MAX8901A

The MAX8901A step-up converters drive from two to six series-connected white LEDs (WLEDs) with constant current to provide uniform WLED intensity for LCD backlighting in cell phones, PDAs, and other handheld devices. The  MAX8901A operate at a fixed 750kHz (typ) switching frequency, allowing for tiny external components, and are optimized for the highest possible efficiency over the full 1-cell Li+/Li-Poly battery range.

Features of the MAX8901A are:(1)high efficiency, up to 91%; (2)2.6V to 5.5V input voltage range; (3)fixed-frequency operation; (4)supplies from 2 to 6 WLEDs with 1.3% LED current accuracy; (5)flexible dimming control; (6)input undervoltage lockout; (7)input overvoltage lockout; (8)WLED overvoltage protection (25v typ); (9)no WLED current in shutdown; (10)internal soft-start and thermal shutdown.These converters use a single input (ON) to enable the IC and to control WLED intensity. The MAX8901A requires a direct PWM input to regulate WLED intensity with the WLED current proportional to the PWM duty cycle. The MAX8901B uses single-wire, serial-pulse dimming that reduces the WLED intensity in 32 linear steps. Full-scale WLED current for serial-pulse dimming is 24.75mA (MAX8901B, 0.75mA/step).

The absolute maximum ratings of the MAX8901A can be summarized as:(1)IN to AGND:-0.3V to +7.0V;(2)storage temperature range:-65 to +150;(3)OVP, LX to GND:-0.3V to +28V;(4)junction temperature:+150;(5)PGND to GND:-0.3V to +0.3V;(6)continuous power dissipation:953mW.Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied.Exposure to absolute maximum rating conditions for extended periods may affect device reliability.These converters use a single input (ON) to enable the IC and to control WLED intensity. The MAX8901A requires a direct PWM input to modulate WLED intensity, with WLED current proportional to the PWM duty cycle.WLED overvoltage protection (OVP) occurs when the WLED output voltage rises above the WLED OVP threshold. The WLED OVP protection circuitry of MAX8901A latches off the IC and the IC enters shutdown when the WLED OVP threshold is exceeded. After OVP is engaged,cycle VIN or toggle ON to reenable the IC and enter soft-start.