June 2011 Doc ID 15699 Rev 7 1/50
1
STM8T141
Single-channel capacitive sensor for touch
or proximity detection with shielded sensing electrode
Features
■Touch or proximity detection (a few
centimeters)
■Built-in driven shield function:
– Enhance proximity detection
– Protect sensing electrode from noise
interference
■Ultra-low power modes suitable for battery
applications (11 µA in extreme low power
mode)
■On-chip integrated voltage regulator
■Environment compensation filter
■User programmable options include:
– Four detection thresholds
– Four output modes
– Four low power modes
– Reference freeze timeout
■Minimal external components
Applications
■Consumer electronics
■Power-critical and battery applications
– Wake-up on proximity
■Home and office appliances
– Find-in-the-dark (FITD) applications using
proximity detection
– Sanitary ware and white goods
■Flameproof human interface devices for use in
hazardous environments
Table 1. Device summary
Feature STM8T141
Operating supply voltage 2.0 V to 5.5 V
Supported interface Single key state output
Operating temperature –40° to +85 °C
Packages 8-pin SO
8-pin UFDFPN
SO8 UFDFPN8
(2 x 3 mm)
(narrow)
www.st.com
Contents STM8T141
2/50 Doc ID 15699 Rev 7
Contents
1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3 Pin descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4 STM8T ProxSense technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1 Capacitive sensing overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2 Charge transfer acquisition principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5 STM8T processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1 Signal and reference calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2 Determining touch/proximity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.3 Environment compensation filter (ECF) . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.3.1 ECF principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.3.2 Reference freeze timeout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.3.3 Debounce filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6 Typical application diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7 Device operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.1 Option byte description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.2 TOUT/POUT output mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.2.1 Active . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.2.2 Toggle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.2.3 3-second latch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.2.4 30-second latch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.3 Detection threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.4 Power modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
7.4.1 Normal Power mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
7.4.2 Low Power mode with Zoom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.4.3 Extreme Low Power mode with Zoom . . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.4.4 Extreme Low Power mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
7.5 Charge transfer frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
STM8T141 Contents
Doc ID 15699 Rev 7 3/50
7.6 Sampling period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
8 Design guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.1 Shield function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.1.1 Shield application example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.2 Sensitivity adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.2.1 CS influence on sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.2.2 PCB layout and construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.3 Influence of power supply variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
9 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.1 Parameter conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.1.1 Minimum and maximum values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.1.2 Typical values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.1.3 Typical curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.1.4 Loading capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.2 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.3 Operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.3.1 General operating conditions and supply characteristics . . . . . . . . . . . 30
9.3.2 Average current consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.3.3 Output characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.4 Regulator and reference voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.5 Capacitive sensing characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
9.6 EMC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
9.6.1 Functional EMS (electromagnetic susceptibility) . . . . . . . . . . . . . . . . . . 35
9.6.2 Prequalification trials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
9.6.3 Electromagnetic interference (EMI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.6.4 Absolute maximum ratings (electrical sensitivity) . . . . . . . . . . . . . . . . . 36
9.6.5 Electrostatic discharge (ESD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.6.6 Static latchup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
10 Package characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
10.1 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
10.1.1 SO8 package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
10.1.2 UFDFPN8 package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
10.2 Package thermal characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
10.2.1 Reference document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Contents STM8T141
4/50 Doc ID 15699 Rev 7
11 Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
11.1 STM8T141 ordering information scheme . . . . . . . . . . . . . . . . . . . . . . . . . 42
11.2 Orderable favorite device lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
11.3 In-factory option byte programming service . . . . . . . . . . . . . . . . . . . . . . . 43
12 STM8T141 development tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
13 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
STM8T141 List of tables
Doc ID 15699 Rev 7 5/50
List of tables
Table 1. Device summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Table 2. STM8T141 pin descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 3. Explanation of ECF example 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 4. Explanation of ECF example 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Table 5. Option bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Table 6. Option byte description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 7. Detection thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 8. Low power period according to selected power mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Table 9. Voltage characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Table 10. Current characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Table 11. Thermal characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Table 12. Operating characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Table 13. Average current consumption without shield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Table 14. Output pin characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Table 15. Regulator and reference voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Table 16. General capacitive sensing characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Table 17. Response times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Table 18. External sensing component characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Table 19. EMS data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Table 20. EMI data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Table 21. ESD absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Table 22. Electrical sensitivities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Table 23. 8-lead plastic small outline - package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Table 24. 8-lead ultra thin fine pitch dual flat - package mechanical data . . . . . . . . . . . . . . . . . . . . . 40
Table 25. Thermal characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Table 26. Orderable favorite device lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Table 27. Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Table 28. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
List of figures STM8T141
6/50 Doc ID 15699 Rev 7
List of figures
Figure 1. STM8T141 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 2. S08 pinout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 3. UFDFPN8 pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 4. Coupling with hand increases the capacitance of the sensing electrode . . . . . . . . . . . . . . 10
Figure 5. STM8T measuring circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 6. Conversion period examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 7. Environmental compensation filter (ECF) example 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure 8. Environmental compensation filter (ECF) example 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Figure 9. Reference freeze timeout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 10. Typical application shematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 11. Possible load configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 12. Active mode output operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 13. Toggle mode output operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 14. 3-second latch mode output operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 15. 30-second latch mode output operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 16. Charge cycle timing diagram in Normal Power mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 17. Charge cycle timing diagram in Low Power mode with Zoom . . . . . . . . . . . . . . . . . . . . . . 24
Figure 18. Charge cycle timing diagram in Extreme Low Power mode with Zoom . . . . . . . . . . . . . . . 24
Figure 19. Charge cycle timing diagram in Extreme Low Power mode . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 20. Connecting the shield (coaxial cable implementation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Figure 21. Pin loading conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Figure 22. IDD average current consumption vs RSHIELD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Figure 23. Sigma variation across VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 24. SO8-lead plastic small outline - package outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Figure 25. UFDFPN8-lead ultra thin fine pitch dual flat package (MLP) package outline . . . . . . . . . . 40
Figure 26. STM8T141 ordering information scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Figure 27. STM8T141-EVAL evaluation kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Figure 28. STM8T141 blank module box. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Figure 29. STM8T141-EVAL programming tool. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
STM8T141 Description
Doc ID 15699 Rev 7 7/50
1 Description
The STM8T141 is a ProxSense™ single-channel, fully integrated, charge-transfer,
capacitive sensor that is designed to replace conventional electromechanical switches in
cost-sensitive applications.
The STM8T141 is offered in 8-pin packages and is ideally suited for 1-button applications. It
can be configured either in touch or proximity sensing mode for wake-up or backlighting on
actuation.
The extremely low current consumption makes it an ideal solution for battery-powered
applications.
The device features an internal voltage regulator to enhance detection sensitivity and
stability.
The STM8T141 touchpad can sense through almost any dielectric and can thereby contain
the electronics in a sealed environment.
The STM8T141 also incorporates the advantages of using a driven shielding capability. This
makes it possible to separate the sealed electronics from the sensing electrode. The shield
feature enables the designer to protect part of the sensing element from unwanted
environmental interference and enhances proximity detection when used with battery (DC)
applications.
