UCC2978
SLUS506A - APRIL 2002 - REVISED NOVEMBER 2003
FULL BRIDGE MAGNETIC TRANSFORMER
BACK LIGHT CONVERTER
1
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FEATURES
D
5-V to 24-V Operation
D
Full-Bridge Topology With Integrated Power
Switches
D
Greater Than 90% Efficiency
D
Programmable Strike and Operating
Frequencies
D
Soft-Start, Shutdown and Open Lamp
Protection
D
Analog or Burst-Mode Dimming
D
Reduced Solution Size Requiring Only
External Transformer
D
24-Pin Power TSSOP Package
APPLICATIONS
D
Notebook Computers
D
Portable Electronic Displays
D
Portable Instruments
DESCRIPTION
Liquid crystal display (LCD) enclosures and cold
cathode fluorescent lamps (CCFLs) used in
notebook computer and portable electronics
displays are becoming increasingly thin and
narrow, generating the need for a miniaturized
CCFL power supply. The UCC2978 full-bridge
converter provides a complete systems solution
for a magnetic transformer based CCFL supply as
shown in the typical application circuit. The
primary inductance of the transformer and a dc
blocking capacitor control current and assure the
transformer does not saturate on the primary.
Leakage inductance and system capacitance on
the transformer secondary provides a nearly
sinusoidal voltage to the lamp with no ballast
capacitor. The UCC2978 integrates four low-
R
DS(on)
power switches (100 m
typical) resulting
in minimal board area and high efficiency. System
functions such as open lamp, transformer voltage
clamp, programmable strike and run frequencies,
soft-start, and low-current shutdown are included.
SIMPLIFIED APPLICATION DIAGRAM
OUT1
OUT2
VDD
GND
OPEN LAMP DETECTION
AND
VOLTAGE REGULATION
6 V
TO
22 V
UCC3978
DIMMING
CONTROL
CURRENT SENSE
XFMR
23
13
5
7
UDG-02002
CCFL
ADV
ANCE INFORMA
TION
ADVANCE INFORMATION concerns new products in the sampling or
preproduction phase of development. Characteristic data and other
specifications are subject to change without notice.
Copyright
2002 - 2003, Texas Instruments Incorporated
UCC2978
SLUS506A - APRIL 2002 - REVISED NOVEMBER 2003
2
www.ti.com
TYPICAL APPLICATION
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
15VC
5V_REG
FLY1
PVDD
OUT1
PGND
OUT2
FLY2
VCO
VCL+
VCL-
GND
15VC
VDD
ZTO3V
RT1
RT2
OPEN/SD
OSC
STDET
STFRQ
VA-
VAO
GND
PWP PACKAGE
(TOP VIEW)
recommended operating conditions
MIN
MAX
UNIT
Input voltage
5.0
24.0
V
Switch current
2
A
absolute maximum ratings over operating free-air temperature (unless otherwise noted)
Input voltage range:
15VC, VCL+, VCL-
16.5 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5V_REG, VAO, VA-, STFRQ, STDET, OSC, OPEN/SD
RT2, RT1, ZTO3V
5.5 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLY1, FLY2
5.5 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RT2, RT1, ZTO3V
V
DD
+ 15 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PVDD, VDD, OUT1, OUT2
25 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PGND
5 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VCO
8 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating virtual temperature range, T
J
-40
C to 100
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage temperature range, T
stg
-55
C to 150
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds
260
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
AVAILABLE OPTIONS
TA
PACKAGE
TA
PowerPad TSSOP (PWP)
- 40
C to 85
C
UCC2978PWP
ADV
ANCE INFORMA
TION
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2003, Texas Instruments Incorporated
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