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Philips Semiconductors
14.2 Thermal behaviour and heatsink calculation
15. Test information
15.1 Quality information
15.2 Test conditions
9397 750 06863
Product specification
The measured maximum thermal resistance of the IC package, R
A calculation for the heatsink can be made, with the following parameters:
T
= 50 C
amb(max)
V
= 18 V and R
= 8
CC
L
T
= 150 C.
j(max)
R
is the total thermal resistance between the junction and the ambient
th(tot)
including the heatsink. In the heatsink calculations the value of R
At V
= 12 V and R
= 8
CC
L
see
Figure
11. For T
j(max)
dissipation - is: 150 – 50 = 100 C.
P
R
= 100 C
th(tot)
R
= 100/18 = 5.56 K/W
th(tot)
R
= R
– R
th(h-a)
th(tot)
th(j-mb)
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
Section
8.2.2). This allows for the use of a smaller heatsink:
P
R
= 100 C
th(tot)
R
= 100/8 = 12.5 K/W
th(tot)
R
= R
– R
th(h-a)
th(tot)
th(j-mb)
To increase the lifetime of the IC, T
heatsink of approximately 4 K/W for music signals.
The General Quality Specification for Integrated Circuits, SNW-FQ-611D is
applicable.
T
= 25 C; V
= 18 V; f = 1 kHz; R
amb
CC
unless otherwise specified.
Remark: In the graphs as function of frequency no bandpass filter was applied; see
Figure
7,
12
and 13.
Rev. 02 — 14 March 2000
2 x 15 W stereo BTL audio amplifier
the measured worst-case sine-wave dissipation is 18 W;
= 150 C the temperature raise - caused by the power
= 5.56 – 4.5 = 1.06 K/W.
= 12.5 – 4.5 = 8.0 K/W.
should be reduced to 125 C. This requires a
j(max)
= 8 ; audio pass band 22 Hz to 22 kHz;
L
TDA8946J
is 4.5 K/W.
th(j-mb)
is ignored.
th(mb-h)
© Philips Electronics N.V. 2000. All rights reserved.
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