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48.5.3 Self-cap sensing mode
Figure 48-5. Self-cap sensing mode
Charge transfer operates through non-overlapping clock ph1/ph2 and trans-conductance
amplifier. Charge accumulates in integration capacitor Ci which creates step voltage Vci.
The basic formula is given by
where
Ci: is integration capacitance. Typical 90pF.
Vp, Vm: dual reference voltage which can be configured by DVOLT<1:0>.
Vdd3v: is analog power supply voltage. Typical 3.3V.
S_XIN, S_XCH: is parameter of analog front end which can be configured by
S_XIN<2:0>, S_XCH<2:0>.
Fsw: is the switching frequency which is controlled by SSC (Spread Spectrum Clocking)
block.
Cs: is the self-capacitance of touch sensor.
DVOLT, S_XIN, S_XCH can be used to adjust the sensing resolution.
If the touch sensor intrinsic sensitivity is limited due to parasitic, sensitivity boost feature
can be activated by setting S_SEN. The formula is given by
Functional description
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
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NXP Semiconductors
Summary of Contents for Kinetis KE1xZ256
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