MPR121_10 FREESCALE [Freescale Semiconductor, Inc], MPR121_10 Datasheet - Page 16

• Manufacturer Part Number: MPR121_10
• Description: Proximity Capactive touch Senosr controller
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

MPR121
16
ELECTRODE CHARGE TIME
AUTO-CONFIGURATION
the Charge Current the Charge Time. This eliminates much of the guess involved with touch sensors and allows the same set-
tings to properly configure the device for a wide range of application and electrodes. As show earlier in this document, the sen-
sitivity of the sensor is maximized by having the baseline be as high as possible for a specific baseline capacitance. The
restriction on the high side is that a system should not charge above V
target voltage used is approximately V
3.0 V. The following three registers should be set based on the V
assuming the lowest voltage necessary for the battery. If the final voltage supply in the system is not known, just use the 1.8 V
values as they represent the worst case. This lower setting will not dramatically affect the performance, thus the 1.8 V could be
considered default and be used in all cases where fine tuning is not required.
One of the new features added in the MPR121 that was not included in the MPR03X is the ability to automatically configure
This implies that the automatic configuration system should target approximately 156 when V
Table 12. Electrode Charge Time Register Field Descriptions
Reset:
CDT#
CDT#
Field
6:4
2:0
W
R
7
0
0
= Unimplemented
Table 13.
Voltage (V
Electrode # Charge Discharge Time – The Charge Discharge Time field selects the
amount of time an electrode charges and discharges.
000 Encoding 0 – Global value is used.
001 Encoding 1 – Time is set to 0.5 μs
010 Encoding 2 – Time is set to 1 μs
~
11 Encoding 7 – Time is set to 32 μs.
Electrode # Charge Discharge Time – The Charge Discharge Time field selects the
amount of time an electrode charges and discharges.
000 Encoding 0 – Global value is used.
001 Encoding 1 – Time is set to 0.5 μs
010 Encoding 2 – Time is set to 1 μs
~
11 Encoding 7 – Time is set to 32 μs.
DD
6
0
1.8 V
- 0.7 V.
Figure 11. Electric Charge Time Register
V
DD
DD
CDT#
)
5
0
V
DD
1.1 V
2.3 V
- 0.7 V
4
0
DD
in the system. If the voltage is unregulated, set the values
DD
Description
ADC
625
785
- 0.7 V due to this being a non-linear region. Thus the
3
0
0
Baseline
156
196
2
0
CDT#
DD
1
0
is 1.8 V and 196 when V
Freescale Semiconductor
0
0
Sensors
DD
is