DT8211 データシートの表示（PDF） - Unspecified
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DT8211 Datasheet PDF : 10 Pages
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DMB Technology
DT8211
LCD Back Light Inverter Drive IC
10. Functional Description (Continued)
Striking Frequency
Striking frequency is generated by increasing charging and discharging current of a
capacitor (CT). RTS pin is normally high impedance, but it goes low when DT8211 is
in striking mode. If a resistor is connected between RTS and RT, a striking frequency
can be generated by increased current and the equation is as below.
fStriking
[Hz]
=
0.228(RT
RT • RTS
+ RTS
• CT
)
Burst Frequency Oscillator
To generate clear PWM pulse, DT8211 includes a precise triangular waveform
generator circuit. The voltage of RT pin is fixed at 2.0V and the current of RT pin is
flow through the resistor which is connected between RT pin and GND. This current
makes charging and discharging current of a capacitor which is connected to CTB pin
and GND. Triangular wave is generated at CTB pin by charging and discharging
(repeated operation) to this capacitor. This triangular wave is one of reference signal
to generate PWM. The frequency of triangular wave can be calculated approximately
as below.
fBurst [Hz]
=
0.11
RT • CTB
Analog Dimming
DT8211 includes three kinds of dimming method. One is analog dimming, burst
dimming and pulse dimming. Analog dimming command feeds DC level to ADIM pin
which is a positive input of internal error amplifier. When 0V<VADIM<2.0V, DT8211
operates in positive polarity mode, but when 3.0V<VADIM<5.0V, DT8211 operates in
negative polarity mode as below figure.
The negative input of error amplifier for current is IFB pin, and control loop is
operated to make IFB level equal to ADIM level. The output of error amplifier for
current, which is ICMP pin, is directly connected to main PWM generator.
Rev1.1– 11 July 2008
© 2007 DMB Tech. All Rights Reserved
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