTRL1

CTRL2 Pin Bias Current

= 1V (Note 3)

10

CTRL2

34661f

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LT3466-1

ELECTRICAL CHARACTERISTICS

The

CTRL1

●

denotes specifications that apply over the full operating temperature

range, otherwise specifications are at T = 25°C. V = 3V, V

= 3V, V

= 3V, unless otherwise specified.

A

IN

CTRL2

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

V

OUT1

V

OUT2

Overvoltage Threshold

39.5

0.85

V

Schottky 1 Forward Drop

Schottky 2 Forward Drop

Schottky 1 Reverse Leakage

Schottky 2 Reverse Leakage

Soft-Start Time (Switcher 1)

Soft-Start Time (Switcher 2)

I

= 300mA

V

SCHOTTKY1

SCHOTTKY2

V

= 20V

5

µA

µs

OUT1

= 20V

OUT2

600

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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T = 25°C unless otherwise specified

A

TYPICAL PERFOR A CE CHARACTERISTICS

Switching Waveforms

(LED Driver)

Switching Waveforms

(Boost Converter)

V_OUT2

V_OUT1

100mV/DIV

(AC-COUPLED)

100mV/DIV

(AC-COUPLED)

V_SW1

20V/DIV

V_SW2

20V/DIV

I_L2

I_L1

100mA/DIV

V

_IN= 3.6V

6 LEDs AT 20mA

CIRCUIT OF FIGURE 1

0.5µs/DIV

34661 G01

V_IN= 3.6V

V_OUT2= 16V/30mA

CIRCUIT OF FIGURE 1

0.5µs/DIV

34661 G02

V

FB1

vs V

V

FB2

vs V

CTRL2

CTRL1

250

900

800

700

600

500

400

300

200

100

0

V

= 3.6V

V

= 3.6V

OUT2

IN

6 LEDs

IN

= 16V

200

150

100

50

0

1

1.5

0

0.5

2

1

1.5

0

0.5

2

V

(V)

V

(V)

CTRL1

CTRL2

34661 G03

34661 G16

34661f

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LT3466-1

TYPICAL PERFOR A CE CHARACTERISTICS ^{T = 25°C unless otherwise specified}

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A

Quiescent Current

(CTRL1 = CTRL2 = 3V)

Shutdown Current

(CTRL1 = CTRL2 = 0V)

Switch Current Limit vs Duty Cycle

500

450

400

350

300

250

200

150

100

50

7

6

5

4

3

2

1

0

70

60

T

= –50°C

T

= 25°C

A

T

= –50°C

A

UVLO

T

= 85°C

A

50

T

= 25°C

A

40

30

20

10

T

= 100°C

A

0

16

24

0

4

8

12

(V)

20

0

20

40

60

80

100

2

8

10

12

V

14

16

22 24

18 20

4

6

(V)

V

DUTY CYCLE (%)

IN

34661 G04

34661 G05

34661 G06

Open-Circuit Output Clamp

Voltage

Open-Circuit Output Clamp

Voltage

Input Current with Output 1 and

Output 2 Open Circuit

42

41

40

39

38

37

41.00

40.50

20

16

12

R

= 63.4k

R

= 63.4k

T

R = 63.4k

T

V

OUT2

40.00

39.50

V

OUT2

OUT1

V

OUT1

8

4

0

39.00

38.50

38.00

2

4

6

8

10 12 14 16 18 20 22 24

(V)

50

125

–50 –25

0

25

75 100

2

4

6

8

10 12 14 16 18 20 22 24

(V)

V

TEMPERATURE (°C)

IN

V

IN

34661 G07

34661 G08

34661 G09

Oscillator Frequency vs V

R vs Oscillator Frequency

IN

T

1000

100

10

1100

1000

900

R

T

= 48.7k

800

600

1000

1400

1800

200

2

4

6

8

10 12 14 16 18 20 22 24

(V)

V

IN

OSCILLATOR FREQUENCY (kHz)

34661 G10

34661 G11

34661f

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LT3466-1

TYPICAL PERFOR A CE CHARACTERISTICS ^{T = 25°C unless otherwise specified}

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Oscillator Frequency

vs Temperature

CTRL Voltages to Shut Down

the IC

1100

1000

900

150

125

100

75

V

= 3.6V

IN

= 48.7k

V

IN

= 3.6V

R

T

CTRL1

CTRL2

50

25

800

0

–50

–25

0

25

50

75

–50

0

25

50

75

100

–25

100

TEMPERATURE (°C)

