FAN7318A Datasheet, PDF (19/24 Pages) Fairchild Semiconductor – LCD Backlight Inverter Drive IC

The IC starts operating in striking mode and remains in
striking
mode
until
17
pulses
of
V min
OLP
higher
than
0.7V
and OLR<1.34V occur. If more than 17 pulses and
OLR<1.34V, the IC changes from striking mode into
normal mode, as shown in Figure 54.
Figure 51. Over-Voltage Protection in Normal Mode
In burst dimming mode, while
V max
OLR
is higher than 1.34V,
burst dimming is disabled, so that the TIMER pin
capacitor is charged continuously by an internal current
source of 50µA. Once the TIMER reaches 1V, the IC
enters shutdown, as shown in Figure 52.
Figure 52. Over-Voltage Protection in Burst
Dimming Mode
Open-Lamp Protection
If
the
minimum
of
the
rectified
OLP
voltages
(
Vmin
OLP
)
is
less than 0.7V during initial operation, the IC operates in
striking mode for a time predetermined by the TIMER pin
capacitor and an internal current source, 2µA, as shown
in Figure 53.
Figure 54. Mode Change from Striking to Normal
After
ignition,
if
V min
OLP
is
less
than
0.5V
for
a
time
predetermined by the TIMER pin capacitor and an
internal current source, 2µA in normal mode; the IC is
shut down, as shown in Figure 55 and Figure 56.
OLP1
OLP2
Min. & Max.
Detector
OLP min.
-
/Full or Half
Wave
0.5V
+
Rectifier
OLP
150μs
Delay
Figure 55. Open-Lamp Protection in Normal Mode
O LP 1
O LP 2
Tim er
Figure 53. Open-Lamp Protection in Striking Mode
© 2009 Fairchild Semiconductor Corporation
FAN7318A • 1.0.0
19
www.fairchildsemi.com