As the intrinsic sensitivity of the touch key is given by ΔCs/Cs, the less intrinsic capacitance would result in more sensitive
touch response. With this sensitivity boost enabled, sensitivity can be improved to ΔCs/ (Cs-S_CTRIM*(S_XDN/S_XCH)).
Sensitivity boost feature in self-cap mode can be activated by setting TSI_MODE[S_SEN].
is a new equation to
calculate NSTEP when sensitivity boost function is enabled.
NESTP =
Ci × Vp − Vm
vdd3v × Cs − S_CTRIM × S_XDN/S_XCH × S_XIN × S_XCH
Equation 6.
• S_CTRIM: configurable, the capacitance to be removed.
• S_XDN/S_XCH: configurable, the capacitance multiplier.
• The actual capacitance to be removed is S_CTRIM × (S_XDN/S_XCH).
2.4.2 TSI scan multiple rounds in self-cap mode
To minimize the noise deviation on the single scan, TSI supports multiple scans per channel. That is, TSI performs single scan
operation for many times from getting the trigger to end of scan.
Figure 12. Multiple scans per channel
Each time the TSI is triggered, multiple scans can be performed inside the TSI. The scan round is set by the registers
(TSI_SINC[DECIMATION], [ORDER] and [CUTOFF]), ranged from 1 to 32
2
. When the TSI_SINC[DECIMATION] is set to 0 (only
once), the single scan is engaged.
The 16-bit counter accumulates all scan results until the scan number reaches predefined number. To get the final scan result,
read TSI_DATA[TSICNT].
There are two kinds of scan number:
• For digital calculation to accumulate the final TSI scan result, as shown in
.
• For TSI IP to execute the scan action practically, as shown in
.
Scan Result: TSICNT = NSTEP × Decimation
Order
Cutoff
Equation 7.
Scan Time: Time = Tnstep × Decimation × Order
Equation 8.
NXP Semiconductors
TSI self-cap mode introduction
KE17Z Dual TSI User Guide, Rev. 0, 05 May 2022
User Guide
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