thermal re sis trance and colling system

8/8/2019 Thermal Re Sis Trance and Colling System

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2/73

What is Power? What is Junction Temperature? What is Thermal Resistance? .Electrical Parameters vs Thermal ParametersThermal SpecificationsHeatsinksDC Thermal Calculations

Dissipation and ThermalResistance


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h a t i s P o w e r ? What is Junction Temperature? What is Thermal Resistance? .Electrical Parameters vs Thermal ParametersThermal SpecificationsHeatsinksDC Thermal Calculations



4/73

What is Power?

Work is the result of a power appliedfor a given amount of time

W ork = Pow er * Tim e


5/73

What is Power?Electrically, power is a product of a

voltage and a current :

For example, a battery that can deliver 10Aat 12V can supply 120W of power:

Pow e r = Voltag e * C u rren t

P = V * I

P = 1 2 V * 1 0 A = 1 2 0 W


6/73

If a battery can provide 120W of power, the batteryload must consume 120W of power

Some of the power put into the battery load is

absorbed and dissipated as heatFrom Ohms Law (V=IR), the power dissipated as

heat in a load is given by:

What is Power?

1 2 0 WS u p p lie d

1 2 0 WC o n su m e d

= * = ( )* =P V I IR I I2R


7/73

,If a b a tte ry can p rovid e 1 2 0 W of p ow e r th e b attery loa d m u st con su m e 1 2 0 W of p ow er

Some of the power put into the battery load is

absorbed and dissipated as heat

( = ),From Ohm s Law V IR the power dissipated as:heat in a load is given by

What is Power?

120WSupplied

120WConsumed

= * = ( )* =P V I IR I2


8/73

Electrical Power

=P VI=P I

2R

The important things you mustremember here:


9/73

W h a t is Po w e r? h a t i s J u n c t i o n T e m p e r a t u r e ? What is Thermal Resistance?

.Electrical Parameters vs ThermalParametersThermal Specifications

Heatsinks

DC Thermal Calculations



10/73

Junction Temperature

Junction temperature is the temperature of the silicon die in an integrated circuit

C Board

S i l i

co

n

d i

e

JunctionTemperature

L e a

d

f r a m e


11/73

This is not the same as the (case or)package temperature or the (ambient or)air temperature

C Board

S i l i

co

n

d i

e

JunctionTemperature

CaseTemperature

AmbientTemperature

L e a

d

f r a m e

&Ambient Case Temperature


12/73

, ,Junction Case and AmbientTemperatures

, (First the system is off no power is being)dissipated , ,The ambient package case and silicon die

junction temperatures are in thermal equilibrium

Tambient = Tcase = Tjunction

C Board

L

e a

d

f r a m e

S i l i

co

n

d i

e

JunctionTemperature

CaseTemperature

AmbientTemperature


13/73

,Next the system is turned onThe silicon die heats up due to the absorbed power being dissipated as heat

Tambient = Tcase < Tjunction

C Board

L

e a

d

f r a m e

S i l i

co

n

d i

e

JunctionTemperature

CaseTemperature

AmbientTemperature



14/73

Some of the heat is transferred to the package( )case ,The case heats up but not as much as the silicon

die

Tambient < Tcase < Tjunction

C Board

L

e a

d

f r a m e

S i l i

co

n

d i

e

JunctionTemperature

CaseTemperature

AmbientTemperature



15/73

( ),From the package case some of the heat is transferred to the ambient air ,The air heats up but not as much as the case

T ,ambientoriginal < Tambient < Tcase < Tjunction

C Board

L

e a

d

f r a m e

S i l i

co

n

d i

e

JunctionTemperature

CaseTemperature

AmbientTemperature



16/73

, :Therefore under almost all conditionsT ,ambientoriginal < Tambient < Tcase

thermal re sis trance and colling system

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