34661 G12

34661 G13

Schottky Forward Voltage Drop

Schottky Leakage Current

8

6

4

2

400

350

300

250

200

150

V

= 36V

R

V

= 20V

R

100

50

0

–50

–25

0

25

50

75

100

200

400

800

0

1000

600

TEMPERATURE (°C)

SCHOTTKY FORWARD DROP (mV)

34661 G015

34661 G14

FB2 Pin Load Regulation

FB2 Pin Voltage vs Temperature

0

–0.20

–0.40

–0.60

0.810

0.805

0.800

0.795

0.790

0.785

0.780

V

= 3V

V

= 3V

OUT2

IN

OUT2

IN

= 16V/30mA

= 16V

–0.80

–1.00

0

10

20

30

–50

0

25

50

75 100 125

–25

LOAD CURRENT (mA)

TEMPERATURE (°C)

34661 G18

34661 G17

34661f

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LT3466-1

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PI FU CTIO S

V_OUT1(Pin1):OutputofConverter1.Thispinisconnected

to the cathode of the internal Schottky diode. Connect an

output capacitor from this pin to ground.

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. Donotleavethepinfloating. Itmustbeconnected

to ground to disable converter 2.

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.

R_T(Pin 8): Timing Resistor to Program the Switching

Frequency. The switching frequency can be programmed

from 200KHz to 2MHz.

SW2 (Pin 4): Switch Pin for Converter 2. Connect the

inductor at this pin.

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.

V

_OUT2(Pin5):OutputofConverter2.Thispinisconnected

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:

FB1 (Pin 10): Feedback Pin for Converter 1. The nominal

voltageatthispinis200mV.Connectcathodeofthelowest

LED and the feedback resistor at this pin. The LED current

can be programmed by :

V_FB2≈ V_CTRL2, when V_CTRL2< 0.8V

I_LED1≈ (V_CTRL1/5 • R_FB1), when V_CTRL1< 1V

I_LED1≈ (200mV/R_FB1), when V_CTRL1> 1.8V

V_FB2= 0.8V, when V_CTRL2> 1V

ExposedPad(Pin11):TheExposedPadmustbesoldered

to the PCB system ground.

34661f

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LT3466-1

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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 regula-

tion.Itincorporatestwosimilar,butfullyindependentPWM

converters. Operationcanbebestunderstoodbyreferring

to the Block Diagram in Figure 2. The oscillator, start-up

bias and the bandgap reference are shared between the

twoconverters.Thecontrolcircuitry,powerswitch,Schot-

tky diode etc., are similar for both converters.

TheLT3466-1candrivea6-LEDstringat3mALEDcurrent

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 3showscircuitoperationwith6whiteLEDsat3mA

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 300Ω resistor across the inductors, al-

though this will degrade efficiency.

At power-up, the output voltages V_OUT1and V_OUT2are

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

FB1pinto200mV.TheoutputoftheerroramplifierA1sets

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.

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

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

responseofthecircuitinFigure1withLED1disconnected.

With the white LEDs disconnected, the converter 1 starts

switchingatthepeakcurrentlimit. Theoutputofconverter

1startsrampingupandfinallygetsclampedat39.5V(typ).

The converter 1 will then switch at low inductor current to

regulate the output voltage. Output voltage and input

currentduringoutputopencircuitareshownintheTypical

Performance Characteristics graphs.

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

CTRL1andCTRL2arepulledlowerthan70mV.TheCTRL1

and CTRL2 pins perform independent dimming and shut-

down control for the two converters.

34661f

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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

otherconverterwillcontinuefunctioningproperly. Thephoto

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

currentduringstart-up. Soft-startisachievedbyclamping

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

showsthestart-upwaveformswithconverter1drivingsix

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.

V

OUT1

10V/DIV

I

L1

200mA/DIV

Undervoltage Lockout

34661 F04a

200µs/DIV

LED1 DISCONNECTED AT THIS POINT

= 3.3V

The LT3466-1 has an undervoltage lockout circuit which

shuts down both converters when the input voltage drops

below2.1V(typ).Thispreventstheconverterfromswitch-

ing in an erratic mode when powered from low supply

voltages.

