OZ960 datasheet(8/12 Pages) O2MICRO

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OZ960

OZ960-DS-1.6

Page 8

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

provided

with

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:

68.5

•104

f[kHz] =

CT[pF]

•R

T[k

Ω

Ω]

The OZ960 also provides an optional striking

frequency as desired. CCFL in a LCD module

possesses parasitic that may require different

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:

1496

f[Hz] =

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

the

LCT

signal

and

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.

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