High-Performance Negative Charge Pump for 6 White LEDs in 3mm x 3mm Thin QFN

The MAX8847Y/MAX8847Z negative charge pumps drive up to 6 white LEDs with regulated constant current for display backlight applications. By utilizing an inverting charge pump and extremely low-dropout adaptive current regulators, these ICs achieve very high efficiency over the full 1-cell Li+ battery voltage range even with large LED forward voltage mismatch. The 1MHz fixed-frequency switching allows for tiny external components. The regulation scheme is optimized to ensure low EMI and low input ripple. The MAX8847Y/MAX8847Z include thermal shutdown, open- and short-circuit protection.

The MAX8847Y/MAX8847Z support independent LED on/off and dimming control. The MAX8847Z has PWM dimming control for LED1–LED6. The MAX8847Y has PWM dimming control for LED1–LED4 and serial-pulse dimming control for LED5 and LED6. The serial-pulse dimming ranges are pseudo-logarithmic from 24mA to 0.1mA and off in 32 steps. All devices include a temperature derating function to safely allow bright 24mA full-scale output current while automatically reducing current gradually to protect LEDs at high ambient temperatures above +60°C.

The MAX8847Y/MAX8847Z are available in 16-pin, 3mm x 3mm thin QFN packages.

Applications

* Cellular Phones * PDAs, Digital Cameras, and Camcorders * White LED Backlighting

* Negative 1x/1.5x Charge Pump

* Adaptive Current Regulators

* Independent Voltage Supply for Each LED

* 24mA to 0.1mA Serial-Pulse Dimming (MAX8847Y)

* 24mA to 0mA PWM Dimming (MAX8847Z)

* 2% (max) LED Current Accuracy, 1% (typ) Matching

* Low 120µA Quiescent Current

* Low 0.4µA Shutdown Current

* Inrush Current Limit

* Temperature Derating Function

* 16-Pin, 3mm x 3mm Thin QFN Packages