STM8T141 STMicroelectronics, STM8T141 Datasheet - Page 27

• Manufacturer Part Number: STM8T141
• Description: Single-channel capacitive sensor for touch or proximity detection with shielded sensing electrode
• Manufacturer: STMicroelectronics

STM8T141
8.2
8.2.1
8.2.2
Figure 20. Connecting the shield (coaxial cable implementation)
Sensitivity adjustment
Several factors impact device sensitivity:
●
●
●
●
●
●
C
In touch mode, the Cs capacitor value has no influence on the sensitivity as the thresholds
are relative to the actual reference value. In proximity mode, the Cs value allows the
sensivity to be tuned. A higher sampling capacitor value increases the resolution and the
sensitivity but also the charging time. Decreasing the sampling capacitor value therefore
decreases the sensitivity.
For more details, please refer to application note AN2966.
PCB layout and construction
The PCB traces, wiring, and components associated or in contact with C
touch sensitive and should be treated with caution to limit the touch area to the desired
location. As an example, multiple touch electrodes connected to a sensing channel can be
used to create control surfaces on both sides of an object.
It is important to limit the amount of stray capacitance on the C
minimizing trace lengths and widths to achieve for higher gain without using higher values of
C
run close to each other for long distances. For detailed information on the impacts of the first
three factors, refer to application note AN2869.
S
S
. To minimize cross-coupling, electrode traces from adjacent sensing channel should not
Plastic jacket
influence on sensitivity
The sensing electrode material and size
The touch panel material and thickness
The board layout and in particular the sensing signal tracks
The value of the sampling capacitor (C
The ground coupling of the object (finger or hand) and sensor.
The touch or proximity detection threshold selected by the option byte.
Coaxial cable
Metal shield
Dielectric insulator
Doc ID 15699 Rev 7
Center core
S
) for proximity thresholds only
2
R
kΩ
X
100 kΩ
R
SHIELD
X
pin. This can be done by
SHLDIN
V DD
SHLDOUT
C X
Design guidelines
X
pins become
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