TDA8948J_1
© NXP B.V. 2008. All rights reserved.
Product data sheet
Rev. 01 — 27 February 2008
18 of 26
NXP Semiconductors
TDA8948J
4-channel audio amplifier
13.3 Thermal behavior and heat sink calculation
The measured maximum thermal resistance of the IC package, R
th(j-mb)
, is 1.3 K/W.
A calculation for the heat sink can be made, with the following parameters:
T
amb(max)
= 60
°
C (example)
V
CC
= 17 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
heat sink. This can be calculated using the maximum temperature increase divided by the
power dissipation:
R
th(tot)
= (T
j(max)
−
T
amb(max)
)/P
At V
CC
= 17 V and R
L
= 4
Ω
(4
×
SE) the measured worst-case sine-wave dissipation is
17 W; see
Figure 8
. For T
j(max)
= 150
°
C the temperature raise, caused by the power
dissipation, is: 150
°
C
−
60
°
C = 90
°
C:
P
×
R
th(tot)
= 90
°
C
R
th(tot)
= 90/17 K/W = 5.29 K/W
R
th(h-a)
= R
th(tot)
−
R
th(j-mb)
= 5.29 K/W
−
2 K/W = 3.29 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 heat sink:
P
×
R
th(tot)
= 90
°
C
R
th(tot)
= 90/9 K/W = 10 K/W
R
th(h-a)
= R
th(tot)
−
R
th(j-mb)
= 10 K/W - 2 K/W = 8 K/W
