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FEATURES

n

LT3743

High Current Synchronous

Step-Down LED Driver with

Three-State Control

DESCRIPTION

The LT

®

3743 is a ﬁxed frequency synchronous step-down

DC/DC controller designed to drive high current LEDs. The

average current mode controller will maintain inductor

current regulation over a wide output voltage range of 0V

to (V

IN

– 2V). LED dimming is achieved through analog

dimming on the CTRL_L, CTRL_H and CTRL_T pins and

with PWM dimming on the PWM and CTRL_SEL pins.

Through the use of externally switched load capacitors,

the LT3743 is capable of changing regulated LED current

levels within several μs, providing accurate, high speed

PWM dimming between two current levels. The switching

frequency is programmable from 200kHz to 1MHz through

an external resistor on the RT pin.

Additional features include voltage regulation and

overvoltage protection set with a voltage divider from the

output to the FB pin. Overcurrent protection is provided

and set by the CTRL_H pin.

L,

LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

Protected by U.S. Patents including 7199560, 7321203 and others pending.

PWM Dimming Provides Up to 3000:1 Dimming Ratio

CTRL_SEL Dimming Provides Up to 3000:1 Dimming

Ratio Between Any Current

Three-State Current Control for Color Mixing

6% Current Regulation Accuracy

6V to 36V Input Voltage Range

Average Current Mode Control

2μs Maximum Recovery Time Between Any Current

Regulation State

<1μA Shutdown Current

Output Voltage Regulation and Open-LED Protection

Thermally Enhanced 4mm

×

5mm QFN and

28-Pin FE Package

APPLICATIONS

n

DLP Projectors

High Power Architectural Lighting

Laser Diodes

TYPICAL APPLICATION

92% Efﬁcient 20A LED Driver

EN/UVLO

PWM

CTRL_SEL

82.5k

EN/UVLO

PWM

CTRL_SEL

RT

SYNC

V

REF

LT3743

2nF

R

HOT

45.3k

40k

CTRL_L

CTRL_H

V

IN

1μF

HG

220nF

CBOOT

SW

20μF

V

CC_INT

LG

GND

CTRL_T

R

NTC

680k

SS

10nF

FB

VCL

34k

9nF

VCH

34k

9nF

3743f

4.7μF

4

V

IN

10V TO 36V

1.1μH

2.5mΩ

V

OUT

20A MAXIMUM

CTRL_SEL

5V/DIV

PWM

5V/DIV

SW

20V/DIV

20μF

1mF

SENSE

+

SENSE

–

PWMGH

PWMGL

51k

1mF

10.0k

3743 TA01a

I

LED

10A/DIV

20μs/DIV

V

IN

= 24V

0A TO 2A TO 20A LED CURRENT STEP

3743 TA01b

1

LT3743

ABSOLUTE MAXIMUM RATINGS

(Note 1)

V

IN

Voltage ................................................................40V

EN/UVLO Voltage ........................................................6V

V

REF

Voltage................................................................3V

CTRL_L, CTRL_H, CTRL_T Voltage ............................3V

PWM, CTRL_SEL Voltage ...........................................6V

SENSE

+

Voltage ........................................................40V

SENSE

–

Voltage ........................................................40V

VCH, VCL Voltage .......................................................3V

SW Voltage ...............................................................40V

CBOOT ......................................................................46V

RT Voltage...................................................................3V

FB Voltage ...................................................................3V

SS Voltage ..................................................................6V

SYNC Voltage ..............................................................6V

Storage Temperature Range................... –65°C to 150°C

Lead Temperature (Soldering, 10 sec)

