AN4038 datasheet(23/39 Pages) STMICROELECTRONICS

No de pièce	AN4038

Description	Guidelines to optimize proximity detection with STM8TL5xxx capacitive sensors

PDF	39 Pages

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Fabricant	STMICROELECTRONICS [STMicroelectronics]

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23 / 39 page

AN4038

Proximity sensor design

Doc ID 022686 Rev 1

23/39

Noise decreases when the electrode width increases as shown in Figure 21. The noise

standard deviation increases significantly when the TX/Rx electrode width is lower than

1.5 mm, but it is almost stable when Tx/Rx value is greater than 1.5 mm.

Figure 21.

Noise standard deviation versus Tx/Rx electrode width

The significant noise variation when the Tx/Rx electrode width is lower than 1.5 mm is

explained by the variation of the projected capacitance (see Figure 22). The smaller the

EPCC compensation is, the lower the projected capacitance is and the higher the noise is.

Figure 22.

EPCC versus Tx/Rx electrode width

In conclusion, it is recommended to design sensors with an electrode width greater than

1.5 mm. This guarantees an acceptable proximity detection distance and ensures the best

noise immunity. As electrode width has only a small effect on the detection distance, it is

recommended to increase first electrode length or electrode spacing to improve the

detection distance.

AN4038 Fiches technique(PDF) 23 Page - STMicroelectronics