TDA8947J Datasheet, PDF (18/24 Pages) NXP Semiconductors – 4-channel audio amplifier (SE: 1 W to 25 W; BTL: 4 W to 50 W)

Philips Semiconductors
TDA8947J
4-channel audio amplifier
13.3 Thermal behavior and heatsink calculation
The measured maximum thermal resistance of the IC package, R_th(j-mb), is 1.3 K/W.
A calculation for the heatsink can be made, with the following parameters:
T_amb(max) = 60 °C (example)
V_CC = 18 V and R_L = 4 Ω (SE)
T_j(max) = 150 °C (specification)
R_th(tot) is the total thermal resistance between the junction and the ambient including
the heatsink. This can be calculated using the maximum temperature increase
divided by the power dissipation:
R_th(tot) = (T_j(max) − T_amb(max))/P_D
At V_CC = 18 V and R_L = 4 Ω (4 × SE) the measured worst-case sine-wave dissipation
is 17 W; see Figure 9. For T_j(max) = 150 °C the temperature raise, caused by the
power dissipation, is: 150 − 60 = 90 °C:
P × R_th(tot) = 90 °C
R_th(tot) = 90/17 = 5.29 K/W
R_th(h-a) = R_th(tot) − R_th(j-mb) = 5.29 − 1.3 = 3.99 K/W
This calculation 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 of 9 W (see
Section 8.2.2). This allows for the use of a smaller heatsink:
P × R_th(tot) = 90 °C
R_th(tot) = 90/9 = 10 K/W
R_th(h-a) = R_th(tot) − R_th(j-mb) = 10 − 1.3 = 8.7 K/W
9397 750 10779
Preliminary data
Rev. 01 — 06 February 2004
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
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