LINEAR TECHNOLOGY LT3518 Technical data

LT3518

Full-Featured LED Driver

with 2.3A Switch Current

FEATURES

n

3000:1 True Color PWM™ Dimming Ratio

n

2.3A, 45V Internal Switch

n

100mV High Side Current Sense

n

Open LED Protection

n

Adjustable Frequency: 250kHz to 2.5MHz

n

Wide Input Voltage Range:
Operation from 3V to 30V
Transient Protection to 40V

n

Operates in Boost, Buck Mode and Buck-Boost Mode

n

Gate Driver for PMOS LED Disconnect*

n

Constant-Current and Constant-Voltage Regulation

n

CTRL Pin Provides 10:1 Analog Dimming

n

Low Shutdown Current: <1μA

n

Available in (4mm × 4mm) 16-Lead QFN and 16-Pin

TSSOP Packages

APPLICATIONS

n

Display Backlighting

n

Automotive and Avionic Lighting

n

Illumination

n

Scanners

DESCRIPTION

The LT®3518 is a current mode DC/DC converter with an
internal 2.3A, 45V switch specifi cally designed to drive
LEDs. The LT3518 operates as a LED driver in boost, buck
mode and buck-boost mode. It combines a traditional
voltage loop and a unique current loop to operate as a
constant-current source or constant-voltage source. Pro­grammable switching frequency allows optimization of the
external components for effi ciency or component size. The
switching frequency of the LT3518 can be synchronized
to an external clock signal. The LED current is externally
programmable with a 100mV sense resistor. The external
PWM input provides 3000:1 LED dimming. The CTRL pin
provides further 10:1 dimming ratio.

The LT3518 is available in the tiny footprint 16-Lead QFN
(4mm × 4mm) and the 16-Pin TSSOP package. The LT3518
provides a complete solution for both constant-voltage
and constant-current applications.

L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. True Color
PWM is a trademark of Linear Technology Corporation. Patent Pending. All other trademarks are
the property of their respective owners. *Patents Pending.

TYPICAL APPLICATION

1.5A Buck Mode LED Driver

ISP

V

IN

SHDN

CTRL

PWM

SYNC

TGEN GNDV

68mΩ M1

ISN

TG

LT3518

REFVC

0.1μF

SW

FB

SS

R

T

PV

24V

V

3.3V

IN

IN

2.2μF

V

REF

PWM

2.2μF

1.5A

16.9k
1MHz

15μH

0.1μF

10μF

3518 TA01a

100

CTRL = V

90

80

70

EFFICIENCY (%)

60

50

40

0

Effi ciency

REF

20 40 60 80

PWM DUTY CYCLE (%)

100

3518 TA01b

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LT3518

ABSOLUTE MAXIMUM RATINGS

VIN, SHDN, PWM, TGEN (Note 3)..............................40V

SW, ISP, ISN, TG ........................................................45V

TG Pin Below ISP Pin ................................................10V

FB, SYNC, SS, CTRL ...................................................6V

V

C

, RT, V

.................................................................3V

REF

Operating Junction Temperature Range (Notes 2, 4)

LT3518E .............................................–40°C to 125°C

LT3518I .............................................. –40°C to 125°C

LT3518H ............................................ –40°C to 150°C

PIN CONFIGURATION

TOP VIEW

TG

ISP

ISN

TGEN

16 15 14 13

FB

1SW

SW

2

V

IN

SHDN

16-LEAD (4mm × 4mm) PLASTIC QFN

T

EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB

JMAX

17

3

4

5 6 7 8

R

REF

V

UF PACKAGE

= 125°C, θJA = 36°C/W

12

V

11

C

CTRL

10

PWM

9

T

SS

SYNC

(Note 1)

Storage Temperature Range

QFN .................................................... –65°C to 125°C

TSSOP ............................................... –65°C to 150°C

Lead Temperature (Soldering, 10 sec)

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

TOP VIEW

1

V

IN

2

SHDN

3

V

REF

4

R

T

5

SYNC

6

SS

7

PWM

8

CTRL

16-LEAD PLASTIC TSSOP

T

= 150°C, θJA = 40°C/W, θ

JMAX

17

GND

FE PACKAGE

16

15

14

13

12

11

10

9

JC(PAD)

