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Figure 51-33. TSI electrode oscillator circuit
The current source applied to the pad capacitance is controlled by the
SCANC[EXTCHRG]. The hysteresis delta voltage is defined inn the module electrical
specifications present in the device data sheet.. The figure below shows the voltage
amplitude waveform of the electrode capacitance charging and discharging with a
programmable current.
Electrode
Voltage
Time
Electrode Capacitor Charging and
Discharging with constant current
Hysteresis
Voltage Delta
Figure 51-34. TSI electrode oscillator chart
The oscillator frequency is given by the following equation
F
elec
I
2 * C
elec
*
ΔV
Figure 51-35. Equation 1: TSI electrode oscillator frequency
Where:
I: constant current
C
elec
: electrode capacitance
Chapter 51 Touch sense input (TSI)
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
Freescale Semiconductor, Inc.
Preliminary
1429
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