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DS3984Z+ Datasheet(PDF) 9 Page - Dallas Semiconductor |
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DS3984Z+ Datasheet(HTML) 9 Page - Dallas Semiconductor |
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9 / 24 page  4-Channel Cold-Cathode Fluorescent Lamp Controller _____________________________________________________________________ 9 DS3984 OVERVOLTAGE LAMP OVERCURRENT LSE BIT AT CR1.0 LAMP REGULATION CHANNEL ENABLE CHANNEL FAULT DIGITAL CCFL CONTROLLER LAMP OUT 1 OF 4 CHANNELS 400mV LCM LAMP CURRENT MONITOR 1.0V 2.0V 1.0V 256 LAMP CYCLE INTEGRATOR PEAK DETECT/ HOLD PEAK DETECT GA OVD OVERVOLTAGE DETECTION MOSFET GATE DRIVERS GB GATE DRIVERS 256 LAMP CYCLE INTEGRATOR DPWM SIGNAL 512 x LAMP FREQUENCY [20.48MHz TO 40.96MHz] PHASED LAMP FREQUENCY [40kHz TO 80kHz] Figure 1. Per Channel Logic Diagram Detailed Description The DS3984 uses a push-pull drive scheme to convert a DC voltage (5V to 24V) to the high-voltage (600VRMS to 1200VRMS) AC waveform that is required to power the CCFLs. The push-pull drive scheme uses a minimal number of external components, which reduces assembly cost and makes the printed circuit board (PC board) design easy to implement. The push-pull drive scheme also provides an efficient DC-to-AC conversion and produces near-sinusoidal waveforms. Each DS3984 channel drives two logic-level n-channel MOSFETs that are connected between the ends of a step-up transformer and ground (see Figure 1 and the Typical Operating Circuit). The transformer has a center tap on the primary side that is connected to a DC voltage supply. The DS3984 alternately turns on the two MOSFETs to create the high-voltage AC waveform on the secondary side. By varying the duration of the MOSFET turn-on times, the controller is able to accurately control the amount of current flowing through the CCFL. A resistor in series with the CCFL’s ground connection enables current monitoring. The voltage across this resistor is fed to the lamp current monitor (LCM) input on the DS3984. The DS3984 compares the peak resistor voltage against an internal reference voltage to deter- mine the duty cycle for the MOSFET gates. Each CCFL receives independent current monitoring and control, which results in equal brightness across all of the lamps and maximizes the lamp’s brightness and lifetime. EEPROM Registers and I2C-Compatible Serial Interface The DS3984 uses an I2C-compatible serial interface for communication with the on-board EEPROM configura- tion registers and user memory. The configuration regis- ters—four Soft-Start Profile registers (SSP1/2/3/4) and two Control Registers (CR1/2)—allow the user to cus- tomize many DS3984 parameters such as the soft-start ramp rate, the lamp and dimming frequency sources, fault-monitoring options, and channel enabling/disabling. The eight bytes of nonvolatile user memory can be used to store manufacturing data such as date codes, serial numbers, or product identification numbers. The device is shipped from the factory with the con- figuration registers programmed to a set of default configuration parameters. To inquire about custom factory programming, please send an email to MixedSignal.Apps@dalsemi.com. |
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