SW

SW

TG

ISP

ISN

TGEN

FB

V

C

= 10°C/W

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LT3518EUF#PBF LT3518EUF#TRPBF 3518

LT3518IUF#PBF LT3518IUF#TRPBF 3518

16-Lead (4mm × 4mm) Plastic QFN

16-Lead (4mm × 4mm) Plastic QFN

–40°C to 125°C

–40°C to 125°C

LT3518EFE#PBF LT3518EFE#TRPBF 3518FE 16-Lead Plastic TSSOP –40°C to 125°C

LT3518IFE#PBF LT3518IFE#TRPBF 3518FE 16-Lead Plastic TSSOP –40°C to 125°C

LT3518HFE#PBF LT3518HFE#TRPBF 3518HFE 16-Lead Plastic TSSOP –40°C to 150°C

Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based fi nish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/

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2

LT3518

ELECTRICAL CHARACTERISTICS

The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum VIN Operating Voltage 3V

Maximum V

Current Sense Voltage (V

10% Scale Current Sense Voltage (V

Current Sense Voltage Line Regulation 2V < V

Supply Current PWM > 1.5V, VC = 0V

V

IN

Switching Frequency R

R

Voltage 1V

T

Soft-Start Pin Current SS = 0.5V, Out of Pin 6 9 12 μA

SYNC Pull-Down Current (Into the Pin) V

SYNC Input Low 0.4 V

SYNC Input High 1.5 V

Maximum Duty Cycle R

Switch Current Limit 2.3 2.8 3.5 A

Switch V

Switch Leakage Current V

CTRL Input Bias Current Current Out of Pin, V

Error Amplifi er Transconductance 550 μS

Output Impedance 1000 kΩ

V

C

Idle Input Bias Current PWM = 0, VC = 1V –20 0 20 nA

V

C

FB Pin Input Bias Current Current Out of Pin, V

FB Pin Threshold

, ISN Idle Input Bias Current PWM = 0V 300 nA

ISP

ISP , ISN Full-Scale Input Bias Current ISP Tied to ISN, V

SHDN Voltage High 1.5 V
SHDN Voltage Low 0.4 V
SHDN Pin Bias Current 60 100 μA

PWM Input High Voltage 1.5 V

PWM Input Low Voltage 0.4 V

PWM Pin Bias Current 60 120 μA

TGEN Input High Voltage 1.5 V

TGEN Input Low Voltage 0.4 V

TGEN Pin Bias Current TGEN = 5V 100 200 μA

Pin Voltage I

V

REF

Operating Voltage Continuous Operation (Note 3) 30 V

IN

– V

ISP

CESAT

)V

ISN

– V

ISP

)V

ISN

= 25°C. (Note 2) VIN = 5V, SHDN = 5V, PWM = 5V unless otherwise noted.

A

l

l

l

96 100

0.85

2.25
220

95
94
85

100

6

4.5

0.1

1.0

2.5

250

97
96
90
74

103 mV

mV

10

mA
mA

1

1.15

2.7

270

MHz
MHz

kHz

μA

V

CTRL
CTRL

CTRL

= 2V, V
= 2V, V

= 100mV, V

ISP

= 24V, VC = 1V

ISP

= 0V, VC = 1V

ISP

= 24V, VC = 1V 9 mV

ISP

< 45V 0.03 %/V

PWM = 0V
SHDN = 0V

= 16.7k

T

R

= 4.03k

T

R

= 91.5k

T

= 2V 60 μA

SYNC

= 91.5k (250kHz)

T

SYNC = 300kHz Clock Signal, R
R

= 16.7k (1MHz)

T

R

= 4.03k (2.5MHz)

T

= 91.5k

T

ISW = 1.5A 400 mV

= 45V, PWM = 0V 2 μA

SW

= 0.1V 20 100 nA

CTRL

= 0.5V 20 100 nA

FB

l

0.98 1.01 1.04 V

= –100μA

REF

= 24V, V

ISP

= 2V 20 μA

CTRL

l

1.96 2 2.04 V

%
%
%
%

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3

LT3518

ELECTRICAL CHARACTERISTICS

The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T

PARAMETER CONDITIONS MIN TYP MAX UNITS

V

Pin Voltage Line Regulation 3V < VIN < 40V 0.03 %/V

REF

Gate Turn-On Delay C

Gate Turn-Off Delay C

(V

Top Gate Drive V

– VTG)V

GS

ISP

= 25°C. (Note 2) VIN = 5V, SHDN = 5V, PWM = 5V unless otherwise noted.

