K60P100M100SF2RM Datasheet, PDF (1780/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Functional descriptions
T_{cap_samp}
2*2*16*20pF*600mV
16µA
48µs
55.7.1.3 TSI reference oscillator
The TSI reference oscillator has the same topology of the TSI electrode oscillator. The
TSI reference oscillator instead of using an external capacitor for the electrode oscillator
has an internal reference capacitor which can be programmable. The SCANC[CAPTRM]
defines the internal reference capacitor trimming value *.
The TSI reference oscillator share the same voltage hysteresis levels defined with the
SCANC[DELVOL] and has an independent programmable current source controlled by
the SCANC[REFCHRG].
* The reference oscillator frequency is given by the following equation:
F_{ref_osc}
Iref
2 *Cref _* ΔV
Figure 55-69. Equation 4: TSI reference oscillator frequency
Where:
C_ref: Internal reference capacitor
I_ref: Reference oscillator current source
∆V : Hysteresis delta voltage
Considering C_ref = 1.0 pF, I_ref = 12 µA and ∆V = 600 mV, follows
F_{ref_osc}
12µA
2 *1.0pF _* 600mV
10.0MHz
55.7.2 TSI measurement result
The capacitance measurement result is defined by the number of TSI reference oscillator
periods during the sample time and is stored in the TSICHnCNT register.
TSICHnCNT = T_{cap_samp} * F_{ref_osc}
Using Equation 2 and Equation 1 follows:
1780
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.