Simplified Block Diagram
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- Low-Cost, Half-Bridge Inverter Topology
- Resonant Mode Striking Ensures Startup
- Constant-Frequency Operation After Lamp Ignition
- Drives Large External MOSFETs
- Supports Multilamp Applications
- Sync and Phase-Shift Controls Allow Daisy-Chained Operation
- Adjustable Switching Frequency and DPWM Frequency
- ±2.5% Lamp-Current Regulation
- 10:1 Dimming Range
- Accurate Analog-Dimming Control
- Lamp-Out Detection with Adjustable Timeout
- Secondary Current and Voltage Limiting
- Primary Current Limit with RDS(ON) Sensing
- Adjustable DPWM Rise and Fall Time
- Low-Cost, 28-Pin QSOP Package
- LCD Monitors
- LCD TVs
- Notebook Computers
The MAX8729 provides accurate lamp-current regulation (±2.5%). The lamp current is adjustable with an external resistor. The MAX8729 changes the brightness by turning the CCFL on and off using a digital pulse-width modulation (DPWM) method, while maintaining the lamp current constant. The brightness can be adjusted with an analog voltage on the CNTL pin, or with an external PWM signal.
The MAX8729 is capable of synchronizing and adjusting the phase of the gate drivers and DPWM oscillator. These features allow multiple MAX8729 ICs to be connected in a daisy-chain configuration. The switching frequency and DPWM frequency of the master IC can be easily adjusted using external resistors, or synchronized with system signals. If the controller loses the external sync signals, it switches over to the internal oscillators and keeps operating. Phase-shift select pins PS1 and PS2 can be used to program four different phase shifts, allowing up to five MAX8729s to be used together.
The MAX8729 protects the inverter from lamp-out, secondary overvoltage, and secondary short-circuit faults. The MAX8729 can drive large-power MOSFETs typically used in applications where one power stage drives four or more CCFL tubes in parallel. An internal 5.35V linear regulator powers the MOSFET drivers and most of the internal circuitry. The MAX8729 is available in a low-cost, 28-pin QSOP package and operates over the -40°C to +85°C extended temperature range.