AN3960
Application note
ESD considerations for touch sensing applications
Introduction
Electrostatic discharge (ESD) is not a new phenomenon. It is often used to describe high
voltage that may produce permanent damage. ESD can be destructive and may leave a
sytem in an unknown state from which recovery is impossible. Fortunately, it can be
prevented by several methods. Some of these methods are cheap whilst some modify the
behavior of the equipment. The ideal situation is to balance both of these factors to obtain a
robust application which is not too expensive and which is unlikely to behave erratically.
This document describes ESD, its causes and risks. Several models and standards relating
to ESD simulation are outlined. Typical ESD protection techniques are explained. Test
results are presented for the STM8T142-EVAL evaluation board which was tested against
ESD events using some of the protection methods detailed in this application note.
October 2011
Doc ID 022082 Rev 1
1/21
www.st.com
Contents
AN3960
Contents
1
What is ESD ? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1
Causes of ESD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2
Risks of ESD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1
Simulation and testing of electronic devices using models . . . . . . . . . . . . 6
2.1.1
2.1.2
Human body model (HBM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Machine model (MM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2
Standards overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
2.2.6
JS-001-2010 international standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
SP723 EIAJ IC121 standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
IEC61000-4-2 international standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
MIL-STD-883H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
ESD standard summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Test results of ESD standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3
Protecting against ESD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1
3.2
3.3
3.4
3.5
3.6
3.7
Dielectric overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Spark gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Ground rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Adding resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Adding diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
ESD protection devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Firmware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4
STM8T142-EVAL evaluation board: ESD tests . . . . . . . . . . . . . . . . . . . 16
4.1
4.2
Test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5
6
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2/21
Doc ID 022082 Rev 1
AN3960
List of tables
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Test conditions for ESD standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Dielectric overlay materials and their dielectric strength. . . . . . . . . . . . . . . . . . . . . . . . . . . 11
ESD protection devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
ESD discharges for tested STM8T142-EVAL evaluation board . . . . . . . . . . . . . . . . . . . . . 18
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Doc ID 022082 Rev 1
3/21
List of figures
AN3960
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Electrostatic discharge test (ESD generator and DUT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
IEC61000-4-2 ESD current waveform (R
D
= 330 W/C
D
= 150 pF). . . . . . . . . . . . . . . . . . . . 8
PCB with spark gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Ground ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Test set up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
STM8T142-EVAL evaluation board modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4/21
Doc ID 022082 Rev 1
AN3960
What is ESD ?
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) - 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.
1.1
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, 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.
2
Risks of ESD
ESD is a serious issue in solid state electronics, such as integrated circuits (ICs). ICs are
made from semiconductor materials such as silicon and insulating materials like silicon
dioxide. Either of these materials can suffer permanent damage when subjected to high
voltages.
The damaging effects of ESD poses unacceptable risks in many areas of technology and it
is necessary to control such interference and reduce the risks to acceptable levels through
the:
●
●
Simulation and testing of electronic devices using models
Definition of standards
Doc ID 022082 Rev 1
5/21
微控制器 MCU
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
