MAXIM MAX1573ETE+

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 a complete charge-pump buck-boost converter requiring only four small ceramic capacitors. The MAX1573 utilizes a proprietary 1x/1.5x fractional charge-pump topology to drive up to four white LEDs with regulated constant current for uniform intensity. The MAX1573 operates with a 1MHz fixed frequency. An external resistor (RSET) programs the full-scale LED current, while two digital inputs control on/off and provide brightness control. The MAX1573 operates in 1x mode until just above dropout. Then the MAX1573 switches to 1.5x charge-pump mode to regulate the lowest of LED1–LED4 to 150mV and maintain constant LED brightness even at very low battery voltages. Using this topology, there is no LED brightness change during the 1x/1.5x switchover, which guarantees no flicker on the display.

• 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×2.1mm×0.6mm) and Thin QFN (4mm x 4mm) Packages

• Cell Phones
• Smart Phones
• PDAs
• Digital Cameras
• Camcorders
• MP3 Players
• Other Handhelds with Color Displays