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MAX1578：Complete Bias and White LED Power Supplies for Small TFT Displays

First Complete LCD Bias and WLED Backlight Supplies for Small TFT Displays

The MAX1578/MAX1579 provide four regulated outputs to meet all the voltage requirements for small activematrix TFT-LCD displays in handheld devices where minimum external components and high efficiency are required. Each device consists of three advanced charge pumps for LCD bias power and a step-up converter for driving up to 8 series white LEDs for backlighting. The input voltage range is from 2.7V to 5.5V. The charge pumps provide fixed +5V, +15V, and -10V for the LCD bias circuits. No external diodes are needed. A high-efficiency, fractional (1.5x/2x) charge pump followed by a low-dropout linear regulator provides +5V to power the source driver. Automatic mode changing achieves the highest conversion efficiency. Two multistage, high-voltage charge pumps generate +15V and -10V to provide VON and VOFF, respectively. Utilizing a unique clocking scheme and internal drivers, these charge pumps eliminate parasitic charge-current glitches and reduce maximum input current, resulting in low electromagnetic emissions. The outputs are sequenced during startup and shutdown. In shutdown, the outputs are discharged to zero. The high-efficiency inductor step-up converter drives up to 8 white LEDs in series with a constant current to provide backlighting. The series connection allows the LED currents to be identical for uniform brightness and minimizes the number of traces to the LEDs. The MAX1578 regulates constant LED current over the entire temperature range. The MAX1579 features a temperature derating function to avoid overdriving the white LEDs during high ambient temperatures, enabling higher drive current below +42°C. The MAX1578/MAX1579 are available in space-saving 24-lead 4mm x 4mm thin QFN packages.

Key Features Four Regulators in One Package Bias Power Using Charge Pumps +5V at 25mA for Source Driver` +15V at 100µA for VON -10V at 100µA for VOFF No External Diodes Required Output Sequencing POS, NEG, and MAIN Are Autodischarged During Shutdown LED Backlight Power Using Boost Converter Series LED Connection for Uniform Illumination Supports Up to 8 LEDs at 25mA (max) 900mW (max) Power PWM or Analog Dimming Control Overvoltage Protection Low Input/Output Ripple Soft-Start with Zero Inrush Current Fast 1MHz PWM Operation for Small Component Size Temperature Derating Function (MAX1579) High Efficiency Bias: 83% (5.0V at 25mA, 15V/-10V at 100µA) LED: 84% (6 LEDs at 20mA) Uses Only Ceramic Capacitors and Only One Inductor Independent Enable Inputs for LED and Bias Power Thermal-Shutdown Protection 1µA Shutdown Current Tiny 4mm x 4mm Thin QFN Package

MAX1578, MAX1579: Typical Application Circuit Applications/Uses Internet Appliances LCD Displays with White LED Backlight PDAs, Palmtops Smartphones

DataSheet

Parametrics

Design kits & evaluation modules

• MAX1579EVKIT

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