STM8T141 datasheet(28/50 Pages) STMICROELECTRONICS

Part #	STM8T141

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

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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28 / 50 page

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



V



STM8T141 Datasheet(PDF) 28 Page - STMicroelectronics