V

IN

CIRCUIT OF FIGURE 1

Figure 4a. Transient Response of Switcher 1 with LED1

Disconnected from the Output

V

I

SW1

IN

50V/DIV

200mA/DIV

I

L1

100mA/DIV

V

OUT1

20V/DIV

V

FB1

V

SW2

50V/DIV

200mV/DIV

CTRL1

5V/DIV

I

L2

100mA/DIV

34661 F05

V

= 3.6V

200µs/DIV

IN

34661 F04b

V

= 3.6V

6 LEDs, 20mA

1µs/DIV

IN

CIRCUIT OF FIGURE 1

Figure 4b. Output 1 Open-Circuit Waveforms

Figure 5. Start-Up Waveforms

34661f

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LT3466-1

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APPLICATIO S I FOR ATIO

DUTY CYCLE

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.

The duty cycle for a step-up converter is given by:

V_OUT+ V_D– V

V_OUT+ V_D– V_CESAT

IN

D =

where:

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

maximumdutycycleincreasesastheswitchingfrequency

is decreased.

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)at2MHz.Alwaysensurethattheconverterisnot

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 (R_T). R_Tis chosen so as to run the

converters at 800kHz (R_T= 63.4k), 1.25MHz (R_T= 38.3k)

and 2MHz (R_T= 20.5k). The efficiency comparison for

different R_Tvalues is shown in Figure 7.

SETTING THE SWITCHING FREQUENCY

INDUCTOR SELECTION

TheLT3466-1usesaconstantfrequencyarchitecturethat

can be programmed over a 200KHz to 2MHz range with a

single external timing resistor from the R_Tpin to ground.

The nominal voltage on the R_Tpin 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 R_Tfor 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 fre-

quencycanbeprogrammedfrom200kHzto2MHz.Higher

switching frequency allows the use of smaller inductors

albeit at the cost of increased switching losses.

90

1000

100

10

CIRCUIT OF FIGURE 1

IN

6 LEDs

V

= 3.6V

R

= 63.4k

T

80

70

60

50

40

R

= 20.5k

T

R

= 38.3k

T

600

1000

1400

1800

200

0

5

10

LED CURRENT (mA)

15

20

OSCILLATOR FREQUENCY (kHz)

34661 F06

34661 F07

Figure 7. Efficiency Comparison for Different R Resistors

Figure 6. Timing Resistor (R ) Value

T

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LT3466-1

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APPLICATIO S I FOR ATIO

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The inductor current ripple (∆I_L), neglecting the drop

across the Schottky diode and the switch, is given by :

Z5U. A 1µF input capacitor is sufficient for most applica-

tions.Alwaysuseacapacitorwithsufficientvoltagerating.

Table2showsalistofseveralceramiccapacitormanufac-

turers. Consultthemanufacturersfordetailedinformation

on their entire selection of ceramic parts.

V

• V_OUT(MAX)– V

(

)

IN(MIN)

∆I_L

=

V_OUT(MAX)• f •L

where:

Table 2. Ceramic Capacitor Manufacturers

Taiyo Yuden

(408) 573-4150

www.t-yuden.com

L = Inductor

f = Operating frequency

AVX

(803) 448-9411

www.avxcorp.com

V

_IN(MIN)= Minimum input voltage

_OUT(MAX)= Maximum output voltage

Murata

(714) 852-2001

www.murata.com

The ∆I_Lis typically set to 20% to 40% of the maximum

inductor current.

INRUSH 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.

Recommendedinductorvaluesrangefrom10µHto68µH.

The LT3466-1 has built-in Schottky diodes. When supply

voltage is applied to the V_INpin, 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.

SeveralinductorsthatworkwellwiththeLT3466-1arelisted

in Table 1. Consult each manufacturer for more detailed

information and for their entire selection of related parts.

