STM8T141 STMicroelectronics, STM8T141 Datasheet - Page 26

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

Design guidelines
8
8.1
Note:
8.1.1
Note:
26/50
Design guidelines
Shield function
The STM8T141 offers a built-in shielding function. This function provides the following
advantages for designing the end-application:
●
●
●
The shield principle consists in actively driving the shield plane or element with the same
signal as that of the electrode. The parasitic capacitance between the electrode and the
shield does not need to be charged anymore and its effect on the sensitivity is cancelled.
Grounding the shield reduces the sensitivity of the keys and may render the system
unusable.
Shield application example
Ideally, a coaxial cable is used for the shield. A R
connected to the C
core of the coaxial cable. The SHLDOUT pin should be connected to the metallic shield part
of the coaxial cable. A pull-up resistor (R
V
The example shown in
This setup has been successfully implemented with a coaxial cable of up to 4 m.
A longer coaxial cable could be used, but this would mean decreasing the R
and consequently increasing current consumption.
A smaller R
Figure
a. V
DD
for the correct power supply operating voltage when using the shield function.
DD
as shown in
Sensing electrode separated from sealed electronics.
Sensing wire shielded from unwanted environmental interferences.
Enhanced proximity detection when used with battery (DC) applications.
20).
must range from 4.5 to 5.5 V to use the shield function.Please refer to
SHIELD
Figure
X
ensures better shielding but increases current consumption (see
pin. The other side of the R
Figure 20
20.
Doc ID 15699 Rev 7
is given for R
SHIELD
X
) should be added between SHLDOUT and
X
= 2 k, R
X
resistor should be connected to the center
(typically 2 k) resistor should be
SHIELD
Table 12: Operating characteristics
= 100 k, and V
SHIELD
DD
STM8T141
= 5 V
resistor,
(a)
.