AM2182

Motor Driver IC

A

s

M

1

- 6 -

Tj

Tt

P

T

T

d

t

j

jt

/

)

(

−

=

ψ

DFEINITION:

Where :

Ψjt (Psi-jt) = Junction-to-Top(of the package) °C/W

Tj= Die Junction Temp.

°C

Tt= Top of package Temp at center.

°C

Pd= Power dissipation. Watts



Practically, most of the device heat goes into the PCB, there is a very low heat flow

through top of the package, So the temperature difference between Tj and Tt shall be

small, that is any error caused by PCB variation is small.



This constant represents that

Ψjt is completely PCB independent and could be used to

predict the Tj in the environment of the actual PCB if Tt is measured properly.

Step 1 : Used the simulated

Ψjt value listed above.

Step 2 : Measure Tt value by using

 Thermocouple Method

We recommend use of a small ~40 gauge(3.15mil diameter) thermocouple. The

bead and thermocouples wires should touch the top of the package and be covered

with a minimal amount of thermally conductive epoxy. The wires should be

heat-insulated to prevent cooling of the bead due to heat loss into wires. This is

important towards preventing “too cool” Tt measurements, which would lead to the

calculated Tj also being too cool.

 IR Spot Method

An IR Spot method should be utilized only when using a tool with a small enough

spot area to acquire the true top center “hot spot”.

Many so-called “small spot size” tools still have a measurement area of 0~100+mils

at “zero” distance of the tool from the surface. This spot area is too big for many