Mobile I/O Expander And QWERTY Keypad Controller For Portable Electronics

The new mobile I/O expander also detects ambient-light conditions, information the processor can use to ensure efficient control of keypad backlighting, resulting in a significant reduction in overall power consumption that can extend battery life by 20 to 50 percent, depending on the usage model.

Similar to its sister devices, the ADP5520 and ADP5501 adaptive lighting management systems, the ADP5588 features intelligent lighting control, which allows the device to automatically sense ambient light levels and adjust backlight brightness according to changing lighting environments, resulting in the optimum viewing conditions for the user. The integrated architecture saves energy by minimizing the required CPU processing for backlight-monitoring functions, reducing current drain on the battery, and increasing available processor bandwidth. As a result, the device can achieve a 20- to 50-percent increase in operating time, depending on the usage model.

Today’s baseband or applications processors are often I/O limited due to the ever-increasing functions smart portable devices provide. The ADP5588 mobile I/O expander enables the processor to control up to an additional 15 general purpose I/Os through the I2C-compatible bus, reducing direct processor routing from 18 lines to three.

For greater flexibility, the CPU can communicate to the ADP5588 through the I2C-compatible serial interface to reconfigure the row and column pins as general-purpose input, general-purpose output, or light-sensor input pins depending on the application. For example, the CPU can configure the port expander’s pins as an 8 x 10 keypad matrix with 80 keys (maximum) for devices that require additional key scan functionality. Alternatively, when working with smaller keypad matrices, unused matrix interface pins can serve as general-purpose I/Os or as light-sensor inputs.

The ADP5588 mobile I/O expander offloads key-scan and GPIO functions from the CPU, freeing up the processor for higher priority functions and saving energy. A key event counter with overflow interrupt capability allows the device to manage up to ten unprocessed key events, while a key-lock option allows designers to choose whether or not to issue a key-press interrupt when the lock is active. The ADP5588 manages all mobile key scanning and decoding functions by storing the key presses and releases, and flagging them to the processor via a single interrupt line and two I2C-compatible interface lines. This enables designers of QWERTY-based portable devices to minimize the number of control lines from the microprocessor, resulting in significant cost and reliability benefits.