NXP Semiconductors K32 L2A Series, Reference Manual, Page: 1276 / 1379

The pin capacitance sampling time is given by the time the module counter takes to go
from 0 to its maximum value, defined by NSCN. The electrode sample time is expressed
by the following equation:
T
cap_samp
PS * NSCN
F
elec
Using Equation 1
T
cap_samp
2 * PS * NSCN * C
elec
*
Δ
V
I
Equation 6. Electrode sampling time
Where:
PS: prescaler value
NSCN: module counter maximum value
I: constant current
C
elec
: electrode capacitance
Δ
V: Hysteresis delta voltage
By this equation we have that an electrode with C = 20 pF, with a current source of I = 16
µA and
Δ
V = 600 mV, PS = 2 and NSCN = 16 have the following sampling time:
T
cap_samp
2*2*16*20pF*600mV
16µA
48µs
49.4.1.3 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.
The TSI reference oscillator has an independent programmable current source controlled
by GENCS[REFCHRG].
The reference oscillator frequency is given by the following equation:
F
ref_osc
I
ref
2 *C
ref
*
Δ
V
Equation 7. TSI reference oscillator frequency
Where:
Functional description
K32 L2A Reference Manual, Rev. 2, 01/2020
1276 NXP Semiconductors