Note: ProxSense™ is a trademark of Azoteq.
Block diagram STM8T141
8/50 Doc ID 15699 Rev 7
2 Block diagram
Figure 1. STM8T141 block diagram
RC oscillator
The 500-kHz RC oscillator is an internal fixed frequency oscillator used to supply the clock
to the MCU system engine.
Power-On-Reset (POR)
The POR generates a reset signal depending on the power supply level and the clock
pulses received from the RC oscillator.
Voltage regulator
The voltage regulator has an internal comparison and feedback circuit that ensures the
VREG voltage is kept stable and constant. The regulator requires an external smoothing
capacitor.
MCU system engine
The MCU system engine controls the capacitive sensing engine and processes touch and
proximity detection signals.
ProxSense engine
The ProxSense engine circuitry employs a charge-transfer method to detect changes in
capacitance.
500 kHz RC
oscillator
CX
VSS
TOUT/POUT
VDD
POR
VREG
ai17207
Voltage
regulator
MCU system engine
CS
SHLDOUT
SHLDIN
ProxSense
engine
STM8T141 Pin descriptions
Doc ID 15699 Rev 7 9/50
3 Pin descriptions
Figure 2. S08 pinout
Figure 3. UFDFPN8 pinout
Table 2. STM8T141 pin descriptions
Pin no.
PIn type(1)
1. I: input pin, OD: open drain, PP: output push-pull pin, S: supply pin and SNS: capacitive sensing pin.
Pin name Pin function
SO8 UFDFPN8
1SV
SS Ground
2SNSC
S
Capacitive sensing channel pin to
CS(2)
2. Use COG or NPO capacitor type.
3SNSC
XCapacitive sensing channel pin to RX
4ISHLDIN
(3)
3. If the active shield is unused, please connect this pin to VSS.
Shield input
5SV
REG Internal voltage regulator output (4)
4. Requires a low ESR, 1µF capacitor to ground. This output must not be used to power other devices.
6 OD SHLDOUT Shield output
7SV
DD Supply voltage
8PPTOUT/POUT
Touch/proximity(5) output
(active high)
5. Depending on the value of bits [1:0] of OPT0.
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62%'
3(,$).
3(,$/54
6$$
#3
633 4/540/54
#8
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62%'
3(,$).
3(,$/54
6$$
#3
633 4/540/54
#8
STM8T ProxSense technology STM8T141
10/50 Doc ID 15699 Rev 7
4 STM8T ProxSense technology
4.1 Capacitive sensing overview
A capacitance exists between any reference point and ground as long as they are
electrically isolated. If this reference point is a sensing electrode, it can help to think of it as
a capacitor. The positive electrode of the capacitor is the sensing electrode, and the
negative electrode is formed by the surrounding area (virtual ground reference in Figure 4).
Figure 4. Coupling with hand increases the capacitance of the sensing electrode
When a conductive object is brought into proximity of the sensing electrode, coupling
appears between them, and the capacitance of the sensing electrode relative to ground
increases. For example, a human hand raises the capacitance of the sensing electrode as it
approaches it. Touching the dielectric panel that protects the electrode increases its
capacitance significantly.
4.2 Charge transfer acquisition principle
To measure changes in the electrode capacitance, STM8T devices employ bursts of charge-
transfer cycles.
The measuring circuitry is connected to the CX pin. It is composed of a serial resistor RX
plus the sensing electrode itself of equivalent capacitance CX (see Figure 5). The sensing
electrode can be made of any electrically conductive material, such as copper on PCBs, or
transparent conductive material like Indium Tin Oxide (ITO) deposited on glass or Plexiglas.
The dielectric panel usually provides a high degree of isolation to prevent ESD discharge
from reaching the STM8T touch sensing controller. Connecting the serial resistor (RX) to the
CX pin improves ESD immunity even more.
CT
Lower capacitance
CX
Higher capacitance
Sensing electrode
STM8T141 STM8T ProxSense technology
Doc ID 15699 Rev 7 11/50
Figure 5. STM8T measuring circuitry
1. RX must be placed as close as possible to the STM8T device.
The principle of charge transfer is to charge the electrode capacitance (CX) using a stable
power supply. When CX is fully charged, part of the accumulated charge is transferred from
CX to an external sampling capacitance, referred to as CS. The transfer cycle is repeated
until the voltage across the sampling capacitor CS reaches the end of acquisition reference
voltage (VTRIP). The change in the electrode capacitance is detected by measuring the
number of transfer cycles composing a burst (see Figure 6).
Throughout this document the following naming conventions apply:
●The charge transfer period (tTRANSFER) refers to the charging of CX and the
subsequent transfer of the charge to CS.
●The burst cycle duration (tBURST) is the time required to charge CS to VTRIP
.
●The sampling period (tSAMPLING) is the acquisition rate.
Figure 6. Conversion period examples
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12/50 Doc ID 15699 Rev 7
5 STM8T processing
The STM8T141 device is designed to ensure reliable operation whatever the environment
and operating conditions. To achieve this high level of robustness, dedicated processing
have been implemented:
●Signal and reference calculation
●Determining touch/proximity
●Self-calibration
●Environmental compensation filter
●Debounce filter
5.1 Signal and reference calculation
Capacitive touch or proximity sensing is a technique based on detecting the electrode
capacitance change when someone is in proximity of the sensing electrode. The
capacitance change, induced by the presence of a finger or a hand in the device detection
area, is sensed by the variation in the number of charge transfer pulses composing the
burst. The charge transfer pulse number, also called “signal” is compared to a reference to
decide if there is a touch/proximity detection or not.
At power-up, a calibration sequence is performed to compute one reference value per
capacitive sensing channel. The reference is extracted from 32 burst measurements. Then,
the ECF takes care of its slow evolution over time.
To speed up the calibration process, the device is kept in normal mode whatever the low
power mode selected. The device operates in the selected low power mode when the
calibration process is completed.
5.2 Determining touch/proximity
The minimum difference between the reference and the signal necessary to report a
touch/proximity is the detection threshold (DTh). A time filtering, similar to the debouncing of
the mechanical switches, is applied to avoid noise induced detections.
Four different detection threshold settings are available and selectable by option byte. The
touch and sensitive touch levels are relative, which means the actual sensing distance is not
influenced by the Cs capacitor. The two thresholds should be able to adapt to various
surroundings and panel material or thickness. The proximity sensitivity thresholds are
absolute. This implies that the detection distance increases with the Cs capacitor. It provides
an easy way to tune the proximity sensing distance according to the application needs.
STM8T141 STM8T processing
Doc ID 15699 Rev 7 13/50
5.3 Environment compensation filter (ECF)
5.3.1 ECF principle
The capacitive sensing channel reference value increases or decreases according to
environmental conditions such as temperature, power supply, moisture, and surrounding
conductive objects. The STM8T141 includes a built-in digital infinite impulse response (IIR)
filter capable of tracking slow changes in the environment called the Environment
Compensation Filter (ECF). This is a first order digital low pass filter with a gain of one. The
filter makes the reference follow slow changes of the signal while fast changes are
recognized as a touch or proximity.
