mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 1232

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

Functional descriptions
48.7.1.1 TSI electrode oscillator
The TSI electrode oscillator circuit is illustrated in the following figure. A configurable
constant current source is used to charge and discharge the external electrode
capacitance. A buffer hysteresis defines the oscillator delta voltage. The delta voltage
defines the margin of high and low voltage which are the reference input of the
comparator in different time.
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.
The oscillator frequency is given by the following equation:
1232
Electrode
Voltage
Figure 48-64. TSI electrode oscillator circuit
Figure 48-65. TSI electrode oscillator chart
MCF51JF128 Reference Manual, Rev. 2, 03/2011
Electrode Capacitor Charging and
Discharging with constant current
Preliminary
Delta Voltage
(DELVOL)
charge current
(EXTCHRG)
Electrode
Time
Freescale Semiconductor, Inc.
Hysteresis
Voltage Delta