DT8211 查看數據表（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)
Burst Dimming
DT8211 includes three kinds of dimming method. One is analog dimming, burst
dimming and pulse dimming. Burst dimming command feeds DC level to BDIM pin
which is an input of internal PWM generator. When 0V<VBDIM<2.0V, DT8211 operates
in positive polarity mode, but when 3.0V<VBDIM<5.0V, DT8211 operates in negative
polarity mode as below figure.
Burst PWM is generated using BDIM and triangular wave of CTB. The rising and
falling slopes of BDIM operation are adjusted by capacitor which is connected
between ICMP pin and GND. The source and sink currents of ICMP are 100uA. We
recommend 300usec as rising and falling time.
Pulse Dimming
DT8211 includes three kinds of dimming method. One is analog dimming, burst
dimming and pulse dimming. In this mode, PWM pulse of pulse dimming feeds to
BDIM pin and a resistor must be connected between CTB and GND. When the pulse
swings 0V to 2V, DT8211 operates in positive polarity mode, but when the pulse
swings 3V to 5V, DT8211 operates in negative polarity mode.
To operate pulse dimming mode, CTB must be a constant level. So a resistor is
recommended between CTB and GND, and its value which makes CTB level to about
1.0V is recommended as below equation.
RCTB ,PDIM = 3.5 ´ RT
Main PWM Generator
The main PWM pulse is generated with ICMP, VCMP and CT. ICMP and VCMP are
connected to comparator negative inputs of PWM generator, and CT is connected to
comparator positive input of PWM generator. CT decides PWM frequency and ICMP
and VCMP decide PWM Duty. Output duty of main PWM is limited approximately 48%
when main frequency is 50kHz to prevent shoot-through of Power FETs.
Rev1.1– 11 July 2008
© 2007 DMB Tech. All Rights Reserved
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