When a touch or proximity condition is detected, the corresponding capacitive sensing
channel reference is frozen.
Figure 7. Environmental compensation filter (ECF) example 1
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Zone 1 Zone 2 Zone 3 Zone 4
Event description
The object (finger) is
outside the
electrode field
range.
Electrode
environment is
stable
The object, is inside the
electrode field range. It
induces a signal change
but, not large enough to
cross the detection
threshold (Dth).
The reference adapts
slowly to the object
proximity.
The object comes inside the
detection range before the
reference compensates for
its presence.
A touch or proximity event is
triggered because the
signal level falls below the
reference - DTh.
The object exits
from the
electrode’s
detection range.
Detection state No detection Detection No detection
ECF operation Active Halt Active
Reference Adapting Frozen Adapting
STM8T processing STM8T141
14/50 Doc ID 15699 Rev 7
Figure 8. Environmental compensation filter (ECF) example 2
Detection
Reference - DTh
Environment changing
Number of counts
Reference
Signal
Zone 1 Zone 2 Zone 3Zone 4
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Table 4. Explanation of ECF example 2
Zone 1 Zone 2 Zone 3 Zone 4
Event description
The system
environment
changes and the
device adapts its
reference according
to this environment
change.
An object (finger) is
detected. The
environment continues
to change.
The object is still under
detection but, the
environment is not
changing anymore.
The object exits
from detection.
Detection operation No detection Detection No detection
ECF state Active Halt Active
Reference Adapting Frozen Adapting
Surrounding
environment Changing Stable
STM8T141 STM8T processing
Doc ID 15699 Rev 7 15/50
5.3.2 Reference freeze timeout
To prevent an object under detection from influencing the reference value, the ECF is halted
as soon as a detection happens. Consequently, the reference is frozen.
In order to be able to recover from a sudden environment change, the reference freeze ends
after a maximum programmable delay called the “reference freeze timeout” (tRFT).
When a detection lasts longer than the tRFT
, the ECF is enabled again and the reference
moves toward the detection signal. After a short period of time, the difference between the
signal and the reference become smaller than the detection threshold and the device
reports no detection.
Note: Reference freeze timeout was incorrectly called “recalibration timeout” in previous versions
of this document.
Figure 9. Reference freeze timeout
1. See max values of tRFT in Table 16: General capacitive sensing characteristics.
2. Between the moment when the finger is removed from the sensor and the instant the reference - DTh curve
crosses the signal limit, the device is unable to detect a new touch. This delay is called “masked detection
window”. It depends on the environmental change or object signal variation speed inside the electrode’s
field. The detection threshold also impacts the masked detection window.
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STM8T processing STM8T141
16/50 Doc ID 15699 Rev 7
5.3.3 Debounce filter
The debounce filter mechanism works together with the ECF to dramatically reduce the
effects of noise on the touch and proximity detection. Debouncing is applied to acquisition
samples to filter undesired abrupt changes.
The number of consecutive detection debounce count (DDC) and end of detection
debounce count (EDDC) needed to identify a proximity/touch detection are defined in
Section 9.5: Capacitive sensing characteristics on page 33.
STM8T141 Typical application diagram
Doc ID 15699 Rev 7 17/50
6 Typical application diagram
Figure 10. Typical application shematic
1. If the active shield is not used, The SHLDIN pin must be grounded, SHLDOUT should be left unconnected, and RSHIELD
can be removed.
2. Use COG or NPO or higher grade capacitor.
The smaller the value of the RSHIELD resistor, the better its effect but, the greater the device
consumption.
Pin TOUT/POUT can directly drive a HV FET (as shown in Figure 11) that, in turn, can drive
any load.
Figure 11. Possible load configurations
A touch or proximity detection is defined as an actuation (high = logical '1' and
low = logical '0').
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Device operation STM8T141
18/50 Doc ID 15699 Rev 7
7 Device operation
The STM8T141 can be configured through a set of selectable one-time programmable
(OTP) option bytes. These options can be used in their default (unconfigured) state or set for
specific applications. For large orders, preconfigured devices are available (please refer to
Section 11: Ordering information).
The STM8T141 can be configured to act as a touch or proximity detection device. A number
of other options are also user programmable, including:
●Four output modes
–Active mode
– Toggle mode
– 3-second Latch mode
– 30-second Latch mode
●TOUT/POUT output mode selection
●Four detection thresholds
– Two for touch detection
– Two for proximity detection
●Four power modes
– Normal power mode
– Three low power modes
●Reference freeze timeout
7.1 Option byte description
A set of tools is supplied by STMicroelectronics to program the user OTP options for
prototyping purposes. Please refer to Section 12: STM8T141 development tools for more
details.
Note: Devices that are not yet programmed (“blank” devices) are delivered cleared (at value ‘0’) for
all bits.
The user options allow the STM8T141 to be customized for each specific application.
Default values for the oscillator, conversion rate (tSAMPLING), filter freeze and device reset
settings should be used initially for first designs.
Table 5. Option bytes
Option
byte
no.
Option bits Factory
default
setting
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
OPT1 Reserved Sampling
period
Charge
transfer
frequency
Reserved 0xX0
OPT0 Power mode Detection threshold Reference freeze
timeout
TOUT/POUT
output mode 0x00
STM8T141 Device operation
Doc ID 15699 Rev 7 19/50
Table 6. Option byte description
Option
byte no. Description
OPT1
Bits [7:3]: Reserved
Bit 2: Sampling period (tSAMPLING)(Section 7.6: Sampling period)
0: Conversion period is 20 ms
1: Conversion period is 10 ms
Bit 1: Charge transfer frequency (fTRANSFER)(Section 7.5: Charge transfer frequency)
0: 125 kHz
1: 250 kHz
Bit 0: Reserved
OPT0
Bits [7:6]: Power mode (Section 7.4: Power modes)
00: Low Power mode with Zoom
01: Normal Power mode
10: Extreme Low Power mode with Zoom
11: Extreme Low Power mode
Bits [5:4]: Detection threshold (Section 7.3: Detection threshold)
00: Standard proximity
01: Standard touch
10: Sensitive proximity
11: Sensitive touch
Bits [3:2]: Reference freeze timeout (Section 5.3.2: Reference freeze timeout)
00: 15-second reference freeze timeout
01: 45-second reference freeze timeout
10: Reserved
11: Infinite reference freeze
Bits [1:0]: TOUT/POUT output mode (Section 7.2: TOUT/POUT output mode)
00: Active mode
01: Toggle mode
10: 3-second Latch mode
11: 30-second Latch mode
Device operation STM8T141
20/50 Doc ID 15699 Rev 7
7.2 TOUT/POUT output mode
Four output modes are available on the STM8T141:
●Active mode
●Toggle mode
●3-second Latch mode
●30-second Latch mode
For each output operation described, touch or proximity detection can be used. Upon the
detection of either of these actions, the TOUT/POUT pin will latch high, otherwise the
TOUT/POUT pin stays low. The detailed working of each user interface is described below.
The TOUT/POUT pin is active high, and can source enough current to directly drive a LED.
The pin is sourced from VDD when active. The TOUT/POUT pin always goes high for a
minimum time of tHIGH. For more information, please refer to Section 9: Electrical
characteristics.
