MAX7359 Key Switch Controller

By Maxim Integrated 250

MAX7359 Key Switch Controller

Maxim's MAX7359 I2C-interfaced peripheral provides microprocessors with management of up to 64 key switches. Key codes are generated for each press and release of a key for easier implementation of multiple key entries. Key inputs are monitored statically, not dynamically, to ensure low-EMI operation. The switches can be metallic or resistive (carbon) with up to 5 kΩ of resistance.

The MAX7359 features autosleep and autowake to further minimize the power consumption of the device. The autosleep feature puts the device in a low-power state (1µA typ) after a sleep timeout period. The autowake feature configures the MAX7359 to return to normal operating mode from sleep upon a key press.

The key controller debounces and maintains a FIFO of key-press and release events (including autorepeat, if enabled). An interrupt (active-low INT) output can be configured to alert key presses either as they occur, or at maximum rate.

Any of the column drivers (COL2/PORT2–COL7/PORT7) or the active-low INT, if not used, can function as a general-purpose output (GPO).

The MAX7359 is offered in small, 24-pin TQFN (3.5 mm x 3.5 mm) and 25-bump WLP (2.31 mm x 2.31 mm) packages for cell phones, pocket PCs, and other portable consumer electronic applications. The MAX7359 operates over the -40°C to +85°C temperature range.

  • Optional key release detection on all keys
  • Monitor up to 64 keys
  • +1.62 V to +3.6 V operation
  • Autosleep and autowake to minimize current consumption
  • Under 1 µA sleep current
  • FIFO queues up to 16 debounced key events
  • Key debounce time, user configurable from 9 ms to 40 ms
  • Low-EMI design uses static matrix monitoring
  • Hardware interrupt at the FIFO level or at the end of definable time period
  • Up to seven open-drain logic outputs available capable of driving LEDs
  • 400 kbps, 5.5 V-tolerant, 2-wire serial interface
  • Selectable 2-wire, serial-bus timeout
  • Four I2C address choices
  • Small, 24-pin TQFN package (3.5 mm x 3.5 mm), or 25-pin WLP package (2.31 mm x 2.31 mm)
  • Cell phones
  • Handheld games
  • PDAs
  • Portable consumer electronics