STM8T141 datasheet(11/50 Pages) STMICROELECTRONICS

Part #	STM8T141

Description	Single-channel capacitive sensor for touch or proximity detection with shielded sensing electrode

PDF	50 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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11 / 50 page

STM8T141

STM8T ProxSense technology

Doc ID 15699 Rev 7

11/50

Figure 5.

STM8T measuring circuitry

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

Ai15249a

Cx (~20 pF)

CT (~5 pF)

Earth

Serial resistor (RX)(1)

STM8T141

CS (a few nF)

STM8T141 Datasheet(PDF) 11 Page - STMicroelectronics