Bits [1:0] of option byte OPT0 are used to select the correct output mode.
7.2.1 Active
Upon the detection of an actuation, the condition of the TOUT/POUT pin will change to high
and stay high for as long as the touch or proximity detection condition occurs. Figure 12
illustrates this output operation.
Figure 12. Active mode output operation
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STM8T141 Device operation
Doc ID 15699 Rev 7 21/50
7.2.2 Toggle
Upon the detection of an actuation, the TOUT/POUT pin will toggle between high and low.
Thus if TOUT/POUT is low, an actuation will change it to high, and also if TOUT/POUT is
high, an actuation will change it to low. Figure 13 illustrates this output operation.
Figure 13. Toggle mode output operation
7.2.3 3-second latch
Upon the detection of an actuation the TOUT/POUT pin will latch high for 3 seconds
minimum. If the actuation occurs for longer than 3 seconds, the TOUT/POUT pin will stay
high and will only go low when the actuation stops.
Figure 14. 3-second latch mode output operation
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Device operation STM8T141
22/50 Doc ID 15699 Rev 7
7.2.4 30-second latch
Upon the detection of an actuation, the TOUT/POUT pin will latch high. After 30 seconds
from when the actuation stops, the TOUT/POUT pin will go low.
If the TOUT/POUT pin is high and another actuation occur before the 30 seconds has
expired, the counter will reset and only 30 seconds after the new actuation has stopped, will
the TOUT/POUT pin go low. Figure 15 illustrates this output operation.
Figure 15. 30-second latch mode output operation
7.3 Detection threshold
The user has a choice between four detection threshold levels (DTh) at which the touch or
proximity detection condition is triggered. This depends on which threshold configuration is
selected. See Ta b le 7 for more details regarding the detection threshold selections.
Bits [5:4] of option byte OPT0 are used to select the correct detection threshold levels.
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Table 7. Detection thresholds
Sensitivity DTh setting Description
Most sensitive
Least sensitive
Sensitive proximity threshold Proximity for battery-powered applications.
Standard proximity threshold Proximity with good ground. Contact through
3 mm acrylic glass and no ground.
Sensitive touch threshold Contact through thin acrylic glass with battery
application.
Standard touch threshold Contact through thin dielectric with good ground.
STM8T141 Device operation
Doc ID 15699 Rev 7 23/50
7.4 Power modes
The STM8T141 device offers four power modes. The low power modes are specifically
designed for battery applications:
●Normal Power mode
●Low Power mode with Zoom
●Extreme Low Power mode with Zoom
●Extreme Low Power mode
Burst cycles can occur either every 10 ms or 20 ms according to the selected sampling
period (tSAMPLING). By selecting low power modes, extra delays are interlaced between
bursts. This improves the device current consumption at the expense of the response time.
Bits [7:6] of option byte OPT0 are used to select the correct power mode.
7.4.1 Normal Power mode
When in Normal Power mode, burst cycles occur at the rate of tSAMPLING. No extra delays
are added between burst cycles (Figure 16).
Figure 16. Charge cycle timing diagram in Normal Power mode
Table 8. Low power period according to selected power mode
Power mode Condition tLP value
Normal Power mode 0
Low Power mode with Zoom Touch or proximity detection 0
Untouched 4 x tSAMPLING
Extreme Low Power mode with
Zoom
Touch or proximity detection 0
Untouched 16 x tSAMPLING
Extreme Low Power mode 16 x tSAMPLING
1234567891011121314151617181920
CS
Burst cycle duration
t
Device operation STM8T141
24/50 Doc ID 15699 Rev 7
7.4.2 Low Power mode with Zoom
With the STM8T141 in Low Power mode with Zoom, burst cycles occur every 5th tSAMPLING
period (or 20% of the Normal Power mode).
Once activity is detected, the STM8T141 device wakes up from Low Power mode with Zoom
to Normal Power mode with charge cycles occurring every tSAMPLING period. The device will
return to Low Power mode after an end of low power period (tELP) when no touch or
proximity detection conditions are detected. This enables the device to reduce power
consumption when not in use, and still have a sufficient response time when needed
(Figure 17).
Figure 17. Charge cycle timing diagram in Low Power mode with Zoom
7.4.3 Extreme Low Power mode with Zoom
With the STM8T141 in Extreme Low Power Mode with Zoom, burst cycles only occur every
17th tSAMPLING period (or 5.88% of the Normal Power mode).
Once activity is detected, the STM8T141 device wakes up from Extreme Low Power mode
and Zoom to Normal Power mode with charge cycles occurring every tSAMPLING. The device
will return to Low Power mode after an end of low power period (tELP) when no touch or
proximity detection conditions are detected. This enables the device to reduce power
consumption when not in use and still have a sufficient response time when needed
(Figure 18).
Figure 18. Charge cycle timing diagram in Extreme Low Power mode with Zoom
1234567891011121314151617181920
CS
t
Zoom to Normal mode after touch
or proximity detection occurred
Burst cycle
duration
tLP
1234567891011121314151617181920
CS
Burst cycle every 17th tSAMPLING period
t
Zoom to Normal mode after touch
or proximity detection occurred
tLP
STM8T141 Device operation
Doc ID 15699 Rev 7 25/50
7.4.4 Extreme Low Power mode
With the STM8T141 in Extreme Low Power mode, burst cycles only occur every 17th
tSAMPLING period (or 5.88% of the Normal Power mode), thus adding 16 extra delays of
tSAMPLING between charge cycles to conserve power.
This reduces the amount of burst cycles in Extreme Low Power mode even more than Low
Power mode which in turn saves even more power but comes at the expense of a higher
system response time (Figure 19).
Figure 19. Charge cycle timing diagram in Extreme Low Power mode
7.5 Charge transfer frequency
The STM8T141 offers two charge transfer frequencies. The charge transfer frequency must
be adjusted depending on the CS capacitor. The charge transfer frequency may need to be
raised to 250 kHz in order to reduce tBURST when the CS capacitance is large.
●125 kHz
●250 kHz
Bit 1 of option byte OPT1 is used to select the correct charge transfer frequency.
7.6 Sampling period
The default sampling period (tSAMPLING) is configurable in order to allow different
compromises between power consumption and conversion rates:
●20-ms sampling rate to reduce average power consumption
●10-ms sampling rate to increase detection response time
When using a faster sampling rate (tSAMPLING = 10 ms), all the timing values of the Power
modes will occur at twice the speed.
BIt 2 of option byte OPT1 is used to select the correct conversion period.
1234567891011121314151617181920
CS
Burst cycle every 17th tSAMPLING period
t
tLP
Design guidelines STM8T141
26/50 Doc ID 15699 Rev 7
8 Design guidelines
8.1 Shield function
The STM8T141 offers a built-in shielding function. This function provides the following
advantages for designing the end-application:
●Sensing electrode separated from sealed electronics.
●Sensing wire shielded from unwanted environmental interferences.
●Enhanced proximity detection when used with battery (DC) applications.
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.
Note: Grounding the shield reduces the sensitivity of the keys and may render the system
unusable.
