LT1768

1

The LT

cathode fluorescent lamp (CCFL) displays. A unique Mul-

timode Dimming scheme* combines both linear and PWM

control functions to maximize lamp life, efficiency, and

dimming range. Accurate maximum and minimum lamp

currents can be easily set. The LT1768 can detect and

protect against lamp failures and overvoltage start-up

conditions. It is designed to provide maximum flexibility

with a minimum number of external components.

The LT1768 is a current mode PWM controller with a 1.5A

MOSFET driver for high power applications. It contains a

350kHz oscillator, 5V reference, and a current sense

comparator with a 100mV threshold. It operates from an

8V to 24V input voltage. The LT1768 also has undervoltage

lockout, thermal limit, and a shutdown pin that reduces

supply current to 65

µA. It is available in a small 16-lead

SSOP package.

s

Ultrawide Multimode Dimming

s

Multiple Lamp Capability

s

Programmable PWM Dimming Range and

Frequency

s

Precision Maximum and Minimum Lamp

Currents Maximize Lamp Lifetime

s

No Lamp Flicker Under All Supply and Load

Conditions

s

Open Lamp Detection and Protection

s

350kHz Switching Frequency

s

1.5A MOSFET Gate Driver

s

100mV Current Sense Threshold

s

5V Reference Voltage Output

s

The 16-Lead SSOP Package

High Power CCFL Controller

for Wide Dimming Range and

Maximum Lamp Lifetime

s

Desktop Flat Panel Displays

s

Multiple Lamp Displays

s

Notebook LCD Displays

s

Point of Sale Terminal Displays

Figure 1. 14W CCFL Supply Produces a 100:1 Dimming Ratio While

Maintaining Minimum and Maximum Lamp Current Specifications

1768 TA01

C4

0.33

µF

250

Ω

1/4W

R5*

0.025

Q1

Q1

L1

68

µH

T1

33pF

33pF

0.1

µF

C1

33

µF

Si3456DY

MBRS130T3

LAMP

LAMP

R3

60.4k

R1

49.9k

R2

40.2k

R4

16.2k

C3

0.1

µF

C4

10

µF

C2

0.033

µF

8V – 24V

PROG

0V TO 5V OR

1kHz PWM

LT1768

DI02

PGND

GATE

AGND

PROG

DI01

SENSE

SHDN

PWM

FAULT

5V

2200pF

100

610

4

53

2

1

C4-WIMA MKP2

L1-COILTRONICS UP4-680

T1-2 CTX110607 IN PARALLEL

Q1-ZDT1048

*R5 CAN BE METAL PCB TRACE

LAMP CURRENT (mA)

0

10000

1000

100

10

1

0.1

8

1768 TA01b

2

4

6

10

DIMMING RATIO (NITS/NITS)

LAMP OUTPUT (NITS)

LAMP MANUFACTURERS

SPECIFIED CURRENT RANGE

Lamp Output and Dimming

Ratio vs Lamp Current

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

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

Multimode Dimming is a trademark of Linear Technology Corporation.

*Patent Pending