For low DCR inductors, which is usually the case for this

application, the peak inrush current can be simplified as

follows:

Table 1. Recommended Inductors

MAX CURRENT

L

(µH)

DCR

(Ω)

RATING

(mA)

PART

VENDOR

V – 0.6

IN

I_PK

=

LQH32CN100

LQH32CN150

LQH43CN330

10

15

33

0.44

0.58

1.00

300

310

Murata

(814) 237-1431

www.murata.com

ωL

where:

ELL6RH330M

ELL6SH680M

33

68

0.38

0.52

600

500

Panasonic

(714) 373-7939

www.panasonic.com

1

ω =

LC_OUT

A914BYW330M

A914BYW470M

A920CY680M

33

47

68

0.45

0.73

0.40

440

360

400

Toko

www.toko.com

Table 3 gives inrush peak current for some component

selections.

CDRH2D18150NC

CDRH4D18-330

CDRH5D18-680

15

33

68

0.22

0.51

0.84

0.35A

0.31A

0.43A

Sumida

(847) 956-0666

www.sumida.com

Table 3. Inrush Peak Current

V

(V)

L (µH)

15

C

OUT

(µF)

I (A)

IN

P

5

0.47

0.78

0.77

0.95

0.53

0.84

0.93

5

33

1.00

2.2

CAPACITOR SELECTION

47

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

5

68

1.00

0.47

0.22

9

47

12

33

34661f

11

LT3466-1

W U U

U

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 result-

ing in a lower peak inrush current.

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.

SETTING THE LED CURRENT

ThecurrentintheLEDstringcanbesetbythechoiceofthe

resistorR_FB1(Figure1).Thefeedbackreferenceis200mV.

In order to have accurate LED current, precision resistors

are preferred (1% is recommended).

ThecornerfrequencyofR1,C1shouldbemuchlowerthan

the frequency of the PWM signal. R1 needs to be much

smallerthantheinternalimpedanceintheCTRLpin,which

is 100kΩ.

200mV

I_LED1

R_FB1

=

LT3466-1

R1

10k

PWM

10kHz TYP

Table 4. R Value Selection

CTRL1

FB1

C1

1µF

I

(mA)

R

FB1

(Ω)

34661 F08

LED1

5

40.2

20.0

13.3

10.0

8.06

10

15

20

25

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:

Most White LEDs are driven at maximum currents of

15mA to 20mA.

R1

R2

⎛

⎝

⎞

⎟

⎠

DIMMING WHITE LEDS

V_OUT2= 0.8V 1+

⎜

TheLEDcurrentinthedrivercanbesetbymodulatingthe

CTRL1 pin. There are two different ways to control the

intensity of white LEDs.

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.

Using a DC Voltage

Forsomeapplications,thepreferredmethodofbrightness

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.

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

voltageontheCTRL2pinisrampedfrom0Vto1V, theFB2

pin voltage ramps up to 0.8V. The feedback voltage can be

programmed as:

The LED current can be set by:

V_FB2≈ V_CTRL2, when V_CTRL2< 0.8V

V_FB2≈ 0.8V, when V_CTRL2> 1V

I_LED1≈ (V_CTRL1/5 • R_FB1), when V_CTRL1< 1V

I_LED1≈ (200mV/R_FB1), when V_CTRL1> 1.8V

34661f

12

LT3466-1

W U U

APPLICATIO S I FOR ATIO

U

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

C

1µF

IN

I

R

–

BASE

Q1

16V

L1

L2

+

30mA

33µH

V

The boost converter output voltage (V_OUT2) is given by:

CE(SAT)

C

OUT3

0.47µF

SW1

V

SW2

R1

475k

OUT2

0.47µF

IN

R1

R2

⎛

⎝

⎞

⎟

⎠

V

OUT2

OUT1

C

V_OUT2= V_FB21+

OUT1

1µF

⎜

LT3466-1

FB1

FB2

CTRL2

Thus a linear change in the feedback (FB2) voltage results

in a linear change in the boost output voltage (V_OUT2).

R

R2

CTRL1

FB1

10Ω

T

24.9k

OFF ON

34661 F10

63.4k

1%

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.

C

: TAIYO YUDEN JMK107BJ105

IN

OUT1

: TAIYO YUDEN GMK316BJ105

, C

: TAIYO YUDEN TMK316BJ474

OUT2 OUT3

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

V

= 3.6V

IN

OUT2

The R_BASEresistor can be calculated as:

I_LOAD= 30mA

= 16V

800

700

600

500

400

300

200

100

0

I_LOAD

0.4h_FE(MIN)

I_BASE

=

I_BASEmust 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:

0.8

1.2

(V)

1.6

0

0.4

2

h_FE(MIN)≅ 100

V

CTRL2

34661 F09

This yields worst case I_BASEas:

Figure 9. V vs V

FB2

CTRL2

30mA

OUTPUT DISCONNECT

I_BASE

=

≅ 0.75mA

0.4(100)

R_BASEis given by:

The LT3466-1 can be used for powering white LEDs

(Channel1)andanOLEDdisplayor, LCDbias(Channel2).