8.1.1 Shield application example
Ideally, a coaxial cable is used for the shield. A RX (typically 2 k) resistor should be
connected to the CX pin. The other side of the RX resistor should be connected to the center
core of the coaxial cable. The SHLDOUT pin should be connected to the metallic shield part
of the coaxial cable. A pull-up resistor (RSHIELD) should be added between SHLDOUT and
VDD as shown in Figure 20.
The example shown in Figure 20 is given for RX = 2 k, RSHIELD = 100 k, and VDD = 5 V(a).
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 RSHIELD resistor,
and consequently increasing current consumption.
Note: A smaller RSHIELD ensures better shielding but increases current consumption (see
Figure 20).
a. VDD must range from 4.5 to 5.5 V to use the shield function.Please refer to Table 12: Operating characteristics
for the correct power supply operating voltage when using the shield function.
STM8T141 Design guidelines
Doc ID 15699 Rev 7 27/50
Figure 20. Connecting the shield (coaxial cable implementation)
8.2 Sensitivity adjustment
Several factors impact device 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 (CS) for proximity thresholds only
●The ground coupling of the object (finger or hand) and sensor.
●The touch or proximity detection threshold selected by the option byte.
8.2.1 CS influence on sensitivity
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.
8.2.2 PCB layout and construction
The PCB traces, wiring, and components associated or in contact with CX pins become
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 CX pin. This can be done by
minimizing trace lengths and widths to achieve for higher gain without using higher values of
CS. To minimize cross-coupling, electrode traces from adjacent sensing channel should not
run close to each other for long distances. For detailed information on the impacts of the first
three factors, refer to application note AN2869.
VDD
SHLDOUT
CX
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Design guidelines STM8T141
28/50 Doc ID 15699 Rev 7
8.3 Influence of power supply variation
The stability of the device power supply is critical in order to provide a precise and
repeatable capacitance measure. For this reason, a linear regulator is embedded into the
device to provide the best power supply noise rejection possible.
Even with the embedded regulator, variations of the power supply voltage may have an
impact on the measured signal, especially in proximity configurations with a large
acquisition gain and small detection threshold.
A variation of the power supply voltage (V) induces a variation of the signal burst count
(BC) according to Equation 1.
Equation 1
The gain, G, of the acquisition is the ratio Cs/Cx.
The parameter Ϭ is the power supply rejection ratio.
For stability reasons, it is advised to limit BC to less than half the detection threshold. If
VDD is less than 2.9 V, special care should be taken of the supply quality. An external
voltage regulator may be necessary.
BC G V=
STM8T141 Electrical characteristics
Doc ID 15699 Rev 7 29/50
9 Electrical characteristics
9.1 Parameter conditions
Unless otherwise specified, all voltages are in reference to VSS.
9.1.1 Minimum and maximum values
Unless otherwise specified, the minimum and maximum values are guaranteed in the worst
conditions of ambient temperature and supply voltage by tests in production on 100% of the
devices with an ambient temperature at TA = 25 °C and TA = TAmax (given by the selected
temperature range).
Data based on characterization results, design simulation and/or technology characteristics
are indicated in the table footnotes and are not tested in production. Based on
characterization, the minimum and maximum values refer to sample tests and represent the
mean value plus or minus three times the standard deviation (mean ±3 ).
9.1.2 Typical values
Unless otherwise specified, typical data are based on TA = 25 °C, and VDD = 5 V. They are
given only as design guidelines and are not tested.
9.1.3 Typical curves
Unless otherwise specified, all typical curves are given only as design guidelines and are
not tested.
9.1.4 Loading capacitor
The loading conditions used for pin parameter measurement are shown in Figure 21.
Figure 21. Pin loading conditions
Output pin
50 pF
Electrical characteristics STM8T141
30/50 Doc ID 15699 Rev 7
9.2 Absolute maximum ratings
Stresses above those listed as “absolute maximum ratings” may cause permanent damage
to the device. This is a stress rating only and functional operation of the device under these
conditions is not implied. Exposure to maximum rating conditions for extended periods may
affect device reliability.
9.3 Operating conditions
9.3.1 General operating conditions and supply characteristics
Table 9. Voltage characteristics
Symbol Ratings Maximum value Unit
VDD VSS Supply voltage 5.5 V
Table 10. Current characteristics
Symbol Ratings Maximum value Unit
IVDD Total current into VDD power lines (source)(1)
1. All power (VDD) and ground (VSS) lines must always be connected to the external supply.
11
mA
IVSS Total current out of VSS ground lines (sink)(1) 11
IIO
Output current sunk by output pin 10
Output current sourced by output pin 10
Table 11. Thermal characteristics
Symbol Ratings Value Unit
TSTG Storage temperature range 65 to +150 °C
TJ
Junction temperature range (SO8 narrow and UFDFPN8
packages) 90 °C
Table 12. Operating characteristics
Symbol Parameter Condition Min. Max. Unit
VDD Supply voltage Shield feature not used
Shield feature used
2.0
4.5
5.5
5.5 V
TAOperating temperature - -40 85 °C
tVDD
Turn-on slope (Rise time
rate) 01
V/s
Turn-off slope (Fall time
rate) 1(1)
1. This constraint must be respected only if the voltage does not reach 0 V.
STM8T141 Electrical characteristics
Doc ID 15699 Rev 7 31/50
9.3.2 Average current consumption
Test conditions: TA = 25 °C, CX = 20 pF, CS = 47 nF and RX = 2 k..
Note: Consumption does not depend on either detection threshold or acquisition rate.
Figure 22. IDD average current consumption vs RSHIELD
1. ExtLP = External Low Power mode
2. LP = Low Power mode
3. NP = Normal Power mode
Table 13. Average current consumption without shield
Symbol Parameter Conditions Typ. Max. Unit
IDD
Normal Power mode – Shield output unconnected
– Shield input grounded
– Options other than Low Power are
left in default configuration
30 45(1)
1. Data based on characterization results, not tested in production.
µA
Low Power 17
Extreme Low Power mode 11
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Electrical characteristics STM8T141
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9.3.3 Output characteristics
9.4 Regulator and reference voltage
Table 14. Output pin characteristics
Symbol Parameter Conditions Typ. Max. Unit
VOL
VDD = 5 V
ILOAD = 8 mA 1200 1600
mV
ILOAD = 4 mA 540 750
ILOAD = 2 mA 250 450
VDD = 3.3 V ILOAD = 4 mA 650 1000
ILOAD = 2 mA 320 500
VDD = 2.9 V ILOAD = 2 mA 400 500
VDD = 2.0 V ILOAD = 1 mA 300 500
VOH
VDD = 5 V
ILOAD = –2 mA 4.7
V
ILOAD = –4 mA 4.4
ILOAD = –8 mA 3.9
VDD = 3.3 V ILOAD = –2 mA 3.0
ILOAD = –4 mA 2.7
VDD = 2.9 V ILOAD = –2 mA 2.5
VDD = 2.0 V ILOAD = -100 µA 1.8
tHIGH Output minimum high time 40 ms
tLOW Output minimum low time 40
Table 15. Regulator and reference voltage
Symbol Parameter Min. Typ. Max. Unit
Cref
Voltage regulator decoupling
capacitance(1)
1. Equivalent serial Rresistor 0.2 at 1 MHz.
110µF
Vreg Regulated voltage during acquisition 2.1 V
Vtrip End of acquisition reference voltage 0.68
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9.5 Capacitive sensing characteristics
.
