Multiplexer Enables Multi-Function Keypads

The efficient use of existing device interfaces is becoming a vexing problem for wireless-handset manufacturers. Due to the demand for smaller handsets with larger feature sets, there is less room for keypad or joystick interfaces. California Micro Devices plans to address this challenge with a single-chip keypad multiplexer. The CM2500-05QF enables device keys or joystick/roller pads to have dual functionality, thereby extending the feature set of today's mobile devices.

The multiplexer's dual nature allows each key or switch to be used for more than one function. In addition, the company's application-specific analog semiconductor chip greatly simplifies the design effort. Compared to other discrete implementations, the CM2500-05QF claims to significantly reduce board-space requirements. According to a company spokesperson, a board-space savings of up to 60% is achievable by using the device in place of a discrete solution comprising five Schottky-diode pairs.

The CM2500-05QF also features a chip-set I/O interface, which is suitable for use in the latest low-core voltage chip sets. The chip is designed to enable keypad switches to drive two sense lines each instead of one. Using the CM2500-05QF with newer low-core voltage chip sets ensures accurate signal integrity. The device outputs a typical voltage drop of only 10 mV from input to output on each channel. When used with these low-core voltage chip sets, current discrete multiplexer solutions—those that utilize Schottky diodes—typically exhibit voltage drops of up to 400 mV. This higher voltage drop can cause "high" signals to be misinterpreted as "low" or undefined.

The CM2500-05QF is a complete integrated solution. It requires no external discrete components. It is housed in a small, low-profile, 16-lead QFN package. The CM2500-05QF is currently sampling. It is priced at $0.50 each in 1000 units. Volume production is scheduled for August.