Protecting against ESD

AN3960

10/21

Doc ID 022082 Rev 1

3

Protecting against ESD

An effective approach for protecting any electronic system against ESD is to mechanically

minimize the pathways by which high voltages enter the system from the outside

environment. This can be especially difficult if the user needs to touch the application or if

there is a void or other opening in the packaging.

Mechanical switches and control potentiometers are classic system entry points for ESD

stress. Changing from mechanical controls to capacitive touch controls eliminates the voids

for these traditional ESD entry paths.

Some methods which protect against ESD stress include:

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Dielectric overlays (see Section 3.1)

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Spark gaps (see Section 3.2)

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Ground rings (see Section 3.3)

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Adding resistance (see Section 3.4)

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Adding diodes (see Section 3.5)

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ESD protection devices (see Section 3.6)

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Firmware (see Section 3.7)

3.1

Dielectric overlays

In the touch sensing application domain, a protective layer of "dielectric" material (any

insulating material that can intrinsically withstand high voltages without breaking down) can

be placed between the ESD source and the touch sensing application. For example, one

layer of 5 mil Kapton® tape withstands 18 kV. Other dielectric overlay materials are listed

inTable 2 together with their dielectric strengths.