LINEAR TECHNOLOGY LT3497 Technical data

LT3497

Dual Full Function White

LED Driver with Integrated

Schottky Diodes

FEATURES

■

Drives Up to 12 White LEDs (6 in Series per

Converter) from a 3V Supply

■

Two Independent Boost Converters Capable of

Driving Asymmetric LED Strings

■

Independent Dimming and Shutdown Control of the

Two LED Strings

■

High Side Sense Allows “One Wire Current Source”

per Converter

■

Internal Schottky Diodes

■

Open LED Protection (32V)

■

2.3MHz Switching Frequency

■

±5% Reference Accuracy

■

VIN Range: 2.5V to 10V

■

Dual Wide 250:1 True Color PWMTM Dimming

■

Requires Only 1µF Output Capacitor per Converter

■

Available in a 3mm × 2mm 10-Pin DFN Package

APPLICATIONS

■

Cellular Phones

■

PDAs, Handheld Computers

■

Digital Cameras

■

MP3 Players

■

GPS Receivers

DESCRIPTION

The LT®3497 is a dual full function step-up DC/DC con­verter specifi cally designed to drive up to 12 white LEDs
(6 white LEDs in series per converter) from a Li-Ion cell. 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 two independent converters are capable of driving
asymmetric LED strings. Accurate LED dimming and
shutdown of the two LED strings can also be controlled
independently. The LT3497 features a unique high side LED
current sense that enables the part to function as a “one
wire current source;” one side of the LED string can be
returned to ground anywhere, allowing a simpler 1-wire
LED connection. Traditional LED drivers use a grounded
resistor to sense LED current, requiring a 2-wire connec­tion to the LED string.

The 2.3MHz switching frequency allows the use of tiny
inductors and capacitors. Few external components are
needed for the dual white LED Driver: open-LED protection
and the Schottky diodes are all contained inside the 3mm
× 2mm DFN package. With such a high level of integra­tion, the LT3497 provides a high effi ciency dual white LED
driver solution in the smallest of spaces.

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

TYPICAL APPLICATION

Li-Ion Power Driver for 4/4 White LEDs

V

IN

3V TO 5V

1µF

15µH

SW1 V

CAP1 CAP2

LED1 LED2
CTRL1

OFF ON
SHUTDOWN

AND DIMMING

CONTROL 1

IN

LT3497

GND

15µH

SW2

CTRL2

SHUTDOWN

AND DIMMING

CONTROL 2

OFF ON

Effi ciency

80

= 3.6V

V

IN

4/4LEDs

1µF

10Ω10Ω

1µF

3497 TA01a

75

70

65

EFFICIENCY (%)

60

55

50

0

5101520

LED CURRENT (mA)

3497 TA01b

3497f

1

LT3497

(Note 1)

Input Voltage (VIN) ...................................................10V

SW1, SW2 Voltages ..................................................35V

CAP1, CAP2 Voltages ................................................35V

CTRL1, CTRL2 Voltages ............................................10V

LED1, LED2 Voltages ................................................35V

Operating Temperature Range ................. –40°C to 85°C

Maximum Junction Temperature .......................... 125°C

Storage Temperature Range ...................–65°C to 125°C

PACKAGE/ORDER INFORMATIONABSOLUTE MAXIMUM RATINGS

TOP VIEW

1

LED1

2

CTRL1

3

GND

4

CTRL2

5

LED2

10-LEAD (3mm × 2mm) PLASTIC DFN

T

JMAX

EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB

DDB PACKAGE

= 125°C, θJA = 76°C/W, θJC = 13.5°C/W

ORDER PART NUMBER DDB PART MARKING

LT3497EDDB LCGT

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 specifi ed with wider operating temperature ranges.

10

CAP1

9

SW1

11

8

V

IN

7

SW2

6

CAP2

ELECTRICAL CHARACTERISTICS

The
temperature range, otherwise specifi cations are at T

= 25°C. VIN = 3V, V

A

●

denotes the specifi cations which apply over the full operating

CTRL1

= V

CTRL2

= 3V.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Operating Voltage 2.5 V

