application
INFO
UC1872
UC2872
UC3872
available
Resonant Lamp Ballast Controller
FEATURES
DESCRIPTION
• Controls Different Types of Lamps:
Cold Cathode Fluorescent, Neon, and
Gas Discharge
The UC3872 is a resonant lamp ballast controller optimized for driving
cold cathode fluorescent, neon, and other gas discharge lamps. The res-
onant power stage develops a sinusoidal lamp drive voltage, and mini-
mizes switching loss and EMI generation. Lamp intensity adjustment is
accomplished with a buck regulator, which is synchronized to the external
power stage’s resonant frequency. Suitable for automotive and battery
powered applications, the UC3872 draws only 1µA when disabled.
• Zero Voltage Switching (ZVS) of
Push-Pull Drivers
• Accurate Control of Lamp Current
• Variable Lamp Intensity Control
• 1µA Disable Current
Soft start and open lamp detect circuitry have been incorporated to mini-
mize component stresses. Open lamp detection is enabled at the comple-
tion of a soft start cycle. The chip is optimized for smooth duty cycle
control to 100%.
• 4.5V to 24V Operation
Other features include a precision 1.2% reference, undervoltage lockout,
and accurate minimum and maximum frequency control.
• Open Lamp Detection Circuitry
BLOCK DIAGRAM
3
2
VC
3.0V
REF
AOUT
VCC 10
UVLO
50k
REF
9
(HIGH=ENABLE)
PUSH PULL
OUTPUTS
ENBL 11
N-CHANNEL
0.1V
+
–
COMP
INV
4
6
TOGGLE
T
OPEN
LAMP
DETECT
–
1
BOUT
EA
20µA
+
50k
50k
1.5V
PWM
1
–
–
+
SS
CT
ZD
5
7
8
200µA
R
S
0.2V
OSCILLATOR
SENSE
OUT
12 COUT
ZERO DETECT
BUCK DRIVE
P-CHANNEL
–
SYNC
0.5V
+
13 PGND
14
GND
UDG-99112
Note: Pin numbers shown are for DIP package.
07/99