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OB3309RP

Highly Integrated U Type CCFL Backlight Controller

Unspecified 

OB3309

Highly Integrated U Type CCFL Backlight Control

If the voltage of POL is higher than 2.05V, the

dimming polarity is changed, and DC voltage from

0.2V to 2V at DIM pin corresponds to the lamp’s

brightness of approximately minimum duty cycle of

burst dimming to 100%, as shown in Figure 6. The

minimum duty cycle of burst dimming can be

calculated by the following equation:

(VDRC − 0.2) ×100% for VDRC > 0.2V

1.8

0%

for VDRC ≤ 0.2V

Duty = (VDIM −VDRC ) ×100% for

2 −VDRC

0.2V < VDRC < VDIM

IVT Figure. 7 Use DRC PIN to set Dimming Range

VDRC

(V

)

=

2

×

R2

R1+ R2

o RT = R1+ R2

t Lamp Fail Safe Functions

idential Figure. 6 Duty of burst vs DIM voltage

f (Positive internal burst mode dimming)

n Function

Co Analog dimming

Internal Burst

ht External LPWM

Pin Connection

BF/DMOD DIM

>4.5V 0.2V-2V

Capacitor 0.2V-2V

<0.2V

PWM

Ratio

Set by

customer

Set by

customer

Set by

customer

g A DC voltage at DRC pin determines the minimum

dimming thus it is used to adjust dimming range for

i analog mode dimming or internal burst mode

r dimming. Because the voltage of RT pin is fixed

2V when OB3309 is in operation, the voltage of

B DRC can be set by RT divided resistors, as shown

On-in Figure 7. (Patent pending)

The OB3309 provides complete protection

features that cover all common lamp fault

conditions including:

z Lamp open or broken

z Two terminals of lamp are short together

z High voltage terminal of lamp is short to ground

The sensed lamp voltage and current signals, CS,

VS and PRT are used to monitor and detect the

faults.

During normal operation, if the peak voltage level

at CS pin is less than Vth_OLP, the lamp open or

lamp broken is recognized and the system will

shutdown after 160ms. If the peak voltage level at

PRT pin is higher than Vth_PRT, an internal source

current (14uA) charges the capacitor which

connected STIME pin to ground. Once the voltage

at STIME pin reaches 3V, the IC will shut down.

But in internal burst mode dimming or external

PWM mode dimming, if the dimming_on time is

less than 480uS, these two protections are

disabled.

During normal operation, if VS peak voltage is

more than 2.0V, it enters latched shutdown mode.

©On-Bright Electronics

Confidential

-9-

Preliminary Datasheet

OB_DOC_DS_330900

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