MPR121_10 FREESCALE [Freescale Semiconductor, Inc], MPR121_10 Datasheet - Page 12

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

MPR121
12
after charging must be in the range that is shown in
ADC (voltage visible to the digital interface) range is given by
When measuring capacitance there are some inherent restrictions due to the methodology used. On the MPR121 the voltage
The valid operating range of the electrode charging source is 0.7 V to (V
These equations are represented in the graph. In the nominal case of V
V
900
800
700
600
500
400
300
200
100
0
1.71
Figure 4. MPR121 Electrode Measurement Charging Pad Capacitance
Electrode Charge Time
Table 7.
1.91
ADC high
V
1.8
DD
ADC low
Electrode
Charging
Figure
625.7778
ADC
=
Valid ADC Values vs. V DD
2.11
=
V
------------------------- - 1024
high
DD
------------ 1024
V DD
V DD
Figure 5.
0.7
5.
ADChigh
V DD (V)
ADCmid
ADClow
T
and
–
(
0.7
398.2222
ADC
(
Electrode voltage measured here
Discharging
Electrode
)
2.31
low
,
Electrode Discharge Time
)
DD
DD
.
= 1.8 V the ADC range is shown below in
- 0.7 V). This means that for a given V
ADC
512
mid
2.51
Freescale Semiconductor
2.71
2T
Equation 3
Equation 4
DD
Sensors
the valid
Table
7.