– V

LED Current Sense Voltage (V

LED Current Sense Voltage (V

LED1

) Between

OS

) – (V

CAP2

– V

Offset Voltage (V
(V

– V

CAP1

CAP1

CAP2

LED2

) Voltages

)V

LED1

– V

)V

LED2

CAP1, LED1 Pin Bias Current V

CAP2, LED2 Pin Bias Current V

, V

V

V

CAP1

CAP2

Common Mode Minimum Voltage 2.5 V

LED1

, V

Common Mode Minimum Voltage 2.5 V

LED2

Supply Current V

CAP1

CAP2

V

OS

CAP1

CAP2

CAP1

V

CTRL1

V

CTRL1

= 16V

= 16V

= |(V

= 16V, V

= 16V, V

= V

= V

= V

– V

CAP1

CAP2

CTRL2

CTRL2

) – (V

LED1

= 16V 20 40 µA

LED1

= 16V 20 40 µA

LED2

= 16V, V

= 3V

= 0V 12 18 µA

LED1

CAP2

= V

– V

)| 0 2 8 mV

LED2

= 15V,

LED2

●

190 200 210 mV

●

190 200 210 mV

6 8.5 mA

Switching Frequency 1.8 2.3 2.8 MHz

Maximum Duty Cycle 88 92 %

●

Converter 1 Switch Current Limit SW1

Converter 2 Switch Current Limit SW2

Converter 1 V

Converter 2 V

CESAT

CESAT

Switch 1 Leakage Current V

Switch 2 Leakage Current V

I

= 200mA 200 mV

SW1

I

= 200mA 200 mV

SW2

= 16V 0.1 5 µA

SW1

= 16V 0.1 5 µA

SW2

300 400 mA

●

300 400 mA

2

3497f

LT3497

ELECTRICAL CHARACTERISTICS

The
temperature range, otherwise specifi cations are at T

PARAMETER CONDITIONS MIN TYP MAX UNITS

Voltage for Full LED Current V

V

CTRL1

Voltage for Full LED Current V

V

CTRL2

or V

V

CTRL1

and V

V

CTRL1

CTRL1, CTRL2 Pin Bias Current 100 nA

CAP1 Pin Overvoltage Protection

CAP2 Pin Overvoltage Protection

Schottky 1 Forward Drop I

Schottky 2 Forward Drop I

Schottky 1 Reverse Leakage Current V

Schottky 2 Reverse Leakage Current 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.

Voltage to Turn On the IC

CTRL2

Voltages to Shut Down the IC 50 mV

CTRL2

= 25°C. VIN = 3V, V

A

= 16V

CAP1

= 16V

CAP2

SCHOTTKY1

SCHOTTKY2

= 25V 4 µA

R1

= 25V 4 µA

R2

●

denotes the specifi cations which apply over the full operating

= V

CTRL1

= 100mA 0.8 V

= 100mA 0.8 V

Note 2: The LT3497E is guaranteed to meet performance specifi cations
from 0°C to 85°C. Specifi cations over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.

CTRL2

= 3V.

●

1.5 V

●

1.5 V

●

100 mV

●

30 32 34 V

●

30 32 34 V

3497f

3

LT3497

TYPICAL PERFORMANCE CHARACTERISTICS

= 25°C unless otherwise specifi ed)

(T

A

Switch Saturation Voltage
(V

)

CESAT

450

400

350

300

250

200

150

100

SWITCH SATURATION VOLTAGE (mV)

50

0

50

0

100

SWITCH CURRENT (mA)

Sense Voltage (V
vs V

240

200

160

120

SENSE VOLTAGE (mV)

CTRL

80

40

150

–50°C

–50°C

125°C

200

CAP

25°C

125°C

250

– V

300

LED

25°C

)

350

3497 G01

Schottky Forward Voltage Drop

400

350

300

250

200

150

100

50

SCHOTTKY FORWARD CURRENT (mA)

400

0

0

SCOTTKY FORWARD DROP (mV)

Open-Circuit Output Clamp
Voltage

34

33

32

31

OUTPUT CLAMP VOLTAGE (V)

125°C

25°C

–50°C

200 400 800

25°C

600

–50°C

125°C

3497 G02

1000

Shutdown Current

= V

(V

CTRL1

15

12

9

6

SHUTDOWN CURRENT (µA)

3

0

2

0

CTRL2

4

VIN (V)

= 0V)

–50°C

Input Current in Output Open
Circuit

30

25

150°C

20

15

10

INPUT CURRENT (mA)

5

–50°C

6

25°C

125°C

25°C

8

10

3497 G03

4

0

0

500 1000 1500 2000

V

(mV)

CTRL

3497 G04

30

2

0

4

VIN (V)

6

8

10

3497 G05

0

2

46 810

VIN (V)

