AN4038 Datasheet, PDF (1/39 Pages) STMicroelectronics – Guidelines to optimize proximity detection with STM8TL5xxx capacitive sensors

AN4038
Application note
Guidelines to optimize proximity detection with STM8TL5xxx
capacitive sensors
Introduction
The STM8TL5xxx is a microcontroller group targeting touch sensing applications. It offers a
high performance capacitive sensing engine which uses the projected Proxsense^TM
acquisition principle. Outstanding STM8TL5xxx performances allow long range proximity
detections. This is a key feature for many end-applications such as personal navigation
devices (PNDs) or stove tops which are equipped with backlighting that switches on when a
user is detected. Proximity detectors are also implemented in white goods, automotive
devices, palm tops, and on any type of kitchen or office appliance where the display needs
to be turned on to allow some parameters to be adjusted by the user.
One of the key features of capacitive sensors versus conventional proximity detectors (such
as infrared light sensors), is the low power scheme, µA versus mA. Such a low power
scheme is a fundamental characteristic of power sensitive applications.
The events described in this document exist in all capacitive sensing implementations.
Because of the high sensitivity required by proximity detection, their impact seems amplified
compared to touch sensors and therefore must be considered with great care.
Every application has specific proximity detection requirements. The design of the proximity
sensing electrode is the result of the sensing requirements of the application and of a
careful analysis of what the sensor environment can become in the lifetime of the
application. The purpose of this application note is to provide designer guidelines on how to
construct proximity electrodes.
The information provided in this application note is based on tests performed using an
STM8TL53xx device, but the information extracted is common for the whole STM8TL5xxx
product group (see Table 1). The absolute performance values, such as detection distance,
depends on the environmental test: STM8TL5x sensitivity setting and approach speed.
Table 1.
Applicable products
Type
Microcontrollers
Part numbers
STM8TL52F4, STM8TL52G4, STM8TL53C4,
STM8TL53F4, STM8TL53G4
May 2012
Doc ID 022686 Rev 1
1/39
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