OZ960 Просмотр технического описания (PDF) - O2Micro International
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OZ960 Datasheet PDF : 12 Pages
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3. Protection
Open-lamp protection in the ignition period is
provided through both OVP and CTIMR to ensure
a rated voltage is achieved and a required timing
is satisfied. Removal of the CCFL during normal
operation will trigger the current amplifier output
and shuts off the inverter. This is a latch function.
4. OVP
The OVP threshold is set at 2V nominal. When
the output voltage reaches the threshold, it
commands the PWM controller to maintain the
driving level. This ensures that output gets
sufficient striking voltage while operating the
power transformer safely.
5. ENA
Applying positive TTL logic to the ENA pin
enables the operation of the IC. The threshold of
the ENA is set at 1.5V. Apply logic low to the
ENA pin will disable the operation of the inverter.
Toggle this signal allows the on/off tests for the
inverter.
6. Soft-Start -- SST
The soft-start function is provided with a
capacitor connected to SST pin. The soft-start
time is not related to the striking time for the
CCFL. It simply provides a rate of rise for the
pulse width where diagonal switches are turned
on. Normally, a 0.47uF capacitor is connected.
7. Error Amplifier
The CCFL current is regulated through this error
amplifier. It also provides an intelligence of
differentiating open-lamp striking versus
removing the lamp during normal operation. The
non-inverting reference is at 1.25V nominal.
8. Operating frequency
A resistor RT and a capacitor CT determine the
operating frequency of OZ960. The frequency is
calculated as:
f[kHz] =
68.5•104
CT[pF]•RT[kΩ]
The OZ960 also provides an optional striking
frequency as desired. CCFL in a LCD module
possesses parasitic that may require different
OZ960
striking voltage and frequency. This add-on
feature could optimally accomplish the ignition
process so that the CCFL life could be extended.
When RT1 is used, it is connected in parallel with
RT during the ignition period.
9. Burst-Mode Dimming Control
The OZ960 integrates a burst-mode dimming
function to perform a wide dimming control for the
CCFLs. The burst-mode frequency is determined
by a capacitor C10 connected to LCT pin. The
frequency can be calculated approximately by:
f[Hz] =
1496
CLCT[nF]
The Dim pin compares with the triangle wave in
LCT and yields a proper pulse width to modulate
the CCFL current. This pulse can also be
monitored through LPWM pin. The peak and
valley of the LCT signal is 3V and 1V
respectively.
10. Output Drives
The four output drives are designed so that
switches QA and QB, QC and QD never turn on
simultaneously. These include two NMOS and
two PMOS transistors. The configuration
prevents any shoot-through issue associated with
bridge-type power conversion applications.
Adjusting the overlap conduction between QA
and QD, QB and QC, the CCFL current
regulation is achieved. This overlap is also
adjusted while the voltage applied from the
battery varies. At a specific CCFL current, the
input power is maintained almost constant.
OZ960-DS-1.6
Page 8
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