AN4038 datasheet(27/39 Pages) STMICROELECTRONICS

Part #	AN4038

Description	Guidelines to optimize proximity detection with STM8TL5xxx capacitive sensors

PDF	39 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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27 / 39 page

AN4038

Proximity sensor design

Doc ID 022686 Rev 1

27/39

Figure 26 shows the measured detection distance versus the distance between the ground

backplane and the sensor for a dielectric epoxy material (FR4). This test was performed

using sensor #3 (see Figure 1).

Figure 26.

Detection distance versus distance between ground plane and electrode

for dielectric material (FR4)

Detection distance significantly decreases for an FR4 dielectric thickness less than 10 mm.

For an FR4 dielectric thickness above 10 mm to maximum thickness, the increase of the

proximity detection distance levels off.

With regard to the dielectric epsilon factor (permittivity), at the same dielectric thickness, the

lower the dielectric epsilon is, the greater the proximity detection distance is.

The permittivity (dielectric constant) for:

●

FR4 is 4.2

●

Air is around 1

AN4038 Datasheet(PDF) 27 Page - STMicroelectronics