ADI DS3992Z-18P+

The DS3992 is a low-cost, two-channel controller for cold-cathode fluorescent lamps (CCFLs) that are used to backlight liquid crystal displays (LCDs). The DS3992 can drive multiple CCFLs per channel, making it ideal for 4- and 6-lamp LCD PC monitor and TV applications. The DS3992 uses a push-pull drive scheme to convert a DC voltage (5V to 24V) to the high voltage (300VRMS to 1400VRMS) AC waveform that is required to power the CCFLs. The push-pull drive scheme uses a minimal number of external components, which reduces component and assembly cost and makes the printed circuit board (PC board) design easy to implement. The pushpull drive scheme also provides an efficient DC-to-AC conversion and produces near-sinusoidal waveforms. Each DS3992 channel drives two logic-level n-channel MOSFETs that are connected between the ends of a step-up transformer and ground. 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 accurately 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 determine the duty cycle for the MOSFET gates. The DS3992 supports a 1 lamp per channel configuration 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. 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 pulsewidth-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).

• Two-Channel CCFL Controller for Backlighting LCD Panels for PC Monitors and LCD-TVs
• Minimal BOM Provides Low-Cost Inverter Solution
• Per-Channel Lamp Fault Monitoring for LampOpen, Lamp Overcurrent, Failure to Strike, and Overvoltage Conditions
• Accurate (±10%) On-Board Oscillator for Lamp Frequency (40kHz to 80kHz)
• Accurate (±10%) On-Board Oscillator for DPWM Burst-Dimming Frequency (90Hz to 220Hz or 180Hz to 440Hz)
• Device Supply Undervoltage Lockout
• Inverter Supply Undervoltage Lockout
• Burst-Dimming Soft-Start Minimizes Audible Transformer Noise
• Strike Frequency Boost
• 100% to <10% Dimming Range
• 4.5V to 5.5V Single-Supply Operation
• -40°C to +85°C Temperature Range
• 16-Pin SO Package (150 mils)

• LCD PC Monitors
• LCD-TVs