Table 16. General capacitive sensing characteristics(1)
1. Values guaranteed by design.
Symbol Parameter Min. Typ. Max. Unit
fTRANSFER
Charge-transfer frequency at 125-kHz
setting 90 125 160
kHz
Charge-transfer frequency at 250-kHz
setting 185 250 315
tSAMPLING
Scanning period at 10-ms setting 7.5 10 12.5
ms
Scanning period at 20-ms setting 15 20 25
tLP
Low Power 4 tSAMPLING
Extreme Low Power 16 tSAMPLING
tELP
Time before switching back to Low
Power mode 540
tRFT(2)
2. See tRFT in Figure 9: Reference freeze timeout.
15 s reference freeze timeout 11 15 19 s
45 s reference freeze timeout 33 45 57
tBURST Burst detection 32 214 tTRANSFER
DDC Detection debounce count 4 Counts
EDDC End of detection debounce count 3
DTh(3)
3. Reference value (Ref.) described in Section 5.3.3: Debounce filter on page 16.
Proximity detection threshold – 8
Counts
Sensitive proximity detection threshold – 2
Touch detection threshold Ref./16
Sensitive touch detection threshold Ref./32
(4)
4. Between 3 V and 3.5 V, evolves as shown in Figure 23.
Power supply rejection ratio VDDMIN <
VDD < 3 V) 0.0250
Count/V
Power supply rejection ratio (3.5 V < VDD
< VDDMAX)0.0005
Electrical characteristics STM8T141
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Figure 23. Sigma variation across VDD
Table 17. Response times (1)
1. Values guaranteed by design.
Mode
tSAMPLING = 10 ms tSAMPLING = 20 ms
Unit
Min. Max. Min. Max.
Normal Power mode 30 50 60 100
ms
Low Power with Zoom mode 30 100 60 200
Extreme Low Power with Zoom mode 30 250 60 500
Extreme Low Power mode 510 850 1020 1700
Table 18. External sensing component characteristics
Symbol Parameter Min. Typ. Max. Unit
CS Sampling capacitor (COG or NPO type)(1)
1. For more information about capacitors, please refer to Application note: AN2966.
47 214 x CXnF
CX Equivalent electrode capacitance 100 pF
CTEquivalent touch capacitance 5
RX Electrode serial resistance 2 22 kOhm
RSHIELD Shield pull-up resistance 1 1000
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STM8T141 Electrical characteristics
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9.6 EMC characteristics
Susceptibility and emission tests are performed on a sample basis during product
characterization.
Both the sample and its applicative hardware environment (Figure 10) are mounted on a
dedicated specific EMC board defined in the IEC61967-1 standard.
9.6.1 Functional EMS (electromagnetic susceptibility)
While running in the above described environment the product is stressed by two
electromagnetic events until a failure occurs.
●ESD: Electrostatic discharge (positive and negative) is applied on all pins of the device
until a functional disturbance occurs. This test complies with the IEC 1000-4-2
standard.
●FTB: A burst of fast transient voltage (positive and negative) is applied to VDD and VSS
through a 100 pF capacitor, until a functional disturbance occurs. This test complies
with the IEC 1000-4-4 standard.
A device reset allows normal operations to be resumed. The test results are given in
Ta bl e 19 based on the EMS levels and classes defined in application note AN1709.
9.6.2 Prequalification trials
Table 19. EMS data
Symbol Parameter Conditions Level/class
VFESD Voltage limits to be applied on any pin to
induce a functional disturbance
VDD 5 V, TA+25 °C, SO8
(Narrow) package, complies
with IEC 1000-4-2
1B
VEFTB
Fast transient voltage burst limits to be
applied through 100pF on VDD and VSS pins
to induce a functional disturbance
VDD5 V, TA+25 °C, SO8
(Narrow) package, complies
with IEC 1000-4-4
4A
Electrical characteristics STM8T141
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9.6.3 Electromagnetic interference (EMI)
Emission tests conform to the IEC61967-2 standard for board layout and pin loading. Worse
case EMI measurements are performed during maximum device activity.
9.6.4 Absolute maximum ratings (electrical sensitivity)
Based on two different tests (ESD and LU) using specific measurement methods, the
product is stressed in order to determine its performance in terms of electrical sensitivity.
For more details, refer to the application note AN1181.
9.6.5 Electrostatic discharge (ESD)
Electrostatic discharges (3 positive then 3 negative pulses separated by 1 second) are
applied to the pins of each sample according to each pin combination. The sample size
depends on the number of supply pins in the device (3 parts*(n+1) supply pin). This test
conforms to the JESD22-A114A/A115A standard. For more details, refer to the application
note AN1181.
Table 20. EMI data
Symbol Parameter General conditions Monitored
frequency band
RCOSC =
500 kHz (1)
1. Data based on characterization results, not tested in production.
Unit
SEMI
Peak level
VDD 5 V, TA +25 °C,
SO8 (Narrow) package,
Complies with SAE
J1752/3, No finger on
touch electrode
0.1 MHz to 30 MHz -4
dBµV30 MHz to 130 MHz -9
130 MHz to 1 GHz -6
SAE EMI level -1
Peak level
VDD 5 V, TA +25 °C,
SO8 (Narrow) package,
Complies with SAE
J1752/3, Finger on
touch electrode
0.1 MHz to 30 MHz 20
dBµV30 MHz to 130 MHz -8
130 MHz to 1 GHz -7
SAE EMI level 15
Table 21. ESD absolute maximum ratings
Symbol Ratings Conditions Class Maximum
value(1)
1. Data based on characterization results, not tested in production
Unit
VESD(HBM) Electrostatic discharge voltage
(Human body model)
TA +25°C, conforming
to JESD22-A114 A2000V
VESD(CDM) Electrostatic discharge voltage
(Charge device model)
TA +25°C, conforming
to JESD22-C101 IV 1000 V
STM8T141 Electrical characteristics
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9.6.6 Static latchup
Two complementary static tests are required on 10 parts to assess the latchup performance.
●A supply overvoltage (applied to each power supply pin) and
●A current injection (applied to each input, output and configurable I/O pin) are
performed on each sample.
This test conforms to the EIA/JESD 78 IC latchup standard. For more details, refer to
application note AN1181.
Table 22. Electrical sensitivities
Symbol Parameter Conditions Class(1)
1. Class description: A Class is an STMicroelectronics internal specification. All its limits are higher than the
JEDEC specifications, that means when a device belongs to class A it exceeds the JEDEC standard. B
class strictly covers all the JEDEC criteria (international standard).
LU Static latchup class TA +25 °C A
TA +85 °C A
Package characteristics STM8T141
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10 Package characteristics
In order to meet environmental requirements, ST offers these devices in different grades of
ECOPACK® packages, depending on their level of environmental compliance. ECOPACK®
specifications, grade definitions and product status are available at www.st.com.
ECOPACK® is an ST trademark.