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.

V

_IN(MAX)+ I_BASE• R_BASE+ V_BE(Q1)= V_OUT2+ V_CE(Q1)

V_OUT2– V_IN(MAX)+ V_CE(Q1)– V_BE(Q1)

Thus;R_BASE

=

I_BASE

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

W U U

U

APPLICATIO S I FOR ATIO

The V_CE(SAT)and V_BE(SAT)values for the transistor Q1 can

ground plane and not shared with any other component,

except the R_Tresistor, ensuring a clean, noise-free con-

nection. Recommended component placement is shown

in the Figure 11.

be obtained from the Philips BC807 data sheet:

16V – 5V + 0.1– 0.9

R_BASE

=

0.75mA

R_BASE= 13.6k

Picking the closest 1% resistor value yields:

_BASE= 14k

GND

C

R

OUT1

R

FB1

C

IN

CTRL1

CTRL2

BOARD LAYOUT CONSIDERATION

10

9

1

2

3

4

5

R

T

L1

L2

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. Minimizethelengthandareaofalltracesconnectedto

the switching node pins (SW1 and SW2). Keep the feed-

back pins (FB1 and FB2) away from the switching nodes.

V

IN

11

8

7

6

R2

R1

C

OUT2

34661 F10

GND

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

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

C

IN

1µF

90

85

80

75

70

65

60

4 LEDs/20mA

= 12V

12V

V

OUT2

L1

L2

30mA AT V = 3V

IN

V

= 5V

IN

15µH

60mA AT V = 5V

IN

R1

4 LEDs

909k

SW1

V

SW2

IN

V

= 3V

IN

V

OUT2

OUT1

C

OUT2

OUT1

0.47µF

1µF

LT3466-1

FB1

FB2

R

R2

CTRL1

CTRL2

FB1

10Ω

T

64.9k

OFF ON

34661 TA01a

38.3k

1%

0

20

30

40

50

60

10

C

: TAIYO YUDEN JMK107BJ105

IN

OUT1

OUT2

LOAD CURRENT (mA)

: TAIYO YUDEN EMK212BJ474

: TAIYO YUDEN EMK212BJ105

34661 TA01b

L1, L2: MURATA LQH32CN150K53

Li-Ion Powered Driver for 6 White LEDs and OLED Display

3V TO 5V

Conversion Efficiency

L1

33µH

L2

33µH

1µF

90

85

80

75

70

65

60

SW1

V

SW2

IN

LED DRIVER

BOOST CONVERTER

16V

6 LEDs

V

OUT2

LT3466-1

OUT1

C

30mA

OUT1

1µF

C

OUT2

1µF

R1

475k

FB1

FB2

R

CTRL1

GND

CTRL2

V

= 3.6V

IN

T

55 6 LEDs

= 16V

50

R

FB1

R2

24.9k

V

63.4k

OUT2

10Ω

SHUTDOWN

AND DIMMING

CONTROL 1

SHUTDOWN

AND DIMMING

CONTROL 2

0

5

10

15

20

25

30

34661 TA02a

OUTPUT CURRENT (mA)