3497 G06

Switching Waveform Transient Response

V

V

SW

10V/DIV

V

CAP

50mV/DIV

100mA/DIV

I

L

VIN = 3.6V
FRONT PAGE
APPLICATION CIRCUIT

200ms/DIV

3497 G07

CAP

5V/DIV

V

CTRL

5V/DIV

200mA/DIV

I

L

VIN = 3.6V
FRONT PAGE
APPLICATION CIRCUIT

1ms/DIV

3497 G08

3497f

TYPICAL PERFORMANCE CHARACTERISTICS

Quiescent Current Current Limit vs Temperature

7

6

5

4

3

2

QUIESCENT CURRENT (mA)

1

0

246 10

0

125°C

25°C

–50°C

8

VIN (V)

3497 G09

500

450

400

CURRENT LIMIT (mA)

350

300

–50

–25 0 25 50

TEMPERATURE (°C)

75 100 125

= 25°C unless otherwise specifi ed)

(T

A

Schottky Leakage Current vs
Temperature (–50°C to 125°C)

3

2

1

SCHOTTKY LEAKAGE CURRENT (µA)

0

–50 –25 0 25 50

3497 G11

TEMPERATURE (°C)

LT3497

24V

16V

75 100 125

3497 G12

Open-Circuit Output Clamp Voltage
vs Temperature (–50°C to 125°C)

36

34

32

30

OUTPUT CLAMP VOLTAGE (V)

28

–50

–25 0 25 50

TEMPERATURE (°C)

75 100 125

Sense Voltage (V
vs V

CAP

208

204

3497 G13

INPUT CURRENT (mA)

– V

CAP

LED

Input Current in Output Open
Circuit vs Temperature
(–50°C to 125°C)

30

VIN = 3V

25

20

15

10

5

0

–50

–25 0

TEMPERATURE (°C)

50 100 125

25 75

)

Switching Frequency vs
Temperature

2.60
VIN = 3.6V

2.50

2.40

2.30

2.20

2.10

2.00

SWITCHING FREQUENCY (MHz)

1.90

1.80

–25 0 50

–50

3497 G14

Sense Voltage vs Temperature

206

202

25

TEMPERATURE (°C)

75 100 125

3497 G15

200

196

SENSE VOLTAGE (mV)

192

188

10

5

15

125°C

–50°C

V

CAP

(V)

25°C

20

25

30

3497 G16

198

SENSE VOLTAGE (mV)

194

190

–50

–25 0 25 50

TEMPERATURE (°C)

75 100 125

3497 G17

3497f

5

LT3497

PIN FUNCTIONS

LED1 (Pin 1): Connection point for the anode of the fi rst
LED of the fi rst set of LEDs and the sense resistor (R

SENSE1

).

The LED current can be programmed by:

200

mV

=

I

LED

R

SENSE11

CTRL1 (Pin 2): Dimming and Shutdown Pin. Connect
CTRL1 below 50mV to disable converter 1. As the pin volt­age is ramped from 0V to 1.5V, the LED current ramps from
0 to (I

= 200mV/R

LED1

). The CTRL1 pin must not

SENSE1

be left fl oating.

GND (Pin 3): Connect the GND pin to the PCB system
ground plane.

CTRL2 (Pin 4): Dimming and Shutdown Pin. Connect
CTRL2 below 50mV to disable converter 2. As the pin volt­age is ramped from 0V to 1.5V, the LED current ramps from
0 to (I

= 200mV/R

LED2

). The CTRL2 pin must not

SENSE2

be left fl oating.

LED2 (Pin 5): Connection point for the anode of the fi rst
LED of the second set of LEDs and the sense resistor
(R

). The LED current can be programmed by:

SENSE2

CAP2 (Pin 6): Output of Converter 2. This pin is connected
to the cathode of internal Schottky diode 2. Connect the
output capacitor to this pin and the sense resistor (R

SENSE2

)

from this pin to LED2 pin.

SW2 (Pin 7): Switch Pin. Minimize trace area at this pin
to minimize EMI. Connect the inductor at this pin.

(Pin 8): Input Supply Pin. This pin must be locally

V

IN

bypassed.

SW1 (Pin 9): Switch Pin. Minimize trace area at this pin
to minimize EMI. Connect the inductor at this pin.

CAP1 (Pin 10): Output of Converter 1. This pin is connected
to the cathode of internal Schottky diode 1. Connect the
output capacitor to this pin and the sense resistor (R

SENSE1

)

from this pin to LED1 pin.

Exposed Pad (Pin 11): Ground. Must be soldered to
PCB.

200

mV

=

I

LED

R

SENSE22

6

3497f