STM8T141AM61T - STMICROELECTRONICS

June 2011 Doc ID 15699 Rev 7 1/50

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
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Block diagram  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Pin descriptions   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
STM8T ProxSense technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1 Capacitive sensing overview   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
2 Charge transfer acquisition principle   . . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
STM8T processing   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1 Signal and reference calculation   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
2 Determining touch/proximity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
3 Environment compensation filter (ECF)  . . . . . . . . . . . . . . . . . . . . . . . . . .  13
3.1 ECF principle  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2 Reference freeze timeout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.3 Debounce filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Typical application diagram  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Device operation  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1 Option byte description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  18
2 TOUT/POUT output mode  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  20
2.1 Active  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2 Toggle   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3 3-second latch  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.4 30-second latch  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3 Detection threshold   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  22
4 Power modes  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  23
4.1 Normal Power mode   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.2 Low Power mode with Zoom  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.3 Extreme Low Power mode with Zoom  . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.4 Extreme Low Power mode  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5 Charge transfer frequency  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25

STM8T141 Contents
Doc ID 15699 Rev 7 3/50
          
6 Sampling period  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25
Design guidelines  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1 Shield function  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  26
1.1 Shield application example   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2 Sensitivity adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  27
2.1 CS influence on sensitivity  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.2 PCB layout and construction  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3 Influence of power supply variation   . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  28
Electrical characteristics   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
1 Parameter conditions  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  29
1.1 Minimum and maximum values  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
1.2 Typical values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
1.3 Typical curves   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
1.4 Loading capacitor   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  30
3 Operating conditions   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  30
3.1 General operating conditions and supply characteristics   . . . . . . . . . . . 30
3.2 Average current consumption   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.3 Output characteristics   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4 Regulator and reference voltage   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  32
5 Capacitive sensing characteristics  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  33
6 EMC characteristics  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  35
6.1 Functional EMS (electromagnetic susceptibility)  . . . . . . . . . . . . . . . . . . 35
6.2 Prequalification trials  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
6.3 Electromagnetic interference (EMI)  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.4 Absolute maximum ratings (electrical sensitivity)   . . . . . . . . . . . . . . . . . 36
6.5 Electrostatic discharge (ESD)  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.6 Static latchup  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Package characteristics  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1 Package mechanical data   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  38
1.1 SO8 package mechanical data   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.2 UFDFPN8 package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
2 Package thermal characteristics   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  41
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

VSS

TOUT/POUT

VDD

POR

VREG

ai17207

Voltage

regulator

MCU system engine

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

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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











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3(,$).

3(,$/54

6$$

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

!)













62%'

3(,$).

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6$$

633 4/540/54

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.

Lower capacitance

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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STM8T processing STM8T141

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

ai17429

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

Burst cycle duration

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

Zoom to Normal mode after touch

or proximity detection occurred

Burst cycle

duration

tLP

1234567891011121314151617181920

Burst cycle every 17th tSAMPLING period

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

Burst cycle every 17th tSAMPLING period

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

Plastic jacket Metal shield

Center core

Dielectric insulator

ai15527

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SHLDIN

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2 kΩ

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.

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

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

32/50 Doc ID 15699 Rev 7

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

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

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

STM8T141 Electrical characteristics

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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

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

34/50 Doc ID 15699 Rev 7

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

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

Doc ID 15699 Rev 7 35/50

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

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

Electrical characteristics STM8T141

36/50 Doc ID 15699 Rev 7

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

38/50 Doc ID 15699 Rev 7

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

ccc

h x 45˚

0.25 mm

GAUGE PLANE

STM8T141 Package characteristics

Doc ID 15699 Rev 7 39/50

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

40/50 Doc ID 15699 Rev 7

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 -

UFDFPN-01

ddd

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

42/50 Doc ID 15699 Rev 7

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

Doc ID 15699 Rev 7 43/50

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

50/50 Doc ID 15699 Rev 7



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