UCC3973PWTRG4 Datasheet, PDF (1/24 Pages) Texas Instruments – BiCMOS Cold Cathode Fluorescent Lamp Driver Controller

UCC1972/3
UCC2972/3
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
(UCC3973)
TYPICAL APPLICATION CIRCUIT
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.
UCC3972 NO INTERNAL VOLTAGE CLAMP
UCC3973
INTERNAL VOLTAGE CLAMP LIMITS TRANS FORMER
VOLTAGE AT S TART-UP OR DURING FAULT
C6 27pF
T1
S YS TEM VOLTAGE
(4.5V TO 25V)
R2 1k
C1
6.8µF
R1
1kΩ
UCC3972/3
8 VDD
C2
1µF
VBAT 2
6 GND
D1
C7
0.1µF
R10
Q2
R11
C5 0.1µF
Q3
BUCK 1
5 MODE
L1
68µH
C3
1µF
3 COMP
OUT 7
R6 75Ω
FB 4
R3 68k
LOW FREQUENCY DIMMING
D2
C4 33nF
D_{LFD RLFD 68k}
LAMP
HV
LAMP
LV
ANALOG
DIMMING
R5 10k
R4 750
0V-5V LOW FREQUENCY CONTROL S IGNAL
SLUS252C - OCTOBER 1998 - REVISED MARCH 2005
UDG-99154