FAN7319 Datasheet, PDF (15/23 Pages) Fairchild Semiconductor – LCD Backlight Inverter Drive IC

Burst-Dimming
Lamp intensity is controlled with the BDIM signal over a
wide range. When BDIM voltage is higher than 2V, the
lamp current is turned on. When BDIM voltage is lower
than 0.8V, the lamp current is turned off. The duty cycle
of the PWM pulse determines the lamp brightness. The
lamp intensity is proportional to BDIM pulse on duty; as
BDIM on duty increases, the lamp intensity increases.
Figure 32 shows the lamp current waveform vs. VBDIM.
Output Drives
FAN7319 can drive topologies for half-bridge and full-
bridge in Super-IP applications. If the MODE pin is
connected to reference voltage, output drive is a push-
pull topology. In Super-IP applications, push-pull
topology can drive a half-bridge resonant circuit. If the
MODE pin is connected to ground, output drive is a full-
bridge topology. FAN7319 uses a phase-shift method for
full-bridge Cold Cathode Fluorescent Lighting (CCFL)
drive. As a result, the temperature difference between
the left and right leg is almost zero because ZVS occurs
in both of the legs by turns. The detail timing is shown in
Figure 34 and Figure 35.
FAN7319 drive voltage is same as VIN supply voltage, so
it can drive a pulse transformer without any additional
buffer. To prevent over-current in output drive, add a
series resistor between the OUT pin and the pulse-
transformer (22~47Ω series resistor is enough).
Figure 32. Burst-Dimming Waveforms
During striking mode, burst-dimming operation is
disabled to guarantee continuous striking time. Figure 33
shows burst-dimming is disabled during striking mode.
Figure 34. Push-Pull Mode Gate Drive Signal
CT
CMP
Fixed dead time
550ns
Fixed dead time
550ns
SYNC
T
T1
OUTA
OUTB
OUTC
OUTD
Figure 33. Burst-Dimming During Striking Mode
Figure 35. Full-Bridge Mode Gate Drive Signal
© 2010 Fairchild Semiconductor Corporation
FAN7319 • 1.0.1
15
www.fairchildsemi.com