OB3309RP 데이터 시트보기 (PDF) - Unspecified

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OB3309RP

Highly Integrated U Type CCFL Backlight Controller

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OB3309

Highly Integrated U Type CCFL Backlight Control

The AC lamp currents are sensed by the sense

resistors (refer to R24 in figure 8) connected in

series with high voltage coupling inductance. The

Vref

_

EA(V)

=

25×(2

36

−VDIM

)

for

AC voltage across the sense resistors are fed into

the CS pins. The peak of the sensed AC voltage is

0.2V

≤ VDIM

≤2−

36

25

×

V

DRC

detected. The peak value is compared with an

internal reference voltage. The error is amplified

that controls the on time of the push pull switches,

as a result, the lamp current is regulated. The lamp

current can be calculated by the following

equation:

Ilamp( A) = N *

1.33

2 × Rsense

Where N is the coupling inductance turns ratio,

N=NLV/NHV, the inductance T2 ,as shown in

The minimum voltage of Vref_EA is determined by

the voltage at DRC which should be set in the

IVT range from 0V to 1.25V for analog dimming mode.

to

figure8.

l Dimming Control

a Three commonly used dimming modes, analog

mode dimming, internal burst mode dimming and

i external burst (PWM) dimming functions, are

t supported without any additional components.

Different dimming modes are selected by

n BF/DMOD pin. The lamp brightness is determined

e by the control signal at DIM pin. Both in internal

burst mode dimming and external PWM mode

d dimming, the polarity can be set by the voltage

i level at POL pin as shown in the following table:

f Function

on Analog dimming

C Internal Burst

Polarity

POL< 2V

POL >2V

Negative

Negative

Negative

Positive

Figure. 4 Vref of EA vs DIM voltage

Internal burst mode dimming is obtained by

connecting a capacitor to BF/DMOD pin. A low

frequency triangular waveform generator is formed

by the capacitor and internal circuit of IC. The

triangular voltage waveform with peak of 2V and

valley of 0.2V at this pin is used for the internal low

frequency burst PWM generation. Duty cycle so as

to lamp brightness is controlled by the analog

signal at DIM pin. The burst mode dimming

frequency Fburst is set by the following equation:

Fburst

(Hz)

=

CBF

158400

[nF]× RT[Kohm]

External LPWM

Positive

Negative

ht External LPWM burst dimming mode is selected

by shorting BF/DMOD pin to ground. OB3309

g accepts an external LPWM signal to DIM pin with a

i swing voltage of 0V to a level greater than 2V. The

lamp brightness is controlled by the duty cycle of

r the LPWM signal. The burst frequency is equal to

B LPWM frequency.

-Connecting BF/DMOD pin to VDD selects analog

nmode dimming. A DC voltage ranging from 0.2V to

O2V at DIM pin performs analog mode dimming

A DC voltage ranging from 0.2V to 2V at DIM pin

corresponds to a lamp brightness of approximately

100% to (2 − VDRC ) ×100% , as shown in Figure 5.

1.8

Duty = (2 − VDIM ) ×100%

1.8

for

0.2V ≤VDIM ≤VDRC

control. The voltage at DIM pin modulates internal

error amplifier reference voltage Vref_EA from 1.25V

to VDRC, which corresponds to a lamp current of

approximately 100% to (VDRC/1.25)×100%. Vref_EA

can be calculated by the following equation:

Figure. 5 Duty of burst vs DIM voltage

(Negative internal burst mode dimming)

©On-Bright Electronics

Confidential

-8-

Preliminary Datasheet

OB_DOC_DS_330900

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