AN4043 datasheet(46/60 Pages) STMICROELECTRONICS

46 / 60 page

Power losses and dissipation

AN4043

46/60

Doc ID 022726 Rev 2

4.3

Thermal impedance overview

During operation, power losses generate heat which elevates the temperature in the

semiconductor junctions contained in the SLLIMM-nano, limiting its performance and

lifetime. To ensure safe and reliable operation, the junction temperature of power devices

must be kept below the limits defined in the datasheet, therefore, the generated heat must

be conducted away from the power chips and into the environment using an adequate

cooling system.

The SLLIMM-nano was designed to drive electric motors up to 100 W without any heatsink.

Therefore, the thermal aspect of the system is one of the key factors in designing high

efficiency and high reliability equipment. In this environment the package and its thermal

resistance play a fundamental role.

Thermal resistance quantifies the capability of a given thermal path to transfer heat in

steady-state and it is generically given as the ratio between the temperature increase above

the reference and the relevant power flow:

Equation 29

The thermal resistance specified in the datasheet is the junction-ambient Rth(j-a) which is

commonly used with natural and forced convection air cooled systems and it is defined as

the difference in temperature between junction and ambient reference divided by the power

dissipation per device:

Equation 30

Figure 28.

Typical switching waveforms of the STGIPN3H60

on=23.5μJ(*)

on = 270ns

LIN = 2V/Div

C = 500mA/Div

CE = 100V/Div

t = 100ns/Div

LIN

Turn on

STGIPN3H60

Low side

Tj=100

°C

Turn off

STGIPN3H60

Low side

Tj=100

°C

toff = 905ns

(*) E

on and Eoff are the areas under the red plots

E =

∫ (V

CE · IC) dt

off=5.1μJ(*)

LIN

LIN = 2V/Div

C = 200mA/Div

CE = 100V/Div

t = 200ns/Div

AM11816v1

Rth

amb

th(j-

−

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