Datasheet

5
UCC1972/3
UCC2972/3
UCC3972/3
UDG-98154
*MODE Output Open Lamp
Detection
S2 Error Amplifier Output S1
<1V OFF DISABLED OPEN DISCONNECTED FROM COMP OPEN
1V< MODE< 3V ON DISABLED OPEN CONNECTED TO COMP CLOSED
>3V ON ENABLED CLOSED CONNECTED TO COMP CLOSED
8
5
3
4
2
1
7
6
VDD
20µA
+
–
+
–
1.5V
ERROR
AMP LIFIE R
S1
R
QS
R
Q
S
+
–
+
–
+
+
1.0V
7.0V
SYNC
OUTRAMP
+
0.2V
OSCILLATOR
*MO D E
SELECT
UVLO
4.0V/3.8V
3V REF
VR E F
UVLO =1
3BIT
UP-DOWN
COUNTER
S2
FROM MO DE S ELECT
OP EN LAMP DETECT
C O MP AR ATO R
ZERO DETECT
C O MP AR ATO R
UVLO
PWM
UVLO
OUTPUT OFF
(FROM MO DE S ELECT)
VDD
MO DE
COMP
FB
GND
OUT
BUCK
VDD
VBAT
18V
+
–
+
TO S3
OVER-VOLTAGE
CLAMP COMP ARATOR
S3
(ALWAYS OP EN ON UCC3972)
FROM
CLAMP
COMP
I
CLAMP
9.0V
BLOCK DIAGRAM
Introduction
Cold Cathode Fluorescent Lamps (CCFL) are frequently
used as the backlight source for Liquid Crystal Displays
(LCDs). These displays are found in numerous applica
-
tions such as notebook computers, portable instrumenta
-
tion, automotive displays, and retail terminals.
Fluorescent lamps provide superior light output effi
-
ciency, making their use ideal for power sensitive porta
-
ble applications where the backlight circuit can consume
a significant portion of the battery’s capacity. The
backlight converter must produce the high voltage
needed to strike and operate the lamp. Although CCFLs
can be operated with a DC voltage, a symmetrical AC
operating voltage is recommended to maintain the rated
life of the lamp. Sinusiodal voltage and current lamp
waveforms are also recommended to achieve optimal
electrical to light conversion and to reduce high voltage
electromagnetic interference (EMI). A topology that pro
-
vides these requirements while maintaining efficient op
-
eration is presented below.
APPLICATION INFORMATION