Data Sheet

MPR121 Sensor

3 Freescale Semiconductor

DEVICE OPERATION OVERVIEW

Power Supply

MPR121 has two supply pins VDD and VREG. Power supply should always be connected to the VDD pin, which should be

decoupled with a 0.1uF ceramic decoupling capacitor from VDD to VSS. The VDD should be clean without excessive noise,

for example, noise ripple big than 100mV may result false function in some case.

To operate from a supply voltage in the range 2.0V to 3.6V, apply the voltage to VDD and internal voltage regulator will

regulate a lower operating voltage on VREG. Connect a 0.1uF ceramic decoupling capacitor between VREG and VSS, but

otherwise do not load VREG.

When power supply voltage is in the range 1.71V to 2.75V, the supply can also be routed into VREG directly to bypass internal

voltage regulator. Bypass VDD and VREG together with a 0.1uF ceramic decoupling capacitor from VDD to VSS. Refer to

Figure 2.

Note: The absolute maximum rating for VREG pin is 2.75V, the voltage applied should be carefully below this limit. The

VDD pin should be always connected with VREG in this case.

(a) (b)

Figure 2. Typical MPR121 power supply connection.

(a) MPR121 runs from a 2.0 V to 3.6 V supply.

(b) MPR121 runs from a 1.71 V to 2.75 V supply.

Serial Communication

The MPR121 is an Inter-Integrated Circuit (I

C) compliant device with an additional interrupt that is triggered any time a touch or

release of a button is detected. The device has a configurable I

C address by connecting the ADDR pin to the VSS, VDD, SDA

or SCL lines, the resulting I

C addresses are 0x5A, 0x5B, 0x5C and 0x5D respectively. The specific details of this system are

described at the end of this document.

LED Driver and GIPO Function

Among the 12 sensing input pins, 8 pins are multifunctional pins capable for LED driver and GPIO functions. When these

sensing input pins are not configured as electrodes inputs, they may be used to drive LEDs or for GPIO functions. When used

for LED driver, connect these electrodes output to LED anodes and a series current limiting resistor to ground. The

configuration of the LED driver and GPIO system is described in application note AN3894.