Freescale Semiconductor Evaluation Kit for MPR03X Proximity Touch Controller KITMPR03XEVM KITMPR03XEVM Ficha De Dados
Códigos do produto
KITMPR03XEVM
MPR03X
Sensors
18
Freescale Semiconductor
Figure 23.
Smaller amounts of change indicate increased sensitivity for the capacitance sensor. Some sample values are shown in
.
In the above cases, the capacitance is assumed to be in the middle of the range for specific settings. Within the capacitance
range the equation is nonlinear, thus the sensitivity is best with the lowest capacitance. This graph shows the sensitivity derivative
reading across the valid range of capacitances for a set I, T, and V
range the equation is nonlinear, thus the sensitivity is best with the lowest capacitance. This graph shows the sensitivity derivative
reading across the valid range of capacitances for a set I, T, and V
DD
. For simple small electrodes (that are approximately
21 pF) and a nominal 1.8V supply the following graph is representative of this effect.
Figure 24.
Table 11.
pF
Sensitivity (pF/ADC count)
10
-0.01953
100
-0.19531
Sensitivity vs. Midpoint Capacitance for VDD = 1.8 V
-5
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
500
1000
1500
2000
2500
Midpoint Capacitance (pF)
S
ens
iti
vi
ty
(pF/
A
D
C
Count
)
dC/dADC @cmid (pF/1 ADC Count)
0
Sensitivity vs. Capacitance for VDD = 1.8 V and I =36 μA and T = .5 μS
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
10
12
14
16
18
20
22
24
26
28
30
Se
ns
itiv
ity
(pF/A
D
C
C
ount
)
Maximum
Minimum
C/ADC
Capacitance