Philips Semiconductors TDA8946J
2 x 15 W stereo BTL audio amplifier
Product specification Rev. 02 — 14 March 2000 16 of 23
9397 750 06863 © Philips Electronics N.V. 2000. All rights reserved.
14.2 Thermal behaviour and heatsink calculation
The measured maximum thermal resistance of the IC package, Rth(j-mb) is 4.5 K/W.
A calculation for the heatsink can be made, with the following parameters:
Tamb(max) =50°C
VCC = 18 V and RL=8Ω
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 =12VandR
L=8Ωthe measured worst-case sine-wave dissipation is 18 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) = 100/18 = 5.56 K/W
Rth(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
Section 8.2.2). This allows for the use of a smaller heatsink:
P×Rth(tot) = 100 °C
Rth(tot) = 100/8 = 12.5 K/W
Rth(h-a) =R
th(tot) –R
th(j-mb) = 12.5 – 4.5 = 8.0 K/W.
To increase the lifetime of the IC, Tj(max) should be reduced to 125 °C. This requires a
heatsink of approximately 4 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=8Ω; 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 7,12 and 13.