The MAX8831 integrates a 60mA, 28V PWM DC-DC step-up converter with five low-dropout LED current regulators for display and keypad backlighting in cell phones, PDAs, and other portable devices. The IC provides up to 90% efficiency over the entire input voltage range of 2.7V to 5.5V. The step-up converter operates at a fixed 2MHz switching frequency, enabling the use of very small external components to achieve a compact circuit area. For improved efficiency, the step-up converter automatically transitions to pulse-skipping mode at light loads.
Each of the five current regulators accommodates up to 9 series LEDs (depending on LED string forward voltage), and is independently programmed using an I²C interface. Two of the current regulators (LED1, LED2) are intended to support display backlight functions and are programmable up to 25mA using a 128-step logarithmic dimming scheme. The other three regulators (LED3, LED4, LED5) are suitable for keyboard backlight functions or for driving signal indicators, and are programmable up to 5mA using a 32-step logarithmic dimming scheme. The low-current regulators (LED3, LED4, LED5) can be operated from the step-up converter or from a separate low-voltage source.
The I²C interface controls all operational aspects of the current regulators, including: on/off state, LED current, ramp-up/ramp-down timers, and blink rate timers (LED3, LED4, LED5). The MAX8831 write/read addresses are factory programmed at 0x9A/0x9B (contact the factory for other address options).
The MAX8831 features open/short LED fault detection, output overvoltage protection, thermal shutdown, and open-circuit Schottky diode detection, with the status of each fault monitored continually for readback through the I²C interface.
The MAX8831 is available in a tiny 2mm x 2mm, 16-bump WLP package.
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