LT1786FCS Linear Technology, LT1786FCS Datasheet - Page 11

• Manufacturer Part Number: LT1786FCS
• Description: IC SW REG CCFL SMBUS PROG 16SOIC
• Manufacturer: Linear Technology

Specifications of LT1786FCS

• Applications: Converter, CCFL
• Voltage - Input: 4.5 ~ 30 V
• Number Of Outputs: 1
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Output: -

APPLICATIONS
Introduction
Current generation portable computers and instruments
use backlit Liquid Crystal Displays (LCDs). Cold Cathode
Fluorescent Lamps (CCFLs) provide the highest available
efficiency in back lighting the display. Providing the most
light out for the least amount of input power is the most
important goal. These lamps require high voltage AC to
operate, mandating an efficient high voltage DC/AC con-
verter. The lamps operate from DC, but migration effects
damage the lamp and shorten its lifetime. Lamp drive
should contain zero DC component. In addition to good
efficiency, the converter should deliver the lamp drive in
the form of a sine wave. This minimizes EMI and RF
TI I G DIAGRA S
ADR
SDA
I
SCL
OUT
W
S = START
P = STOP
* = OPTIONAL
S
U
0
1
1
2
SDA
SCL
SMBUS ADDRESS
0
3
U
1
4
STOP
1
5
INFORMATION
t
BUF
U
0
6
START
W
1
7
SMBus Write Byte Protocol, with SMBus Address = 0101101B,
Command Byte = 0XXXXXXXB and Data Byte = 111111XXB
t
8
LOW
t
W
HD:STA
9
10
t
r
11
X
Timing for SMBus Interface
U
12
X
t
HD:DAT
Operating Sequence
COMMAND BYTE
t
13
X
HIGH
14
X
15
X
t
f
emissions. Such emissions can interfere with other
devices and can also degrade overall operating efficiency.
Sinusoidal CCFL drive maximizes current-to-light conver-
sion in the lamp. The circuit should also permit lamp
intensity control from zero to full brightness with no
hysteresis or “pop-on.”
The small size and battery-powered operation associated
with LCD equipped apparatus dictate low component
count and high efficiency for these circuits. Size con-
straints place severe limitations on circuit architecture and
long battery life is a priority. Laptop and handheld portable
computers offer an excellent example. The CCFL and its
power supply can be responsible for almost 50% of the
16
X
t
t
SU:DAT
SU:STA
17
X
18
START
19
1
20
1
t
21
HD:STA
1
DATA BYTE
22
1
1
23
t
SU:STO
24
1
25
X
STOP
26
X
27
1786 TD01
LT1786F
1786 TD02
*
P
11
V
GND
FULL-SCALE
CURRENT
ZERO-SCALE
CURRENT
CC