MPR121 FREESCALE [Freescale Semiconductor, Inc], MPR121 Datasheet - Page 2

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

MPR121
2
SCHEMATIC DRAWINGS AND IMPLEMENTATION
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.
1.71 V to 2.75 V
Figure 1. Configuration 1: MPR121 runs from a 1.71 V to 2.75 V supply.
2.5 V to 3.6 V
Figure 2. Configuration 2: MPR121 runs from a 2.5 V to 3.6 V supply.
VDD
VDD
GND
GND
0.1 μF
0.1 μF
0.1 μF
GND
1.71 V to 2.75 V
2.5 V to 3.6 V
VDD
VDD
GND
GND
75 k 1%
75 k 1%
20
20
6
5
1
2
3
4
7
6
5
1
2
3
4
7
VDD
VSS
VREG
IRQ
SCL
SDA
ADDR
REXT
VDD
VSS
VREG
IRQ
SCL
SDA
ADDR
REXT
TOUCH SENSOR
TOUCH SENSOR
MPR121Q
MPR121Q
ELE11/LED7
ELE10/LED6
ELE11/LED7
ELE10/LED6
ELE9/LED5
ELE8/LED4
ELE7/LED3
ELE6/LED2
ELE5/LED1
ELE4/LED0
ELE9/LED5
ELE8/LED4
ELE7/LED3
ELE6/LED2
ELE5/LED1
ELE4/LED0
ELE3
ELE2
ELE1
ELE0
ELE3
ELE2
ELE1
ELE0
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Sensors