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TDA8945 Datasheet PDF : 21 Pages
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Philips Semiconductors
TDA8945S
15 W mono BTL audio amplifier
14.2 Thermal behaviour and heatsink calculation
The measured maximum thermal resistance of the IC package, Rth(j-mb) is 9 K/W.
A calculation for the heatsink can be made, with the following parameters:
Tamb(max) = 50 °C
VCC = 18 V and RL = 8 Ω
Tj(max) = 150 °C.
Rth(tot) is the total thermal resistance between the junction and the ambient
including the heatsink. In the heatsink calculations the value of Rth(mb-h) is ignored.
At VCC = 18 V and RL = 8 Ω the measured worst-case sine-wave dissipation is 8.5 W;
see Figure 11. For Tj(max) = 150 °C the temperature raise – caused by the power
dissipation – is: 150 − 50 = 100 °C.
P × Rth(tot) = 100 °C
Rth(tot) = 100/8.5 = 11.8 K/W
Rth(h-a) = Rth(tot) − Rth(j-mb) = 11.8 − 9 = 2.8 K/W.
The calculation above is for an application at worst-case 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 × Rth(tot) = 100 °C
Rth(tot) = 100/4 = 25 K/W
Rth(h-a) = Rth(tot) − Rth(j-mb) = 25 − 9 = 16 K/W.
To increase the lifetime of the IC, Tj(max) should be reduced to 125 °C. This requires a
heatsink of approximately 10 K/W for music signals.
15. Test information
15.1 Quality information
The General Quality Specification for Integrated Circuits, SNW-FQ-611D is
applicable.
15.2 Test conditions
Tamb = 25 °C; VCC = 18 V; f = 1 kHz; RL = 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 Figure 7 and 12.
9397 750 06866
Product specification
Rev. 02 — 7 April 2000
© Philips Electronics N.V. 2000. All rights reserved.
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