The valid operating range of the electrode charging source is 0.7V to (V
參數資料
型號: DEMOMPR031
廠商: Freescale Semiconductor
文件頁數: 9/33頁
文件大小: 0K
描述: BOARD DEMO FOR MPR031 CTLR
產品培訓模塊: MPR03x - Low-Power Proximity Sensors
視頻文件: DEMOPR031 Touch Sensor
標準包裝: 1
傳感器類型: 觸摸,電容式
接口: I²C
電源電壓: 1.71 V ~ 2.75 V
嵌入式:
已供物品:
已用 IC / 零件: MPR031
產品目錄頁面: 2808 (CN2011-ZH PDF)
相關產品: MPR031EPR2DKR-ND - IC CTLR TOUCH SENSOR 8-DFN
MPR031EPR2CT-ND - IC CTLR TOUCH SENSOR 8-DFN
MPR031EPR2TR-ND - IC CTLR TOUCH SENSOR 8-DFN
MPR03X
Sensors
Freescale Semiconductor
17
The valid operating range of the electrode charging source is 0.7V to (VDD-.7)V. This means that for a given VDD the valid ADC
(voltage visible to the digital interface) range is given by
,
Equation 3
and
.
Equation 4
These equations are represented in the graph. In the nominal case of VDD = 1.8V the ADC range is shown below in Table 10.
Any ADC counts outside of the range shown are invalid and settings must be adjusted to be within this range. If capacitance
variation is of importance for an application after the current output, charge time and supply voltage are determined then the
following equations can be used. The valid range for capacitance is calculated by using the minimum and maximum ADC values
in the capacitance equation. Substituting the low and high ADC equations into the capacitance equation yields the equations for
the minimum and maximum capacitance values which are
and
.
Equation 5
7.3
Sensitivity
The sensitivity of the MPR03X is relative to the capacitance range being measured. Given the ADC value, current and time
settings capacitance can be calculated,
.
Equation 6
For a given capacitance the sensitivity can be measured by taking the derivative of this equation. The result of this is the
following equation, representing the change in capacitance per one ADC count, where the ADC in the equation represents the
current value.
Equation 7
This relationship is shown in the following graph by taking the midpoints off all possible ranges by varying the current and time
settings. The midpoint is assumed to be 512 for ADC and the nominal supply voltage of 1.8V is used.
Table 10.
VDD
ADChigh
ADClow
ADCmid
1.8
625.7778
398.2222
512
1024
7
.
DD
low
V
ADC
1024
7
.
DD
high
V
ADC
7
.
DD
low
V
T
I
C
7
.
T
I
C
high
ADC
V
T
I
C
DD
1024
2
1024
ADC
V
T
I
dADC
dC
DD
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