Low-Cost, SMBus, CCFL Backlight Controller

The MAX8759 integrated cold-cathode fluorescent lamp (CCFL) inverter controller is designed to drive CCFLs using a full-bridge resonant inverter. The resonant operation ensures reliable striking and provides near-sinusoidal waveforms over the entire input range. The controller operates over a wide input-voltage range of 4.5V to 28V with high power to light efficiency. The device also includes safety features that effectively protect against single-point fault conditions such as lamp-out, secondary overvoltage, and secondary short-circuit faults.

The MAX8759 provides accurate lamp-current regulation (±2.5%) for superior CCFL inverter performance. The lamp current is adjustable with an external resistor; 10:1 dimming range can be achieved by turning the CCFL on and off using a digital pulse-width modulation (DPWM) method, while maintaining the lamp-current constant. The MAX8759 provides three mechanisms for controlling brightness: 2-wire SMBus™-compatible interface, external ambient-light sensor (ALS), or system PWM control. The MAX8759 supports Intel display power-saving technology (DPST) to maximize battery life. The device includes two lamp-current feedback input pins that support dual-lamp applications with a minimum number of external components.

The MAX8759 controls a full-bridge inverter for maximum efficiency and directly drives four external n-channel power MOSFETs. An internal 5.35V linear regulator powers the MOSFET drivers and most of the internal circuitry. The MAX8759 is available in a space-saving, 28-pin, thin QFN package and operates over a -40°C to +85°C temperature range.

Applications

* LCD Monitors * Notebooks

* Accurate Dimming Control Using SMBus, PWM Interface, or Ambient Light Sensor

* 10:1 Dimming Range with 256-Step Resolution

* Resonant-Mode Operation

* Longer Lamp Life with Near Sinusoidal Lamp-Current Waveform

* Guaranteed Striking Capability

* High-Power-to-Light Efficiency

* Wide Input-Voltage Range (4.5V to 28V)

* Input Feed-Forward for Excellent Line Rejection

* ±2.5% Lamp-Current Regulation

* Adjustable 1.5% Accurate DPWM Frequency

* Dual Lamp-Current Feedback Inputs

* Comprehensive Fault Protection

* Secondary Voltage Limiting

* Primary Current Limit with Lossless Sensing

* Lamp-Out Protection with Adjustable Timeout

* Secondary Short-Circuit Protection

* Small 28-Pin, 5mm x 5mm, Thin QFN Package