OB3309RP Просмотр технического описания (PDF) - Unspecified

Номер в каталоге

Компоненты Описание

Список матч

OB3309RP

Highly Integrated U Type CCFL Backlight Controller

Unspecified 

OB3309

Highly Integrated U Type CCFL Backlight Control

lower than 1.25V, then the system enters normal

Function Description

operating mode. Otherwise, the duty cycle of the

gate drive signal will increase further to deliver

General Operation

more power to ignite the lamp. Once the duty cycle

of gate drive signal reaches maxima of 45%, the

OB3309 CCFL controller is designed for U-type

CCFL’s LCD backlight system applications

configured in push pull topology; it converts the

DC input voltage to pure sinusoidal waveforms for

CCFL operating with high efficiency and low EMI

emission. The resonant frequency of the tank is

set by the transformer leakage inductance and

internal striking timer will be triggered. If the lamps

are lit before the time out, OB3309 enters the

normal operation mode. Otherwise, it enters the

shutdown mode. The striking time is given by:

T T(sec) = 2.31× C[uF]

V After the striking time out, the striking frequency

I will be switched to normal frequency and last for

secondary parallel capacitor.

The lamp fault protection functions are integrated

to provide a high reliability & simplifier solution with

low system cost. Dimming polarity selection can

64ms, if any one of the lamps still can not be lit,

OB3309 will enters the shutdown mode as show in

to Figure 3.

be achieved by setting the voltage level at POL Pin.

A typical application scheme is shown in figure 8

l on page 10.

a Enable the Controller

i OB3309 is activated by applying logic high to the

t ENA input. It is TTL logic compatible. The

n controller is enabled when the voltage at ENA pin

is higher than 2.0V. Toggling the ENA signal

e resets the state machine hence restarts the

d inverter system.

i Normal Operation and Striking Frequency

f The normal operation frequency, FOP, is set by the

n resistor connected to RT pin. It is given by

o 1800

C FOP (KHz) = RT(Kohm)

Vstime

64ms

3V

1.5s

t

0

Striking frequency

Normal frequency

Figure 3 Striking mode control

Soft Start and Soft On/off

External capacitor connected to CMP pin provides

soft start and soft on/off control. At start up, an

internal current source starts to charge the

capacitor. Consequently, voltage at CMP pin

The striking frequency, Fstriking, is set by the

resistors connected to both RI and RT pins. It can

t be calculated by the following equation:

h 1800

g FSTRIKING (KHz) = RT//RI(Kohm)

i Lamp Ignition and Striking Voltage Regulation

r To ignite CCFL, a much higher voltage than that in

B normal operation is required, especially for aged

-lamp or in low ambiance temperature. The output

voltage is divided by the capacitive voltage divider.

nA voltage signal is fed into VS pins with diodes and

Otheir peaks are compared with internal 2.0V

increases gradually and so as to the pulse width of

the PWM Gate signals. This soft start control helps

to reduce the MOSFET inrush current and voltage

stresses, thus expand the lamp life time. The slope

of the soft start ΔV / ΔT can be approximated as:

ΔV[V] =

217

ΔT[mS] CCMP[nF] × RT//RI[kohm]

Once lamps are ignited, the capacitor connected

to CMP pin performs the loop compensation

function. In internal burst mode dimming or

external burst (PWM) mode dimming conditions,

the voltage ramping up and down at this pin

performs a soft on/off control function in each burst

threshold voltage. Consequently, the maximum cycle.

output voltage is regulated and limited.

During ignition, OB3309 monitors the peak voltage Lamp Current Regulation

levels at CS & PRT pins, it is recognized that all

lamps are lit If the peak voltage of CS pin is higher

than 0.85V and the voltage level at PRT pin is

Lamp current is regulated by the currents

feedback loop with an internal transconductance

error amplifier.

©On-Bright Electronics

Confidential

-7-

Preliminary Datasheet

OB_DOC_DS_330900

Share Link: