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Electrical Design Considerations

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Electric component

Any device that handles electricity

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Passive Components

Contributes no power gain

No control action

Does not require any input other than a signalto perform its function

Gain < 1

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Examples:

Resistors

Capacitors

Inductors

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Active Components

Capable of controlling voltages or currents

Can create a switching action in the circuit

Amplify or interpret a signal

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Examples:

Diodes

Transistors

ICs

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Discrete

Integrated Circuit

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Discrete

Component packaged with one or twofunctional elements

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Integrated Circuit

Combination of several interconnected discretecomponents

Packaged in a single case to perform multiple

functions

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Through-hole

Surface Mount

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Through-hole

Have leads that can be inserted through mountingholes

Surface Mount

Attached directly on the surface of the board

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Component Leads

Axial leads

Two leads, extending from each side of thecomponent

Radial leads

Leads emanate from the bottom of the component

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Single in-line

Dual In-line

Pin-grid array

Leadless components

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Conductor Dimensions

Conductor width

Component packing density

Minimum spacing between conductors and

components Geometrical constraints due to component outlines

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Resistance

Capacitance

Inductance

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Resistance

Measure of how strongly a material opposesthe flow of electric current

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Resistance of conductor

Depends on the specific resistivity of copper

@ 20oC 1.724x10-6 ohm-cm

@ 25oC

1.78x10

-6

ohm-cm

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Assume:

Standard copper foil of 35 um thickness (withoutplating)

R = L / A

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Example 1

Compute the resistance of a 1mm wide copperconductor per cm length at 20oC

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Example 2

Compute the resistance of a copper conductorat 25oC with a 0.3 mm conductor width and35um copper thickness and 500 mm length

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Example 3

Compute the resistance of an 8 mil wide copperconductor with a length of 120 mm and acopper thickness of 70 um. Assume thetemperature to be 25oC

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Resistance and Temperature

When a current flows through a conductor, itstemperature rises due to the joule effect

Rt= R

0[1 + (T

1-T

0)]

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Example 1

Assume that the inside temperature in anelectric equipment is 80oC while the outsidetemperature is 20oC. Compute the resistanceat 80oC given copper conductivity of 0.0039, theresistance of 0.5mm conductor, 10 cm long(with 100 ohm resistance)

E l 2

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Example 2

Rt= 2.706x10-8

= 0.0043

T1 = 25

o

C T

2= 20oC

Recommended Current Carrying

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Recommended Current CarryingCapacity of Traces

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C it

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Capacitance

Ability of a body to hold electrical charge

2 situations:

Capacitance between conductors on opposite sides

Capacitance between adjacent conductor

Capacitance between conductors

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Capacitance between conductorson opposite sides of the PCB

C = 0.886 x x A/b

relativedielectric constant

A totaloverlapping area

b thickness of

dielectric

Capacitance between adjacent

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Capac ta ce bet ee adjace tconductors

Function of Width

Thickness

Spacing Dielectric constant of the board material

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Coupling capacitance for a G-10 laminate withdielectric constant of 5.4 and conductorthickness of 35um

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