10.1 Package mechanical data
10.1.1 SO8 package mechanical data
Figure 24. SO8-lead plastic small outline - package outline
SO-A
E1
8
ccc
b
e
A
D
c
1
E
h x 45˚
A2
k
0.25 mm
L
L1
A1
GAUGE PLANE
STM8T141 Package characteristics
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Table 23. 8-lead plastic small outline - package mechanical data
Symbol
millimeters inches (1)
1. Values in inches are rounded to 4 decimal digits
Min. Typ. Max. Min. Typ. Max.
A- - 1.750 - - 0.0689
A1 0.100 - 0.250 0.0039 - 0.0098
A2 1.250 - - 0.0492 - -
b0.280 - 0.480 0.0110 - 0.0189
c0.170 - 0.230 0.0067 - 0.0091
ccc - - 0.100 - - 0.0039
D (2)
2. Dimension D does not include mold flash, protrusions or gate burrs. Mold flash, protrusions or gate burrs
shall not exceed 0.15mm in total (both side).
4.800 4.900 5.000 0.1890 0.1929 0.1969
E5.800 6.000 6.200 0.2283 0.2362 0.2441
E1 (3)
3. Dimension E1 does not include interlead flash or protrusions. Interlead flash or protrusions shall not
exceed 0.25 mm per side.
3.800 3.900 4.000 0.1496 0.1535 0.1575
e- 1.270 - - 0.0500 -
h0.250 - 0.500 0.0098 - 0.0197
k0° - 8° 0° - 8°
L0.400 - 1.270 0.0157 - 0.0500
L1 - 1.040 - - 0.0409 -
Package characteristics STM8T141
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10.1.2 UFDFPN8 package mechanical data
Figure 25. UFDFPN8-lead ultra thin fine pitch dual flat package (MLP) package
outline
Table 24. 8-lead ultra thin fine pitch dual flat - package mechanical data
Symbol
millimeters inches (1)
1. Values in inches are rounded to 4 decimal digits
Min Typ Max Min Typ Max
A0.450 0.550 0.600 0.0177 0.0217 0.0236
A1 0.000 0.020 0.050 0.0000 0.0008 0.0020
b0.200 0.250 0.300 0.0079 0.0098 0.0118
D1.900 2.000 2.100 0.0748 0.0787 0.0827
D2 1.500 1.600 1.700 0.0591 0.0630 0.0669
E2.900 3.000 3.100 0.1142 0.1181 0.1220
E2 0.100 0.200 0.300 0.0039 0.0079 0.0118
e- 0.500 - - 0.0197 -
L0.400 0.450 0.500 0.0157 0.0177 0.0197
L1 - - 0.150 - - 0.0059
L3 0.300 - - 0.0118 - -
Tolerance millimeters inches
ddd (2)
2. Applied for exposed die paddle and terminals. Exclude embedding part of exposed die paddle from
measuring.
- 0.080 - - 0.0031 -
D
E
UFDFPN-01
A
A1
ddd
L1
eb
D2
L
E2
L3
STM8T141 Package characteristics
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10.2 Package thermal characteristics
The maximum chip junction temperature (TJmax) must never exceed the values given in
Ta bl e 12: Operating characteristics on page 30.
The maximum chip-junction temperature, TJmax, in degrees Celsius, may be calculated
using the following equation:
TJmax = TAmax + (PDmax x JA)
Where:
●TAmax is the maximum ambient temperature in C
●JA is the package junction-to-ambient thermal resistance in C/W
●PDmax is the sum of PINTmax and PI/Omax (PDmax = PINTmax + PI/Omax)
●PINTmax is the product of IDD and VDD, expressed in Watts. This is the maximum chip
internal power.
●PI/Omax represents the maximum power dissipation on output pins
Where:
PI/Omax = (VOL*IOL) + ((VDD-VOH)*IOH),
taking into account the actual VOL/IOL and VOH/IOH of the I/Os at low and high level in
the application.
10.2.1 Reference document
JESD51-2 integrated circuits thermal test method environment conditions - natural
convection (still air). Available from www.jedec.org.
Table 25. Thermal characteristics(1)
1. Thermal resistances are based on JEDEC JESD51-2 with 4-layer PCB in a natural convection
environment.
Symbol Parameter Value Unit
JA
Thermal resistance junction-ambient
SO8 (Narrow) 130 °C/W
JA
Thermal resistance junction-ambient
UFDFPN 8 (2 x 3 mm) 120 °C/W
Ordering information STM8T141
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11 Ordering information
11.1 STM8T141 ordering information scheme
Figure 26. STM8T141 ordering information scheme
1. See Table 26: Orderable favorite device lists and the explanation below of “in factory option byte
programming service”
2. The STM8T141 OTP devices are available for production and development. These parts are blank devices
with unconfigured option bytes (all option bits are set to ‘0’). For more
information, please refer to Section 7: Device operation.
STM8T 141 A M XXXY TR
Device type
STM8T: ST touch sensing MCU
Package
M: S08 (small outline)
U: FPN (dual flat no lead)
Packing
No character: tray or tube
TR: tape and reel
Example:
Pin count
A: 8 pins
Device sub-family
141 = 1 channel/proximity
Device configuration
XXXY: device with specific configuration(1)
61T: OTP blank device (all user bits set to 0)(2)
STM8T141 Ordering information
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11.2 Orderable favorite device lists
11.3 In-factory option byte programming service
For specific configurations not listed in Ta bl e 26: Orderable favorite device lists, in-factory
option byte programming is available on customer request and for large order quantities.
Customers have to fill out the option list (see below) and send it back to STMicroelectronics.
Customers are then informed by STMicroelectronics about the ordering part number
corresponding to the customer configuration. The XXXY parameter of the final ordering part
number (e.g. STM8T141AMXXXY) depends on the device configuration and is assigned by
STMicroelectronics.
Table 26. Orderable favorite device lists
Config.
Option byte configuration(1) Part numbers
Sampling
period
Charge
transfer
frequency
Power
modes
Detection
threshold
Reference
freeze
timeout
TOUT/
POUT output
mode
SO8 UFDFPN8
Default
config.
(OTP)
20 ms 125 kHz
Low Power
mode with
zoom
Standard
proximity 15 s Active mode STM8T141AM61T STM8T141AU61TTR
20 ms 125 kHz
Low Power
mode with
zoom
Sensitive
touch Infinite Active mode Not yet available STM8T141AUMAJ1TR
(XXXY = MAJ1)
1. Please refer to Section 7: Device operation.
Ordering information STM8T141
44/50 Doc ID 15699 Rev 7
1. Configuration by default in OTP devices.
STM8T141 programming service option list
(last update: February 2010)
Customer name:
Address:
Contact name:
Phone number:
Select the package type (tick one box)
STM8T141AM6 - S08 or STM8T141AU6  DFN8
Customer settings
(tick one box by option)
Sampling period (see Section 7.6: Sampling period)
10 ms sampling period
20 ms sampling period(1)
Charge transfer frequency (see Section 7.5: Charge transfer frequency)
125 kHz(1)
250 kHz
Power modes (see Section 7.4: Power modes)
Normal Power mode
Low Power mode with Zoom(1)
Extreme Low Power mode with Zoom
Extreme Low Power mode
Detection threshold (see Section 7.3: Detection threshold)
Sensitive proximity
Standard proximity(1)
Sensitive touch
Standard touch
Reference freeze timeout (see Section 5.3.2:Reference freeze timeout)
15-second reference freeze timeout(1)
45-second reference freeze timeout
Infinite reference freeze
TOUT/POUT output mode (see Section 7.2: TOUT/POUT output mode)
Active mode(1)
Toggle mode
3-second Latch mode
30-second Latch mode
Packaging
Tape & reel
Tube
Comment :
Date Signature :
STM8T141 STM8T141 development tools
Doc ID 15699 Rev 7 45/50
12 STM8T141 development tools
STM8T141 evaluation kit
The STM8T141-EVAL is an evaluation kit which introduces developers to the STM8T141. It
contains an STM8T141 evaluation board, plus a set of preconfigured plug-in modules which
allow the STM8T141 device performances to be evaluated in either touch or proximity
detection.