TSSOP .............................................................. 300°C

PIN CONFIGURATION

TOP VIEW

V

CC_INT

CBOOT

SW

V

IN

HG

LG

V

CC_INT

GND

V

IN

22 PWMGL

21 GND

20 GND

29

GND

19 PWMGH

18 PWM

17 CTRL_SEL

16 SYNC

15 RT

9 10 11 12 13 14

GND

FB

+

1

2

3

4

5

6

7

8

9

29

GND

28 LG

27 GND

26 CBOOT

25 SW

24 HG

23 PWMGL

22 GND

21 PWMGH

20 PWM

19 CTRL_SEL

18 SYNC

17 RT

16 VCH

15 VCL

28 27 26 25 24 23

GND 1

EN/UVLO 2

V

REF

3

CTRL_T 4

GND 5

CTRL_H 6

CTRL_L 7

SS 8

SENSE

–

VCL

EN/UVLO

V

REF

CTRL_T

GND

CTRL_H

CTRL_L

SS 10

GND 11

FB 12

SENSE

+

13

SENSE

–

14

UFD PACKAGE

28-LEAD (4mm 5mm) PLASTIC QFN

T

JMAX

= 125°C,

θ

JA

= 37°C/W

EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB

SENSE

VCH

FE PACKAGE

28-LEAD PLASTIC TSSOP

T

JMAX

= 125°C,

θ

JA

= 30°C/W

EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB

ORDER INFORMATION

LEAD FREE FINISH

LT3743EUFD#PBF

LT3743IUFD#PBF

LT3743EFE#PBF

LT3743IFE#PBF

TAPE AND REEL

LT3743EUFD#TRPBF

LT3743IUFD#TRPBF

LT3743EFE#TRPBF

LT3743IFE#TRPBF

PART MARKING*

3743

LT3743FE

PACKAGE DESCRIPTION

28-Lead (4mm

×

5mm) Plastic QFN

28-Lead (4mm

×

5mm) Plastic QFN

28-Lead Plastic TSSOP

TEMPERATURE RANGE

–40°C to 125°C

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges. *The temperature grade is identiﬁed by a label on the shipping container.

Consult LTC Marketing for information on non-standard lead based ﬁnish parts.

For more information on lead free part marking, go to:

http://www.linear.com/leadfree/

For more information on tape and reel speciﬁcations, go to:

http://www.linear.com/tapeandreel/

3743f

2

LT3743

ELECTRICAL CHARACTERISTICS

PARAMETER

Input Voltage Range

V

IN

Pin Quiescent Current (Note 3)

Non-Switching Operation

Shutdown Mode

EN/UVLO Pin Falling Threshold

EN/UVLO Hysteresis

EN/UVLO Pin Current

PWM Pin Threshold

CTRL_SEL Threshold

SYNC Pin Threshold

CTRL_H and CTRL_L Pin Control Range

CTRL_H and CTRL_L Pin Current

Reference

Reference Voltage (V

REF

Pin)

Inductor Current Sensing

Full Range SENSE

+

to SENSE

–

SENSE

+

Pin Current

SENSE

–

Pin Current

Internal V

CC

Regulator (V

CC_INT

Pin)

Regulation Voltage

NMOS FET Driver (Note 2)

Non-Overlap time HG to LG

Non-Overlap time LG to HG

Minimum On-Time LG

Minimum On-Time HG

Minimum Off-Time LG

High Side Driver Switch On-Resistance

Gate Pull Up

Gate Pull Down

Low Side Driver Switch On-Resistance

Gate Pull Up

Gate Pull Down

Switching Frequency

f

SW

Soft-Start

Charging Current

Voltage Regulation Ampliﬁer

Input Bias Current

g

m

Feedback Regulation Voltage

l

The

l

denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T

A

= 25°C. V

IN

= 12V, V

EN/UVLO

= 5V, unless otherwise noted.

CONDITIONS

(Note 2)

V

PWM

= V

CTRL_SEL

= 0V, Not Switching

V

EN/UVLO

= 0V

MIN

6

1.8

0.1

1.49

V

IN

= 6V, EN/UVLO = 1.45V

1.55

130

5.5

1.0

0

100

With a 67kΩ Resistor from V

REF

to GND

V

CTRL_H

or V

CTRL_L

= 1.5V

With V

OUT

~ 4V

4.7

l

TYP

MAX

36

2.5

1

1.61

UNITS

V

mA

μA

V

mV

μA

V

l

1.5

V

nA

1.96

48

2

51

50

10

5

100

60

2.04

54

V

mV

nA

μA

5.2

V

ns

Ω

(Note 4)

