STM8T143 datasheet(12/65 Pages) STMICROELECTRONICS

12 / 65 page

STM8T ProxSense technology

STM8T143

12/65

DocID18315 Rev 6

Figure 5. STM8T143 measuring circuitry

1. RX must be placed as close as possible to the 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 internal 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, caused by the presence or

absence of the human body, 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 burst

count is the number of charge transfer periods (tTRANSFER) during one tBURST cycle.

•

The sampling period (tSAMPLING) is the acquisition rate.

Figure 6. Signal monitored on CX pin

STM8T143 Arkusz danych(PDF) 12 Page - STMicroelectronics