mpr084 Freescale Semiconductor, Inc, mpr084 Datasheet - Page 25

• Manufacturer Part Number: mpr084
• Description: Proximity Capacitive Touch Sensor Controller
• Manufacturer: Freescale Semiconductor, Inc

Sensors
Freescale Semiconductor
9
9.1
The MPR084 can operate in a variety of environments with a variety of different electrode patterns. Because of this it is necessary
to adjust the relative sensitivity of the sensor controller. Usually this requires fine tuning in any final application.
There are many factors that must be taken into account, but much of the time this value is relative to the capacitance changes
generated by a touch. Since capacitance is directly proportional to the dielectric constant of the material and the area of the pad,
while inversely proportional to the distance between pads these are the primary factors.
As the relative capacitance rises the sensitivity setting of the MPR084 should be adjusted accordingly. Thus a very high sensitivity
value represents a large A and a small d.
9.2
The sensitivity of the MPR084 is adjusted by varying the Sensitivity Threshold Registers.
9.2.1 Sensitivity Threshold Registers
The Sensitivity Threshold registers all sensitivity of the MPR084 to be adjusted for any situation. The I
Sensitivity Threshold Registers is 0x04 - 0x0B.
Table 17. Sensitivity Threshold Register Format Descriptions
Sensitivity
Introduction
Adjusting the Sensitivity
Reset:
Field
7:0
ST
W
R
7
0
= Unimplemented
Sensitivity Threshold – The Sensitivity Threshold selects or reports the sensitivity
setting of the Sensor Controller. The resulting value must be in the range 1 to 64
units. If the value is outside of this range the ST will be set to 00111111.
00000000 Encoding 0 – Sets the sensitivity to level 1
~
00111111 Encoding 63 – Sets the sensitivity to level 64
Figure 28. Sensitivity Threshold Register Format
6
0
C
5
0
=
ke
----------- -
d
0
A
4
0
SL
Description
3
0
2
0
1
0
2
C slave address of the
0
0
Equation 8
MPR084
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