QST102 STMicroelectronics, QST102 Datasheet - Page 8

• Manufacturer Part Number: QST102
• Description: Capacitive Touch Sensor Device 2 Keys With Individual Key State Outputs
• Manufacturer: STMicroelectronics

QST touch sensing technology
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Figure 3
samples are necessary to trigger the key detection or end of detection
Figure 3.
Self-calibration
On power-up, all keys are self-calibrated to provide reliable operation under almost any
conditions. The calibration phase is used to compute a reference value per key which is then
used by the process determining if a key is touched or not. The reference is an average of 8
single acquisitions. As a result, the calibration time of the system can be simply calculated
using the following formula: t
burst period is described in application note AN2547. For a maximum calibration duration
(t
Fast positive recalibration
The device autorecalibrates a key when its signal reflects a decrease in capacitance higher
than a fixed threshold (PosRecalTh) for a defined number of acquisitions (PosRecalI).
Max on-duration
The device can time out and automatically recalibrate each key independently after a fixed
duration of continuous touch detection. This prevents the keys from becoming ‘stuck on’ due
to foreign objects or other sudden influences. This is known as the Max On-Duration feature.
After recalibration, the key will continue to operate normally, even if partially or fully
obstructed. Max On-Duration works independently per channel: a timeout on one channel
has no effect on another channel.
CAL
), please refer to
= Sampling point
shows an example of detection with DI=2 and EDI=2 meaning 3 consecutive
Detection signals
Hysteresis
Section 6.6: Capacitive sensing characteristics on page
CAL
= 8 * Burst_Period. The methodology used to measure the
Time
Reference + EofDeTh
Key Detection signal
Reference + DeTh
Reference count
19.
QST102