Introduction
The electrostatic discharge (ESD) is often used to describe a high voltage that may produce a permanent damage. ESD can be
destructive and may leave a system in an unknown state from which recovery is impossible.
Fortunately, this damage can be prevented by several methods; some of these methods are cheap but other methods can
modify the behavior of the equipment. The ideal situation is to find a balance and to obtain a robust application which is not too
expensive and which is unlikely to behave erratically.
This document describes ESD causes and risks. Several models and standards relating to ESD simulation are outlined and
some typical ESD protection techniques are explained.
Table 1. Applicable products
Type Product series
Microcontrollers
STM32F0 Series, STM32F3 Series, STM32L0 Series, STM32L1 Series, STM32L4 Series,
STM32L4+ Series, STM32L5 Series, STM32U5 Series, STM32WB Series
ESD considerations for touch sensing applications on MCUs
AN3960
Application note
AN3960 - Rev 5 - October 2021
For further information contact your local STMicroelectronics sales office.
www.st.com
1 What is ESD ?
ESD is the sudden and momentary electric current that flows between two objects at different electrical potentials.
ESD immunity is a category of electromagnetic compatibility (EMC). EMC is the branch of electrical sciences
which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to
its unwanted effects.
EMC describes the ability of a piece of equipment or a system to function satisfactorily in its electromagnetic
environment without introducing intolerable electromagnetic disturbances to anything in that environment.
Causes of ESD
One of the causes of ESD events is static electricity. Static electricity is often generated through the separation of
electric charges when two materials are brought into contact and then separated, for example, rubbing a plastic
comb against dry hair or removing some types of plastic packaging. In these cases, the friction between two
materials creates a difference of electrical potential that can lead to an ESD stress.
Another cause of ESD damage is through electrostatic induction. This occurs when an electrically charged
object is placed near a conductive object isolated from ground. The presence of the charged object creates an
electrostatic field that causes electrical charges on the surface of the other object to redistribute. Even though
the net electrostatic charge of the object has not changed, it now has regions of excess positive and negative
charges.
An ESD stress may occur when the object comes into contact with a conductive path. For example, charged
regions on the surfaces of styrofoam cups or plastic bags can induce potential on nearby ESD sensitive
components via electrostatic induction and an ESD stress may occur if the component is touched with a metallic
tool.
AN3960
What is ESD ?
AN3960 - Rev 5
page 2/15
