LT1768_15 Datasheet, PDF (1/20 Pages) Linear Technology – High Power CCFL Controller for Wide Dimming Range and Maximum Lamp Lifetime

FEATURES
s _{Ultrawide Multimode Dimming}^TM _Range
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 SSOUP Package}
APPLICATIO S
s _{Desktop Flat Panel Displays}
s _{Multiple Lamp Displays}
s _{Notebook LCD Displays}
s _{Point of Sale Terminal Displays}
LT1768
High Power CCFL Controller
for Wide Dimming Range and
Maximum Lamp Lifetime
DESCRIPTIO
The LT^®1768 is designed to control single or multiple cold
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 65µA. It is available in a small 16-lead
SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Multimode Dimming is a trademark of Linear Technology Corporation.
*Patent Pending
TYPICAL APPLICATIO
C4-WIMA MKP2
L1-COILTRONICS UP4-680
T1-2 CTX110607 IN PARALLEL
Q1-ZDT1048
*R5 CAN BE METAL PCB TRACE
LAMP
PGND GATE
33pF
LAMP
V_IN
8V – 24V
C1
33µF
33pF
T1
4
6
10
53
2
1
C4
0.33µF
PROG
0V TO 5V OR
1kHz PWM
C2
0.033µF
C3
0.1µF
DI02
DI01
V_IN
V_REF
SENSE FAULT
LT1768
V_C
SHDN
AGND
C_T
R_MIN
R_MAX
R4
16.2k
PROG PWM
R1
49.9k
C4
10µF
250Ω
5V
1/4W
Q1
0.1µF
R2
40.2k
R3
60.4k
MBRS130T3
100
2200pF
Q1
L1
68µH
Si3456DY
R5*
0.025
1768 TA01
Figure 1. 14W CCFL Supply Produces a 100:1 Dimming Ratio While
Maintaining Minimum and Maximum Lamp Current Specifications
Lamp Output and Dimming
Ratio vs Lamp Current
10000
1000
DIMMING RATIO (NITS/NITS)
100
LAMP OUTPUT (NITS)
10
1
0.1
0
LAMP MANUFACTURERS
SPECIFIED CURRENT RANGE
2
4
6
8
10
LAMP CURRENT (mA)
1768 TA01b
1