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AMC1100

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SBAS562B – APRIL 2012 – REVISED DECEMBER 2019

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Copyright © 2012–2019, Texas Instruments Incorporated

11 Device and Documentation Support

11.1 Device Support

11.1.1 Device Nomenclature

11.1.1.1 Isolation Glossary

Creepage Distance: The shortest path between two conductive input-to-output leads measured along the

surface of the insulation. The shortest distance path is found around the end of the package body.

Clearance: The shortest distance between two conductive input-to-output leads measured through air (line of

sight).

Input-to-Output Barrier Capacitance: The total capacitance between all input terminals connected together,

and all output terminals connected together.

Input-to-Output Barrier Resistance: The total resistance between all input terminals connected together, and

all output terminals connected together.

Primary Circuit: An internal circuit directly connected to an external supply mains or other equivalent source that

supplies the primary circuit electric power.

Secondary Circuit: A circuit with no direct connection to primary power that derives its power from a separate

isolated source.

Comparative Tracking Index (CTI): CTI is an index used for electrical insulating materials. It is defined as the

numerical value of the voltage that causes failure by tracking during standard testing. Tracking is the process that

produces a partially conducting path of localized deterioration on or through the surface of an insulating material

as a result of the action of electric discharges on or close to an insulation surface. The higher CTI value of the

insulating material, the smaller the minimum creepage distance.

Generally, insulation breakdown occurs either through the material, over its surface, or both. Surface failure may

arise from flashover or from the progressive insulation surface degradation by small localized sparks. Such

sparks result from a surface film of a conducting contaminant breaking on the insulation. The resulting break in

the leakage current produces an overvoltage at the site of the discontinuity, and an electric spark is generated.

These sparks often cause carbonization on insulation material and lead to a carbon track between points of

different potential. This process is known as tracking.

11.1.1.1.1

Insulation:

Operational insulation—Insulation needed for correct equipment operation.

Basic insulation—Insulation to provide basic protection against electric shock.

Supplementary insulation—Independent insulation applied in addition to basic insulation in order to ensure

protection against electric shock in the event of a failure of the basic insulation.