C

: TAIYO YUDEN JMK107BJ105

34661 TA02b

IN

OUT1 OUT2

, C

: TAIYO YUDEN GMK316BJ105

L1, L2: 33µH TOKO D52LC

34661f

15

LT3466-1

TYPICAL APPLICATIO S

U

Li-Ion Powered Driver for 6 White LEDs and OLED with Output Disconnect

3V TO 5V

14k

C

IN

1µF

Q1

16V

30mA

L1

33µH

L2

33µH

C

OUT3

0.47µF

6 LEDs

R1

475k

SW1

V

SW2

IN

V

OUT1

V

OUT2

C

OUT1

1µF

C

OUT2

0.47µF

LT3466-1

FB1

FB2

R

T

R2

24.9k

CTRL1

CTRL2

FB1

10Ω

OFF ON

34661 TA03a

63.4k

1%

C

: TAIYO YUDEN JMK107BJ105

IN

: TAIYO YUDEN GMK316BJ105

OUT1

, C

: TAIYO YUDEN TMK316BJ474

OUT2 OUT3

L1, L2: 33µH TOKO D52LC

Q1: PHILIPS BC807

Conversion Efficiency

90

V

= 3.6V

OUT2

IN

= 16V

V

OUT2

80

20V/DIV

I

L2

70

60

200mA/DIV

CTRL2

5V/DIV

50

40

34661 TA03c

V

= 3.6V

2ms/DIV

IN

OUT2

= 16V

0

10

15

20

25

30

5

LOAD CURRENT (mA)

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

C

IN

1µF

16V

30mA

Q1

L1

L2

33µH

C

OUT3

33µH

0.47µF

6 LEDs

R1

475k

SW1

V

SW2

IN

V

OUT1

V

OUT2

C

OUT1

1µF

C

OUT2

0.47µF

LT3466-1

FB1

FB2

R

FB1

10Ω

R

T

R2

24.9k

CTRL1

CTRL2

OFF ON

34661 TA04a

63.4k

1%

C

: TAIYO YUDEN JMK107BJ105

NOTE: ENSURE THAT V

> V + 5V

IN(MAX)

IN

OUT2

: TAIYO YUDEN GMK316BJ105

OUT1

, C

: TAIYO YUDEN TMK316BJ474

OUT2 OUT3

L1, L2: 33µH TOKO D52LC

Q1: SILICONIX TPO610

Conversion Efficiency

90

V

= 3.6V

IN

OUT2

= 16V

85

80

75

V

OUT2

20V/DIV

I

L2

200mA/DIV

70

65

CTRL2

5V/DIV

60

55

50

34661 TA04c

V

= 3.6V

2ms/DIV

IN

OUT2

= 16V

5

10

20

0

25

30

15

LOAD CURRENT (mA)

34661 TA04b

34661f

17

LT3466-1

TYPICAL APPLICATIO S

U

Li-Ion to 10 White LEDs and LCD Bias (±8V) with Output Disconnect

3V TO 5V

C

IN

C1

0.1µF

1µF

D1

–8V

L1

L2

10mA

68µH

33µH

C

OUT2

1µF

10 LEDs

C2

0.1µF

SW1

V

SW2

IN

D2

8V

10mA

V

OUT2

OUT1

C

OUT1

1µF

LT3466-1

909k

10k

C

OUT3

FB1

FB2

1µF

R

T

CTRL1

CTRL2

FB1

16.5Ω

OFF ON

147k

C

: TAIYO YUDEN JMK107BJ105

IN

34661 TA05a

: TAIYO YUDEN UMK325BJ105

OUT1

, C

: TAIYO YUDEN GMK316BJ105

OUT2 OUT3

C1, C2: TAIYO YUDEN UMK212BJ104

D1, D2: PHILIPS BAT54S

L1: 68µH TOKO D52LC

L2: 33µF TOKO D52LC

Conversion Efficiency

84

82

80

78

76

74

72

V

= 3.6V

IN

10 LEDs

+8V OUTPUT

10V/DIV

+8V/10mA

–8V/10mA

–8V OUTPUT

10V/DIV

CTRL2

5V/DIV

34661 TA05c

V

= 3.6V

2ms/DIV

IN

+8V/10mA

–8V/10mA

0

4

6

8

10

12

2

LED CURRENT (mA)

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

2.15 ±0.05 (2 SIDES)

1.65 ±0.05

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

0.38 ± 0.10

10

3.00 ±0.10

(4 SIDES)

1.65 ± 0.10

(2 SIDES)

PIN 1

TOP MARK

(SEE NOTE 6)

(DD10) DFN 1103

5

1

0.25 ± 0.05

0.50 BSC

0.75 ±0.05

0.200 REF

2.38 ±0.10

(2 SIDES)

0.00 – 0.05

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 represen-

tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.