Figure 27. STM8T141-EVAL evaluation kit
STM8T141 development tools STM8T141
46/50 Doc ID 15699 Rev 7
STM8T141 “blank” modules
An additional box of 10 STM8T141 “blank” modules (STM8T141AM-MOD) can be ordered
separately, where the device option bytes are left unprogrammed (see Figure 28).
Figure 28. STM8T141 blank module box
1. The above figure is not binding.
STM8T141 STM8T141 development tools
Doc ID 15699 Rev 7 47/50
Programming tool
Figure 29 shows the STM8T141-EVAL programming tool.
To program the device option bytes so that the device can be tested in different
configurations, the following materials are available:
●A programming socket board (STM8T14X-SB). When connected to the programming
dongle, this board allows SO8 and DFN8 devices as well as plug-in modules delivered
in the evaluation kit to be programmed.
●A programming dongle (ST-TSLINK) and its associated programming software, STVP.
Figure 29. STM8T141-EVAL programming tool
Ordering information
Table 27. Ordering information
Part number Order codes Description
STM8T141-EVAL STM8T141-EVAL STM8T141 evaluation kit
STM8T-MOD STM8T141AM-MOD
Box containing 10 blank modules based on
STM8T141AM61T (OTP device in SO8
package)
ST-TSLINK ST-TSLINK(1)
1. The ST-TSLINK dongle and the STM8T14X-SB socket board are not part of the STM8T141-EVAL
evaluation kit, and consequently must be ordered separately.
STM8T141 programming dongle
STM8T14X-SB STM8T14X-SB(1) STM8T141 socket board
Programming dongle (ST-TSLINK)
Programming socket boards (STM8T14X-SB)
Revision history STM8T141
48/50 Doc ID 15699 Rev 7
13 Revision history
Table 28. Document revision history
Date Revision Changes
09-Jun-2009 1 Initial release.
02-Jul-2009 2
VDD range changed to 2.9 to 5.5V. Ta b l e 1 2 and Table 14 updated.
Internal voltage regulator bypassed configuration removed.
IDDLP removed from Table 13.
31-Jul-2009 3
Upgraded document from Preliminary Data to full Datasheet.
Updated oscillator information in Figure 1: STM8T141 block diagram
on page 8.
Added detection threshold values in Table 16: General capacitive
sensing characteristics on page 33.
Updated values in Table 17: Response times on page 34.
05-Oct-2009 4
Updated Section 11: Ordering information.
Section 11.2: Orderable favorite device lists: added information on
option byte programming; added option list.
Added Section 12: STM8T141 development tools
24-Feb-2010 5
Lower operating supply voltage changed from 2.9 V to 2.0 V. The
following tables were impacted: Table 1: Device summary, Table 12:
Operating characteristics, Table 13: Average current consumption
without shield, Table 16: General capacitive sensing characteristics,
and Table 16: General capacitive sensing characteristics.
Introduced trademark for ProxSense (ProxSense™)
Throughout document, “sensitivity threshold or level” replaced with
“detection threshold”, “automatic recalibration” with “reference freeze
timeout”, “STH” with “DTh”, and “SO” with “SO8”.
Section 2: Block diagram: replaced ‘capacitive sensing engine’ with
‘ProxSense engine’.
Added Figure 3: UFDFPN8 pinout.
Updated Table 2: STM8T141 pin descriptions.
Renamed Section 4 as STM8T ProxSense technology
Renamed Section 4.2 as Charge transfer acquisition principle and
updated text.
Figure 5: STM8T measuring circuitry: updated.
Figure 6: Conversion period examples: updated.
Sections 4.3 renamed Section 5: STM8T processing. Section re-
organised and reworked with new figures and tables added.
Section 6: Typical application diagram: removed introductory text;
modified Figure 10, modified footnote 1, added footnote 2, added text
regarding RSHIELD resistor, define a touch or proximity detection.
Section 7: Device operation: Re-organisation of text; removed
reference related to low power modes.
Section 7.1: Option byte description: added reference to Section 12.
Table 5: Option bytes: updated factory default setting of OPT1,
recalibration timeout renamed reference freeze timeout.
STM8T141 Revision history
Doc ID 15699 Rev 7 49/50
24-Feb-2010 5 cont’d
Section 7.2.1, Section 7.2.2, Section 7.2.3, and Section 7.2.4:
replaced “output configuration” with “output operation”.
Section 7.2.3: 3-second latch: removed some text concerning the
TOUT/POUT pin.
Renamed Section 7.3: Detection threshold.
Section 7.4: Power modes: small text changes; Ta ble 8 moved to this
section from Section 7.4.4: Extreme Low Power mode.
Section 8.1: Shield function: removed text about RSHIELD.
Figure 20: Connecting the shield (coaxial cable implementation):
amended ohm symbol.
Section 8.2: Sensitivity adjustment/ added text regarding sensitivity;
updated bullet points.
Added Section 8.3: Influence of power supply variation.
Table 12: Operating characteristics: added tVDD data.
Section 9.3.2: Average current consumption: for test conditions,
100 nF replaced with 47 nF; modified Ta bl e 1 3 and note underneath
it; added Figure 22.
Table 14: Output pin characteristics: removed tVDD data.
Added Section 9.4: Regulator and reference voltage and Table 15.
Section 9.5: Capacitive sensing characteristics: amended Ta bl e 1 6
for values of fTRANSFER, tRFT
, and tBURST; updated symbols for tRFT
,
DTh, and ; added Figure 23.
Table 18: External sensing component characteristics: modified CS
parameter and RSHIELD min value.
Section 11: Ordering information: updated Figure 26; added
Section 11.2 and Section 11.3.
Section 11.2: Orderable favorite device lists: updated ordering part
number; added footnote to option list concerning default
configuration of OPT devices, added packaging information to the
option list, updated headings and date.
Section 12: STM8T141 development tools: replaced STM8T1X1 with
STM8T141.
01-Apr-2010 6 Added that ProxSense™ is a trademark of Azoteq.
28-Jun-2011 7
Figure 26: STM8T141 ordering information scheme: updated
footnote 2.
Programming tool: replaced STM8T141-SB with STM8T14X-SB.
Figure 29: STM8T141-EVAL programming tool: replaced
STM8T141-SB with STM8T14X-SB.
Table 27: Ordering information: replaced STM8T1X1-EVAL and
STM8T141-SB with STM8T141-EVAL and STM8T14X-SB
respectively.
Table 28. Document revision history (continued)
Date Revision Changes
STM8T141
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