Smartlight driver integrates control of three separate banks of indicator LEDs

August 27, 2012 // By Paul Buckley
ams AG has released the AS3661, a new smart LED driver which controls up to nine LEDs to produce sophisticated indicator lighting effects in mobile devices independent of the power-hungry baseband processor.

The device is useful for many consumer electronics devices such as 3G and LTE modems, USB memory sticks, game controllers and headsets in which indicator lighting can enhance the user interface, and in which high-value light effects and low power consumption are required.

The AS3661 allows easy command-based programming of all light patterns. Three independent program execution engines form three independently programmable LED banks. This means that LED drivers can be grouped based on their function so that, for example, the first bank of drivers could be assigned to keypad illumination, the second bank to ‘funlights’ (patterns of light outputs produced by multiple LEDs), and the third group to notification LED(s).

Each bank can contain from one to nine LED driver outputs; the AS3661 offers nine LED channels in total with up to 25 mA per channel. A dedicated 12-bit PWM for each of the nine channels delivers absolutely smooth color transitions and enables the production of linear, logarithmic and ratiometric fading effects.

Instructions for the program execution engines are stored in the program memory. The total capacity of the program memory is 96 instructions and the user can allocate a memory of 1.5 kbit as required by the engines. The AS3661 smart LED driver has an I2C-compatible control interface with four pin-selectable addresses. The device also has a flexible General Purpose Output (GPO) which can be used as a digital control pin for other devices. The INT pin can be used to notify the central processor when a lighting sequence has ended. The device also provides a trigger input interface which allows for synchronization between multiple devices.

To optimize battery lifetime the design of the AS3661 includes various power-saving features. Each channel operates on a dropout voltage of less than 50 mV at 10 mA powered by a high-efficiency 150 mA charge pump with automatic switching between 1:1 and 1:1.5 mode. Furthermore, a power save mode is automatically entered