Lighting the way
21 April 2009
Lighting management unit for smart phones and devices with two camera modules.
Given the complexity and diversity of feature sets found in today's mobile phone product lines, designers can gain tremendous advantage in terms of design time and cost by using the same power management solution in multiple products.
By delivering I2C programmability across nine different LED combinations and I2C control across 16 different voltage settings for each LDO, AnalogicTech's AAT2862 allows designers to build complex products in shorter design cycles.
The AAT2862 is a Lighting Management Unit (LMU) that drives up to eight LEDs and integrates four Low-DropOut (LDOs) linear regulators. Optimised for single-cell Lithium-ion/polymer powered systems, the AAT2862 is suitable for I2C-based high performance smart phones and other mobile devices that require the integration of two camera modules. The LMU also adds an automatic fade-in/fade-out backlight control that simplifies design and reduces processor overhead.
Operating from a 2.7 V to 5.5 V input voltage, the AAT2862 drives up to eight backlight LEDs at up to 30 mA each. To ensure constant current over the entire battery range, the LEDs are driven from a tri-mode charge pump that automatically switches between 1x, 1.5x and 2x modes to maximise operating efficiency. The charge pump's high 1 MHz operating frequency permits the use of small 1 uF ceramic capacitors.
The eight LED outputs are programmable from 500 uA up to 30 mA. Two LED outputs can be programmed up to 60 mA each. Current can be set to any of 32 separate levels via an industry-standard I2C interface. To ensure uniform display brightness, current matching is better than 3%. To balance power dissipation, high current matching exceeds 5%.
The LMU features three programmable automatic fade-in/fade-out times for backlight control. By implementing this function in hardware instead of software, processor overhead is reduced.
The AAT2862 also features four high performance low noise LDOs. The output of each LDO is programmable via the I2C serial interface to any of 16 voltages between 1.2 V and 3.3 V. Each regulator can supply up to 200 mA load current. To support battery-operated applications, ground-pin current is limited to 80 uA.
To ensure device integrity, the AAT2862 also features automatic soft start and built-in thermal protection. The AAT2862 is qualified across the -40 to +85°C temperature range. It is available in a PB-free, 24-pin TQFN34 package.
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