MPR121 FREESCALE [Freescale Semiconductor, Inc], MPR121 Datasheet - Page 3

• Manufacturer Part Number: MPR121
• Description: Proximity Capacitive Touch Sensor Controller
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

MPR121
3
Touch Sensing
Once the capacitance is determined at any given moment, this information must then be translated into intelligent touch
recognition. The MPR121 has a couple of systems that have improved over the previous generation in the MPR03x series
devices. A baseline tracking system allows the system to track the untouched capacitance in the system. For information on how
to set up the baseline capacitance system refer to application note AN3891. The baseline value is then compared with the current
value to determine if a touch has occurred. A designer has the ability to set both the rising and falling thresholds in addition to a
debounce to eliminate jitter and false touches due to noise. These elements are described in application note AN3892.
Proximity Sensing
A new feature of the MPR121 is the use of a proximity sensing system whereby all of a system’s electrodes can be shorted
together internally and create a single large electrode. The capacitance of this electrode is larger and projected capacitance can
be measured. When enabled, this “13
independent set of configuration registers. This system is described in application note AN3893.
LED Driver
The MPR121 includes eight shared LED driving pins. When these pins are not configured as electrodes, they may be used to
drive LEDs. The system allows for both pull up and pull down LED configurations as well as general GPIO push/pull functionality.
The configuration of the LED driver system is described in application note AN3894.
Serial Communication
The MPR121 is an Inter-Integrated Circuit (I
release of a button is detected. The device has a configurable I
or SCL lines. The resulting I
described in AN3895. For reference the register map of the MPR121 is included in
2
C addresses are 0x4C, 0x4D, 0x4E and 0x4F respectively. The specific details of this system are
th
” electrode will be included at the end of a normal detection cycle and will have its own
2
C) compliant device with an additional interrupt that is triggered any time a touch or
2
C address by connecting the ADDR pin to the VDD, VSS, SDA
Table
1.
Freescale Semiconductor
Sensors