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The measured maximum thermal resistance of the IC package, R

th(j-mb)

 is 4.5 K/W.

A calculation for the heatsink can be made, with the following parameters:

T

amb(max)

= 50

°

C

V

CC

= 18 V and R

L

= 8

Ω

T

j(max)

= 150

°

C.

R

th(tot)

 is the total thermal resistance between the junction and the ambient

including the heatsink. In the heatsink calculations the value of R

th(mb-h)

 is ignored.

At V

CC

= 12 V and R

L

= 8

Ω

the measured worst-case sine-wave dissipation is 18 W;

see

. For T

j(max)

= 150

°

C the temperature raise - caused by the power

dissipation - is: 150 – 50 = 100

°

C.

P

×

R

th(tot)

= 100

°

C

R

th(tot)

= 100/18 = 5.56 K/W

R

th(h-a)

= R

th(tot)

– R

th(j-mb)

= 5.56 – 4.5 = 1.06 K/W.

The calculation above is for an application at worst-case (stereo) sine-wave output
signals. In practice music signals will be applied, which decreases the maximum
power dissipation to approximately half of the sine-wave power dissipation (see

). This allows for the use of a smaller heatsink:

P

×

R

th(tot)

= 100

°

C

R

th(tot)

= 100/8 = 12.5 K/W

R

th(h-a)

= R

th(tot)

– R

th(j-mb)

= 12.5 – 4.5 = 8.0 K/W.

To increase the lifetime of the IC, T

j(max)

should be reduced to 125

°

C. This requires a

heatsink of approximately 4 K/W for music signals.

The

 General Quality Specification for Integrated Circuits, SNW-FQ-611D is

applicable.

T

amb

= 25

°

C; V

CC

= 18 V; f = 1 kHz; R

L

= 8

Ω

; audio pass band 22 Hz to 22 kHz;

unless otherwise specified.

Remark: In the graphs as function of frequency no bandpass filter was applied; see

 and