K60P100M100SF2RM Datasheet, PDF (1778/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Functional descriptions
Electrode
charge current
(EXTCHRG)
Delta Voltage
(DELVOL)
Figure 55-64. TSI electrode oscillator circuit
The current source applied to the pad capacitance is 5-bit binary controlled by the
SCANC[EXTCHRG]. The hysteresis delta voltage is also configurable and is 3-bit binary
controlled by the SCANC[DELVOL]. The figure below shows the voltage amplitude
waveform of the electrode capacitance charging and discharging with a programmable
current.
Electrode
Voltage
Electrode Capacitor Charging and
Discharging with constant current
Hysteresis
Voltage Delta
Time
Figure 55-65. TSI electrode oscillator chart
The oscillator frequency is given by the following equation:
F_elec
I
2 * Celec _* ΔV
Figure 55-66. Equation 1: TSI electrode oscillator frequency
Where:
I: constant current
C_elec: electrode capacitance
ΔV: Hysteresis delta voltage
1778
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.