MPR121

Sensors

2

Freescale Semiconductor

SCHEMATIC DRAWINGS AND IMPLEMENTATION

Figure 1. Configuration 1: MPR121 runs from a 1.71 V to 2.75 V supply.

Figure 2. Configuration 2: MPR121 runs from a 2.5 V to 3.6 V supply.

Capacitance Sensing

The MPR121 uses a constant current touch sensor system with two primary types of control. It can measure capacitances

ranging from 10 pF to 2000 pF by varying the current and the amount of time supplied to each electrode. The electrodes are

controlled independently allowing for a great deal of flexibility in electrode pattern design. To make setup of the device easier, an

automatic configuration system can be used to set the ideal capacitance of each electrode. For information on how to set up this

system refer to application note AN3889.

Once capacitance is calculated, it runs through a couple of levels of digital filtering allowing for good noise immunity in different

environments without sacrificing response time or power consumption. The MPR121 can be configured for sample rates between

1 ms and 128 ms. For information on how to set up this system refer to application note AN3890.

20

6

5

1

2

3

4

7

19

18

17

16

15

14

13

12

11

10

9

8

VDD

VDD

ELE11/LED7

GND

0.1 μF

GND

1.71 V to 2.75 V

VDD

1.71 V to 2.75 V

VSS

VREG

IRQ

SCL

SDA

ADDR

REXT

ELE10/LED6

ELE9/LED5

ELE8/LED4

ELE7/LED3

ELE6/LED2

ELE5/LED1

ELE4/LED0

ELE3

ELE2

ELE1

ELE0

MPR121Q

TOUCH SENSOR

75 k 1%

20

6

5

1

2

3

4

7

19

18

17

16

15

14

13

12

11

10

9

8

VDD

VDD

ELE11/LED7

GND

0.1 μF

75 k 1%

2.5 V to 3.6 V

VDD

2.5 V to 3.6 V

VSS

VREG

IRQ

SCL

SDA

ADDR

REXT

ELE10/LED6

ELE9/LED5

ELE8/LED4

ELE7/LED3

ELE6/LED2

ELE5/LED1

ELE4/LED0

ELE3

ELE2

ELE1

ELE0

MPR121Q

TOUCH SENSOR

GND

GND

0.1 μF