UCC1972/3
UCC2972/3
UCC3972/3
BLOCK DIAGRAM
VBAT
2
OVER-VOLTAGE
CLAMP COMPARATOR
9.0V
+
–
TO S3
UVLO
4.0V/3.8V
VDD
8
UVLO=1
VREF
OPEN LAMP DETECT
COMP ARATOR
18V
3V REF
7.0V
S2
3 BIT
UP-DOWN
COUNTER
+
–
1
BUCK
ZERO DETECT
COMP ARATOR
OSCILLATOR
FROM MODE SELECT
1.0V
+
–
SYNC
VDD
UVLO
R
S
RAMP OUT
Q
UVLO
7
6
OUT
GND
0.2V
R
S
+
PWM
–
OUTPUT OFF
(FROM MODE SELECT)
Q
FROM
CLAMP
COMP
VDD
20µA
I
CLAMP
ERROR
AMP LIFIER
S1
*MO DE
SELECT
1.5V
+
–
MODE
5
S3
4
FB
(ALWAYS OPEN ON UCC3972)
3
UDG-98154
COMP
*MODE
Output
Open Lamp
Detection
S2
Error Amplifier Output
S1
<1V
1V< MODE< 3V
>3V
OFF
ON
ON
DISABLED
DISABLED
ENABLED
OPEN
OPEN
CLOSED
DISCONNECTED FROM COMP
CONNECTED TO COMP
CONNECTED TO COMP
OPEN
CLOSED
CLOSED
APPLICATION INFORMATION
Introduction
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.
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
5
TI [ TEXAS INSTRUMENTS ]
