White LED 1x/1.5x Charge Pump in UCSP and Thin QFN

The MAX1573 fractional charge pump drives up to four white LEDs with regulated constant current for uniform intensity. By utilizing proprietary adaptive 1x/1.5x modes and ultra-low-dropout current regulators, it maintains the highest possible efficiency over the full 1-cell Li+ battery input voltage range. The 1MHz fixed-frequency switching allows for tiny external components and the regulation scheme is optimized to ensure low EMI and low input ripple.

An external resistor sets the full-scale LED current, while two digital inputs control on/off and select amongst three levels of brightness. A pulse-width modulation (PWM) signal can also be used to modulate LED brightness, requiring no additional components.

The MAX1573 is available in the tiny chip-scale UCSP™ (4 x 4 grid) and 16-pin thin QFN packages.

Applications

* Cell Phones/Smartphones * MP3 Players * Other Handhelds with Color Displays * PDAs, Digital Cameras, and Camcorders

* Proprietary Adaptive 1x/1.5x Modes

* High Efficiency (PLEDs/PBATT), Up to 92%

* 0.2% LED Current Matching

* 28mA/LED Drive Capability

* Low Input Ripple and EMI

* Eliminates Ballast Resistors

* Logic or PWM Dimming Control

* Low 0.1µA Shutdown Current

* 2.7V to 5.5V Input Voltage Range

* Soft-Start Limits Inrush Current

* Output Overvoltage Protection

* Thermal Shutdown Protection

* No External Schottky Diode Required

* Tiny UCSP (2.1mm x 2.1mm x 0.6mm) and Thin QFN (4mm x 4mm) Packages