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DS3992Z-18P+ Datasheet(PDF) 7 Page - Maxim Integrated Products |
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DS3992Z-18P+ Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 13 page Detailed Description Each DS3992 channel drives two logic-level n-channel MOSFETs that are connected between the ends of a step-up transformer and ground (See the Typical Operating Circuits). The transformer has a center tap on the primary side that is connected to the DC inverter voltage supply. The DS3992 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 DS3992 is able to accurate- ly control the CCFL current. 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 and compared to an internal reference voltage to deter- mine the duty cycle for the MOSFET gates. The DS3992 supports a 1 lamp per channel configura- tion with fully independent lamp control and minimal external components. The DS3992 is also capable of controlling more than 1 lamp per channel using a wired-OR feedback circuit. See the Typical Operating Circuits section for more information. Block diagrams of the DS3992 are shown in Figures 1 and 2. More operating details of the DS3992 are dis- cussed on the following pages of this data sheet. Dimming Control The DS3992 uses “burst” dimming to control the lamp brightness. An analog voltage applied at the BRIGHT input pin determines the duty cycle of a digital pulse- width-modulated (DPWM) signal (90Hz to 220Hz for DS3992Z-09P/DS3992Z-09N and 180Hz to 440Hz for DS3992Z-18P/DS3992Z-18N). During the high period of the DPWM cycle, the lamp is driven at the selected lamp frequency (40kHz to 80kHz) as shown in Figure 3. This part of the cycle is also called the “burst” period because of the lamp frequency burst that occurs Two-Channel, Push-Pull CCFL Controller _____________________________________________________________________ 7 Functional Diagrams (continued) GATE DRIVERS GAn GBn DIGITAL CCFL CONTROLLER CHANNEL FAULT 512 x LAMP FREQUENCY [20.48MHz TO 40.96MHz] LAMP FREQUENCY [40kHz TO 80kHz] DIMMING PWM SIGNAL CHANNEL ENABLE MOSFET GATE DRIVERS LCMn LAMP CURRENT MONITOR 400mV 2.0V LAMP OVERCURRENT LAMP STRIKE AND REGULATION LAMP OUT 1.0V 1.0V OVDn OVERVOLTAGE DETECTOR LAMP MAXIMUM VOLTAGE REGULATION 64 LAMP CYCLE INTEGRATOR OVERVOLTAGE Figure 2. DS3992 Per Channel Logic Diagram 90Hz TO 220Hz OR 180Hz TO 440Hz LAMP CURRENT DPWM SIGNAL Figure 3. Digital-PWM Dimming and Soft-Start |
Similar Part No. - DS3992Z-18P+ |
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Similar Description - DS3992Z-18P+ |
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