OZ9939
To resume operation, toggle the ENA signal or
restart VDDA.
Controlled Recipient #106805 printed on 3/6/2006. Updates will be provided to registered
recipients.
8. Over-Voltage and Over-Current
Protection
Over-voltage and over-current protection are
monitored by the voltage on VSEN (pin 6).
During normal operation, if a CCFL is damaged
or removed, the voltage at VSEN (pin 6)
increases. Once the voltage at VSEN exceeds
the user-defined, preset voltage set by OVPT (pin
7), the driver output duty cycle is regulated and
the shutdown delay timer is activated. OVPT
sets the overall protection threshold voltage that
is lower than ~3V (VSEN threshold). Once the
voltage at TIMR pin reaches ~3V, the IC will shut
down and latch.
OVPT voltage setting is
determined by a resistor divider (R13 and R16)
connected to the OVPT.
The approximate shutdown delay
calculated by the following equation.
T
d
[Sec] = 0.33 XC
TIMER
[uF]
To resume operation, toggle the PWM signal or
restart VDDA.
time
is
External PWM dimming is implemented by
setting LCT to a DC voltage between 0.5V to
1.0V using a resistor divider (R8 and R17)
between VDDA and GND. Apply the external
PWM pulse to DIM (pin 4).
.
9. Dimming Control
A built-in function enables the user to select one
of the following dimming controls: analog, internal
LPWM or external PWM signal.
Analog dimming control is activated when the
voltage to LCT (pin 11) is greater than 3V. A
voltage of 0.5V to 1.25V applied to DIM (pin 4)
controls the amplitude of the lamp current.
Internal LPWM dimming control is determined by
resistor R8 and capacitor C14 connected to LCT.
The low frequency sawtooth waveform is
compared with the voltage at DIM to generate the
LPWM signal. The peak and valley of the
waveform are 1.5V and 0.1V respectively.
The frequency is approximated by the following
equation:
3102
f
LOSC
=
[Hz]
R
LCT
[MΩ]*C
LCT
[nF]
With negative PWM dimming polarity, the LPWM
duty cycle will be 100% when DIM pin voltage is
lower than 0.1V. LCD panel will have maximum
brightness. When DIM pin voltage is higher than
1.5V, the LPWM duty cycle will be 0%. LCD
panel will be totally dark.
CONFIDENTIAL
OZ9939-DS-1.1
Page 7
MICRO-ELECTRONICS [ Micro Electronics ]
