LT1182 LINER [Linear Technology], LT1182 Datasheet - Page 14

• Manufacturer Part Number: LT1182
• Description: CCFL/LCD Contrast Switching Regulators
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
LT1182/LT1183/LT1184/LT1184F
BLOCK
Introduction
Current generation portable computers and instruments
use backlit Liquid Crystal Displays (LCDs). These displays
also appear in applications extending to medical equip-
ment, automobiles, gas pumps, and retail terminals. Cold
Cathode Fluorescent Lamps (CCFLs) provide the highest
available efficiency in backlighting 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
14
REF
LT1184/LT1184F: REFERENCE IS BROUGHT OUT TO PIN 1.
PINS 7, 8, 9, 10 ARE NO CONNECT.
11
1.24V
V
SHUTDOWN 6
REF
DIAGRAM
0 A TO
100 A
U
I
CCFL
2
INFORMATION
U
SHUTDOWN
W
V1
0.465V
+
–
CCFL
LT1184/LT1184F CCFL Regulator Top Level Block Diagram
W
REGULATOR
2
200kHz
Q3
2.4V
OSC
AGND
V
12
IN
5
1
Q5
Q4
5
U
VOLTAGE
LOCKOUT
9
UNDER-
Q7
DIO
3
SHUTDOWN
Q6
2
Q8
1
converter. 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 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”.
THERMAL
D1
BULB
15
D2
6V
3
Q9
Q11
R3
1k
BAT
14
–
0.1
R4
g
m
Q10
2
ROYER
13
+
CCFL
LT1184: HIGH-SIDE SENSE RESISTOR
R4 AND GM AMPLIFIER ARE REMOVED.
PIN 13 IS NO CONNECT.
V
4
LOGIC 1
C
COMP1
DRIVE 1
ANTI-
SAT1
GAIN = 4.4
AMP1
I
LIM
–
+
PGND
CCFL
CCFL
V
16
SW
1
Q1
R1
0.125
1184 BD02