19

LT3466-1

U

TYPICAL APPLICATIO

Li-Ion to 8 White LEDs and ±15V TFT LCD Bias Supply

3V TO 5V

Conversion Efficiency

C

C1

IN

D1

1µF

0.1µF

86

84

82

80

78

76

74

V

= 3.6V

8 LEDs

+15V/10mA

–15V/10mA

IN

–15V

10mA

L2

33µH

L1

33µH

C

OUT3

1µF

SW1

V

SW2

IN

8 LEDs

V

OUT1

15V

10mA

V

OUT2

C

OUT1

1µF

LT3466-1

475k

C

OUT2

FB1

FB2

1µF

R

T

26.7k

CTRL1

CTRL2

OFF ON

R

63.4k

FB1

13.3Ω

0

5

7.5

10

12.5

15

2.5

34661 TA06a

LED CURRENT (mA)

C

: TAIYO YUDEN JMK107BJ105

IN

: TAIYO YUDEN GMK316BJ105

OUT1 OUT2 OUT3

34661 TA06b

, C

C1: TAIYO YUDEN UMK212BJ104

L1, L2: 33µH TOKO D52LC

D1: PHILIPS BAT54S

RELATED PARTS

PART NUMBER

DESCRIPTION

COMMENTS

LT1618

Constant Current, Constant Voltage 1.4MHz, High Efficiency

Boost Regulator

V : 1.6V to 18V, V

MS/EDD Packages

= 34V, I = 1.8mA, I < 1µA,

OUT(MAX) Q SD

IN

LT1932

Constant Current, 1.2MHz, High Efficiency White LED Boost

Regulator

V : 1V to 10V, V

= 34V, I = 1.2mA, I < 1µA,

IN

OUT(MAX) Q SD

ThinSOT^TMPackage

V : 2.5V to 10V, V

LT1937

Constant Current, 1.2MHz, High Efficiency White LED Boost

Regulator

= 34V, I = 1.9mA, I < 1µA,

OUT(MAX) Q SD

IN

ThinSOT, SC70 Packages

LTC^®3200-5

LTC3202

LTC3205

LTC3216

LTC3453

LT3465/LT3465A

LT3466

Low Noise, 2MHz, Regulated Charge Pump White LED Driver

Low Noise, 1.5MHz, Regulated Charge Pump White LED Driver

High Efficiency, Multidisplay LED Controller

V : 2.7V to 4.5V, V

ThinSOT Package

= 5V, I = 8mA, I < 1µA,

OUT(MAX) Q SD

IN

V : 2.7V to 4.5V, V

= 5.5V, I = 5mA, I < 1µA,

Q SD

IN

OUT(MAX)

MS/EDD Packages

V : 2.8V to 4.5V, V

= 6V, I = 50µA, I < 1µA,

Q SD

IN

QFN-24 Package

1A Low Noise High Current LED Charge Pump with Independent V : 2.9V to 4.4V, V

Flash/Torch Current Control

= 5.5V, I = 300µA, I < 2.5µA,

Q SD

IN

DFN Package

500mA Synchronous Buck-Boost High Current LED Driver

in Q FN

V : 2.7V to 5.5V, V

= 5.5V, I = 0.6mA, I < 6µA,

Q SD

IN

QFN Package

Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED

Boost Regulator with Integrated Schottky Diode

V : 2.7V to 16V, V

= 34V, I = 1.9mA, I < 1µA,

Q SD

IN

ThinSOT Package

Dual Constant Current, 2MHz High Efficiency White LED Boost

Regulator with Integrated Schottky Diode

V : 2.7V to 24V, V

= 40V, I = 5mA, I < 16µA,

Q SD

IN

DFN Package

LT3479

3A, Full Featured DC/DC Converter with Soft-Start and Inrush

Current Protection

V : 2.5V to 24V, V

IN

= 40V, I = 6.5mA, I < 1µA,

Q SD

DFN/TSSOP Packages

ThinSOT is a trademark of Linear Technology Corporation.

34661f

LT/TP 0705 500 • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

20

●

(408) 432-1900 FAX: (408) 434-0507 www.linear.com


型号：	LT3466EDD-1#PBF
厂家：	Linear
描述：	LT3466-1 - White LED Driver and Boost Converter in 3mm x 3mm DFN Package; Package: DFN; Pins: 10; Temperature Range: -40°C to 85°C 开关光电二极管
文件：	总20页 (文件大小：380K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LT3466EDD-1#PBF [Linear]

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