Datasheet

14
LT1182/LT1183/LT1184/LT1184F
BLOCK DIAGRAM
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LT1184/LT1184F CCFL Regulator Top Level Block Diagram
COMP1
UNDER-
VOLTAGE
LOCKOUT
THERMAL
SHUTDOWN
2.4V
REGULATOR
SHUTDOWN
200kHz
OSC
SHUTDOWN
6
REF
I
CCFL
AGND DIO
BULB
CCFL
V
C
CCFL
PGND
CCFL
V
SW
ROYERBAT
V
IN
LOGIC 1
DRIVE 1
GAIN = 4.4
Q3
2 ×
Q5
1 ×
Q4
5 ×
Q8
1 ×
Q10
2 ×
R1
0.125Ω
R4
0.1Ω
LT1184/LT1184F: REFERENCE IS BROUGHT OUT TO PIN 1.
PINS 7, 8, 9, 10 ARE NO CONNECT.

Q6
2 ×
R3
1k
D2
6V
D1
Q11
Q1
13
14
12
Q7
9 ×
Q9
3 ×
11
25
3
15
4
16
1
V
REF

1.24V
V1
0.465V
–
+
CCFL
0µA TO 
100µA
–
+
g
m
–
+
I
LIM

AMP1
ANTI-
SAT1
1184 BD02
LT1184: HIGH-SIDE SENSE RESISTOR
R4 AND GM AMPLIFIER ARE REMOVED. 
PIN 13 IS NO CONNECT.
APPLICATIONS INFORMATION
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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
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”.