UCC2979
SLUS520B - OCTOBER 2002 - REVISED NOVEMBER 2003
FULL BRIDGE CCFL CONVERTER FOR
PIEZOELECTRIC TRANSFORMERS
1
www.ti.com
FEATURES
D
5-V to 24-V Operation
D
Full-Bridge Topology With Integrated
Power Switches
D
Greater Than 90% Efficiency Over a Wide
Input Voltage Range
D
Frequency Loop Controls Lamp Current
D
Programmable Strike and Operating
Frequencies
D
Voltage Loop Controls PZT Primary Voltage
D
Soft-Start, Shutdown, and Open Lamp
Protection
D
Dimming Control
APPLICATIONS
D
Notebook Computers
D
Portable Electronic Displays
D
Portable Instruments
DESCRIPTION
Liquid crystal display (LCD) enclosures used in
notebook computers and portable electronic
devices are becoming increasingly thin and
narrow, generating the need for a miniaturized
cold cathode fluorescent lamp (CCFL) backlight
supply. Piezoelectric transformers (PZTs) are
becoming popular for these size-constrained
applications, offering higher efficiency ( > 90%),
lower profile, and narrower footprint when
compared to their magnetic transformer
counterparts. These transformers provide
inherent sinusoidal operation, non-flammability,
and low electromagnetic noise, making them ideal
for CCFL backlight applications. The UCC2979
full-bridge converter provides a simplified
systems solution for a piezoelectric transformer-
based CCFL supply.
The UCC2979 has a patent-pending 2-loop
design. The first control loop regulates lamp
current by adjusting the operating frequency. The
second loop regulates the PZT primary voltage
over the full input voltage range, improving system
efficiency.
ADV
ANCE INFORMA
TION
UDG-02010
SIMPLIFIED APPLICATION DIAGRAM
OUT1
OUT2
VDD
GND
6 V
TO
24 V
UCC2979
DIMMING
CONTROL
CURRENT SENSE
PIEZOELECTRIC
TRANSFORMER
EA
VOLTAGE SENSE
OPEN LAMP
DETECTION
CCFL
VA
LRES
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
UCC2979
SLUS520B - OCTOBER 2002 - REVISED NOVEMBER 2003
2
www.ti.com
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
DAO
DA+
DA-
GND
15VC
VDD
ZTO3V
RT1
RT2
OPEN/SD
OSC
EA-
EAO
VA-
VAO
GND
PWP PACKAGE
(TOP VIEW)
recommended operating conditions
MIN
MAX
UNIT
Input voltage
5
24
V
Switch current
2
A
absolute maximum ratings over operating free-air temperature (unless otherwise noted)
Input voltage range:
15VC, DA+, DA-
16.5 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5V_REG, EA-, EAO, VAO, VA-,OSC, OPEN/SD
RT2, RT1, ZTO3V
5.5 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLY1, FLY2
V
DD
+ 15 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PVDD, VDD, OUT1, OUT2
25 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PGND
5 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DAO
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
UCC2979PWP
Dissipation Ratings
(1)
AIRFLOW IN LFM
DERATING FACTOR
ABOVE TA = 25
C
TA < 25
C
POWER RATING
TA = 85
C
POWER RATING
0
33.2 mW/
C
3.8 W
1.8 W
150
42.3 mW/
C
4.8 W
2.3 W
250
45.9 mW/
C
5.2 W
2.5 W
NOTE 1: For more information on the PWP package, refer to TI technical brief, literature number SLMA002.
ADV
ANCE INFORMA
TION
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2003, Texas Instruments Incorporated
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