UCC1972/3
UCC3972/3
BiCMOS Cold Cathode Fluorescent Lamp Driver Controller
FEATURES
•
1mA Typical Supply Current
•
Accurate Lamp Current Control
•
Analog or Low Frequency Dimming
Capability
•
Open Lamp Protection
•
Programmable Startup Delay
•
4.5V to 25V Operation
•
PWM Frequency Synchronized to
External Resonant Tank
•
8 Pin TSSOP and SOIC Packages
Available
•
Internal Voltage Clamp Protects
Transformer from Over-voltage
DESCRIPTION
Design goals for a Cold Cathode Fluorescent Lamp (CCFL) converter used
in a notebook computer or portable application include small size, high effi-
ciency, and low cost. The UCC3972/3 CCFL controllers provide the neces-
sary circuit blocks to implement a highly efficient CCFL backlight power
supply in a small footprint 8 pin TSSOP package. The BiCMOS controllers
typically consume less than 1mA of operating current, improving overall
system efficiency when compared to bipolar controllers requiring 5mA to
10mA of operating current.
External parts count is minimized and system cost is reduced by integrating
such features as a feedback controlled PWM driver stage, open lamp pro-
tection, startup delay and synchronization circuitry between the buck and
push-pull stages. The UCC3972/3 include an internal shunt regulator, al-
lowing the part to operate with input voltages from 4.5V up to 25V. The part
supports both analog and externally generated low frequency dimming
modes of operation.
The UCC3973 adds a programmable voltage clamp at the BUCK pin. This
feature can be used to protect the transformer from overvoltage during
startup or when an open lamp occurs. Transformer voltage is controlled by
reducing duty cycle when an over-voltage is detected.
C6 27pF
T1
TYPICAL APPLICATION CIRCUIT
UCC3972 NO INTERNAL VOLTAGE CLAMP
INTERNAL VOLTAGE CLAMP LIMITS TRANS FORMER
VOLTAGE AT S TART-UP OR DURING FAULT
S YS TEM VOLTAGE
(4.5V TO 25V)
R1
1kΩ
C1
6.8µF
8
C2
1µF
6
5
C3
1µF
3
GND
MODE
COMP
BUCK
1
L1
68µH
R6 75Ω
OUT
FB
C4 33nF
7
R2 1k
C5 0.1µF
D1
2
C7
0.1µF
R11
R10
Q2
Q3
LAMP
HV
UCC3972/3
VDD
VBAT
LAMP
LV
ANALOG
DIMMING
R5 10k
R3 68k
4
LOW FREQUENCY DIMMING
D
LFD
R
LFD
68k
D2
R4 750
0V-5V LOW FREQUENCY CONTROL S IGNAL
UDG-99154
SLUS252C - OCTOBER 1998 - REVISED MARCH 2005
TI [ TEXAS INSTRUMENTS ]