A

= 1nF Between ISP and TG 200 ns

LOAD

= 1nF Between ISP and TG 200 ns

LOAD

= 24V, TGEN = 5V

ISP

PWM = 0V

7
0 0.3

V

V

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 LT3518E is guaranteed to meet performance specifi cations
from 0°C to 125°C junction temperature. Specifi cations over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT3518I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT3518H is guaranteed over the full –40°C to
150°C operating junction temperature range. Operating lifetime is derated
at junction temperatures greater than 125°C.

Note 3: Absolute maximum voltage at VIN, SHDN, PWM and TGEN pins
is 40V for nonrepetitive 1 second transients and 30V for continuous
operation.

Note 4: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed the maximum operating junction temperature
when overtemperature protection is active. Continuous operation above
the specifi ed maximum operating junction temperature may impair device
reliability.

4

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TYPICAL PERFORMANCE CHARACTERISTICS

V

– V

Threshold vs V

ISN

= 24V

CTRL

3.0

2.5

2.0

120

100

80

ISP

VIN = 5V
V

ISP

= 1V

V

C

= 25°C

T

A

LT3518

Switch Current Limit
vs Duty Cycle

60

THRESHOLD (mV)

ISN

40

– V

ISP

V

20

0

0

0.4 0.8

0.2 0.6
V

CTRL

Oscillator Frequency vs R

10000

TA = 25°C

1000

OSCILLATOR FREQUENCY (kHz)

100

1

RT (kΩ)

1.2

1.0

(V)

1.4

3518 G01

T

10 100

3518 G03

1.6

1.5

1.0

CURRENT LIMIT (A)

0.5

TA = 25°C

0

0

20 40 60 80

V

– V

ISP

Temperature

105

V

= 2V

CTRL

104

= 5V

V

IN

= 25°C

T

A

103

= 1V

V

C

102

101

100

THRESHOLD (mV)

99

ISN

98

– V

ISP

V

97

96

95

10

0

DUTY CYCLE (%)

Threshold vs

ISN

20

V

(V)

ISP

100

3518 G02

30

40

50

3518 G04

Switch Current Limit vs
Temperature

3.0
VIN = 5V

2.8

2.6

2.4

CURRENT LIMIT (A)

2.2

2.0

–40 –15

35

–10

TEMPERATURE (°C)

Oscillator Frequency vs
Temperature

2.5
VIN = 5V

= 6.04k

R

T

2.3

2.1

1.9

1.7

OSCILLATOR FREQUENCY (MHz)

60

85

110 135 160

3518 G05

1.5

–40 –20

40

20

0

TEMPERATURE (°C)

60

80

160100 120 140

3518 G06

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LT3518

TYPICAL PERFORMANCE CHARACTERISTICS

V

– V

ISN

= 2V

= 5V

10

Threshold vs V

30

20

V

(V)

ISP

ISP

40

3518 G07

2.02

2.01

(V)

2.00

REF

V

1.99

50

1.98

ISP

105

V

CTRL

104

V

IN

= 25°C

T

A

103

= 1V

V

C

102

101

100

THRESHOLD (mV)

99

ISN

98

– V

ISP

V

97

96

95

0

Reference Voltage vs
Temperature

VIN = 5V

–40

–20 0 20 40

60 80 100 120 140 160

TEMPERATURE (°C)

3518 G08

Quiescent Current vs V

8

TA = 25°C

= 0V

V

C

7

6

5

4

CURRENT (mA)

3

IN

V

2

1

0

0

10

VIN (V)

IN

1.04

1.03

1.02

1.01

1.00

FB PIN THRESHOLD (V)

0.99

0.98

20

30

40

3518 G09

–40

PMOS Turn-On PMOS Turn-Off

5V

PWM

0V

5V

PWM

0V

FB Pin Threshold vs Temperature

VIN = 5V

–20 0 20 40

60 80 140 160100 120

TEMPERATURE (°C)

3518 G10

6

40V

TG

30V

ISP

= 40V

200ns/DIVV

3518 G11

40V

TG

30V

ISP

= 40V

200ns/DIVV

3518 G12

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