V

CBOOT

– V

SW

= 5V

50

200

60

2.3

1.3

V

CC_INT

= 5V

2.5

1.3

R

T

= 40kΩ

R

T

= 200kΩ

l

930

200

1000

218

5.5

1

200

1070

233

kHz

μA

nA

μA/V

0.945

0.99

1.025

V

3743f

3

LT3743

ELECTRICAL CHARACTERISTICS

PARAMETER

PWMG Control Signals

CTRL_SEL High to PWMGL Low Delay

CTRL_SEL High to PWMGH High Delay

CTRL_SEL Low to PWMGH Low Delay

CTRL_SEL Low to PWMGL High Delay

PWMGH and PWMGL Pull-up Impedance

PWMGH and PWMGL Pull-Down Impedance

Current Control Loop g

m

Amp

Offset Voltage

Input Common Mode Range

V

CM(LOW)

V

CM(HIGH)

Output Impedance

g

m

Differential Gain

Note 1:

Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 2:

The LT3743 will function with a supply voltage as low as 4.5V, but

to keep the gate drive voltages above 4V, the V

CC_INT

pin must be tied to

V

IN

for operation below 6.0V

375

l

The

l

denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T

A

= 25°C. V

IN

= 12V, V

EN/UVLO

= 5V, unless otherwise noted.

CONDITIONS

MIN

TYP

10

150

30

170

3.2

1.75

–2.75

0

2

3.5

475

1.7

625

2.75

MAX

40

200

60

220

UNITS

ns

Ω

mV

V

MΩ

μA/V

mV/V

V

CM(HIGH)

Measured from V

IN

to V

CM

Note 3:

The LT3743E is guaranteed to meet performance speciﬁcations

from 0°C to 125°C junction temperature. Speciﬁcations over the –40°C

to 125°C operating junction temperature range are assured by design,

characterization and correlation with statistical process controls. The

LT3743I is guaranteed to meet performance speciﬁcations over the –40°C

to 125°C operating junction temperature range.

Note 4:

The minimum on and off times are guaranteed by design and are

not tested.

3743f

4

LT3743

TYPICAL PERFORMANCE CHARACTERISTICS

EN/UVLO Threshold (Falling)

1.70

10

EN/UVLO Pin Current

0.5

I

Q

in Shutdown

–50°C

1.52

130°C

I

Q

(μA)

1.58

EN/UVLO PIN CURRENT (μA)

EN/UVLO THRESHOLD (V)

1.64

8

0.4

6

0.3

130°C

0.2

4

1.46

2

25°C

130°C

–50°C

6

12

18

24

V

IN

(V)

30

36

3743 G02

0.1

25°C

0

8

16

24

V

IN

(V)

32

40

3743 G03

1.40

6

12

18

24

V

IN

(V)

30

36

3743 G01

0

Quiescent Current (Non-Switching)

2.0

2.02

V

REF

Pin Voltage

1.6

V

REF

Current Limit

QUIESCENT CURRENT (mA)

1.6

V

REF

VOLTAGE (V)

2.01

1.4

2.00

V

IN

= 36V

I

LIMIT

(mA)

T

A

= 25°C

T

A

= 130°C

1.2

T

A

= –50°C

1.0

1.2

0.8

1.99

V

IN

= 6V

0.4

0

T

A

= 25°C

T

A

= 130°C

T

A

= –50°C

6

12

18

24

V

IN

(V)

30

36

3743 G04

1.98

1.97

–50

–15

55

20

TEMPERATURE (°C)

90

125

3743 G05

0.8

6

12

18

24

V

IN

(V)

30

36

3743 G06

Oscillator Frequency

1.5

1.2MHz

1.2

FREQUENCY (MHz)

900kHz

I

LIMIT

(μA)

80

90

RT Pin Current Limit

7

Soft-Start Pin Current

6

V

IN

= 36V

I

SS

(μA)

5

V

IN

= 6V

0.9

70

0.6

60

4

0.3

220kHz

50

0

–50

–15

55

20

TEMPERATURE (°C)

90

125

3743 G07

40

–50

–15

55

20

TEMPERATURE (°C)

90

125

3743 G08

3

–50

–15

55

20

TEMPERATURE (°C)

90

125

3743 G09

3743f

5

LT3743EFETRPBF

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